Methods of removing heat from an electrode using thermal shunting

Abstract

According to some embodiments, a medical instrument (for example, an ablation device) comprises an elongate body having a proximal end and a distal end, an energy delivery member positioned at the distal end of the elongate body, a first plurality of temperature-measurement devices carried by or positioned within the energy delivery member, the first plurality of temperature-measurement devices being thermally insulated from the energy delivery member, and a second plurality of temperature-measurement devices positioned proximal to a proximal end of the energy delivery member, the second plurality of temperature-measurement devices being thermally insulated from the energy delivery member.

Claims

1. A method of heat removal from an electrode assembly during a tissue treatment procedure, the method comprising: delivering energy to an electrode assembly of an ablation system, the ablation system comprising a catheter comprising a distal end, the electrode assembly positioned along the distal end of the catheter; the catheter of the ablation system extending along a central axis, the catheter comprises a plurality of thermal shunt members along its distal end, a first one of the plurality of thermal shunt members extends at least partially through an interior of the electrode assembly; a second one of the plurality of thermal shunt members being disposed proximal to the first one of the plurality of thermal shunt members, a third one of the plurality of shunt members being distal to and spaced apart from the second one of the plurality of shunt members along an axis that is parallel to the central axis by at least a portion of the electrode assembly, wherein the first one of the plurality of thermal shunt members has a first radial thickness, wherein the second one of the plurality of thermal shunt members and the third one of the plurality of shunt members each has a second radial thickness, and wherein the first radial thickness is different than the second radial thickness; the catheter further comprises at least one fluid passage extending at least partially through the interior of the electrode assembly and an interior of the plurality of thermal shunt members; and delivering a fluid through the at least one fluid passage.

2. The method of claim 1, wherein the plurality of thermal shunt members is configured to transfer heat while not retaining heat, and wherein the plurality of thermal shunt members comprises a thermal diffusivity greater than 1.5 cm.sup.2/sec; wherein the electrode assembly comprises at least one radiofrequency electrode; and wherein the at least one fluid passage is configured to place the electrode assembly in fluid communication with a fluid source to selectively remove heat from the electrode assembly and/or tissue of a subject located adjacent the electrode assembly.

3. The method of claim 1, wherein the plurality of thermal shunt members is configured to transfer heat while not retaining heat, and wherein the plurality of thermal shunt members comprises a thermal diffusivity greater than 1.5 cm.sup.2/sec.

4. The method of claim 1, wherein the plurality of thermal shunt members comprises a diamond or other carbon-based material.

5. The method of claim 1, wherein the electrode assembly comprises a composite electrode, the composite electrode comprising a first electrode portion and at least a second electrode portion, wherein an electrically insulating gap is located between the first electrode portion and the at least a second electrode portion to facilitate high-resolution mapping along a targeted anatomical area.

6. The method of claim 1, wherein the at least one fluid passage is configured to place the electrode assembly in fluid communication with a fluid source to selectively remove heat from the electrode assembly and tissue of a subject located adjacent the electrode assembly.

7. The method of claim 1, wherein the at least one fluid passage is in direct thermal communication with plurality of thermal shunt members.

8. The method of claim 1, wherein the at least one fluid passage comprises at least one opening, wherein the at least one opening allows fluid flowing through the at least one fluid passage to exit the catheter.

9. A method of heat removal from an electrode assembly during a tissue treatment procedure, comprising: delivering energy to an electrode assembly of an ablation system, the electrode assembly positioned along a distal end of an elongate body, the elongate body extending along a central axis; a plurality of thermal shunt members extends at least partially through an interior of the electrode assembly, the plurality of thermal shunt members further includes a first thermal shunt member spaced from a second thermal shunt member, a third one of the plurality of shunt members being distal to and spaced apart from the second one of the plurality of shunt members along an axis that is parallel to the central axis by at least a portion of the electrode assembly, wherein the first one of the plurality of thermal shunt members has a first radial thickness, wherein the second one of the plurality of thermal shunt members and the third one of the plurality of shunt members each has a second radial thickness, and wherein the first radial thickness is different than the second radial thickness; and the elongate body further comprises at least one fluid passage extending at least partially through the interior of the plurality of thermal shunt members; and delivering a fluid through the at least one fluid passage.

10. The method of claim 9, wherein the at least one thermal shunt member is configured to transfer heat while not retaining heat, and wherein the at least one thermal shunt member comprises a thermal diffusivity greater than 1.5 cm.sup.2/sec; and wherein the at least one fluid passage is configured to place the electrode assembly in fluid communication with a fluid source to selectively remove heat from the electrode assembly and/or tissue of a subject located adjacent the electrode assembly.

11. The method of claim 9, wherein the plurality of thermal shunt members is configured to transfer heat while not retaining heat, and wherein the at least one thermal shunt member comprises a thermal diffusivity greater than 1.5 cm.sup.2/sec.

12. The method of claim 9, wherein the plurality of thermal shunt members comprises a diamond or other carbon-based material.

13. The method of claim 9, wherein the electrode assembly comprises a composite electrode, the composite electrode comprising a first electrode portion and at least a second electrode portion, wherein an electrically insulating gap is located between the first electrode portion and the at least a second electrode portion to facilitate high-resolution mapping along a targeted anatomical area.

14. The method of claim 9, wherein the at least one fluid passage is in direct thermal communication with the plurality of thermal shunt members.

15. A method of heat removal from an ablation member during a tissue treatment procedure, comprising: delivering energy to an ablation member of an ablation system, the ablation member positioned along a distal end of an elongate body, the elongate body extending along a central axis; a plurality of thermal shunt members extends at least partially through an interior of the ablation member; and at least one fluid passage extends at least partially through an interior of the plurality of thermal shunt members, the plurality of thermal shunt members further includes a first thermal shunt member spaced from a second thermal shunt member, at least a portion of the ablation member being disposed between the first and second thermal shunt members along an axis that is parallel to the central axis, a third one of the plurality of thermal shunt members being differently sized than the first thermal shunt member and the second thermal shunt member, wherein a distal portion of the distal end of the elongate body is located distally of the third one of the plurality of thermal shunt members; and delivering a fluid through the at least one fluid passage.

16. The method of claim 15, wherein the plurality of thermal shunt members is configured to transfer heat while not retaining heat, and wherein the plurality of thermal shunt members comprises a thermal diffusivity greater than 1.5 cm.sup.2/sec; and wherein the at least one fluid passage is configured to place the ablation member in fluid communication with a fluid source to selectively remove heat from the ablation member and tissue of a subject located adjacent the ablation member.

17. The method of claim 15, wherein the plurality of thermal shunt members is configured to transfer heat while not retaining heat, and wherein plurality of thermal shunt members comprises a thermal diffusivity greater than 1.5 cm.sup.2/sec.

18. The method of claim 15, wherein the plurality of thermal shunt members comprises a diamond or other carbon-based material.

19. The method of claim 15, wherein the ablation member comprises a composite electrode, the composite electrode comprising a first electrode portion and at least a second electrode portion, wherein an electrically insulating gap is located between the first electrode portion and the at least a second electrode portion to facilitate high-resolution mapping along a targeted anatomical area.

20. The method of claim 16, wherein the at least one fluid passage is in direct thermal communication with the plurality of thermal shunt members.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects and advantages of the present application are described with reference to drawings of certain embodiments, which are intended to illustrate, but not to limit, the concepts disclosed herein. The attached drawings are provided for the purpose of illustrating concepts of at least some of the embodiments disclosed herein and may not be to scale.

(2) FIG. 1 schematically illustrates one embodiment of an energy delivery system configured to selectively ablate or otherwise heat targeted tissue of a subject;

(3) FIG. 2 illustrates a side view of a system's catheter comprises a high-resolution-tip design according to one embodiment;

(4) FIG. 3 illustrates a side view of a system's catheter comprises a high-resolution-tip design according to another embodiment;

(5) FIG. 4 illustrates a side view of a system's catheter comprises a high-resolution-tip design according to yet another embodiment;

(6) FIG. 5 illustrates an embodiment of a system's catheter comprising two high-resolution-section electrodes each consisting of separate sections circumferentially distributed on the catheter shaft;

(7) FIG. 6 schematically illustrates one embodiment of a high-pass filtering element consisting of a coupling capacitor. The filtering element can be incorporated into a system's catheter that comprises a high-resolution-tip design;

(8) FIG. 7 schematically illustrates one embodiment of four high-pass filtering elements comprising coupling capacitors. The filtering elements can operatively couple, in the operating RF frequency range, the separate electrode sections of a system's catheter electrodes, e.g., those illustrated in FIG. 5;

(9) FIG. 8 illustrates embodiments of EKGs obtained from a high-resolution-tip electrode systems disclosed herein configured to detect whether an ablation procedure has been adequately performed;

(10) FIG. 9 illustrates a perspective view of an ablation system's catheter comprising an electrode and heat shunt network to facilitate the transfer of heat to an irrigation conduit during use, according to one embodiment;

(11) FIG. 10 illustrates a partially exposed view of the system of FIG. 9;

(12) FIG. 11 illustrates a perspective view of an ablation system's catheter comprising an electrode and heat shunt network to facilitate the transfer of heat to an irrigation conduit during use, according to another embodiment;

(13) FIG. 12 illustrates a cross-sectional view of an ablation system's catheter comprising an electrode and heat shunt network to facilitate the transfer of heat to an irrigation conduit during use, according to one embodiment;

(14) FIG. 13 illustrates a partial cross-sectional perspective view of one embodiment of an ablation system's catheter comprising an open irrigation cooling system;

(15) FIG. 14 illustrates a partial cross-sectional perspective view of one embodiment of an ablation system's catheter comprising a closed irrigation cooling system;

(16) FIG. 15 illustrates a partial cross-sectional perspective view of another embodiment of an ablation system's catheter;

(17) FIG. 16A illustrates a side perspective view of a distal end of one embodiment of a split-tip RF ablation system comprising heat transfer (e.g. heat shunt) members;

(18) FIG. 16B illustrates a partial cross-sectional perspective view of the system of FIG. 16A;

(19) FIG. 16C illustrates a partial cross-sectional perspective view of another embodiment of an ablation system comprising a split-tip electrode and heat transfer (e.g. heat shunt) members;

(20) FIG. 17A illustrates a side perspective view of a distal end of one embodiment of a split-tip RF ablation system comprising heat transfer (e.g. heat shunt) members and fluid outlets extending through a proximal electrode or slug;

(21) FIG. 17B illustrates a partial cross-sectional perspective view of the system of FIG. 17A;

(22) FIG. 18A illustrates a perspective view of a distal portion of an open-irrigated ablation catheter having multiple temperature-measurement devices, according to one embodiment;

(23) FIGS. 18B and 18C illustrate a perspective view and a cross-sectional view, respectively, of a distal portion of an open-irrigated ablation catheter having multiple temperature-measurement devices, according to another embodiment;

(24) FIG. 18D illustrates a perspective view of a distal portion of an ablation catheter having multiple temperature-measurement devices, according to another embodiment;

(25) FIGS. 18E and 18F illustrate a perspective view and a cross-sectional view, respectively, of a distal portion of an ablation catheter showing isolation of the distal temperature-measurement devices from an electrode tip, according to one embodiment;

(26) FIG. 19A illustrates a perspective view of a distal portion of a closed-irrigation ablation catheter having multiple temperature-measurement devices, according to one embodiment;

(27) FIGS. 19B and 19C illustrate a perspective view and a cross-sectional view, respectively, of a distal portion of a closed-irrigation ablation catheter having multiple temperature-measurement devices, according to another embodiment;

(28) FIG. 20 illustrates a perspective view of a distal portion of an open-irrigated ablation catheter comprising a non-split-tip design according to one embodiment;

(29) FIG. 21A schematically illustrates a distal portion of an open-irrigated ablation catheter in contact with tissue to be ablated in a perpendicular orientation and a lesion formed using the ablation catheter, according to one embodiment;

(30) FIG. 21B schematically illustrates a distal portion of an open-irrigated ablation catheter in contact with tissue to be ablated in a parallel orientation and a lesion formed using the ablation catheter, according to one embodiment;

(31) FIG. 22A is a graph illustrating that temperature of a lesion peak may be correlated to the temperature of the temperature-measurement devices by a correction factor or function, according to one embodiment;

(32) FIG. 22B is a plot showing an estimated peak temperature determined by an embodiment of an ablation catheter having multiple temperature-measurement devices compared against actual tissue measurements at various depths within a tissue;

(33) FIGS. 23A and 23B illustrate plots showing temperature measurements obtained by the multiple temperature-measurement devices of an embodiment of an ablation catheter for a parallel orientation and an oblique orientation, respectively;

(34) FIG. 24 schematically illustrates one embodiment of variable frequency being applied to the split-tip electrode design of FIG. 2 to determine whether the split-tip electrode is in contact with tissue;

(35) FIG. 25A is a plot showing normalized resistance of blood/saline and tissue across a range of frequencies;

(36) FIG. 25B is a plot of a four tone waveform utilized for impedance measurements;

(37) FIG. 25C is a plot of impedance vs. frequency, with tones at four frequencies;

(38) FIG. 25D schematically illustrates one embodiment of a contact sensing subsystem configured to perform contact sensing functions while simultaneously conducting electrogram (EGM) measurements, in accordance with one embodiment;

(39) FIG. 26A illustrates zero crossings of a frequency spectrum and is used to illustrate that switching between frequencies may be designed to occur at the zero crossings to avoid interference at EGM frequencies;

(40) FIG. 26B schematically illustrates one embodiment of a circuit model to describe the behavior of the impedance of tissue or blood or blood/saline combination, as measured across two electrodes or electrode portions;

(41) FIG. 26C schematically illustrates one embodiment of a circuit configured to switch between contact sensing circuitry in standby mode and radiofrequency energy delivery circuitry in treatment mode, in accordance with one embodiment;

(42) FIG. 27 schematically illustrates one embodiment of a circuit configured to perform contact sensing functions while radiofrequency energy is being delivered, in accordance with one embodiment;

(43) FIG. 28 is a plot of impedance of an LC circuit element across a range of frequencies;

(44) FIG. 29 is a plot showing resistance, or impedance magnitude, values of ablated tissue, viable tissue and blood across a range of frequencies;

(45) FIG. 30 is a plot showing the phase of impedance values of ablated tissue, viable tissue and blood across a range of frequencies;

(46) FIG. 31 illustrates one embodiment of a sensing algorithm that utilizes impedance magnitude, ratio of impedance magnitude at two frequencies, and impedance phase data to determine contact state as well as tissue state;

(47) FIG. 32 illustrates an embodiment of a contact criterion process, and FIG. 32A illustrates an embodiment of a sub-process of the contact criterion process of FIG. 32;

(48) FIG. 33 illustrates an embodiment of a graphical user interface of a display of output indicative of tissue contact by a high resolution combination electrode device;

(49) FIG. 34A illustrates a schematic representation of possible hardware components of a network measurement circuit;

(50) FIG. 34B illustrates a schematic representation of an embodiment of an auto-calibration circuit configured to calibrate (for example, automatically) the network measurement circuit so as to remove the effects of one or more hardware components present in the circuit; and

(51) FIG. 34C illustrates a schematic representation of one embodiment of an equivalent circuit model for a hardware component present in an impedance measurement circuit.

DETAILED DESCRIPTION

(52) According to some embodiments, successful electrophysiology procedures require precise knowledge about the anatomic substrate being targeted. Additionally, it may be desirable to evaluate the outcome of an ablation procedure within a short period of time after the execution of the procedure (e.g., to confirm that the desired clinical outcome was achieved). Typically, ablation catheters include only regular mapping electrodes (e.g., ECG electrodes). However, in some embodiments, it may be desirable for such catheters to incorporate high-resolution mapping capabilities. In some embodiments, high-resolution mapping electrodes can provide more accurate and more detailed information about the anatomic substrate and about the outcome of ablation procedures. For example, such high-resolution mapping electrodes can allow the electrophysiology (EP) practitioner to evaluate the morphology of electrograms, their amplitude and width and/or to determine changes in pacing thresholds. According to some arrangements, morphology, amplitude and/or pacing threshold are accepted as reliable EP markers that provide useful information about the outcome of ablation. Thus, high-resolution electrodes are defined as any electrode(s) capable of delivering ablative or other energy to tissue capable of transferring heat to/from such tissue, while being capable of obtaining accurate mapping data of adjacent tissue, and include, without limitation, split-tip RF electrodes, other closely oriented electrodes or electrode portions and/or the like.

(53) According to some embodiments, the present application discloses devices, systems and/or methods that include one or more of the following features: a high-resolution electrode (e.g., split tip electrode), heat shunting concepts to help dissipate heat away from the electrode and/or the tissue of the subject being treated, multiple temperature sensors located along the exterior of the device to determine, among other things, temperature of the subject at a depth and contact sensing features that help determine if and to what extent the device is contacting targeted tissue.

(54) Several embodiments of the invention are particularly advantageous because they include one, several or all of the following benefits: (i) provides the ability to obtain accurate tissue mapping data using the same electrode that delivers the ablative energy, (ii) reduces proximal edge heating, (iii) reduces likelihood of char or thrombus formation, (iv) provides feedback that may be used to adjust ablation procedures in real time, (v) provides noninvasive temperature measurements, (vi) does not require use of radiometry; (vii) provides tissue temperature monitoring and feedback during irrigated or non-irrigated ablation; and (vii) provides multiple forms of output or feedback to a user; and (ix) provides safer and more reliable ablation procedures.

(55) High-Resolution Electrode

(56) According to some embodiments, various implementations of electrodes (e.g., radiofrequency or RF electrodes) that can be used for high-resolution mapping are disclosed herein. For example, as discussed in greater detail herein, an ablation or other energy delivery system can comprise a high-resolution-tip design, wherein the energy delivery member (e.g., radiofrequency electrode) comprises two or more separate electrodes or electrode portions. As also discussed herein, in some embodiments, such separate electrodes or electrode portions can be advantageously electrically coupled to each other (e.g., to collectively create the desired heating or ablation of targeted tissue).

(57) FIG. 1 schematically illustrates one embodiment of an energy delivery system 10 that is configured to selectively ablate, stimulate, modulate and/or otherwise heat or treat targeted tissue (e.g., cardiac tissue, pulmonary vein, other vessels or organs, etc.). Although certain embodiments disclosed herein are described with reference to ablation systems and methods, any of the systems and methods can be used to stimulate, modulate, heat and/or otherwise affect tissue, with or without partial or complete ablation, as desired or required. As shown, the system 10 can include a medical instrument 20 (e.g., catheter) comprising one or more energy delivery members 30 (e.g., radiofrequency electrodes) along a distal end of the medical instrument 20. The medical instrument can be sized, shaped and/or otherwise configured to be passed intraluminally (e.g., intravascularly) through a subject being treated. In various embodiments, the medical instrument 20 comprises a catheter, a shaft, a wire, and/or other elongate instrument. In other embodiments, the medical instrument is not positioned intravascularly but is positioned extravascularly via laparoscopic or open surgical procedures. In various embodiments, the medical instrument 20 comprises a catheter, a shaft, a wire, and/or other elongate instrument. In some embodiments, one or more temperature sensing devices or systems 60 (e.g., thermocouples, thermistors, etc.) may be included at the distal end of the medical instrument 20, or along its elongate shaft or in its handle. The term “distal end” does not necessarily mean the distal terminus or distal end. Distal end could mean the distal terminus or a location spaced from the distal terminus but generally at a distal end portion of the medical instrument 20.

(58) In some embodiments, the medical instrument 20 is operatively coupled to one or more devices or components. For example, as depicted in FIG. 1, the medical instrument 20 can be coupled to a delivery module 40 (such as an energy delivery module). According to some arrangements, the energy delivery module 40 includes an energy generation device 42 that is configured to selectively energize and/or otherwise activate the energy delivery member(s) 30 (for example, radiofrequency electrodes) located along the medical instrument 20. In some embodiments, for instance, the energy generation device 42 comprises a radiofrequency generator, an ultrasound energy source, a microwave energy source, a laser/light source, another type of energy source or generator, and the like, and combinations thereof. In other embodiments, energy generation device 42 is substituted with or use in addition to a source of fluid, such a cryogenic fluid or other fluid that modulates temperature. Likewise, the delivery module (e.g., delivery module 40), as used herein, can also be a cryogenic device or other device that is configured for thermal modulation.

(59) With continued reference to the schematic of FIG. 1, the energy delivery module 40 can include one or more input/output devices or components 44, such as, for example, a touchscreen device, a screen or other display, a controller (e.g., button, knob, switch, dial, etc.), keypad, mouse, joystick, trackpad, or other input device and/or the like. Such devices can permit a physician or other user to enter information into and/or receive information from the system 10. In some embodiments, the output device 44 can include a touchscreen or other display that provides tissue temperature information, contact information, other measurement information and/or other data or indicators that can be useful for regulating a particular treatment procedure.

(60) According to some embodiments, the energy delivery module 40 includes a processor 46 (e.g., a processing or control unit) that is configured to regulate one or more aspects of the treatment system 10. The module 40 can also comprise a memory unit or other storage device 48 (e.g., computer readable medium) that can be used to store operational parameters and/or other data related to the operation of the system 10. In some embodiments, the processor 46 is configured to automatically regulate the delivery of energy from the energy generation device 42 to the energy delivery member 30 of the medical instrument 20 based on one or more operational schemes. For example, energy provided to the energy delivery member 30 (and thus, the amount of heat transferred to or from the targeted tissue) can be regulated based on, among other things, the detected temperature of the tissue being treated.

(61) According to some embodiments, the energy delivery system 10 can include one or more temperature detection devices, such as, for example, reference temperature devices (e.g., thermocouples, thermistors, etc.) and/or the like. For example, in some embodiments, the device further comprises a one or more temperature sensors or other temperature-measuring devices to help determine a peak (e.g., high or peak, low or trough, etc.) temperature of tissue being treated. In some embodiments, the temperature sensors (e.g., thermocouples) located at, along and/or near the ablation member (e.g., RF electrode) can help with the determination of whether contact is being made between the ablation member and targeted tissue (and/or to what degree such contact is being made). In some embodiments, such peak temperature is determined without the use of radiometry. Additional details regarding the use of temperature sensors (e.g., thermocouples) to determine peak tissue temperature and/or to confirm or evaluate tissue contact are provided herein.

(62) With reference to FIG. 1, the energy delivery system 10 comprises (or is in configured to be placed in fluid communication with) an irrigation fluid system 70. In some embodiments, as schematically illustrated in FIG. 1, such a fluid system 70 is at least partially separate from the energy delivery module 40 and/or other components of the system 10. However, in other embodiments, the irrigation fluid system 70 is incorporated, at least partially, into the energy delivery module 40. The irrigation fluid system 70 can include one or more pumps or other fluid transfer devices that are configured to selectively move fluid through one or more lumens or other passages of the catheter 20. Such fluid can be used to selectively cool (e.g., transfer heat away from) the energy delivery member 30 during use.

(63) FIG. 2 illustrates one embodiment of a distal end of a medical instrument (e.g., catheter) 20. As shown, the catheter 20 can include a high-resolution tip design, such that there are two adjacent electrodes or two adjacent electrode portions 30A, 30B separated by a gap G. According to some embodiments, as depicted in the configuration of FIG. 2, the relative length of the different electrodes or electrode portions 30A, 30B can vary. For example, the length of the proximal electrode 30B can be between 1 to 20 times (e.g., 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18, 18-19, 19-20, values between the foregoing ranges, etc.) the length of the distal electrode 30A, as desired or required. In other embodiments, the length of the proximal electrode 30B can be greater than 20 times (e.g., 20-25, 25-30, more than 30 times, etc.) the length of the distal electrode 30A. In yet other embodiments, the lengths of the distal and proximal electrodes 30A, 30B are about equal. In some embodiments, the distal electrode 30A is longer than the proximal electrode 30B (e.g., by 1 to 20 times, such as, for example, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18, 18-19, 19-20, values between the foregoing ranges, etc.).

(64) In some embodiments, the distal electrode or electrode portion 30A is 0.5 mm long. In other embodiments, the distal electrode or electrode portion 30A is between 0.1 mm and 1 mm long (e.g., 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.-0.8, 0.8-0.9, 0.9-1 mm, values between the foregoing ranges, etc.). In other embodiments, the distal electrode or electrode portion 30A is greater than 1 mm in length, as desired or required. In some embodiments, the proximal electrode or electrode portion 30B is 2 to 4 mm long (e.g., 2-2.5, 2.5-3, 3-3.5, 3.5-4 mm, lengths between the foregoing, etc.). However, in other embodiments, the proximal electrode portion 30B is greater than 4 mm (e.g., 4-5, 5-6, 6-7, 7-8, 8-9, 9-10 mm, greater than 10 mm, etc.) or smaller than 1 mm (e.g., 0.1-0.5 0.5-1, 1-1.5, 1.5-2 mm, lengths between the foregoing ranges, etc.), as desired or required. In embodiments where the high-resolution electrodes are located on catheter shafts, the length of the electrodes can be 1 to 5 mm (e.g., 1-2, 2-3, 3-4, 4-5 mm, lengths between the foregoing, etc.). However, in other embodiments, the electrodes can be longer than 5 mm (e.g., 5-6, 6-7, 7-8, 8-9, 9-10, 10-15, 15-20 mm, lengths between the foregoing, lengths greater than 20 mm, etc.), as desired or required.

(65) As noted above, the use of a high-resolution tip design can permit a user to simultaneously ablate or otherwise thermally treat targeted tissue and map (e.g., using high-resolution mapping) in a single configuration. Thus, such systems can advantageously permit precise high-resolution mapping (e.g., to confirm that a desired level of treatment occurred) during a procedure. In some embodiments, the high-resolution tip design that includes two electrodes or electrode portions 30A, 30B can be used to record a high-resolution bipolar electrogram. For such purposes, the two electrodes or electrode portions can be connected to the inputs of an EP recorder. In some embodiments, a relatively small separation distance (e.g., gap G) between the electrodes or electrode portions 30A, 30B enables high-resolution mapping.

(66) In some embodiments, a medical instrument (e.g., a catheter) 20 can include three or more electrodes or electrode portions (e.g., separated by gaps), as desired or required. Additional details regarding such arrangements are provided below. According to some embodiments, regardless of how many electrodes or electrode portions are positioned along a catheter tip, the electrodes or electrode portions 30A, 30B are radiofrequency electrodes and comprise one or more metals, such as, for example, stainless steel, platinum, platinum-iridium, gold, gold-plated alloys and/or the like.

(67) According to some embodiments, as illustrated in FIG. 2, the electrodes or electrode portions 30A, 30B are spaced apart from each other (e.g., longitudinally or axially) using a gap (e.g., an electrically insulating gap). In some embodiments, the length of the gap G (or the separation distance between adjacent electrodes or electrode portions) is 0.5 mm. In other embodiments, the gap G or separation distance is greater or smaller than 0.5 mm, such as, for example, 0.1-1 mm (e.g., 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0 mm, values between the foregoing ranges, less than 0.1 mm, greater than 1 mm, etc.), as desired or required.

(68) According to some embodiments, a separator 34 is positioned within the gap G, between the adjacent electrodes or electrode portions 30A, 30B, as depicted in FIG. 2. The separator can comprise one or more electrically insulating materials, such as, for example, Teflon, polyetheretherketone (PEEK), polyetherimide resins (e.g., ULTEM™), ceramic materials, polyimide and the like.

(69) As noted above with respect to the gap G separating the adjacent electrodes or electrode portion, the insulating separator 34 can be 0.5 mm long. In other embodiments, the length of the separator 34 can be greater or smaller than 0.5 mm (e.g., 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0 mm, values between the foregoing ranges, less than 0.1 mm, greater than 1 mm, etc.), as desired or required.

(70) According to some embodiments, as discussed in greater detail herein, to ablate or otherwise heat or treat targeted tissue of a subject successfully with the high-resolution tip electrode design, such as the one depicted in FIG. 2, the two electrodes or electrode portions 30A, 30B are electrically coupled to each other at the RF frequency. Thus, the two electrodes or electrode portions can advantageously function as a single longer electrode at the RF frequency.

(71) FIGS. 3 and 4 illustrate different embodiments of catheter systems 100, 200 that incorporate a high-resolution tip design. For example, in FIG. 3, the electrode (e.g., radiofrequency electrode) along the distal end of the electrode comprises a first or distal electrode or electrode portion 110 and a second or proximal electrode or electrode portion 114. As shown and discussed in greater detail herein with reference to other configurations, the high-resolution tip design 100 includes a gap G between the first and second electrodes or electrode portions 110, 114. In some configurations, the second or proximal electrode or electrode portion 114 is generally longer than the first or distal electrode or electrode portion 110. For instance, the length of the proximal electrode 114 can be between 1 to 20 times (e.g., 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18, 18-19, 19-20, values between the foregoing ranges, etc.) the length of the distal electrode 110, as desired or required. In other embodiments, the length of the proximal electrode can be greater than 20 times (e.g., 20-25, 25-30, more than 30 times, etc.) the length of the distal electrode. In yet other embodiments, the lengths of the distal and proximal electrodes are about the same. However, in some embodiments, the distal electrode 110 is longer than the proximal electrode 114 (e.g., by 1 to 20 times, such as, for example, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18, 18-19, 19-20, values between the foregoing ranges, etc.).

(72) As shown in FIG. 3 and noted above, regardless of their exact design, relative length diameter, orientation and/or other characteristics, the electrodes or electrode portions 110, 114 can be separated by a gap G. The gap G can comprise a relatively small electrically insulating gap or space. In some embodiments, an electrically insulating separator 118 can be snugly positioned between the first and second electrodes or electrode portions 110, 114. In certain embodiments, the separator 118 can have a length of about 0.5 mm. In other embodiments, however, the length of the separator 118 can be greater or smaller than 0.5 mm (e.g., 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0 mm, values between the foregoing ranges, less than 0.1 mm, greater than 1 mm, etc.), as desired or required. The separator can include one or more electrically insulating materials (e.g., materials that have an electrical conductivity less than about 1000 or less (e.g., 500-600, 600-700, 700-800, 800-900, 900-1000, 1000-1100, 1100-1200, 1200-1300, 1300-1400, 1400-1500, values between the foregoing, less than 500, greater than 1500, etc.) than the electrical conductivity of metals or alloys). The separator can comprise one or more electrically insulating materials, such as, for example, Teflon, polyetheretherketone (PEEK), polyoxymethylene, acetal resins or polymers and the like.

(73) As shown in FIG. 3, the separator 118 can be cylindrical in shape and can have the identical or similar diameter and configuration as the adjacent electrodes or electrode portions 110, 114. Thus, in some embodiments, the outer surface formed by the electrodes or electrode portions 110, 114 and the separator 118 can be generally uniform or smooth. However, in other embodiments, the shape, size (e.g., diameter) and/or other characteristics of the separator 118 can be different than one or more of the adjacent electrodes or electrode portions 110, 114, as desired or required for a particular application or use.

(74) FIG. 4 illustrates an embodiment of a system 200 having three or more electrodes or electrode portions 210, 212, 214 separated by corresponding gaps G1, G2. The use of such additional gaps, and thus, additional electrodes or electrode portions 210, 212, 214 that are physically separated (e.g., by gaps) yet in close proximity to each other, can provide additional benefits to the high-resolution mapping capabilities of the system. For example, the use of two (or more) gaps can provide more accurate high-resolution mapping data related to the tissue being treated. Such multiple gaps can provide information about the directionality of cardiac signal propagation. In addition, high-resolution mapping with high-resolution electrode portions involving multiple gaps can provide a more extended view of lesion progression during the ablation process and higher confidence that viable tissue strands are not left behind within the targeted therapeutic volume. In some embodiments, high-resolution electrodes with multiple gaps can optimize the ratio of mapped tissue surface to ablated tissue surface. Preferably, such ratio is in the range of 0.2 to 0.8 (e.g., 0.2-0.3, 0.3-0.4, 0.4-.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, ratios between the foregoing, etc.). Although FIG. 4 illustrates an embodiment having a total of three electrodes or electrode portions 210, 212, 214 (and thus, two gaps G1, G2), a system can be designed or otherwise modified to comprise additional electrodes or electrode portions, and thus, additional gaps. For example, in some embodiments, an ablation or other treatment system can include 4 or more (e.g., 5, 6, 7, 8, more than 8, etc.) electrodes or electrode portions (and thus, 3 or more gaps, e.g., 3, 4, 5, 6, 7 gaps, more than 7 gaps, etc.), as desired or required. In such configurations, a gap (and/or an electrical separator) can be positioned between adjacent electrodes or electrode portions, in accordance with the embodiments illustrated in FIGS. 2 to 4.

(75) As depicted in FIGS. 3 and 4, an irrigation tube 120, 220 can be routed within an interior of the catheter (not shown for clarity). In some embodiments, the irrigation tube 120, 220 can extend from a proximal portion of the catheter (e.g., where it can be placed in fluid communication with a fluid pump) to the distal end of the system. For example, in some arrangements, as illustrated in the side views of FIGS. 3 and 4, the irrigation tube 120, 220 extends and is in fluid communication with one or more fluid ports 211 that extend radially outwardly through the distal electrode 110, 210. Thus, in some embodiments, the treatment system comprises an open irrigation design, wherein saline and/or other fluid is selectively delivered through the catheter (e.g., within the fluid tube 120, 220) and radially outwardly through one or more outlet ports 111, 211 of an electrode 110, 210. The delivery of such saline or other fluid can help remove heat away from the electrodes and/or the tissue being treated. In some embodiments, such an open irrigation system can help prevent overheating of targeted tissue, especially along the tissue that is contacted by the electrodes. An open irrigation design is also incorporated in the system that is schematically illustrated in FIG. 2. For instance, as depicted in FIG. 2, the distal electrode or electrode portion 34 can include a plurality of outlet ports 36 through which saline or other irrigation fluid can exit.

(76) According to some embodiments, a catheter can include a high-resolution-tip electrode design that includes one or more gaps in the circumferential direction (e.g., radially), either in addition to or in lieu of gaps in the longitudinal direction. One embodiment of a system 300 comprising one or more electrodes 310A, 310B is illustrated in FIG. 5. As shown, in arrangements where two or more electrodes are included, the electrodes 310A, 310B can be longitudinally or axially offset from each other. For example, in some embodiments, the electrodes 310A, 310B are located along or near the distal end of a catheter. In some embodiments, the electrodes 310A, 310B are located along an exterior portion of a catheter or other medical instrument. However, in other configurations, one or more of the electrodes can be positioned along a different portion of the catheter or other medical instrument (e.g., along at least an interior portion of a catheter), as desired or required.

(77) With continued reference to FIG. 5, each electrode 310A, 310B can comprises two or more sections 320A, 322A and/or 320B, 320B. As shown, in some embodiments, the each section 320A, 322A and/or 320B, 320B can extend half-way around (e.g., 180 degrees) the diameter of the catheter. However, in other embodiments, the circumferential extent of each section can be less than 180 degrees. For example, each section can extend between 0 and 180 degrees (e.g., 15, 30, 45, 60, 75, 90, 105, 120 degrees, degrees between the foregoing, etc.) around the circumference of the catheter along which it is mounted. Thus, in some embodiments, an electrode can include 2, 3, 4, 5, 6 or more circumferential sections, as desired or required.

(78) Regardless of how the circumferential electrode sections are designed and oriented, electrically insulating gaps G can be provided between adjacent sections to facilitate the ability to use the electrode to conduct high-resolution mapping, in accordance with the various embodiments disclosed herein. Further, as illustrated in the embodiment of FIG. 5, two or more (e.g., 3, 4, 5, more than 5, etc.) electrodes 310A, 310B having two or more circumferential or radial sections can be included in a particular system 300, as desired or required.

(79) In alternative embodiments, the various embodiments of a high-resolution tip design disclosed herein, or variations thereof, can be used with a non-irrigated system or a closed-irrigation system (e.g., one in which saline and/or other fluid is circulated through or within one or more electrodes to selectively remove heat therefrom). Thus, in some arrangements, a catheter can include two or more irrigation tubes or conduits. For example, one tube or other conduit can be used to deliver fluid toward or near the electrodes, while a second tube or other conduit can be used to return the fluid in the reverse direction through the catheter.

(80) According to some embodiments, a high-resolution tip electrode is designed to balance the current load between the various electrodes or electrode portions. For example, if a treatment system is not carefully configured, the electrical load may be delivered predominantly to one or more of the electrodes or electrode portions of the high-resolution tip system (e.g., the shorter or smaller distal electrode or electrode portion). This can lead to undesirable uneven heating of the electrode, and thus, uneven heating (e.g., ablation) of the adjacent tissue of the subject. Thus, in some embodiments, one or more load balancing configurations can be used to help ensure that the heating along the various electrodes or electrode portions of the system will be generally balanced. As a result, the high-resolution tip design can advantageously function more like a longer, single electrode, as opposed to two or more electrodes that receive an unequal electrical load (and thus, deliver an unequal amount of heat or level of treatment to the subject's targeted tissue).

(81) One embodiment of a configuration that can be used to balance the electrical current load delivered to each of the electrodes or electrode portions in a high-resolution tip design is schematically illustrated in FIG. 6. As shown, one of the electrodes (e.g., the distal electrode) 30A can be electrically coupled to an energy delivery module 40 (e.g., a RF generator). As discussed herein, the module 40 can comprise one or more components or features, such as, for example, an energy generation device that is configured to selectively energize and/or otherwise activate the energy members (e.g., RF electrodes), one or more input/output devices or components, a processor (e.g., a processing or control unit) that is configured to regulate one or more aspects of the treatment system, a memory and/or the like. Further, such a module can be configured to be operated manually or automatically, as desired or required.

(82) In the embodiment that is schematically depicted in FIG. 6, the distal electrode 30A is energized using one or more conductors 82 (e.g., wires, cables, etc.). For example, in some arrangements, the exterior of the irrigation tube 38 comprises and/or is otherwise coated with one or more electrically conductive materials (e.g., copper, other metal, etc.). Thus, as shown in FIG. 6, the conductor 82 can be placed in contact with such a conductive surface or portion of the tube 38 to electrically couple the electrode or electrode portion 30A to an energy delivery module. However, one or more other devices and/or methods of placing the electrode or electrode portion 30A in electrical communication with an energy delivery module can be used. For example, one or more wires, cables and/or other conductors can directly or indirectly couple to the electrodes, without the use of the irrigation tube.

(83) With continued reference to FIG. 6, the first or distal electrode or electrode portion 30A can be electrically coupled to the second or proximal electrode or electrode portion 30B using one more band-pass filtering elements 84, such as a capacitor, a filter circuit (see, e.g., FIG. 16), etc. For instance, in some embodiments, the band-pass filtering element 84 comprises a capacitor that electrically couples the two electrodes or electrode portions 30A, 30B when radiofrequency current is applied to the system. In one embodiment, the capacitor 84 comprises a 100 nF capacitor that introduces a series impedance lower than about 3Ω at 500 kHz, which, according to some arrangements, is a target frequency for RF ablation. However, in other embodiments, the capacitance of the capacitor(s) or other band-pass filtering elements 84 that are incorporated into the system can be greater or less than 100 nF, for example, 5 nF to 300 nF, according to the operating RF frequency, as desired or required. In some embodiments, the capacitance of the filtering element 84 is selected based on a target impedance at a particular frequency or frequency range. For example, in some embodiments, the system can be operated at a frequency of 200 kHz to 10 MHz (e.g., 200-300, 300-400, 400-500, 500-600, 600-700, 700-800, 800-900, 900-1000 kHz, up to 10 MHz or higher frequencies between the foregoing ranges, etc.). Thus, the capacitor that couples adjacent electrodes or electrode portions to each other can be selected based on the target impedance for a particular frequency. For example, a 100 nF capacitor provides about 3Ω of coupling impedance at an operating ablation frequency of 500 kHz.

(84) In some embodiments, a series impedance of 3Ω across the electrodes or electrode portions 30A, 30B is sufficiently low when compared to the impedance of the conductor 82 (e.g., wire, cable, etc.), which can be about 5-10Ω, and the impedance of tissue, which can be about 100Ω, such that the resulting tissue heating profile is not negatively impacted when the system is in use. Thus, in some embodiments, a filtering element is selected so that the series impedance across the electrodes or electrode portions is lower than the impedance of the conductor that supplies RF energy to the electrodes. For example, in some embodiments, the insertion impedance of the filtering element is 50% of the conductor 82 impedance, or lower, or 10% of the equivalent tissue impedance, or lower.

(85) In some embodiments, a filtering element (e.g., capacitor a filter circuit such as the one described herein with reference to FIG. 16, etc.) can be located at a variety of locations of the device or accompanying system. For example, in some embodiments, the filtering element is located on or within a catheter (e.g., near the distal end of the catheter, adjacent the electrode, etc.). In other embodiments, however, the filtering element is separate of the catheter. For instance, the filtering element can be positioned within or along a handle to which the catheter is secured, within the generator or other energy delivery module, within a separate processor or other computing device or component and/or the like).

(86) Similarly, with reference to the schematic of FIG. 7, a filtering element 384 can be included in an electrode 310 comprising circumferentially-arranged portions 320, 322. In FIG. 7, the filtering element 384 permits the entire electrode 310 to be energized within RF frequency range (e.g., when the electrode is activated to ablate). One or more RF wires or other conductors 344 can be used to deliver power to the electrode from a generator or source. In addition, separate conductors 340 can be used to electrically couple the electrode 310 for mapping purposes.

(87) In embodiments where the high-resolution-tip design (e.g., FIG. 4) comprises three or more electrodes or electrode portions, additional filtering elements (e.g., capacitors) can be used to electrically couple the electrodes or electrode portions to each other. Such capacitors or other filtering elements can be selected to create a generally uniform heating profile along the entire length of the high-resolution tip electrode. As noted in greater detail herein, for any of the embodiments disclosed herein or variations thereof, the filtering element can include something other than a capacitor. For example, in some arrangements, the filtering element comprises a LC circuit (e.g., a resonant circuit, a tank circuit, a tuned circuit, etc.). Such embodiments can be configured to permit simultaneous application of RF energy and measurement of EGM recordings.

(88) As discussed above, the relatively small gap G between the adjacent electrodes or electrode portions 30A, 30B can be used to facilitate high-resolution mapping of the targeted tissue. For example, with continued reference to the schematic of FIG. 6, the separate electrodes or electrode portions 30A, 30B can be used to generate an electrogram that accurately reflects the localized electrical potential of the tissue being treated. Thus, a physician or other practitioner using the treatment system can more accurately detect the impact of the energy delivery to the targeted tissue before, during and/or after a procedure. For example, the more accurate electrogram data that result from such configurations can enable the physician to detect any gaps or portions of the targeted anatomical region that was not properly ablated or otherwise treated. Specifically, the use of a high-resolution tip design can enable a cardiac electrophysiologist to more accurately evaluate the morphology of resulting electrograms, their amplitude and width and/or to determine pacing thresholds. In some embodiments, morphology, amplitude and pacing threshold are accepted and reliable EP markers that provide useful information about the outcome of an ablation or other heat treatment procedure.

(89) According to some arrangements, the high-resolution-tip electrode embodiments disclosed herein are configured to provide localized high-resolution electrogram. For example, the electrogram that is obtained using a high-resolution-tip electrode, in accordance with embodiments disclosed herein, can provide electrogram data (e.g., graphical output) 400a, 400b as illustrated in FIG. 8. As depicted in FIG. 8, the localized electrograms 400a, 400b generated using the high-resolution-tip electrode embodiments disclosed herein include an amplitude A1, A2.

(90) With continued reference to FIG. 8, the amplitude of the electrograms 400a, 400b obtained using high-resolution-tip electrode systems can be used to determine whether targeted tissue adjacent the high-resolution-tip electrode has been adequately ablated or otherwise treated. For example, according to some embodiments, the amplitude A1 of an electrogram 400a in untreated tissue (e.g., tissue that has not been ablated or otherwise heated) is greater that the amplitude A2 of an electrogram 400b that has already been ablated or otherwise treated. In some embodiments, therefore, the amplitude of the electrogram can be measured to determine whether tissue has been treated. For example, the electrogram amplitude A1 of untreated tissue in a subject can be recorded and used as a baseline. Future electrogram amplitude measurements can be obtained and compared against such a baseline amplitude in an effort to determine whether tissue has been ablated or otherwise treated to an adequate or desired degree.

(91) In some embodiments, a comparison is made between such a baseline amplitude (A1) relative to an electrogram amplitude (A2) at a tissue location being tested or evaluated. A ratio of A1 to A2 can be used to provide a quantitative measure for assessing the likelihood that ablation has been completed. In some arrangements, if the ratio (i.e., A1/A2) is above a certain minimum threshold, then the user can be informed that the tissue where the A2 amplitude was obtained has been properly ablated. For example, in some embodiments, adequate ablation or treatment can be confirmed when the A1/A2 ratio is greater than 1.5 (e.g., 1.5-1.6, 1.6-1.7, 1.7-1.8, 1.8-1.9, 1.9-2.0, 2.0-2.5, 2.5-3.0, values between the foregoing, greater than 3, etc.). However, in other embodiments, confirmation of ablation can be obtained when the ratio of A1/A2 is less than 1.5 (e.g., 1-1.1, 1.1-1.2, 1.2-1.3, 1.3-1.4, 1.4-1.5, values between the foregoing, etc.).

(92) For any of the embodiments disclosed herein, a catheter or other minimally-invasive medical instrument can be delivered to the target anatomical location of a subject (e.g., atrium, pulmonary veins, other cardiac location, renal artery, other vessel or lumen, etc.) using one or more imaging technologies. Accordingly, any of the ablation systems disclosed herein can be configured to be used with (e.g., separately from or at least partially integrated with) an imaging device or system, such as, for example, fluoroscopy technologies, intracardiac echocardiography (ICE) technologies and/or the like.

(93) Thermal Shunting

(94) FIG. 9 illustrates one embodiment of a system 1100 comprising an electrode 1130 (e.g., a unitary RF electrode, a split-tip electrode having two, three or more portions, other types of electrodes, etc.) located at or near the distal end of a catheter 1120. In addition, as with any other embodiments disclosed herein, the system can further include a plurality of ring electrodes 1170 to assist with the execution of a treatment procedure (e.g., mapping of tissue adjacent the treatment site, monitoring of the subject, etc.). Although the embodiments of the various systems and related methods disclosed herein are described in the context of radiofrequency (RF) based ablation, the heat transfer concepts (including heat shunting embodiments), either alone or in conjunction with other embodiments described herein (e.g., split-tip concepts, temperature sensing concepts, etc.), can be implemented in other types of ablation systems as well, such as those, for example, that use microwave emitters, ultrasound transducers, cryoablation members and/or the like to target tissue of a subject.

(95) With reference to FIG. 9 and the corresponding partially-exposed view of the distal end of the catheter illustrated in FIG. 10, one or more heat transfer members or other heat transfer components or features, including any of the heat shunting embodiments disclosed herein, can be used to facilitate the heat transfer from or near the electrode to the irrigation conduit 1108 that extends through the interior of the catheter 1120. For example, in some embodiments, as depicted in FIG. 10, one or more heat transfer disks or members 1140 (e.g., heat shunt disks or members) can be positioned along the length of the electrode 1130. In some arrangements, the disks or other heat transfer members 1140 (including any of the heat shunting embodiments disclosed herein) comprise separate components that may or may not contact each other. In other embodiments, however, the heat transfer disks or other heat transfer members 1140 comprise a unitary or monolithic structure, as desired or required. The disks 1140 can be in direct or indirect thermal communication with the irrigation conduit 1108 that passes, at least partially, through an interior portion (e.g., along the longitudinal centerline) of the catheter. For example, the disks 1140 can extend to and make contact with an exterior surface of the irrigation conduit and/or another interior portion of the catheter (e.g., non-irrigation component or portion for embodiments that do not include active cooling using open or closed irrigation). However, in other embodiments, as illustrated in FIG. 11, the disks 1140 can be in thermal communication (e.g., directly via contact or indirectly) with one or more other heat exchange components or members, including any heat shunting components or members, located between the disks and the irrigation conduit.

(96) A heat sink includes both (i) a heat retention transfer in which heat is localized to/retained by a certain component, and (ii) a heat shunt (which can also be called a heat transfer member) that is used to shunt or transfer heat from, e.g., an electrode to an irrigation passageway. In one embodiment, a heat retention sink is used to retain heat for some period of time. Preferably, a heat shunt (heat transfer member) is used rather than a heat retention sink. A heat shunt (heat transfer member), in some embodiments, provides more efficient dissipation of heat and improved cooling, thus, for example, offering a protective effect to tissue that is considered non-target tissue. For any of the embodiments disclosed herein, one or more heat shunting components can be used to effectively and safely transfer heat away from an electrode and/or the tissue being heated. In some embodiments, a device or system can be configured to adequately transfer heat away from the electrode without any additional components or features (e.g., solely using the heat shunting configurations disclosed herein).

(97) In any of the embodiments disclosed herein, the ablation system can include one or more irrigation conduits that extend at least partially along (e.g., through an interior portion of) a catheter or other medical instrument configured for placement within a subject. The irrigation conduit(s) can be part of an open irrigation system, in which fluid exits through one or more exit ports or openings along the distal end of the catheter (e.g., at or near the electrode) to cool the electrode and/or the adjacent targeted tissue. Alternatively, however, the irrigation conduit(s) can be part of a closed irrigation system, in which irrigation fluid is circulated at least partially through (e.g., as opposed to being expelled from) the catheter (e.g., in the vicinity of the electrode or other ablation member to selectively cool the electrode and/or the adjacent tissue of the subject. For example, in some arrangements, the catheter comprises at least two internal fluid conduits (e.g., a delivery conduit and a return conduit) to circulate irrigation fluid to and perform the desired or necessary heat transfer with the distal end of the catheter, as desired or required. Further, in some embodiments, in order to facilitate the heat transfer between the heat transfer members or components included in the ablation system (e.g., heat shunting members or components), the system can comprise an irrigation conduit that comprises one or more metallic and/or other favorable heat transfer materials (e.g., copper, stainless steel, other metals or alloys, ceramics, polymeric and/or other materials with relatively favorable heat transfer properties, etc.). In yet other embodiments, the catheter or other medical instrument of the ablation system does not include any active fluid cooling system (e.g., open or closed irrigation passage or other components extending through it), as desired or required. As discussed in greater detail herein, such embodiments that do not include active cooling using fluid passage through the catheter can take advantage of enhanced heat transfer components and/or designs to advantageously dissipate and/or distribute heat away from the electrode(s) and/or the tissue being treated.

(98) In some embodiments, the irrigation conduit is fluid communication only with exit ports located along the distal end of the elongate body. In some embodiments, the catheter only comprises irrigation exit openings along a distal end of the catheter (e.g., along a distal end or the electrode). In some embodiments, the system does not comprise any irrigation openings along the heat transfer members (e.g., heat shunt members), and/or, as discussed herein, the system does not comprise an active irrigation system at all. Thus, in such embodiments, the use of heat transfer members along the catheter (e.g., at or near the electrode or other ablation member) help more evenly distribute the heat generated by the electrode or other ablation member and/or assist in heat transfer with the surrounding environment (e.g., blood or other fluid passing along an exterior of the ablation member and/or catheter).

(99) With continued reference to FIG. 10, the proximal end 1132 of the electrode 1130 comprises one or more additional heat transfer members 1150, including any heat shunt embodiments disclosed herein. For example, according to some embodiments, such additional heat transfer members 1150 (e.g., heat shunt members) comprise one or more fins, pins and/or other members that are in thermal communication with the irrigation conduit 108 extending through an interior of the catheter of the system. Accordingly, as with the heat transfer disks or other heat transfer members 1140 positioned along the length of the electrode 1130, including heat shunting members, heat can be transferred and thus removed, from the electrode, the adjacent portions of the catheter and/or the adjacent tissue of the subject, when the electrode is activated, via these heat transfer members 1150.

(100) In any of the embodiments disclosed herein or variations thereof, the heat transfer members 1140, 1150 of the system 1100 that are placed in thermal communication with the irrigation conduit 1108 can comprise one or more materials that include favorable heat transfer properties, including, but not limited to, favorable heat shunting properties. For example, in some embodiments, the thermal conductivity of the material(s) included in the heat transfer members and/or of the overall heat transfer assembly (e.g., when viewed as a unitary member or structure) is greater than 300 W/m/° C. (e.g., 300-350, 350-400, 400-450, 450-500, 500-600, 600-700 W/m/° C., ranges between the foregoing, greater than 700 W/m/° C., etc. Possible materials with favorable thermal conductivity properties include, but are not limited to, copper, brass, beryllium, other metals and/or alloys, aluminal ceramics, other ceramics, industrial diamond and/or other metallic and/or non-metallic materials.

(101) According to certain embodiments where the heat transfer members comprise heat shunting members, the thermal diffusivity of the material(s) included in the heat shunt members and/or of the overall heat shunt assembly (e.g., when viewed as a unitary member or structure) is greater than 1.5 cm.sup.2/sec (e.g., 1.5-2, 2-2.5, 2.5-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20 cm.sup.2/sec, values between the foregoing ranges, greater than 20 cm.sup.2/sec). Thermal diffusivity measures the ability of a material to conduct thermal energy relative to its ability to store thermal energy. Thus, even though a material can be efficient as transferring heat (e.g., can have a relatively high thermal conductivity), it may not have favorable thermal diffusivity properties, because of its heat storage properties. Heat shunting, unlike heat transferring, requires the use of materials that possess high thermal conductance properties (e.g., to quickly transfer heat through a mass or volume) and a low heat capacity (e.g., to not store heat). Possible materials with favorable thermal diffusivity, and thus favorable heat shunting properties, include, but are not limited to, industrial diamond, Graphene, silica, other carbon-based materials and/or the like.

(102) The use of materials with favorable thermal diffusivity properties can help ensure that heat can be efficiently transferred away from the electrode and/or the adjacent tissue during a treatment procedure. In contrast, materials that have favorable thermal conductivity properties, but not favorable thermal diffusivity properties, such as, e.g., copper, other metals or alloys, thermally conductive polypropylene or other polymers, etc., will tend to retain heat. As a result, the use of such materials that store heat may cause the temperature along the electrode and/or the tissue being treated to be maintained at an undesirably elevated level (e.g., over 75 degrees C.) especially over the course of a relatively long ablation procedure, which may result in charring, thrombus formation and/or other heat-related problems.

(103) Industrial diamond and other materials with the requisite thermal diffusivity properties for use in a thermal shunting network, as disclosed in the various embodiments herein, comprise favorable thermal conduction characteristics. Such favorable thermal conduction aspects emanate from a relatively high thermal conductance value (k) and the manner in which the heat shunt members of a network are arranged with respect to each other within the tip and with respect to the tissue. For example, in some embodiments, as RF energy is emitted from the tip and the ohmic heating within the tissue generates heat, the exposed distal most shunt member (e.g., located 0.5 mm from the distal most end of the tip) can actively extract heat from the lesion site. The thermal energy can advantageously transfer through the shunting network in a relatively rapid manner and dissipate through the shunt residing beneath the RF electrode surface the heat shunt network, through a proximal shunt member and/or into the ambient surroundings. Heat that is shunting through an interior shunt member can be quickly transferred to an irrigation conduit extending through an interior of the catheter or other medical instrument. In other embodiments, heat generated by an ablation procedure can be shunted through both proximal and distal shunt members (e.g., shunt members that are exposed to an exterior of the catheter or other medical instrument, such as shown in many of the embodiments herein).

(104) Further, as noted above, the materials with favorable thermal diffusivity properties for use in a heat shunt network not only have the requisite thermal conductivity properties but also have sufficiently low heat capacity values (c). This helps ensure that the thermal energy is dissipated very quickly from the tip to tissue interface as well as the hot spots on the electrode, without heat retention in the heat shunting network. The thermal conduction constitutes the primary heat dissipation mechanism that ensures quick and efficient cooling of the tissue surface and of the RF electrode surface. Conversely a heat transfer (e.g., with relatively high thermal conductivity characteristics but also relatively high heat capacity characteristics) will store thermal energy. Over the course of a long ablation procedure, such stored heat may exceed 75 degrees C. Under such circumstances, thrombus and/or char formation can undesirably occur.

(105) The thermal convection aspects of the various embodiments disclosed herein two-fold. First, an irrigation lumen of the catheter can absorb thermal energy which is transferred to it through the shunt network. Such thermal energy can then be flushed out of the distal end of the RF tip via the irrigation ports. In closed irrigation systems, however, such thermal energy can be transferred back to a proximal end of the catheter where it can be removed. Second, the exposed shunt surfaces along an exterior of the catheter or other medical instrument can further assist with the dissipation of heat from the electrode and/or the tissue being treated. For example, such heat dissipation can be accomplished via the inherent convective cooling aspects of the blood flowing over the surfaces of the electrode.

(106) Accordingly, the use of materials in a heat shunting network with favorable thermal diffusivity properties, such as industrial diamond, can help ensure that heat is quickly and efficiently transferred away from the electrode and treated tissue, while maintaining the heat shunting network cool (e.g., due to its low heat capacity properties). This can create a safer ablation catheter and related treatment method, as potentially dangerous heat will not be introduced into the procedure via the heat shunting network itself.

(107) For example, in some embodiments, during the course of an ablation procedure that attempts to maintain the subject's tissue at a desired temperature of about 60 degrees C., the temperature of the electrode is approximately 60 degrees Celsius. Further, the temperature of traditional heat transferring members positioned adjacent the electrode (e.g., copper, other metals or alloys, thermally-conductive polymers, etc.) during the procedure is approximately 70 to 75 degrees Celsius. In contrast, the temperature of the various portions or members of the heat shunting network for systems disclosed herein can be approximately 60 to 62 degrees Celsius (e.g., 10% to 30% less than comparable heat transferring systems) for the same desired level of treatment of tissue.

(108) In some embodiments, the heat shunt members disclosed herein draw out heat from the tissue being ablated and shunt it into the irrigation channel. Similarly, heat is drawn away from the potential hot spots that form at the edges of RF electrodes and are shunted through the heat shunt network into the irrigation channel. From the irrigation channel, via convective cooling, heat can be advantageously released into the blood stream and dissipated away. In closed irrigation systems, heat can be removed from the system without expelling irrigation fluid into the subject.

(109) According to some embodiments, the various heat shunting systems disclosed herein rely on heat conduction as the primary cooling mechanism. Therefore, such embodiments do not require a vast majority of the heat shunting network to extend to an external surface of the catheter or other medical instrument (e.g., for direct exposure to blood flow). In fact, in some embodiments, the entire shunt network can reside within an interior of the catheter tip (i.e., with no portion of the heat shut network extending to an exterior of the catheter or other medical instrument). Further, the various embodiments disclosed herein do not require electrical isolation of the heat shunts from the RF electrode or from the irrigation channel.

(110) According to some embodiments, the heat transfer disks and/or other heat transfer members 1140, 1150 included in a particular system, including heat shunting members or components, can continuously and/or intermittently or partially extend to the irrigation conduit 108, as desired or required for a particular design or configuration. For instance, as illustrated in the embodiment of FIG. 10, the proximal heat transfer member 1150 (e.g., heat shunt members) can comprise one or more (e.g., 2, 3, 4, 5, more than 5, etc.) wings or portions 1154 than extend radially outwardly from a base or inner member 1152. In some embodiments, such wings or radially-extending portion 1154 are equally spaced from each other to more evenly transfer heat toward the irrigation conduit 1108 with which the heat transfer member 1150 is in thermal communication. Alternatively, however, the heat transfer member 1150, including, but not limited to, a heat shunt member, can include a generally solid or continuous structure between the irrigation conduit 1108 and a radially exterior portion or region of the catheter.

(111) According to some embodiments, heat transfer members (e.g., fins) 1150 can extend proximally to the proximal end of the electrode(s) included along the distal end of a catheter. For example, as illustrated in FIG. 10, the heat transfer members 1150 (e.g., heat shunt members) can extend to, near or beyond the proximal end of the electrode 1130. In some embodiments, the heat transfer members 1150 terminate at or near the proximal end 1132 of the electrode 1130. However, in other arrangements, the heat transfer members 1150, including, without limitation, heat shunt members, extend beyond the proximal end 1132 of the electrode 1130, and in some embodiments, contact and/or are otherwise in direct or indirect thermal communication with distally-located heat transfer members (e.g., heat transfer disks or other heat transfer members located along or near the length of the electrode 1130), including heat shunt members, as desired or required. In yet other embodiments, proximal heat transfer members (e.g., heat shunt members) terminate proximally to the proximal end 1132 of the electrode or other ablation member.

(112) In any of the embodiments disclosed herein, including the systems comprising the enhanced heat transfer (e.g., heat shunting) properties discussed in connection with FIGS. 9-12, the system can include one or more temperature sensors or temperature detection components (e.g., thermocouples) for the detection of tissue temperature at a depth. For example, in the embodiments illustrated in FIGS. 9 and 10, the electrode and/or other portion of the distal end of the catheter can include one or more sensors (e.g., thermocouples, thermistors, etc.) and/or the like. Thus, signals received by sensors and/or other temperature-measurement components can be advantageously used to determine or approximate the extent to which the targeted tissue is being treated (e.g., heated, cooled, etc.). Temperature measurements can be used to control an ablation procedure (e.g., module power provided to the ablation member, terminate an ablation procedure, etc.), in accordance with a desired or required protocol.

(113) In some embodiments, the device further comprises a one or more temperature sensors or other temperature-measuring devices to help determine a peak (e.g., high or peak, low or trough, etc.) temperature of tissue being treated. In some embodiments, the temperature sensors (e.g., thermocouples) located at, along and/or near the ablation member (e.g., RF electrode) can help with the determination of whether contact is being made between the ablation member and targeted tissue (and/or to what degree such contact is being made). In some embodiments, such peak temperature is determined without the use of radiometry. Additional details regarding the use of temperature sensors (e.g., thermocouples) to determine peak tissue temperature and/or to confirm or evaluate tissue contact are provided herein.

(114) In some embodiments, for any of the systems disclosed herein (including but not limited to those illustrated herein) or variations thereof, one or more of the heat transfer members, including, but not limited to, heat shunt members, that facilitate the heat transfer to an irrigation conduit of the catheter are in direct contact with the electrode and/or the irrigation conduit. However, in other embodiments, one or more of the heat transfer members (e.g., heat shunt members) do not contact the electrode and/or the irrigation conduit. Thus, in such embodiments, the heat transfer members are in thermal communication with the electrode and/or irrigation conduit, but not in physical contact with such components. For example, in some embodiments, one or more intermediate components, layers, coatings and/or other members are positioned between a heat transfer member (e.g., a heat shunt member) and the electrode (or other ablation member) and/or the irrigation conduit.

(115) FIG. 11 illustrates another embodiment of an ablation system 1200 comprising an electrode (e.g., a RF electrode, a split-tip electrode, etc.) or other ablation member 1230 located along or near the distal end of a catheter or other elongated member. In some embodiments, an interior portion 1236 of the electrode or other ablation member (not shown in FIG. 11, for clarity) can include a separate, internal heat transfer member 1250B, including any heat shunt embodiments disclosed herein. Such a heat transfer member 1250B can be in addition to or in lieu of any other heat transfer members located at, within and/or near the electrode or other ablation member. For example, in the depicted embodiment, in the vicinity of the electrode 1230, the system 1200 comprises both an internal heat transfer member 1250B and one or more disk-shaped or cylindrical heat transfer members 1240 (e.g., heat shunting members).

(116) For any of the embodiments disclosed herein, at least a portion of heat transfer member, including a heat shunt member, that is in thermal communication with the irrigation conduit extends to an exterior surface of the catheter, adjacent to (and, in some embodiments, in physical and/or thermal contact with) the electrode or other ablation member. Such a configuration, can further enhance the cooling of the electrode or other ablation member when the system is activated, especially at or near the proximal end of the electrode or ablation member, where heat may otherwise tend to be more concentrated (e.g., relative to other portions of the electrode or other ablation member). According to some embodiments, thermal conductive grease and/or any other thermally conductive material (e.g., thermally-conductive liquid or other fluid, layer, member, coating and/or portion) can be used to place the thermal transfer, such as, for example, a heat shunt member or heat shunt network, in thermal communication with the irrigation conduit, as desired or required. In such embodiments, such a thermally conductive material places the electrode in thermal communication, at least partially, with the irrigation conduit.

(117) With continued reference to FIG. 11, the heat transfer member (e.g., heat shunt member) 1250B located along an interior portion of the electrode 1230 can include one or more fins, wings, pins and/or other extension members 1254B. Such members 1254B can help enhance heat transfer with the (e.g., heat shunting to, for heat shunting embodiments) irrigation conduit 1208, can help reduce the overall size of the heat transfer member 1254B and/or provide one or more additional advantages or benefits to the system 1200.

(118) Another embodiment of an ablation system 1300 comprising one or more heat transfer (e.g., heat shunt) components or features that facilitate the overall heat transfer of the electrode or other ablation member during use is illustrated in FIG. 12. As shown, heat transfer (e.g., shunting) between one or more heat transfer members 1350B located along an interior of an electrode or other ablation member 1330 can be facilitated and otherwise enhanced by eliminating air gaps or other similar spaces between the electrode and the heat transfer members. For example, in the illustrated embodiment, one or more layers 1356 of an electrically conductive material (e.g., platinum, gold, other metals or alloys, etc.) have been positioned between the interior of the electrode 1330 and the exterior of the heat transfer member 1350B. Such layer(s) 1356 can be continuously or intermittently applied between the electrode (or another type of ablation member or energy delivery member) and the adjacent heat transfer member(s), including, but not limited to, heat shunting member(s). Further, such layer(s) 1356 can be applied using one or more methods or procedures, such as, for example, sputtering, other plating techniques and/or the like. Such layer(s) 1356 can be used in any of the embodiments disclosed herein or variations thereof.

(119) FIG. 13 illustrates a distal portion of a catheter or other medical instrument of an ablation system 1800 comprising one or more heat transfer members 1850 (e.g., heat shunt members) that facilitate the efficient transfer of heat generated by the electrode or other energy delivery member 1830. As shown in FIG. 13, the heat shunt members 1850 are positioned immediately adjacent (e.g., within an interior of) the electrode 1830. Accordingly, as discussed in greater detail herein, heat generated by the electrode or other energy delivery member 1830 can be transferred via the one or more heat shunt members 1850. As discussed above, the heat shunt members advantageously comprise favorable thermal diffusivity properties to quickly transfer heat while not retaining heat. Thus, the likelihood of localized hot spots (e.g., along the distal and/or proximal ends of the electrode) can be prevented or reduced. In addition, the heat dissipation or removal (e.g., away from the electrode) can be more easily and/or quickly realized using the heat shunt members 1850.

(120) As discussed herein, for example, the heat shunt members 1850 can include industrial diamond, Graphene, silica or other carbon-based materials with favorable thermal diffusivity properties and/or the like. In some embodiments, the heat shunt members 1850 comprise a combination of two, three or more materials and/or portions, components or members. In some embodiments, the thermal diffusivity of the material(s) included in the heat shunt members and/or of the overall heat shunting network or assembly (e.g., when viewed as a unitary member or structure) is greater than 1.5 cm.sup.2/sec (e.g., 1.5-2, 2-2.5, 2.5-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20 cm.sup.2/sec, values between the foregoing ranges, greater than 20 cm.sup.2/sec).

(121) The heat shunt members 1850 (e.g., fins, rings, blocks, etc.) can be in direct or indirect contact with the electrode or other energy delivery member 1830. Regardless of whether direct physical contact is made between the electrode and one or more of the heat transfer shunt 1850, the heat shunt members 1850 can be advantageously in thermal communication with the electrode, thereby facilitating the heat dissipation and/or heat transfer properties of the catheter or other medical instrument. In some embodiments, for example, one or more intermediate layers, coatings, members and/or other components are positioned between the electrode (or other energy delivery member) and the heat shunt members, as desired or required.

(122) With continued reference to FIG. 13, as discussed with other embodiment herein, a catheter or other medical instrument of the ablation system 1800 comprises an open irrigation system configured to deliver a cooling fluid (e.g., saline) to and through the distal end of the catheter or other medical instrument. Such an open irrigation system can help remove heat from the electrode or other energy delivery member during use. In some embodiments, the heat shunting network and the favorable thermal diffusivity properties it possesses can help to quickly and efficiently transfer heat from the electrode and/or the tissue being treated to an irrigation conduit or passage 1804 or chamber 1820 during use. For example, as depicted in FIG. 13, an irrigation conduit or passage 1804 extends through an interior of the catheter and is in fluid communication with one or more outlet ports 1811 along the distal member 1810 of the catheter. However, as discussed in greater detail herein, enhanced heat shunt members can be incorporated into the design of a catheter or other medical instrument without the use of an open irrigation system and/or without an active fluid cooling system, as desired or required. In some embodiments, the flow of irrigation fluid (e.g., saline) through the irrigation conduit or chamber of the catheter or other medical instrument can be modified to vary the heat shunting that occurs through the heat shunting network. For example, in some embodiments, due to the favorable heat transfer properties of the heat shunting network and its ability to not retain heat, the flow rate of irrigation fluid through a catheter can be maintained below 5 ml/min (e.g., 1-2, 2-3, 3-4, 4-5 ml/min, flow rates between the foregoing ranges, less than 1 ml/min, etc.). In one embodiment, the flow rate of irrigation fluid through a catheter is maintained at approximately 1 ml/min. In other embodiments, the flow rate of irrigation fluid passing through the catheter can be between 5 and 15 ml/min (e.g., 5-6, 6-7, 7-8, 8-9, 9-10, 11-12, 12-13, 13-14, 14-15 ml/min, flow rates between the foregoing rates, etc.) or greater than 15 ml/min (e.g., 15-16, 16-17, 17-18, 18-19, 19-20 ml/min, flow rates between the foregoing rates, etc.), as desired or required. In some embodiments, such irrigation flow rates are significantly less than would otherwise be required if non-heat shunting members (e.g., metals, alloys, thermally-conductive polymers, other traditional heat transferring members, etc.) were being used to transfer heat away from the electrode and/or the tissue between treated. For example, the required flow rate of the irrigation fluid passing through an interior of a catheter that has a heat shunting member in accordance with the various embodiments disclosed herein or variations thereof, can be decreased by 20% to 90% (e.g., 20-25, 25-30, 30-35, 35-40, 40-45, 45-50, 50-55, 55-60, 60-65, 65-70, 70-75, 75-80, 80-85, 85-90%, percentages between the foregoing ranges, etc.), as compared to systems that use traditional heat transferring members or no heat transferring members at all (e.g., assuming the same amount of heating is produced at the electrode, the same anatomical location is being treated and other parameters are the same). For example, in some commercially available RF ablation systems, an irrigation flow rate of about 30 ml/min (e.g., 25-35 ml/min) is typically required to accomplish a desired level of heat transfer way from the electrode. As noted above, in some arrangements, the systems disclosed herein that utilize a heat shunting network can utilize a irrigation flow rate of about 10 ml/min or lower to effectively shunt the heat away from the electrode. Thus, in such embodiments, the irrigation flow rate can be reduced by at least 60% to 70% relative to traditional and other commercially available systems.

(123) Thus, as noted in greater detail herein, the use of heat shunting materials to shunt heat away from the electrode and/or the adjacent tissue can also reduce the amount of irrigation fluid that is being discharged into the subject's blood stream in an open irrigation system. Since the discharge of irrigation fluid into the subject is not desirable, the use of heat shunting in an ablation catheter can provide additional benefits to an ablation procedure. For example, in some arrangements, discharging excessive saline or other cooling fluid into the heart, blood vessel and/or other targeted region of the subject can bring about negative physiological consequences to the subject (e.g., heart failure).

(124) As noted above, the use of heat shunting components at or near the electrode can also provide one or more additional benefits and advantages. For example, a significantly lower irrigation flow rate is required to effectively remove heat away from the electrode and the surrounding tissue using heat shunting components (e.g., vis-à-vis traditional heat transferring components and members), the irrigation fluid in such systems is less likely to negatively impact any temperature sensors that are located along or near the outside of the distal end of a catheter, allowing more accurate temperature measurements. This is particularly relevant for systems, such as those disclosed herein, where temperature sensors are configured to detect the temperature of adjacent tissue of a subject (e.g., not the temperature of the electrode or another component or portion of the treatment system). Thus, the lower volume of fluid being discharged at or in the vicinity of the sensors (e.g., compared to systems that do not use heat shunting, systems that include traditional heat transfer components, systems that rely primarily or strictly on heat transfer between the electrode (and/or tissue) and blood passing adjacent the electrode (and/or tissue), other open-irrigation systems, etc.) can increase the accuracy of the temperature measurements obtained by the sensors located at or near the distal end of a catheter or other medical instrument.

(125) Also, since the irrigation fluid can be delivered at a lower flow rate which is characterized by a laminar flow profile (e.g., as opposed to a turbulent flow profile that may be required when the irrigation flow rate is higher), any disruptive fluid dynamic effects resulting from an otherwise higher flow rate can be advantageously avoided or at least reduced. Thus, the laminar flow of fluid (and/or in conjunction with the significantly lower flow rate of the fluid relative to higher flow systems) can help with the accuracy of the temperature measurements by the sensors located near the electrode, the tissue being treated and/or any other location along the distal end of the catheter or other medical instrument.

(126) Further, since heat shunting components positioned along or near the electrode are so effective in transferring heat away from the electrode and/or the adjacent tissue of the subject being treated without retaining the heat being transferred, the need to have a longer electrode and/or larger heat transferring members or portions can be advantageously eliminated. For example, traditional systems that utilize one or more heat transferring members (as opposed and in contrast to heat shunting members) or systems that do not use any heat transferring members or components at all rely on the heat transfer between the electrode and the surrounding environment (e.g., blood that flows past the electrode, irrigation fluid passing through an interior of the catheter, etc.) to attempt to cool the electrode. As a result, the length, size and/or other dimensions of the electrode or traditional heat transferring members needs to be increased. This is done to increase the surface area for improved heat transfer between the electrode and/or the heat transferring members and the fluid that will provide the heat transfer (e.g., blood, irrigation fluid, etc.). However, in various embodiments disclosed herein, it is advantageously not necessary to provide such enlarged surface areas for the electrode and/or the heat shunting components or other members of the heat shunting network. Accordingly, the electrode can be sized based on the intended ablation/heating and/or mapping (e.g., high-resolution) properties without the need to oversize based on heat transfer capacity. Such oversizing can negatively impact the safety and efficacy of a lesion formation procedure.

(127) Therefore, as discussed herein, in some embodiments, the size of the heat shunting members can be advantageously reduced (e.g., as compared to the size of heat transferring members in traditional systems). Heat generated during a treatment procedure can be efficiently and rapidly transferred away from electrode and/or the tissue being treated via the heat shunting network without the fear of such network retaining the heat being transferred. In some embodiments, the heat can be shunted to irrigation fluid passing through an interior of the catheter or other medical instrument. In other embodiments, heat can be transferred to surrounding bodily fluid of the subject (e.g., blood) via heat shunting members that are positioned along an exterior of the catheter or other medical instrument, either in addition or in lieu of heat shunting to an irrigation fluid.

(128) According to some embodiments, the total length (e.g., along a longitudinal direction) of the heat shunting members that extend to the exterior of the catheter or other medical instrument (such as, e.g., in the configurations depicted in FIGS. 13 to 17B) can be 1 to 3 mm (e.g., 1-1.5, 1.5-2, 2-2.5, 2.5-3 mm, lengths between the foregoing values, etc.). As noted above, despite such a relatively short exposure length, the heat shunting members can effectively transfer heat away from the electrode and/or the tissue being ablated without retaining heat.

(129) According to some embodiments, the total length (e.g., along a longitudinal direction) of the heat shunting members that extend along an interior of the catheter or other medical instrument (such as, e.g., in the configurations depicted in FIGS. 13 to 17B) can be 1 to 30 mm (e.g., 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20, 20-25, 25-30 mm, lengths between the foregoing values, etc.). As noted above, despite such a relatively short overall length, the heat shunting members can effectively transfer heat away from the electrode and/or the tissue being ablated to fluid passing through the irrigation channel of the catheter or other medical instrument without retaining heat.

(130) According to some embodiments, the total length (e.g., along a longitudinal direction) of the heat shunting members that extend along an interior of the catheter or other medical instrument plus the electrode (such as, e.g., in the configurations depicted in FIGS. 13 to 17B) can be 1 to 30 mm (e.g., 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20, 20-25, 25-30 mm, lengths between the foregoing values, etc.). As noted above, despite such a relatively short overall length, the heat shunting members can effectively transfer heat away from the electrode and/or the tissue being ablated to fluid passing through the irrigation channel of the catheter or other medical instrument without retaining heat.

(131) As illustrated in FIG. 13, an interior of the distal end of the catheter or other medical instrument can comprise a cooling chamber or region 1820 that is in fluid communication with the irrigation conduit or passage 1804. As shown, according to some embodiments, the cooling chamber 1820 includes a diameter or cross-sectional dimension that is greater than the diameter or cross-sectional dimension of the fluid conduit or passage 1804. For example, in some arrangements, the diameter or other cross-sectional dimension of the cooling chamber or region 1820 is approximately 1 to 3 times (e.g., 1 to 1.1, 1.1 to 1.2, 1.2 to 1.3, 1.3 to 1.4, 1.4 to 1.5, 1.5 to 1.6, 1.6 to 1.7, 1.7 to 1.8, 1.8 to 1.9, 1.9 to 2.0, 2.0 to 2.1, 2.1 to 2.2, 2.2 to 2.3, 2.3 to 2.4, 2.4 to 2.5, 2.5 to 2.6, 2.6 to 2.7, 2.7 to 2.8, 2.8 to 2.9, 2.9 to 3, values between the foregoing, etc.) the diameter or cross-section dimension of the fluid conduit or passage 1804, as desired or required. In other embodiments, the diameter or other cross-sectional dimension of the cooling chamber or region 1820 is approximately greater than 3 times the diameter or cross-section dimension of the fluid conduit or passage 1804, as desired or required (e.g., 3 to 3.5, 3.5 to 4, 4 to 5, values between the foregoing, greater than 5, etc.). In other embodiments, the diameter or cross-section dimension of the cooling chamber or region 1820 is similar or identical to that of the fluid conduit or passage 1804 (or smaller than that of the fluid conduit or passage), as desired or required.

(132) FIG. 14 illustrates a distal end of a catheter or other medical instrument of another embodiment of an ablation system 1900. As shown, the catheter comprises one or more energy delivery members 1930 (e.g., a split-tip RF electrode, another type of electrode, another type of ablation member, etc.) along its distal end. Like in FIG. 13, the depicted arrangement comprises an active cooling system using one or more fluid conduits or passages that extend at least partially through the interior of the catheter or other medical instrument.

(133) With continued reference to FIG. 14, the catheter or medical instrument of the ablation system 1900 includes a closed irrigation system (e.g., non-open irrigation system) in which cooling fluid (e.g., saline) is circulated at least partially through an interior of the catheter (e.g., to and/or near the location of the electrode or other energy delivery member) to transfer heat away from such electrode or other energy delivery member. As shown, the system can include two separate conduits or passages 1904, 1906 extending at least partially through the interior of the catheter or other medical instrument configured for placement within and/or adjacent targeted tissue of a subject. In some embodiments, one fluid conduit or passage 1904 is configured to deliver fluid (e.g., saline) to the distal end of the catheter or instrument (e.g., adjacent the electrode, ablation member or other energy delivery member), while a separate conduit or passage 1906 is configured to return the cooling fluid delivered to or near the distal end of the catheter or other medical instrument proximally. In other embodiments, more than one passage or conduit delivers fluid to the distal end and/or more than one passage or fluid returns fluid from the distal end, as desired or required.

(134) In the embodiment of FIG. 14, the fluid delivery conduit or passage 1904 is in fluid communication with a cooling chamber or region 1920 that extends within an interior of the electrode or other energy delivery member 1930. In the depicted arrangement, the outlet 1905 of the fluid delivery conduit or passage 1904 is located at a location proximal to the distal end or inlet 1907 of the fluid return conduit or passage 1906. Thus, in the illustrated embodiment, the cooling chamber or region 1920 generally extends between the outlet 1905 of the fluid delivery conduit or passage 1904 and the inlet 1907 of the fluid return conduit or passage 1906. However, in other embodiments, the length, orientation, location and/or other details of the cooling chamber or portion 1920 can vary, as desired or required. Further, in some embodiments, a catheter or other medical instrument can include a closed fluid cooling system (e.g., wherein cooling fluid is circulated through the catheter or medical instrument) without the inclusion of a separate cooling chamber or portion. Regardless of the exact orientation of the various fluid delivery and/or return lines (e.g., passages, conduits, etc.) of the catheter or medical instrument in a closed-loop fluid cooling system, fluid is simply circulated through at least a portion of the catheter or other medical instrument (e.g., adjacent and/or in the vicinity of the electrode or energy delivery member being energized) to selectively and advantageously transfer heat away from the electrode or energy delivery member. Thus, in such embodiments, the various fluid conduits or passages are in thermal communication with the electrode or other energy delivery member.

(135) In some embodiments, it is advantageous to transfer heat away from the electrode (or other energy delivery member) of an ablation system, and thus, the targeted tissue of the subject, without expelling or discharging cooling fluid (e.g., saline) into the subject. For example, in some arrangements, discharging saline or other cooling fluid into the heart, blood vessel and/or other targeted region of the subject can bring about negative physiological consequences to the subject (e.g., heart failure). Thus, in some embodiments, it is preferred to treat a subject with an ablation system that includes a catheter or other medical instrument with a closed fluid cooling system or without an active fluid cooling system altogether.

(136) As with the embodiment of FIG. 14 (and/or other embodiments disclosed herein), the depicted catheter includes one or more heat shunt members 1950 that are in thermal communication with the electrode, ablation member or other energy delivery member 1930 of the system 1900. As discussed above, the heat shunt members 1950 can include industrial diamond, Graphene, silica, other carbon-based materials with favorable thermal diffusivity properties and/or the like. In some embodiments, the thermal diffusivity of the material(s) included in the heat shunt members and/or of the overall heat shunt network or assembly (e.g., when viewed as a unitary member or structure) is greater than 1.5 cm.sup.2/sec (e.g., 1.5-2, 2-2.5, 2.5-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20 cm.sup.2/sec, values between the foregoing ranges, greater than 20 cm.sup.2/sec).

(137) FIG. 15 illustrates yet another embodiment of a catheter or other medical instrument of an ablation system 2000 can includes one or more heat transfer members 2050 (e.g., heat shunt members) along and/or near its distal end. Unlike the arrangements of FIGS. 13 and 14 discussed herein, the depicted embodiment does not include an active fluid cooling system. In other words, the catheter or other medical instrument does not comprise any fluid conduits or passages. Instead, in some embodiments, as illustrated in FIG. 15, the distal end of the catheter comprises one or more interior members (e.g., interior structural members) 2070 along its interior. Such interior members 2070 can include a member or material having favorable thermal diffusivity characteristics. In some embodiments, the interior member 2070 comprises identical or similar thermal diffusivity characteristics or properties as the heat shunt members 2050, such as, for example, industrial diamond or Graphene. In some embodiments, the thermal diffusivity of the material(s) included in the interior member 2070 and/or of the overall heat shunt network or assembly (e.g., when viewed as a unitary member or structure) is greater than 1.5 cm.sup.2/sec (e.g., 1.5-2, 2-2.5, 2.5-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20 cm.sup.2/sec, values between the foregoing ranges, greater than 20 cm.sup.2/sec). However, in other embodiments, the interior member(s) do not include high heat shunting materials and/or members. In other embodiments, however, the interior member 2070 does not include materials or members similar to those as the heat shunt members 2050. For example, in some arrangements, the interior member(s) 2070 can include one or more components or members that comprise material(s) having a thermal diffusivity less than 1 cm.sup.2/sec.

(138) With continued reference to the embodiment of FIG. 15, the volume along the distal end of the catheter or medical instrument includes a structural member that at least partially occupies said volume. This is in contrast to other embodiments disclosed herein, wherein at least a portion of the distal end of the catheter or medical instrument includes a cavity (e.g., a cooling chamber) that is configured to receive cooling fluid (e.g., saline) when such cooling fluid is delivered and/or circulated through the catheter or medical instrument.

(139) In embodiments such as the one illustrated in FIG. 15, wherein no active fluid cooling is incorporated into the design of the catheter or other medical instrument of the ablation system 2000, heat generated by and/or at the electrode (or other energy delivery member) 2030 can be more evenly dissipated along the distal end of the catheter or medical instrument as a result of the heat dissipation properties of the heat transfer members 2050, including, without limitation, heat shunt members, (and/or the interior member 2070, to the extent that the interior member 2070 also comprises favorable heat shunting properties, e.g., materials having favorable thermal diffusivity characteristics). Thus, the heat shunt members 2050 can help dissipate heat away from the electrode or other energy delivery member (e.g., either via direct or indirect thermal contact with the electrode or other energy delivery member) to reduce the likelihood of any localized hotspots (e.g., along the distal and/or proximal ends of the electrode or other energy delivery member). Accordingly, heat can be more evenly distributed with the assistance of the heat shunt member 2050 along a greater volume, area and/or portion of the catheter. As discussed above, the use of heat shunting members can quickly and efficiently transfer heat away from the electrode and the tissue being treated during use. The use of materials that comprises favorable thermal diffusivity properties can accomplish the relatively rapid heat transfer without the negative effect of heat retention (e.g., which may otherwise cause charring, thrombus formation and/or other heat-related problems).

(140) Further, in some embodiments, the flow of blood or other natural bodily fluids of the subject in which the catheter or medical instrument is positioned can facilitate with the removal of heat away from the electrode or other energy delivery member. For example, the continuous flow of blood adjacent the exterior of the catheter during use can help with the removal of heat away from the distal end of the catheter. Such heat transfer can be further enhanced or otherwise improved by the presence of one or more heat shunt members that are in thermal communication with the exterior of the catheter. For example, in some arrangements, such as shown in FIG. 15, one or more heat shunt members 2050 can extend to the exterior of the catheter or other medical instrument. Thus, as blood (and/or other bodily fluids) moves past the catheter or other medical instrument when the catheter or medical instrument is inserted within the subject during use, heat can be advantageously transferred through the heat shunt members 2050 to the blood and/or other bodily fluids moving adjacent the catheter. Again, the use of heat shunt materials with favorable thermal diffusivity characteristics will ensure that heat is not retained within such materials, thereby creating a safer ablation system and treatment procedure.

(141) FIGS. 16A and 16B illustrate another embodiment of a catheter or other medical instrument of an ablation system 2100 that includes one or more heat transfer members 2050 (e.g., heat shunt members) along and/or near its distal end. Unlike other embodiments disclosed herein, the illustrated system includes a proximal electrode or electrode portion 2130 that extends deeper into the interior of the catheter. For example, as depicted in the side cross-sectional view of FIG. 16B, the proximal electrode 2130 can extend to or near the outside of the irrigation channel 2120. As discussed herein, the irrigation channel 2120 can comprise one or more metals, alloys and/or other rigid and/or semi-rigid materials, such as, for example, stainless steel.

(142) With continued reference to FIGS. 16A and 16B, the proximal electrode or proximal electrode portion 2130 can be part of a split-tip electrode system, in accordance with the various split-tip embodiments disclosed herein. Thus, in some embodiments, in order for the split tip electrode configuration to operate properly, the distal electrode 2110 is electrically isolated from the proximal electrode 2130. In the illustrated configuration, since the proximal electrode 2130 extends to or near the metallic (and thus, electrically conductive) irrigation tube 2120, at least one electrically insulative layer, coating, member, portion, barrier and/or the like 2128 can be advantageously positioned between the electrode 2130 and the irrigation tube 2120. In some embodiments, for example, the electrically insulative member 2128 comprises one or more layers of polyimide, other polymeric material and/or another electrically insulative material, as desired or required. Such an electrically-insulative layer and/or other member 2128 can take the place of diamond and/or another electrically-insulative heat shunting member that may otherwise be positioned around the irrigation tube 2120 to electrically isolate the distal electrode 2110 from the proximal electrode 2130.

(143) According to any of the embodiments disclosed herein, the proximal and/or the distal electrodes 2130, 2110 can comprise one or more metals and/or alloys. For example, the electrodes can include platinum, stainless steel and/or any other biocompatible metal and/or alloy. Thus, in some embodiments, the thicker proximal electrode 2130 that extends to or near the irrigation tube 2120 can be referred to as a “slug,” e.g., “a platinum slug.” As discussed, in such arrangements, the need for an internal diamond and/or other heat shunting member can be eliminated. Instead, in such embodiments, as depicted in FIG. 16B, the proximal and distal ends of the “slug” or thicker proximal electrode 2130 can be placed in thermal communication with one or more heat shunting members (e.g., diamond) to help shunt heat away from the electrode 2130 and/or the tissue of the subject being treated. Thus, in some embodiments, the proximal and/or the distal faces of the proximal electrode or slug 2130 can be placed in good thermal contact with adjacent heat shunting members, as desired or required.

(144) With continued reference to FIG. 16B, according to some embodiments, at least a portion 2222 of the irrigation tube 2120 is perforated and/or has one or more openings 2123. In some embodiments, such openings 2123 can place an irrigation fluid carried within the interior of the irrigation channel 2120 in direct physical and thermal communication with an adjacent heat shunting member (e.g., diamond, Graphene, silica, etc.) to quickly and efficiently transfer heat away from the electrode and/or tissue being treated. In some embodiments, the direct physical and/or thermal communication between the irrigation fluid and the shunting member helps provide improved heat transfer to the irrigation fluid (e.g., saline) passing through the interior of the irrigation channel 2120. In the illustrated embodiment, the openings 2123 along the perforated portion 2222 are generally circular in shape and evenly distributed relative to each other (e.g., comprise a generally even distribution or spacing relative to each other). However, in other arrangements, the size, shape, spacing and/or other characteristics of the openings 2123 along the perforated or direct contact region 2122 of the channel 2120 can vary, as desired or required. For example, in some embodiments, the openings 2123 can be oval, polygonal (e.g., square or rectangular, triangular, pentagonal, hexagonal, octagonal, etc.), irregular and/or the like. In some embodiments, the openings are slotted or elongated.

(145) Regardless of their exact shape, size, orientation, spacing and/or other details, the openings 2123 that comprise the perforated or direct contact region 2122 of the channel 2120 can provide direct contact between the irrigation fluid and the adjacent diamond (and/or another heat shunting member) 1150 for 30% to 70% (e.g., 30-35, 35-40, 40-45, 45-50, 50-55, 55-60, 60-65, 65-70%, percentages between the foregoing ranges, etc.) of the surface area of the perforated or direct contact region 2122 of the channel 2120. In other embodiments, the openings 2123 that comprise the perforated or direct contact region 2122 of the channel 2120 can provide direct contact between the irrigation fluid and the adjacent diamond (and/or another heat shunting member) 2150 for less than 30% (e.g., 1-5, 5-10, 10-15, 15-20, 20-25, 25-30%, percentages between the foregoing ranges, less than 1%, etc.) or greater than 70% (e.g., 70-75, 75-80, 80-85, 85-90, 90-95, 95-99%, percentages between the foregoing ranges, greater than 99%, etc.) of the surface area of the perforated or direct contact region 2122 of the channel 2120, as desired or required. Such a perforated or direct contact region 2122 can be incorporated into any of the embodiments disclosed herein. In addition, any of the embodiments disclosed herein, including, without limitation, the system of FIGS. 16A and 16B, can include more than one perforated or direct contact region 2122. For example, the embodiment of FIGS. 16A and 16B can include a second perforated or direct contact region along the distal end of the proximal slug or electrode 2130 and/or along any other portion adjacent a heat shunting member.

(146) As illustrated in FIG. 16B, the distal end of an irrigation tube (e.g., a flexible polyurethane or other polymeric conduit) 2104 that is in fluid communication with the irrigation channel 2120 that extends through the distal end of the catheter or other medical instrument can be positioned at least partially within an interior of such a channel 2120. Such a configuration can be incorporated into any of the embodiments disclosed herein or variations thereof. In some embodiments, the distal portion of the irrigation tube 2104 can be sized, shaped and/or otherwise configured to press-fit within an interior of the distal channel 2120. However, in some embodiments, one or more other attachment devices or methods, such as, for example, adhesives, heat bonding, fasteners, etc., can be used to help secure the irrigation tube 2104 to the irrigation channel 2120, as desired or required.

(147) Another embodiment of a distal end of a catheter or other medical instrument 2200 comprising heat shunting characteristics is illustrated in FIG. 16C. As shown, the proximal electrode or slug 2230 extends toward the interior of the catheter (e.g., to or near the irrigation channel 2220). However, the depicted electrode 2230 is generally thinner than (e.g., does not extend as far as) the embodiment of FIGS. 16A and 16B. In the illustrated embodiment, one or more heating shunting members (e.g., diamond, Graphene, silica, etc.) with favorable thermal diffusivity characteristics are positioned between the interior of the proximal electrode or slug 2230 and the irrigation channel 2220. Thus, is such an arrangement, not only can heat generated at or along the electrode 2230 and/or the tissue of the subject being treated be more quickly and efficiently transferred away from the electrode and/or tissue, but the diamond or other electrically-insulating heat shunting member or network 2250 provides the necessary electrical insulation between the metallic (e.g., stainless steel) irrigation channel 2220 and the proximal electrode or slug 2230. As noted herein, such electrical isolation is helpful with a split-tip design.

(148) A distal portion 2300 of another embodiment of an ablation system is illustrated in FIGS. 17A and 17B. As shown, the system comprises a split-tip design, with a proximal electrode or slug 2330 and a distal electrode 2310. Further, the catheter or other medical instrument includes one or more heat transfer members 2350, including, without limitation, a heat shunt network (e.g., comprising diamond, Graphene, silica and/or other materials with favorable thermal diffusivity properties). According to some embodiments, as depicted in the illustrated arrangement, the heat shunt network 2350 can include rings that extend to the exterior of the catheter or instrument and/or one or more interior members that are positioned within (e.g., underneath) the proximal electrode 2330, as desired or required. In addition, as with other embodiments disclosed herein, one or more temperature sensors 2392, 2394 can be provide along one or more portions of the system (e.g., along or near the distal electrode 2310, along or near the proximal heat shunt member, along or near the proximal electrode 2330, etc.) to help detect the temperature of tissue being treated. As discussed in greater detail in such temperature sensors (e.g., thermocouples) can also be used to detect the orientation of the tip, to determine whether (and/or to what extent) contact is being made between the tip and tissue and/or the like.

(149) With continued reference to the embodiment of FIGS. 17A and 17B, the catheter or other medical instrument can include a proximal coupling or member 2340. As shown, such a coupling or member 2340 is configured to connect to and be placed in fluid communication with an irrigation conduit (e.g., polyurethane, other polymeric or other flexible conduit, etc.) 2304. For example, in the illustrated embodiment, the distal end of the irrigation conduit 2304 is sized, shaped and otherwise configured to be inserted within a proximal end (e.g., recess) of the coupling 2340. In some embodiments, the irrigation conduit 2304 is press-fit within the recess of the coupling 2340. In other arrangements, however, one or more other attachment devices or methods can be used to secure the conduit 2304 to the coupling 2340 (e.g., adhesive, weld, fasteners, etc.), either in lieu or in addition to a press-fit connection, as desired or required. Regardless of the exact mechanism of securement between the irrigation conduit 2304 and the coupling 2340, fluid passing through the conduit 2304 can enter into a manifold 2342 of the coupling 2340. In some embodiments, the manifold 2342 can divide the irrigation fluid flow into two or more pathways 2344. However, in some embodiments, the coupling 2340 does not have a manifold. For example, irrigation fluid entering the coupling 2340 can be routed only along a single fluid pathway, as desired or required.

(150) In the embodiment of FIGS. 17A and 17B, the manifold (or other flow dividing feature, device or component) 2342 of the coupling 2340 separates the irrigation flow into three different fluid pathways. As shown, each such fluid pathway can be placed in fluid communication with a separate fluid conduit or sub-conduit 2320. In some embodiments, such fluid conduits 2320 are equally spaced apart (e.g., radially) relative to the centerline of the catheter or other medical instrument. For example, the conduits 2320 can be spaced apart at or approximately at 120 degrees relative to each other. As shown, the conduits 2320 extend, at least partially, through the proximal heat shunt member 2350 and the proximal slug or electrode 2330. However, in other embodiments, the orientation, spacing and/or other details of the manifold 2342, 2344 and/or the fluid conduits 2320 can vary. In addition, the number of fluid conduits 2320 originating from the manifold system can be greater than 3 (e.g., 4, 5, 6, 7, greater than 7, etc.) or less than 3 (e.g., 1, 2), as desired or required.

(151) In some embodiments in which the system comprises an open-irrigation system, as illustrated in the longitudinal cross-sectional view of FIG. 17B, one or more irrigation fluid outlets 2332a, 2332b, 2332c can be provided along one or more of the fluid conduits 2320. As shown, such fluid outlets 2332 can provided within the proximal electrode 2330. However, in other embodiments, such outlets 2332 can be included within one or more other portions of the system (e.g., a heat shunt member 2350, the distal electrode 2310, etc.), either in lieu of or in addition to the proximal electrode 2330. Such a configuration (e.g., one including a manifold and/or openings through the proximal electrode) can be incorporated into any of the ablation system embodiments disclosed herein. As with other irrigation system arrangements disclosed herein, heat can be shunted (e.g., from the electrode, the tissue being treated, one or more other portions of the system, etc.) to the irrigation fluid passing through the conduits and/or fluid outlets to help quickly and efficiently dissipate (e.g., shunt) heat from the system during use. In some embodiments, as illustrated in FIGS. 17A and 17B, the relative size, shape and/or other configuration of two or more of the fluid outlets 2332 can vary. For example, in some arrangements, in order to better balance the fluid hydraulics of fluid passing through each conduit 2320 (e.g., to better balance the flow rate passing through each outlet 2332), the proximal fluid outlets can be smaller than one or more of the distal fluid outlets. However, in other embodiments, two or more (e.g., most or all) of the fluid outlets 2332 include the identical shape, size and/or other properties.

(152) In some embodiments, the orientation of the fluid outlets can be skewed relative to the radial direction of the catheter or other medical instrument in which they are located. Such a skewing or offset can occur for any fluid outlets located along the distal end of the catheter or other medical instrument (e.g., fluid outlets located along the distal electrode as shown in FIGS. 13, 16A and 16B and 16C, fluid outlets located along the proximal electrode as shown in FIGS. 17A and 17B, etc.). The extent to which the outlets are skewed or offset (e.g., relative to the radial direction of the catheter or medical instrument, relative to a direction perpendicular to the longitudinal centerline of the catheter or medical instrument) can vary, as desired or required. By way of example, the fluid openings can be skewed or offset relative to the radial direction by 0 to 60 degrees (e.g., 0-5, 5-10, 10-15, 15-20, 20-25, 25-30, 30-35, 35-40, 40-45, 45-50, 50-55, 55-60 degrees, angles between the foregoing ranges, etc.). In some embodiments, the fluid openings are skewed or offset relative to the radial direction by more than 60 degrees (e.g., 60-65, 65-70, 70-75 degrees, angles between the foregoing ranges, greater than 70 degrees, etc.), as desired or required.

(153) According to some embodiments, fluid outlets or openings located along or near the distal electrode are skewed or offset distally (e.g., in a direction distal to the location of the corresponding fluid outlet or opening). In some embodiments, fluid outlets or openings located along or near the proximal electrode are skewed or offset proximally (e.g., in a direction proximal to the location of the corresponding fluid outlet or opening). Thus, in some embodiments, irrigation fluid exiting at or near the distal electrodes is delivered in a direction distal to the corresponding fluid outlet(s), and irrigation fluid exiting at or near the proximal electrodes is delivered in a direction proximal to the corresponding fluid outlet(s). In some embodiments, such a configuration can assist with cooling hot spots that may otherwise be created along or near the electrode. Such a configuration could also help dilute the blood in those areas to help reduce the chance of thrombus and/or coagulation formation.

(154) Multiple Temperature Sensors

(155) According to some embodiments, a medical instrument (for example, ablation catheter) can include multiple temperature-measurement devices (for example, thermocouples, thermistors, other temperature sensors) spaced axially at different locations along a distal portion of the medical instrument. The axial spacing advantageously facilitates measurement of a meaningful spatial temperature gradient. Each of the temperature-measurement devices may be isolated from each of the other temperature-measurement devices to provide independent temperature measurements. The temperature-measurement devices may be thermally insulated from one or more energy delivery members (for example, radiofrequency electrodes) so as not to directly measure the temperature of the energy delivery member(s), thereby facilitating temperature measurements that are isolated from the thermal effects of the energy delivery member(s). The medical instrument may comprise a first plurality (for example, set, array, group) of temperature sensors positioned at or adjacent a distal tip, or terminus, of the medical instrument. The first plurality of temperature sensors may be spaced apart (for example, circumferentially, radially) around the medical instrument along a first cross-sectional plane of the medical instrument, in an equidistant manner or non-equidistant manner. The medical instrument may also comprise a second plurality of temperature sensors spaced proximally from the first plurality of temperature sensors along a second cross-sectional plane of the medical instrument that is proximal of the first cross-sectional plane, thereby allowing for temperature measurements to be obtained at multiple locations. In some embodiments, the second plurality of temperature sensors is positioned adjacent to a proximal end (for example, edge) of the electrode or other energy delivery member (if the medical instrument (for example, ablation catheter) comprises a single electrode or other energy delivery member) or of the proximal-most electrode or other energy delivery member (if the medical instrument comprises multiple electrode members or other energy delivery members).

(156) The temperature measurements obtained from the temperature sensors may advantageously be used to determine, among other things, an orientation of the distal tip of the medical instrument with respect to a tissue surface, to determine an estimated temperature of a peak temperature zone of a lesion formed by the medical instrument (for example, ablation catheter), and/or an estimated location of the peak temperature zone of the lesion. In some embodiments, the determinations made using the temperature sensors or other temperature-measurement devices can be used to adjust treatment parameters (for example, target temperature, power, duration, orientation) so as to prevent char or thrombus if used in a blood vessel and/or to control lesion parameters (for example, depth, width, location of peak temperature zone, peak temperature), thus providing more reliable and safer treatment (for example, ablation) procedures. Accordingly, upon implementation of a control scheme that regulates the delivery of power or other parameters to an energy delivery member (for example, RF electrode, microwave emitter, ultrasound transducer, cryogenic emitter, other emitter, etc.) located along the distal end of a medical apparatus (for example, catheter, probe, etc.), the target level of treatment can be accomplished without negatively impacting (for example, overheating, over-treating, etc.) the subject's tissue (for example, within and/or adjacent a treatment volume).

(157) The term peak temperature, as used herein, can include either a peak or high temperature (for example, a positive peak temperature) or a trough or low temperature (for example, negative peak temperature). As a result, determination of the peak temperature (for example, maximum or minimum temperature or other extreme temperature) within targeted tissue can result in a safer, more efficient and more efficacious treatment procedure. In some embodiments, when, for example, cryoablation is performed, the systems, devices and/or methods disclosed herein can be used to determine the trough or lowest temperature point, within the treatment (for example, ablation) volume. In some embodiments, technologies that cool tissue face similar clinical challenges of controlling the tissue temperature within an efficacious and safe temperature range. Consequently, the various embodiments disclosed herein can be used with technologies that either cool or heat targeted tissue.

(158) Several embodiments of the invention are particularly advantageous because they include one, several or all of the following benefits: (i) reduction in proximal edge heating, (ii) reduced likelihood of char or thrombus formation, (iii) providing feedback that may be used to adjust ablation procedures in real time, (iv) provides noninvasive temperature measurements, (v) does not require use of radiometry; (vi) provides safer and more reliable ablation procedures; and (vii) tissue temperature monitoring and feedback during irrigated or non-irrigated ablation.

(159) For any of the embodiments disclosed herein, a catheter or other minimally-invasive medical instrument can be delivered to the target anatomical location of a subject (for example, atrium, pulmonary veins, other cardiac location, renal artery, other vessel or lumen, etc.) using one or more imaging technologies. Accordingly, any of the ablation systems disclosed herein can be configured to be used with (for example, separately from or at least partially integrated with) an imaging device or system, such as, for example, fluoroscopy technologies, intracardiac echocardiography (“ICE”) technologies and/or the like. In some embodiments, energy delivery is substituted with fluid delivery (for example, hot fluid, cryogenic fluid, chemical agents) to accomplish treatment.

(160) FIG. 18A illustrates a perspective view of a distal portion of an open-irrigated ablation catheter 3120A comprising multiple temperature-measurement devices 3125, according to one embodiment. As shown, the embodiment of the ablation catheter 3120A of FIG. 18A is an open-irrigated catheter comprising a split-tip electrode design. The split-tip electrode design comprises a dome- or hemispherical-shaped distal tip electrode member 3130, an insulation gap 3131 and a proximal electrode member 3135. The ablation catheter 3120A comprises multiple irrigation ports 3140 and a thermal transfer member 3145.

(161) The temperature-measurement devices 3125 comprise a first (for example, distal) group of temperature-measurement devices 3125A positioned in recesses or apertures formed in the distal electrode member 3130 and a second (for example, proximal) group of temperature-measurement devices 3125B positioned in slots, notches or openings formed in the thermal transfer member 3145 proximate or adjacent the proximal edge of the proximal electrode member 3135. The temperature-measurement devices 3125 may comprise thermocouples, thermistors, fluoroptic sensors, resistive temperature sensors and/or other temperature sensors. In various embodiments, the thermocouples comprise nickel alloy, platinum/rhodium alloy, tungsten/rhenium alloy, gold/iron alloy, noble metal alloy, platinum/molybdenum alloy, iridium/rhodium alloy, pure noble metal, Type K, Type T, Type E, Type J, Type M, Type N, Type B, Type R, Type S, Type C, Type D, Type G, and/or Type P thermocouples. A reference thermocouple may be positioned at any location along the catheter 120A (for example, in a handle or within a shaft or elongate member of the catheter 3120A. In one embodiment, the reference thermocouple is thermally insulated and/or electrically isolated from the electrode member(s). The electrode member(s) may be substituted with other energy delivery members.

(162) In some embodiments, the temperature-measurement devices are thermally insulated from the electrode members 3130, 3135 so as to isolate the temperature measurements from the thermal effects of the electrode members (for example, to facilitate measurement of surrounding temperature, such as tissue temperature, instead of measuring temperature of the electrode members). As shown, the temperature-measurement devices 3125 may protrude or extend outward from an outer surface of the ablation catheter 3120A. In some embodiments, the temperature-measurement devices 3125 may protrude up to about 1 mm away from the outer surface (for example, from about 0.1 mm to about 0.5 mm, from about 0.5 mm to about 1 mm, from about 0.6 mm to about 0.8 mm, from about 0.75 mm to about 1 mm, or overlapping ranges thereof). The dome shape of the distal tip electrode member 3130 and/or the outward protrusion or extension of the temperature-measurement devices 3125 may advantageously allow the temperature-measurement devices to be buried deeper into tissue and away from effects of the open irrigation provided by irrigation ports 3140, in accordance with several embodiments. The proximal group of temperature-measurement devices and the distal group of temperature-measurement devices may protrude the same amount or different amounts (as a group and/or individually within each group). In other embodiments, the temperature-measurement devices 3125 are flush or embedded within the outer surface (for example, 0.0 mm, −0.1 mm, −0.2 mm, −0.3 mm, −0.4 mm, −0.5 mm from the outer surface).

(163) With reference to FIG. 18D, a portion of the ablation catheter 3120C where the temperature-measurement devices 3125 are positioned may have a larger outer diameter or other outer cross-sectional dimension than adjacent portions of the ablation catheter 3120C so as to facilitate deeper burying of the temperature-measurement devices within tissue and to further isolate the temperature measurements from the thermal effects of the electrode members or fluid (for example, saline or blood). As shown in FIG. 18D, the portion of the ablation catheter 3120C comprising the proximal group of temperature-measurement devices 3125B comprises a bulge, ring or ridge 3155 having a larger outer diameter than adjacent portions.

(164) In some embodiments, the temperature-measurement devices 3125 are adapted to be advanced outward and retracted inward. For example, the temperature-measurement devices 3125 may be in a retracted position (within the outer surface or slightly protruding outward) during insertion of the ablation catheter and movement to the treatment location to reduce the outer profile and facilitate insertion to the treatment location and may be advanced outward when at the treatment location. The features described above in connection with ablation catheter 3120C of FIG. 18D may be employed with any of the other ablation catheters described herein.

(165) Returning to FIG. 18A, the proximal and distal groups of temperature-measurement devices 3125 may each comprise two, three, four, five, six, or more than six temperature-measurement devices. In the illustrated embodiment, the proximal and distal groups of temperature-measurement devices 3125 each consist of three temperature-measurement devices, which may provide a balance between volumetric coverage and reduced number of components, according to one embodiment. The number of temperature-measurement devices may be selected to balance accuracy, complexity, volumetric coverage, variation in tip to tissue apposition, cost, number of components, and/or size constraints. As shown in FIG. 18A, the temperature-measurement devices may be equally spaced apart around a circumference of the ablation catheter 3120A or spaced an equal number of degrees apart from each other about a central longitudinal axis extending from a proximal end to a distal end of the ablation catheter. For example, when three temperature-measurement devices are used, they may be spaced about 120 degrees apart and when four temperature-measurement devices are used, they may be spaced about 90 degrees apart. In other embodiments, the temperature-measurement devices 3125 are not spaced apart equally.

(166) As shown in the embodiment of FIG. 18A, the temperature-measurement devices 3125 of each group may be positioned along the same cross-sectional plane of the ablation catheter 3120A. For example, the distal temperature-measurement devices 3125A may be positioned to extend the same distance outward from the dome-shaped surface and the proximal temperature-measurement devices 3125B may each be spaced the same distance from the distal tip of the ablation catheter 3120A. As shown in the embodiment of FIG. 18A, the distal temperature-measurement devices 3125A extend in axial direction that is parallel or substantially parallel with a central longitudinal axis of the distal portion of the ablation catheter 3120A and the proximal temperature-measurement devices 3125B extend radially outward from the outer surface of the ablation catheter 3120A. In other embodiments, the distal temperature-measurement devices 3125A may not be positioned on the distal surface of the distal terminus but may be positioned on a lateral surface to extend radially outward (similar to the illustrated proximal temperature-measurement devices 3125B).

(167) As shown in the embodiment of FIG. 18A, the distal temperature-measurement devices 3125A may be positioned distal of the insulation gap 3131 and/or of the irrigation ports 3140 and the proximal temperature-measurement devices 3125B may be positioned proximal to the distal edge of the proximal electrode member 3135 within the thermal transfer member 3145. In other embodiments (for example, as shown in FIGS. 22A and 22B), the proximal temperature-measurement devices 3125B may be positioned distal to the distal edge of the proximal electrode member 3135 (for example, within recesses or apertures formed within the proximal electrode member 3135 similar to the recesses or apertures formed in the distal tip electrode member illustrated in FIG. 18A). In other embodiments, the distal temperature-measurement devices 3125A and/or the proximal temperature-measurement devices 3125B may be positioned at other locations along the length of the ablation catheter 3120A. In some embodiments, each distal temperature-measurement device 3125A is axially aligned with one of the proximal temperature-measurement devices 3125B and the spacing between the distal temperature-measurement devices 3125A and the proximal temperature-measurement devices is uniform or substantially uniform.

(168) The irrigation ports 3140 may be spaced apart (equidistant or otherwise) around a circumference of the shaft of the ablation catheter 3120A. The irrigation ports 3140 are in communication with a fluid source, such as a fluid source provided by the irrigation fluid system 70 of FIG. 1. The irrigation ports facilitate open irrigation and provide cooling to the electrode members 3130, 3135 and any blood surrounding the electrode members 3130, 3135. In some embodiments, the ablation catheter 3120A comprises three, four, five, six, seven, eight or more than eight exit ports 3140. In various embodiments, the exit ports 3140 are spaced between 0.005 and 0.015 inches from the proximal edge of the distal electrode member 3130 so as to provide improved cooling of the thermal transfer member 3145 at the tissue interface; however, other spacing can be used as desired and/or required. In other embodiments, the exit ports 3140 are spaced apart linearly and/or circumferentially along the proximal electrode member 3135 (as shown, for example, in FIG. 18E).

(169) FIGS. 18B and 18C illustrate a perspective view and a cross-sectional view, respectively, of a distal portion of an open-irrigated ablation catheter 3120B having multiple temperature-measurement devices, according to another embodiment. The ablation catheter 3120B may include all of the structural components, elements and features of the ablation catheter 3120A described above and ablation catheter 3120A may include all of the structural components, elements and features described in connection with FIGS. 18B and 18C. The ablation catheter 3120B comprises a flat tip electrode member 3130 instead of a dome-shaped tip electrode member as shown in FIG. 18A.

(170) As best shown in FIG. 18C, the thermal transfer member 3145 is in thermal contact with one or both of the electrode members 3130, 3135. The thermal transfer member 3145 can extend to, near or beyond the proximal end of the proximal electrode member 3135. In some embodiments, the thermal transfer member 3145 terminates at or near the proximal end of the proximal electrode member 3135. However, in other arrangements (as shown in FIG. 18C), the thermal transfer member 3145 extends beyond the proximal end of the proximal electrode member 3135. In yet other embodiments, the thermal transfer member 3145 terminates distal of the proximal end (for example, edge) of the proximal electrode member 3135. The thermal transfer member 3145 may extend from the proximal surface of the tip electrode member 3130 to location beyond the proximal end of the proximal electrode member 3135. Embodiments wherein the thermal transfer member 3145 extends beyond the proximal end of the proximal electrode member 3135 may provide increased shunting of proximal edge heating effects caused by the increased amount of current concentration at the proximal edge by reducing the heat at the proximal edge through conductive cooling. In some embodiments, at least a portion of the thermal transfer member 3145 is in direct contact with the tissue (for example, within insulation gap 3131) and can remove or dissipate heat directly from the targeted tissue being heated.

(171) The thermal transfer member 3145 can comprise one or more materials that include favorable heat transfer properties. For example, in some embodiments, the thermal conductivity of the material(s) included in the thermal transfer member is greater than 300 W/m/° C. (for example, 300-350, 350-400, 400-450, 450-500, 500-600, 600-700 W/m/° C., ranges between the foregoing, greater than 700 W/m/° C., etc.).

(172) Possible materials with favorable thermal conductivity properties include, but are not limited to, copper, brass, beryllium, other metals and/or alloys, aluminal ceramics, other ceramics, industrial diamond and/or other metallic and/or non-metallic materials.

(173) According to certain embodiments where the heat transfer members comprise heat shunting members, the thermal diffusivity of the material(s) included in the heat shunt members and/or of the overall heat shunt assembly (for example, when viewed as a unitary member or structure) is greater than 1.5 cm.sup.2/sec (for example, 1.5-2, 2-2.5, 2.5-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-0, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20 cm.sup.2/sec, values between the foregoing ranges, greater than 20 cm.sup.2/sec). Thermal diffusivity measures the ability of a material to conduct thermal energy relative to its ability to store thermal energy. Thus, even though a material can be efficient as transferring heat (for example, can have a relatively high thermal conductivity), it may not have favorable thermal diffusivity properties, because of its heat storage properties. Heat shunting, unlike heat transferring, requires the use of materials that possess high thermal conductance properties (for example, to quickly transfer heat through a mass or volume) and a low heat capacity (for example, to not store heat). Possible materials with favorable thermal diffusivity, and thus favorable heat shunting properties, include, but are not limited to, industrial diamond, graphene, silica alloys, ceramics, other carbon-based materials and/or other metallic and/or non-metallic materials. In various embodiments, the material used for the heat transfer (for example, diamond) provides increased visibility of the catheter tip using ICE imaging or other imaging techniques.

(174) The use of materials with favorable thermal diffusivity properties can help ensure that heat can be efficiently transferred away from the electrode and/or the adjacent tissue during a treatment procedure. In contrast, materials that have favorable thermal conductivity properties, but not favorable thermal diffusivity properties, such as, for example, copper, other metals or alloys, thermally conductive polypropylene or other polymers, etc., will tend to retain heat. As a result, the use of such materials that store heat may cause the temperature along the electrode and/or the tissue being treated to be maintained at an undesirably elevated level (for example, over 75 degrees C.) especially over the course of a relatively long ablation procedure, which may result in charring, thrombus formation and/or other heat-related problems.

(175) Industrial diamond and other materials with the requisite thermal diffusivity properties for use in a thermal shunting network, as disclosed in the various embodiments herein, comprise favorable thermal conduction characteristics. Such favorable thermal conduction aspects emanate from a relatively high thermal conductance value and the manner in which the heat shunt members of a network are arranged with respect to each other within the tip and with respect to the tissue. For example, in some embodiments, as radiofrequency energy is emitted from the tip and the ohmic heating within the tissue generates heat, the exposed distal most shunt member (for example, located 0.5 mm from the distal most end of the tip) can actively extract heat from the lesion site. The thermal energy can advantageously transfer through the shunting network in a relatively rapid manner and dissipate through the shunt residing beneath the radiofrequency electrode surface the heat shunt network, through a proximal shunt member and/or into the ambient surroundings. Heat that is shunting through an interior shunt member can be quickly transferred to an irrigation conduit extending through an interior of the catheter or other medical instrument. In other embodiments, heat generated by an ablation procedure can be shunted through both proximal and distal shunt members (for example, shunt members that are exposed to an exterior of the catheter or other medical instrument, such as shown in many of the embodiments herein).

(176) Further, as noted above, the materials with favorable thermal diffusivity properties for use in a heat shunt network not only have the requisite thermal conductivity properties but also have sufficiently low heat capacity values. This helps ensure that the thermal energy is dissipated very quickly from the tip to tissue interface as well as the hot spots on the electrode, without heat retention in the heat shunting network. The thermal conduction constitutes the primary heat dissipation mechanism that ensures quick and efficient cooling of the tissue surface and of the radiofrequency electrode surface. Conversely a heat transfer (for example, with relatively high thermal conductivity characteristics but also relatively high heat capacity characteristics) will store thermal energy. Over the course of a long ablation procedure, such stored heat may exceed 75 degrees Celsius. Under such circumstances, thrombus and/or char formation can undesirably occur.

(177) The thermal convection aspects of the various embodiments disclosed herein two-fold. First, an irrigation lumen of the catheter can absorb thermal energy which is transferred to it through the shunt network. Such thermal energy can then be flushed out of the distal end of the electrode tip via the irrigation ports. In closed irrigation systems, however, such thermal energy can be transferred back to a proximal end of the catheter where it can be removed. Second, the exposed shunt surfaces along an exterior of the catheter or other medical instrument can further assist with the dissipation of heat from the electrode and/or the tissue being treated. For example, such heat dissipation can be accomplished via the inherent convective cooling aspects of the blood flowing over the surfaces of the electrode.

(178) Accordingly, the use of materials in a heat shunting network with favorable thermal diffusivity properties, such as industrial diamond, can help ensure that heat is quickly and efficiently transferred away from the electrode and treated tissue, while maintaining the heat shunting network cool (for example, due to its low heat capacity properties). This can create a safer ablation catheter and related treatment method, as potentially dangerous heat will not be introduced into the procedure via the heat shunting network itself.

(179) In some embodiments, the heat shunt members disclosed herein draw out heat from the tissue being ablated and shunt it into the irrigation channel. Similarly, heat is drawn away from the potential hot spots that form at the edges of electrodes and are shunted through the heat shunt network into the irrigation channel. From the irrigation channel, via convective cooling, heat can be advantageously released into the blood stream and dissipated away. In closed irrigation systems, heat can be removed from the system without expelling irrigation fluid into the subject.

(180) According to some embodiments, the various heat shunting systems disclosed herein rely on heat conduction as the primary cooling mechanism. Therefore, such embodiments do not require a vast majority of the heat shunting network to extend to an external surface of the catheter or other medical instrument (for example, for direct exposure to blood flow). In fact, in some embodiments, the entire shunt network can reside within an interior of the catheter tip (i.e., with no portion of the heat shut network extending to an exterior of the catheter or other medical instrument). Further, the various embodiments disclosed herein do not require electrical isolation of the heat shunts from the electrode member or from the irrigation channel.

(181) As shown in FIG. 18C, the thermal transfer member 3145 is also in thermal contact with a heat exchange chamber (for example, irrigation conduit) 3150 extending along an interior lumen of the ablation catheter 3120B. For any of the embodiments disclosed herein, at least a portion of a thermal transfer member (for example, heat shunt member) that is in thermal communication with the heat exchange chamber 3150 extends to an exterior surface of the catheter, adjacent to (and, in some embodiments, in physical and/or thermal contact with) one or more electrodes or other energy delivery members. Such a configuration, can further enhance the cooling of the electrode(s) or other energy delivery member(s) when the system is activated, especially at or near the proximal end of the electrode(s) or energy delivery member(s), where heat may otherwise tend to be more concentrated (for example, relative to other portions of the electrode or other energy delivery member). According to some embodiments, thermal conductive grease and/or any other thermally conductive material (for example, thermally-conductive liquid or other fluid, layer, member, coating and/or portion) can be used to place the thermal transfer member 3145 in thermal communication with the heat exchange chamber (for example, irrigation conduit) 3150, as desired or required. In such embodiments, such a thermally conductive material places the electrode members 3130, 3135 in thermal communication, at least partially, with the irrigation conduit 3150.

(182) The irrigation conduit(s) 3150 can be part of an open irrigation system, in which fluid exits through the exit ports or openings 3140 along the distal end of the catheter (for example, at or near the electrode member 3130) to cool the electrode members and/or the adjacent targeted tissue. In various embodiments, the irrigation conduit 3150 comprises one or more metallic and/or other favorable heat transfer (for example, heat shunting) materials (for example, copper, stainless steel, other metals or alloys, ceramics, polymeric and/or other materials with relatively favorable heat transfer properties, etc.). The irrigation conduit 3150 can extend beyond the proximal end of the proximal electrode member 3135 and into the proximal portion of the thermal transfer member 3145. The inner wall of the irrigation conduit 3150 may comprise a biocompatible material (such as stainless steel) that forms a strong weld or bond between the irrigation conduit 3150 and the material of the electrode member(s).

(183) In some embodiments, the ablation catheters 3120 only comprise irrigation exit openings 3140 along a distal end of the catheter (for example, along a distal end of the distal electrode member 3130). In some embodiments, the system does not comprise any irrigation openings along the thermal transfer member 3145.

(184) The thermal transfer member 3145 may advantageously facilitate thermal conduction away from the electrode members 3130, 3135, thereby further cooling the electrode members 3130, 3135 and reducing the likelihood of char or thrombus formation if the electrode members are in contact with blood. The thermal transfer member 3145 may provide enhanced cooling of the electrode members 3130, 3135 by facilitating convective heat transfer in connection with the irrigation conduit 3150 in addition to thermal conduction.

(185) Heat transfer (for example, heat shunting) between the thermal transfer member 3145 and the electrode members 3130, 3135 can be facilitated and otherwise enhanced by eliminating air gaps or other similar spaces between the electrode members and the thermal transfer member. For example, one or more layers of an electrically conductive material (for example, platinum, gold, other metals or alloys, etc.) may be positioned between the interior of the electrode member and the exterior of the thermal transfer member 3145. Such layer(s) can be continuously or intermittently applied between the electrode member (or another type of ablation member) and the adjacent thermal transfer member. Further, such layer(s) can be applied using one or more methods or procedures, such as, for example, sputtering, other plating techniques and/or the like. Such layer(s) can be used in any of the embodiments disclosed herein or variations thereof. In addition, the use of a heat shunting network specifically can help transfer heat away from the tissue being treated by the electrode member(s) without itself absorbing heat.

(186) In some embodiments, the ablation catheter 3120 comprises multiple thermal transfer members 3145 (for example, heat shunt disks or members). For example, according to some embodiments, such additional heat transfer members may be positioned proximal of thermal transfer member 3145 and may comprise one or more fins, pins and/or other members that are in thermal communication with the irrigation conduit 3150 extending through an interior of the ablation catheter. Accordingly, as with the thermal transfer members 3145 positioned in contact with the electrode members 3130, 3135 heat can be transferred and thus removed or dissipated, from other energy delivery members or electrodes, the adjacent portions of the catheter and/or the adjacent tissue of the subject via these additional heat transfer members (for example, heat shunting members). In other embodiments, ablation catheters do not comprise any thermal transfer members.

(187) In some embodiments, for any of the ablation catheters disclosed herein or variations thereof, one or more of the thermal transfer members (for example, heat shunting members) that facilitate the heat transfer to a heat exchange chamber (for example, irrigation conduit) of the catheter are in direct contact with the electrode members and/or the heat exchange chamber. However, in other embodiments, one or more of the thermal transfer members do not contact the electrode members and/or the irrigation conduit. Thus, in such embodiments, the thermal transfer members are in thermal communication with the electrode members or single electrode and/or irrigation conduit, but not in physical contact with such components. For example, in some embodiments, one or more intermediate components, layers, coatings and/or other members are positioned between a thermal transfer member (for example, heat shunting member) and the electrode (or other ablation member) and/or the irrigation conduit. In some embodiments, irrigation is not used at all due to the efficiency of the thermal transfer members. For example, where multiple levels or stacks of thermal transfers are used, the heat may be dissipated over a larger area along the length of the ablation catheter. Additional details regarding function and features of thermal transfer members (for example, heat shunting members) are provided herein. The features of the various embodiments disclosed therein (for example, of thermal shunt systems and members) may be implemented in any of the embodiments of the medical instruments (for example, ablation catheters) disclosed herein.

(188) As best shown in FIGS. 18C, 18E and 18F, the temperature-measurement devices 3125 are thermally insulated from the electrode members 3130, 3135 by tubing 3160 and/or air gaps. In some embodiments, the tubing 3160 extends along an entire length (and beyond in some embodiments) of the electrode members 3130, 3135 such that no portion of the electrode member is in contact with the temperature-measurement devices 3125, thereby isolating the temperature measurements from the thermal effects of the electrode members. The outer tubing 3160 of the temperature-measurement devices may comprise an insulating material having low thermal conductivity (for example, polyimide, ULTEM™, polystyrene or other materials having a thermal conductivity of less than about 0.5 W/m/° K). The tubing 3160 is substantially filled with air or another gas having very low thermal conductivity. The distal tip 3165 of the temperature-sensing device (for example, the portion where the temperature is sensed) may comprise an epoxy polymer covering or casing filled with a highly conductive medium (for example, nanotubes comprised of graphene, carbon or other highly thermally conductive materials or films) to increase thermal conduction at a head of the temperature-measurement device where temperature is measured. In some embodiments, the distal tip 3165 comprises an epoxy cap having a thermal conductivity that is at least 1.0 W/m/° K. The epoxy may comprise metallic paste (for example, containing aluminum oxide) to provide the enhanced thermal conductivity. In some embodiments, the distal tip 3165 or cap creates an isothermal condition around the temperature-measurement device 3125 that is close to the actual temperature of tissue in contact with the temperature-measurement device. Because the distal tip 3165 of each temperature-measurement device 3125 is isolated from thermal conductive contact with the electrode member(s), it retains this isothermal condition, thereby preventing or reducing the likelihood of dissipation by the thermal mass of the electrode member(s). FIGS. 18E and 18F illustrate a perspective view and a cross-sectional view, respectively, of a distal portion of an ablation catheter showing isolation of the distal temperature-measurement devices from an electrode tip, according to one embodiment. As shown, the distal temperature measurement devices 3125A may be surrounded by air gaps or pockets 3162 and/or insulation. The outer tubing 3160 may comprise an insulation sleeve that extends along the entire length, or at least a portion of the length, of the distal electrode member 3130. The sleeve may extend beyond the distal electrode member 3130 or even to or beyond the proximal electrode member 3135.

(189) The electrode member(s) (for example, the distal electrode 3130) can be electrically coupled to an energy delivery module (for example, energy delivery module 40 of FIG. 1). As discussed herein, the energy delivery module 40 can comprise one or more components or features, such as, for example, an energy generation device 42 that is configured to selectively energize and/or otherwise activate the energy delivery members (for example, RF electrodes), one or more input/output devices or components, a processor (for example, a processing or control unit) that is configured to regulate one or more aspects of the treatment system, a memory and/or the like. Further, such a module can be configured to be operated manually or automatically, as desired or required.

(190) The temperature-measurement devices 3125 can be coupled to one or more conductors (for example, wires, cables, etc.) that extend along the length of the ablation catheter 3120 and communicate the temperature signals back to a processing device (for example, processor 46 of FIG. 1) for determining temperature measurements for each of the temperature-measurement devices, as will be discussed in greater detail below.

(191) According to some embodiments, the relative length of the different electrodes or electrode members 3130, 3135 can vary. For example, the length of the proximal electrode member 3135 can be between 1 to 20 times (for example, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18, 18-19, 19-20, values between the foregoing ranges, etc.) the length of the distal electrode member 3130, as desired or required. In yet other embodiments, the lengths of the distal and proximal electrode members 3130, 3135 are about equal. In some embodiments, the distal electrode member 3130 is longer than the proximal electrode member 3135 (for example, by 1 to 20 times, such as, for example, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18, 18-19, 19-20, values between the foregoing ranges, etc.).

(192) In some embodiments, the distal electrode member 3130 is 0.5 mm long. In other embodiments, the distal electrode member 130 is between 0.1 mm and 1 mm long (for example, 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.-0.8, 0.8-0.9, 0.9-1 mm, values between the foregoing ranges, etc.). In other embodiments, the distal electrode member 3130 is greater than 1 mm in length, as desired or required. In some embodiments, the proximal electrode member 3135 is 2 to 4 mm long (for example, 2-2.5, 2.5-3, 3-3.5, 3.5-4 mm, lengths between the foregoing, etc.). However, in other embodiments, the proximal electrode member 3135 is greater than 4 mm (for example, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10 mm, greater than 10 mm, etc.) or smaller than 1 mm (for example, 0.1-0.5 0.5-1, 1-1.5, 1.5-2 mm, lengths between the foregoing ranges, etc.), as desired or required. In embodiments where the split electrodes are located on catheter shafts, the length of the electrode members can be 1 to 5 mm (for example, 1-2, 2-3, 3-4, 4-5 mm, lengths between the foregoing, etc.). However, in other embodiments, the electrode members can be longer than 5 mm (for example, 5-6, 6-7, 7-8, 8-9, 9-10, 10-15, 15-20 mm, lengths between the foregoing, lengths greater than 20 mm, etc.), as desired or required.

(193) The electrode member(s) may be energized using one or more conductors (for example, wires, cables, etc.). For example, in some arrangements, the exterior of the irrigation conduit 3150 comprises and/or is otherwise coated with one or more electrically conductive materials (for example, copper, other metal, etc.). Thus, the conductor can be placed in contact with such a conductive surface or portion of the irrigation conduit 3150 to electrically couple the electrode member(s) to an energy delivery module. However, one or more other devices and/or methods of placing the electrode member(s) in electrical communication with an energy delivery module can be used. For example, one or more wires, cables and/or other conductors can directly or indirectly couple to the electrode member(s), without the use of the irrigation conduit.

(194) The use of a split tip design can permit a user to simultaneously ablate or otherwise thermally treat targeted tissue and map (for example, using high-resolution mapping) in a single configuration. Thus, such systems can advantageously permit precise high-resolution mapping (for example, to confirm that a desired level of treatment occurred) during a procedure. In some embodiments, the split tip design that includes two electrode members or electrode portions 3130, 3135 can be used to record a high-resolution bipolar electrogram. For such purposes, the two electrodes or electrode portions can be connected to the inputs of an electrophysiology (EP) recorder. In some embodiments, a relatively small separation distance (for example, gap G) between the electrode members or electrode portions 3130, 3135 enables high-resolution mapping. The features of any of the embodiments disclosed therein may be implemented in any of the embodiments disclosed herein.

(195) In some embodiments, a medical instrument (for example, a catheter) 3120 can include three or more electrode members or electrode portions (for example, separated by gaps), as desired or required. According to some embodiments, regardless of how many electrodes or electrode portions are positioned along a catheter tip, the electrode members or electrode portions 3130, 3135 are radiofrequency electrodes and comprise one or more metals, such as, for example, stainless steel, platinum, platinum-iridium, gold, gold-plated alloys and/or the like.

(196) According to some embodiments, the electrode members or electrode portions 3130, 3135 are spaced apart from each other (for example, longitudinally or axially) using the gap (for example, an electrically insulating gap) 3131. In some embodiments, the length of the gap 3131 (or the separation distance between adjacent electrode members or electrode portions) is 0.5 mm. In other embodiments, the gap or separation distance is greater or smaller than 0.5 mm, such as, for example, 0.1-1 mm (for example, 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0 mm, values between the foregoing ranges, less than 0.1 mm, greater than 1 mm, etc.), as desired or required

(197) According to some embodiments, a separator is positioned within the gap 3131 between the adjacent electrode members or electrode portions 3130, 3135. The separator can comprise one or more electrically insulating materials, such as, for example, Teflon, polyetheretherketone (PEEK), diamond, epoxy, polyetherimide resins (for example, ULTEM™), ceramic materials, polyimide and the like. As shown in FIGS. 18A-18C and 19A-19C, the separator may comprise a portion of the thermal transfer member 3145 extending within the gap 3131.

(198) As noted above with respect to the gap 3131 separating the adjacent electrode members or electrode portions, the insulating separator can be 0.5 mm long. In other embodiments, the length of the separator can be greater or smaller than 0.5 mm (for example, 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0 mm, values between the foregoing ranges, less than 0.1 mm, greater than 1 mm, etc.), as desired or required.

(199) According to some embodiments, to ablate or otherwise heat or treat targeted tissue of a subject successfully with the split tip electrode design, such as the ones depicted in FIGS. 18A-18C and 19A-19C, the two electrode members or electrode portions 3130, 3135 are electrically coupled to each other at the RF frequency. Thus, the two electrode members or electrode portions can advantageously function as a single longer electrode at the RF frequency. Additional details regarding function and features of a split-tip electrode design are provided herein.

(200) FIGS. 19A-19C illustrate a distal portion of closed-irrigation ablation catheters 3220 having multiple temperature-measurement devices 3225, according to various embodiments. The embodiment of the ablation catheter 3220A of FIG. 19A comprises a dome-shaped tip electrode member 3230 similar to the ablation catheter 3120A of FIG. 18A. The embodiment of the ablation catheter 3220B of FIGS. 19B and 19C comprises a flat tip electrode member similar to the ablation catheter 3120B of FIGS. 18B and 18C. The ablation catheters 3220A and 3220B include similar components and features as those described above in connection with FIGS. 18A-18C. For example, temperature-measurement devices 3225 correspond to temperature-measurement devices 3125, electrode members 3230, 3235 correspond to electrode members 3130, 3135, thermal transfer member 3245 corresponds to thermal transfer member 3145 and irrigation conduit 3250 corresponds to irrigation conduit 3150. Accordingly, these features will not be described again in connection with FIGS. 19A-19C. The ablation catheter 3220 does not include irrigation ports because it operates as a closed irrigation device.

(201) The ablation catheter 3220 comprises two lumens 3265 within the irrigation conduit 3250, an inlet lumen (for example, fluid delivery channel) 3265A and an outlet lumen (for example, return channel) 3265B. As illustrated in the cross-sectional view of FIG. 19C, the outlet of the inlet lumen 3265A and the inlet of the outlet lumen 3265B terminate at spaced-apart locations within the irrigation conduit 3250. The outlet of the inlet lumen 3265A terminates within the distal electrode member 3230 or adjacent to a proximal end surface of the distal electrode member 3230. The inlet of the outlet lumen terminates proximal to the proximal end of the proximal electrode member 3235. The offset spacing of the distal ends of the lumens 3265 advantageously induces turbulence, vortexing or other circulating fluid motions or paths within the irrigation conduit, thereby facilitating enhanced cooling by circulating the fluid to constantly refresh or exchange the fluid in contact with the thermal transfer member 3245 and/or electrode members.

(202) In accordance with several embodiments, ablation catheters having multiple temperature-measurement devices do not require a split-tip electrode design and/or thermal transfer members. FIG. 20 illustrates a perspective view of a distal portion of an open-irrigated ablation catheter 3320 that does not include a split-tip electrode design or a thermal transfer member. The ablation catheter 3320 comprises a first (for example, distal) plurality of temperature-measurement devices 3325A and a second (for example, proximal) plurality of temperature-measurement devices 3325B. The temperature-measurement devices 3325 comprise similar features, properties, materials, elements and functions as the temperature-measurement devices 3125, 3225 (FIGS. 18A-19C). The ablation catheter 3320 may comprise or consist of a single unitary tip electrode 3330. The tip electrode 3330 may comprise apertures, slots, grooves, bores or openings for the temperature-measurement devices 3325 at their respective spaced-apart locations. As shown in FIG. 20, the proximal temperature-measurement devices 3325B are positioned distal but adjacent to the proximal edge of the tip electrode 3330. The proximal temperature-measurement devices 3325B could be positioned within 1 mm of the proximal edge (for example, within 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1 mm, depending on the length of the tip electrode 330). In other embodiments, the proximal temperature-measurement devices 3325B are positioned proximal of the proximal edge of the tip electrode 3330 and within the same distance as described above of distal placement. In various embodiments, the temperature-measurement devices are positioned at or near the proximal and distal edges of the electrode or split-tip electrode assembly because those locations tend to be the hottest. Based on manufacturing tolerances, these temperature measurement devices may be embedded at the proximal or distal edge of the electrode 3330. Accordingly, positioning of the temperature-measurement devices at or near these locations may facilitate prevention, or reduced likelihood, of overheating or char or thrombus formation. Additionally, such temperature-measurement device placement offers the ability to monitor tissue temperature during irrigated ablation.

(203) In some embodiments, epoxy comprising a conductive medium (such as graphene or other carbon nanotubes) may be blended in to the distal tubing (typically formed of plastic) of the ablation catheter shaft and the distal tubing of the ablation catheter itself may function as a thermal transfer. In some embodiments, the addition of the conductive epoxy could increase the thermal conductivity of the distal tubing by 2-3 times or more. These conductive tubing features and other features described in connection with FIG. 20 may be used in connection with the ablation catheters 3120, 3220 as well.

(204) FIGS. 21A and 21B schematically illustrate a distal portion of an open-irrigated ablation catheter 3420 in perpendicular contact and parallel contact, respectively, with tissue and formation of thermal lesions by delivering energy to the tissue using the ablation catheter 3420. In accordance with several embodiments, the ablation catheters having multiple temperature-measurement devices described herein advantageously facilitate determination of, among other things: an orientation of the distal tip of the ablation catheter with respect to the tissue, an estimated peak temperature within the thermal lesion, and/or a location of the peak temperature zone within the thermal lesion.

(205) As mentioned above, the temperature-measurement devices 3425 may send or transmit signals to a processing device (for example, processor 46 of FIG. 1). The processing device may be programmed to execute instructions stored on one or more computer-readable storage media to determine temperature measurements for each of the temperature-measurement devices 3425 and to compare the determined temperature measurements with each other to determine an orientation of the distal tip of the ablation catheter with respect to the tissue based, at least in part, on the comparison. The processing device may select an orientation from one of parallel, perpendicular, or angled (for example, skewed or oblique) orientations.

(206) For example, if the temperature measurements received from the distal temperature-measurement devices are all greater (for example, hotter) than the temperature measurements received from the proximal temperature-measurement devices, then the processor may determine that the orientation is perpendicular. If the temperature measurements received from at least one proximal temperature-measurement device and at least one corresponding distal temperature-measurement device are similar, then the processor may determine that the orientation is parallel.

(207) As other examples, for embodiments using three temperature-measurement devices, if two of three proximal temperature-measurement devices generate much lower (and generally equal) temperature measurements than the third proximal-temperature measurement device, then the processing device may determine that the orientation is parallel. For embodiments using three temperature-measurement devices, if the temperature measurements received from a first proximal temperature-measurement device are appreciably greater than temperature measurements from a second proximal temperature-measurement device and if the temperature measurements received from the second proximal temperature-measurement device are appreciably greater than temperature measurements received from a third proximal temperature-measurement device, then the processing device may determine that the orientation is neither parallel nor perpendicular but skewed at an angle. In some embodiments, orientation may be confirmed using fluoroscopic imaging, ICE imaging or other imaging methods or techniques.

(208) In some embodiments, the determined orientation may be output on a display (for example, a graphical user interface) for visibility by a user. The output may comprise one or more graphical images indicative of an orientation or alphanumeric information indicative of the orientation (for example, a letter, word, phrase or number). The processing device may apply correction factors to the temperature measurements received from the temperature-measurement devices based on the determined orientation in order to generate more accurate estimates of a peak temperature of the thermal lesion. For example, if a perpendicular orientation is determined, then a correction factor or function corresponding to the distal temperature-measurement devices may be applied to determine the estimated peak temperature.

(209) The processing device may comprise a temperature acquisition module and a temperature processing module, in some embodiments. The temperature acquisition module may be configured to receive as input temperature signals (for example, analog signals) generated by each of the temperature-measurement devices. The input signals may be continuously received at prescribed time periods. The temperature acquisition module may be configured to covert analog signals into digital signals. The temperature processing module may receive the digital signals output from the temperature acquisition module and apply correction factors or functions to them to estimate a hottest tissue temperature, a peak temperature or a peak temperature in a thermal lesion created in the vicinity of the electrode or other energy delivery member(s). The temperature processing module may compute a composite temperature from the temperature-measurement devices (for example, thermocouples) based on the following equation:
Tcomp(t)=k(t)*f(TC1(t),TC2(t), . . . ,TCn(t));
where Tcomp is the composite temperature, k is the k function or correction or adjustment function, f is a function of the thermocouple readings TCi, i=1 to n. The k function may comprise a function over time or a constant value. For example, a k function may be defined as follows:
k(t)=e.sup.(−t/τ)+k.sub.final*(1−e.sup.(−t/τ));
where τ is a time constant representative of the tissue time constant and k.sub.final is a final value of k, as per a correction factor or function, such as described in connection h FIG. 22A below.

(210) The temperature processing module may also be configured to determine an orientation of a distal tip of a medical instrument with respect to tissue, as described above. The processing device may further comprise an output module and a feedback/monitoring module. The output module may be configured to generate output for display on a display, such as the various outputs described herein. The feedback/monitoring modules may be configured to compare measured temperature values against a predetermined setpoint temperature or maximum temperature and to initiate action (for example, an alert to cause a user to adjust power or other ablation parameters or automatic reduction in power level or termination of energy delivery (which may be temporary until the temperature decreases below the setpoint temperature). In various embodiments, the setpoint, or maximum, temperature is between 50 and 90 degrees Celsius (for example, 50, 55, 60, 65, 70, 75, 80, 85 degrees Celsius).

(211) In accordance with several embodiments, there is a proportional relationship between the temperature gradient determined by the temperature-measurement devices and the peak temperature of the lesion. From this relationship, a function or correction factor is generated or applied based on numerical modeling (for example, finite element method modeling techniques) and/or measurements stored in a look-up table to adjust or correct from the thermal gradient identified by the temperature-measurement devices to determine the peak temperature. The thermal gradient of an open-irrigated lesion is such that the lesion surface is a little bit cooled and the peak temperature zone is deeper. The further the temperature-measurement devices can be buried into tissue, the better or more accurate the proportional relationship may be between the thermal gradient determined by the temperature-measurement devices and the peak temperature. For example, the thermal gradient can be estimated as:
ΔT/Δd=(T.sub.distal−T.sub.proximal)/TC_separation distance
In other words, the temperature spatial gradient is estimated as the difference in temperature between the distal and proximal temperature-measurement devices divided by the distance between the distal and proximal temperature-measurement devices. The peak tissue temperature (where peak can be a hill or a valley) can then be estimated as:
T.sub.peak=ΔT/Δd*T.sub.peak_dist+T.sub.distal

(212) The processing device may also determine an estimated location of the peak temperature zone of the thermal lesion based, at least in part, on the determined orientation and/or the temperature measurements. For example, for a perpendicular orientation, the peak temperature location may be determined to be horizontally centered in the thermal lesion. In some embodiments, the processor may be configured to output information indicative of the peak temperature location on a display (for example, a graphical user interface). The information may include textual information and/or one or more graphical images.

(213) FIG. 22A is a graph illustrating that temperature measurements obtained from the temperature-measurement devices may be used to determine a peak temperature by applying one or more analytical correction factors or functions to the temperature measurements (for example, using numerical modeling approximations or look-up tables). As shown in FIG. 6A, a single correction factor or function (k) may be applied to each of the distal temperature-measurement devices to determine the peak temperature. In some embodiments, different correction factors or functions may be applied to each individual temperature-measurement device or to subsets of the groups of temperature-measurement devices depending on a determined orientation or on a comparison of the temperature measurements obtained by the temperature-measurement devices, thereby providing increased accuracy of peak temperature and peak temperature zone location. The increased accuracy of peak temperature and peak temperature zone location may advantageously result in safer and more reliable ablation procedures because the ablation parameters may be adjusted based on feedback received by the processing unit from the temperature-measurement devices. In accordance with several embodiments, peak temperatures at a depth beneath the tissue surface are accurately estimated without requiring microwave radiometry. With reference to FIG. 22A, the peak tissue temperature can be estimated as follows:
T.sub.peak(t)=e.sup.(−t/τ)+k*(1−e.sup.(−t/τ))*max(TCi(t));
where i spans the range of temperature-measurement devices, with max(TCi(t)) representing the maximum temperature reading of the temperature-measurement devices at time t. For example, FIG. 22B shows an implementation of the above formula. Trace 1 shows the estimated peak tissue temperature (T.sub.peak) at a constant k value of 1.8 and a τ value of 1, whereas Traces 2, 3 and 4 show the actual tissue temperatures measured at 1 mm, 3 mm and 5 mm, respectively, from the tissue surface using tissue-embedded infrared probes. As seen, the estimated peak tissue temperature (T.sub.peak) of Trace 1 tracks well the actual peak tissue temperature measured at 1 mm depth (Trace 2).

(214) In another embodiment, a predictive model-based approach utilizing the bioheat equation may be utilized to estimate peak tissue temperature. A recursive algorithm for determining the temperature T at a time point n, at a single point in a volume during treatment (for example, RF ablation) may be defined as follows:

(215) $T_n=\frac{\frac{\rho .Math.C}{\mathrm{dt}}.Math.T_{n-1}+W_e.Math.C.Math.T_a+P.Math.N}{\frac{\rho .Math.C}{\mathrm{dt}}+W_e.Math.C}$
where T.sub.n is the current temperature, T.sub.n-1 is the previous temperature, t is time, ρ is the tissue density, C is the specific heat of tissue, T.sub.a is the core arterial temperature, W.sub.e is an effective perfusion rate, and P.Math.N provides an estimate of the volumetric power deposited in tissue. The above equation can be formulated at various spatial locations, including the temperature-measurement device location(s) as well as the location of peak temperature (for example, hot spot). By utilizing this model at different locations, along with calibration to determine the model parameters, mapping techniques can be utilized to predict the temperature at one spatial location using measurement data from the other spatial location.

(216) In some embodiments, the processing device is configured to output the peak temperature or other output indicative of the peak temperature on a display (for example, a graphical user interface). The output may comprise alphanumeric information (for example, the temperature in degrees), one or more graphical images, and/or a color indication. In some embodiments, the processor may generate an output configured to terminate energy delivery if the determined peak temperature is above a threshold or maximum temperature. The output may comprise a signal configured to cause automatic termination of energy delivery or may comprise an alert (audible and/or visual) to cause a user to manually terminate energy delivery.

(217) In various embodiments, ablation parameters may be adjusted based on temperature measurements received from the temperature-measurement devices. The ablation parameters may comprise, among other things, duration of ablation, power modulation, contact force, target or setpoint temperature, a maximum temperature. The processor 46 (FIG. 1) may be configured to send control signals to the energy delivery module 40 based on the temperature measurements (and other measurements or estimations derived or otherwise determined therefrom) received from the temperature-measurement devices.

(218) In one embodiment, the energy delivery module 40 (FIG. 1) may be set to run in a temperature control mode, wherein radiofrequency energy of a certain power level is delivered and a maximum temperature is identified which cannot be exceeded. Each of the temperature-measurement devices may be monitored (either simultaneously or via toggled queries) on a periodic or continuous basis. If the maximum temperature is reached or exceeded, as determined by temperature measurements received from any of the temperature-measurement devices of the ablation catheters described herein, control signals may be sent to the energy delivery module to adjust ablation parameters (for example, reduction in power level) to reduce the temperature or to terminate energy delivery (temporarily or otherwise) until the temperature is reduced below the maximum temperature. The adjustments may be effected for example by a proportional-integral-derivative controller (PID controller) of the energy delivery module 40. In another embodiment, the energy delivery module 40 may be set to run in a power control mode, in which a certain level of power is applied continuously and the temperature measurements received from each of the temperature-measurement devices are monitored to make sure a maximum temperature is not exceeded. In some embodiments, a temperature-controlled mode comprises specifying a setpoint temperature (for example, 70 degrees Celsius, 75 degrees Celsius, 80 degrees Celsius, and then adjusting power or other parameters to maintain temperature at, below or near the setpoint temperature, as determined from the temperature measurements received from each of the temperature-measurement devices.

(219) Table 1 below shows examples of ablation parameters used in various test ablation procedures using an embodiment of an ablation catheter described herein.

(220) TABLE-US-00001 TABLE 1 Max Blood Irrigation Tissue Lesion Lesion Imped- Orien- flow (ml/ Power Temp width depth ance tation (cm/s) min) (W) (° C.) (mm) (mm) (Ohms) Parallel 0.5 15 13.3 91.7 9.8 5.2 85 Parallel 25 15 15.8 94.9 9.2 5.4 85 Parallel 0.5 0 8.6 98.8 11.2 4.7 85 Parallel 25 0 14.9 94.8 10.0 5.3 85 Perpend. 0.5 15 16.8 99.4 11 5.6 83 Perpend. 25 15 18.1 99.9 10.3 5.8 83 Perpend. 0.5 0 10.4 97.9 10.3 4.8 83 Perpend. 25 0 16.9 95.7 9.3 5.3 83

(221) As can be seen from the data in Table 1, the maximum tissue temperature and lesion sizes remained relatively constant with or without irrigation and/or with or without significant blood flow by modulating the power. The multi-variant or multiple temperature-measurement device system according to embodiments of this invention ensures appropriate tissue ablation under different electrode-tissue orientations. As explained above, the electrode-tissue orientation can be determined based on readings from the multiple temperature-measurement devices. If both proximal and distal temperatures become dominant, then the electrode orientation is estimated or indicated to be parallel to tissue. Similarly, when the distal temperatures are dominant, then the electrode orientation is inferred, estimated and/or indicated to be perpendicular to tissue. Combinations of proximal and distal dominant temperatures may provide indications for oblique electrode orientations. FIG. 23A illustrates a plot of temperature data from the multiple temperature-measurement devices (for example, thermocouples) that are indicative of a perpendicular orientation and FIG. 23B illustrates a plot of temperature data from the multiple temperature-measurement devices (for example, thermocouples) that are indicative of an oblique orientation.

(222) Contact Sensing

(223) According to some embodiments, various implementations of electrodes (for example, radiofrequency or RF electrodes) that can be used for high-resolution mapping and radiofrequency ablation are disclosed herein. For example, as discussed in greater detail herein, an ablation or other energy delivery system can comprise a high-resolution, or combination electrode, design, wherein the energy delivery member (for example, radiofrequency electrode, laser electrode, microwave transmitting electrode) comprises two or more separate electrodes or electrode members or portions. As also discussed herein, in some embodiments, such separate electrodes or electrode portions can be advantageously electrically coupled to each other (for example, to collectively create the desired heating or ablation of targeted tissue). In various embodiments, the combination electrode, or split-tip, design may be leveraged to determine whether or not one or more portions of the electrodes or other energy delivery members are in contact with tissue (for example, endocardial tissue) and/or whether or not contacted tissue has been ablated (for example, to determine whether the tissue is viable or not).

(224) Several embodiments of the invention are particularly advantageous because they include one, several or all of the following benefits: (i) confirmation of actual tissue contact that is easily ascertainable; (ii) confirmation of contact with ablated vs. unablated (viable) tissue that is easily ascertainable; (iii) low cost, as the invention does not require any specialized sensor; (iv) does not require use of radiometry; (v) provides multiple forms of output or feedback to a user; (vi) provides output to a user without requiring the user to be watching a display; and/or (vii) provides safer and more reliable ablation procedures.

(225) With reference to FIG. 1, according to some embodiments, the delivery module 40 includes a processor 46 (for example, a processing or control device) that is configured to regulate one or more aspects of the treatment system 10. The delivery module 40 can also comprise a memory unit or other storage device 48 (for example, non-transitory computer readable medium) that can be used to store operational parameters and/or other data related to the operation of the system 10. In some embodiments, the processor 46 comprises or is in communication with a contact sensing and/or a tissue type detection module or subsystem. The contact sensing subsystem or module may be configured to determine whether or not the energy delivery member(s) 30 of the medical instrument 20 are in contact with tissue (for example, contact sufficient to provide effective energy delivery). The tissue type detection module or subsystem may be configured to determine whether the tissue in contact with the one or more energy delivery member(s) 30 has been ablated or otherwise treated. In some embodiments, the system 10 comprises a contact sensing subsystem 50. The contact sensing subsystem 50 may be communicatively coupled to the processor 46 and/or comprises a separate controller or processor and memory or other storage media. The contact sensing subsystem 50 may perform both contact sensing and tissue type determination functions. The contact sensing subsystem 50 may be a discrete, standalone sub-component of the system (as shown schematically in FIG. 1) or may be integrated into the energy delivery module 40 or the medical instrument 20. Additional details regarding a contact sensing subsystem are provided below.

(226) In some embodiments, the processor 46 is configured to automatically regulate the delivery of energy from the energy generation device 42 to the energy delivery member 30 of the medical instrument 20 based on one or more operational schemes. For example, energy provided to the energy delivery member 30 (and thus, the amount of heat transferred to or from the targeted tissue) can be regulated based on, among other things, the detected temperature of the tissue being treated, whether the tissue is determined to have been ablated, or whether the energy delivery member 30 is determined to be in contact (for example, “sufficient” contact, or contact above a threshold level) with the tissue to be treated.

(227) With reference to FIG. 24, the distal electrode 30A may be energized using one or more conductors (for example, wires, cables, etc.). For example, in some arrangements, the exterior of an irrigation tube comprises and/or is otherwise coated with one or more electrically conductive materials (for example, copper, other metal, etc.). Thus, the one or more conductors can be placed in contact with such a conductive surface or portion of the irrigation tube to electrically couple the electrode or electrode portion 30A to an energy delivery module (for example, energy delivery module 40 of FIG. 1). However, one or more other devices and/or methods of placing the electrode or electrode portion 30A in electrical communication with an energy delivery module can be used. For example, one or more wires, cables and/or other conductors can directly or indirectly couple to the electrodes, without the use of the irrigation tube. The energy delivery module may be configured to deliver electromagnetic energy at frequencies useful for determining contact (for example, between 5 kHz and 1000 kHz).

(228) FIG. 24 schematically illustrates one embodiment of a combination, or split-tip, electrode assembly that can be used to perform contact sensing or determination by measuring the bipolar impedance between the separated electrodes or electrode portions 30A, 30B at different frequencies. Resistance values may be determined from voltage and current based on Ohm's Law: Voltage=Current*Resistance, or V=IR. Accordingly, resistance equals voltage divided by current. Similarly, if the impedance between the electrodes is complex, the complex voltage and current may be measured and impedance (Z) determined by V_complex=I_complex*Z_complex. In this case, both magnitude and phase information for the impedance can be determined as a function of frequencies. The different frequencies may be applied to the split-tip electrode assembly by an energy delivery module (for example, by energy generation device 42 of energy delivery module 40 of FIG. 1) or a contact sensing subsystem (such as contact sensing subsystem 50 of system 10 of FIG. 1). Because the voltage and current values may be known or measured, the resistance and/or complex impedance values can be determined from the voltage and current values using Ohm's Law. Thus, the impedance values may be calculated based on measured voltage and/or current values in accordance with several embodiments rather than directly obtaining impedance measurements.

(229) FIG. 25A is a plot showing resistance, or magnitude impedance, values of blood (or a blood/saline combination) and of cardiac tissue across a range of frequencies (5 kHz to 1000 kHz). The impedance values are normalized by dividing the measured impedance magnitude by the maximum impedance magnitude value. As can be seen, the normalized impedance of blood (or a blood/saline combination) does not vary significantly across the entire range of frequencies. However, the normalized impedance of cardiac tissue does vary significantly over the range of frequencies, forming a roughly “s-shaped” curve.

(230) In one embodiment, resistance or impedance measurements can be obtained at two, three, four, five, six or more than six different discrete frequencies within a certain range of frequencies. In several embodiments, the range of frequencies may span the range of frequencies used to ablate or otherwise heat targeted tissue. For example, resistance or impedance measurements may be obtained at two different frequencies f.sub.1 and f.sub.2 within the range of frequencies, where f.sub.2 is greater than f.sub.1. Frequency f.sub.1 may also be below the ablation frequency range and f.sub.2 may be above the ablation frequency range. In other embodiments, f.sub.1 and/or f.sub.2 can be in the range of ablation frequencies. In one embodiment, f.sub.1 is 20 kHz and f.sub.2 is 800 kHz. In various embodiments, f.sub.1 is between 10 kHz and 100 kHz and f.sub.2 is between 400 kHz and 1000 kHz. By comparing the impedance magnitude values obtained at the different frequencies, a processing device (for example, a contact sensing subsystem or module coupled to or executable by processor 46 of FIG. 1) can determine whether or not the electrode portion 30A is in contact with issue (for example, cardiac tissue) upon execution of specific program instructions stored on a non-transitory computer-readable storage medium.

(231) For example, if the ratio r of an impedance magnitude value obtained at the higher frequency f.sub.2 to the impedance magnitude value obtained at the lower frequency f.sub.1 is smaller than a predetermined threshold, the processing device may determine that the electrode portion 30A is in contact with cardiac tissue or other target region (for example, upon execution of specific program instructions stored on a non-transitory computer-readable storage medium). However, if the ratio r of an impedance magnitude value obtained at the higher frequency f.sub.2 to the impedance magnitude value obtained at the lower frequency f.sub.1 is greater than a predetermined threshold, the processing device may determine that the electrode portion 30A is not in contact with cardiac tissue but instead is in contact with blood or a blood/saline combination. The contact determinations may be represented as follows:

(232) $\frac{r_{f2}}{r_{f1}}<\mathrm{threshold}=\mathrm{CONTACT}$$\frac{r_{f2}}{r_{f1}}>\mathrm{threshold}=\mathrm{NO\_CONTACT}$

(233) In various embodiments, the predetermined threshold has a value between 0.2 and less than 1 (for example, between 0.2 and 0.99, between 0.3 and 0.95, between 0.4 and 0.9, between 0.5 and 0.9 or overlapping ranges thereof).

(234) In various embodiments, resistance or impedance measurements are periodically or continuously obtained at the different frequencies (for example, two, three, four or more different frequencies) by utilizing a source voltage or current waveform that is a multi-tone signal including the frequencies of interest, as shown in FIG. 25B. The multi-tone signal or waveform may be sampled in the time-domain and then transformed to the frequency domain to extract the resistance or impedance at the frequencies of interest, as shown in FIG. 25C. In some embodiments, measurements or determinations indicative of contact may be obtained in the time domain instead of the frequency domain. Signals or waveforms having different frequencies may be used. In accordance with several embodiments, performing the contact sensing operations is designed to have little or no effect on the electrogram (EGM) functionality of the combination, or split-tip, electrode assembly. For example, common mode chokes and DC blocking circuits may be utilized in the path of the impedance measurement circuitry as shown in FIG. 25D. The circuitry may also include a reference resistor R to limit the maximum current flow to the patient, as well as dual voltage sampling points V1 and V2 to enhance the accuracy of the impedance measurements. Additionally, a low-pass filter circuit (with, for example, a cut-off frequency of 7 kHz) may be utilized in the path of the EGM recording system, as shown in FIG. 4D. In several embodiments, all or portions of the circuitry shown in FIG. 25D are used in a contact sensing subsystem, such as contact sensing subsystem 50 of FIG. 1 or contact sensing subsystem 4650 of FIG. 27. The frequencies used for contact sensing may be at least greater than five times, at least greater than six times, at least greater than seven times, at least greater than eight times, at least greater than nine times, at least greater than ten times the EGM recording or mapping frequencies. The contact sensing subsystem may be controlled by a processing device including, for example, an analog-to-digital converter (ADC) and a microcontroller (MCU). The processing device may be integral with the processing device 46 of FIG. 1 or may be a separate, stand-alone processing device. If a separate processing device is used, the separate processing device may be communicatively coupled to the processing device 46 of FIG. 1.

(235) In various embodiments, resistance or impedance measurements (for example, total impedance or component parts of complex impedance) are periodically or continuously obtained at the different frequencies (for example, two or three different frequencies) by switching between the different frequencies. In accordance with several embodiments, performing the contact sensing operations may be designed to have little or no effect on the electrogram (EGM) functionality of the combination electrode, or split-tip, assembly. Accordingly, switching between the different frequencies may advantageously be synched to zero crossings of an AC signal waveform, as illustrated in FIG. 26A. In some embodiments, if the frequency switching does not occur at zero crossings, artifacts may be induced in the electrograms, thereby degrading the quality of the electrograms. In some embodiments, impedance measurements (for example, bipolar impedance measurements) are obtained at multiple frequencies simultaneously. In other embodiments, impedance measurements are obtained at multiple frequencies sequentially.

(236) In another embodiment, contact sensing or determination is performed by obtaining resistance or impedance measurements across a full range of frequencies from an f.sub.min, to an f.sub.max (for example, 5 kHz to 1 MHz, 10 kHz to 100 kHz, 10 kHz to 1 MHz). In such embodiments, the variation in the frequency response, or the impedance measurements over the range of frequencies, is indicative of whether the electrode portion 30A is in contact with tissue (for example, cardiac tissue) or not.

(237) The impedance measurements may be applied to a model. For example, a frequency response function r(f) may be created and fit to a polynomial or other fitting function. The function may take the form, for example, of:
r(f)=a.Math.f.sup.3+b.Math.f.sup.2+c.Math.f+d
where a, b, c and d are the terms for the polynomial function that match the response of r(f) to measured data. Thresholds may then be set on the polynomial terms to determine whether or not the electrode is in contact with tissue. For example, a large d term may indicate a large impedance indicative of tissue contact. Similarly, a large c term may indicate a large slope in the impedance which is also indicative of tissue contact. The higher-order terms may be utilized to reveal other subtle differences in the impedance response that indicate tissue contact.

(238) In some embodiments, a circuit model such as that shown in FIG. 26B is used to determine the frequency response function r(f). The model may comprise resistors and capacitors that predict the response of tissue and the tissue to electrode interfaces. In this approach, the R and C values may be determined that best fit the measured data and thresholds may be utilized based on the R and C values to determine whether or not the electrode is in contact with tissue. For example a small value of capacitance (C2) may indicate a condition of tissue contact, while a large value may indicate no contact. Other circuit configurations are also possible to model the behavior of the electrode impedance as desired and/or required.

(239) In some embodiments, the contact sensing or contact determination assessments are performed prior to initiation of ablative energy delivery and not performed during energy delivery. In this case, switching may be utilized to separate the contact impedance measurement circuitry from the ablative energy, as shown in FIG. 26C. In this implementation, a switch SW1 is opened to disconnect the split-tip capacitor (C.sub.ST) and allow measurement of impedance in the higher frequency ranges where C.sub.ST might present a short circuit (or low impedance in parallel with the measurement). At the same time, switches SW2 and SW3 are set to connect to the impedance measurement circuitry, or contact sensing subsystem. As shown in FIG. 26C, the impedance measurement circuit, or contact sensing subsystem, is the same as that shown in FIG. 25D. When ablations are to be performed, SW2 and SW3 connect the tip electrodes to the ablative energy source (for example, RF generator labeled as RF in FIG. 26C) and disconnect the impedance measurement circuit. SW1 is also switched in order to connect the split tip capacitor C.sub.ST, thereby allowing the pair of electrodes to be electrically connected via a low impedance path. In one embodiment, the split-tip capacitor C.sub.ST comprises a 100 nF capacitor that introduces a series impedance lower than about 4Ω at 460 kHz, which, according to some arrangements, is a target frequency for radiofrequency ablation. As FIG. 26C also shows, the ablation current path is from both electrodes to a common ground pad. The impedance measurement path is between the two electrodes, although other current paths for the impedance measurement are also possible. In one embodiment, the switch is a relay such as an electromechanical relay. In other embodiments, other types of switches (for example, solid-state, MEMS, etc.) are utilized.

(240) In some embodiments, the contact sensing or contact determination assessments described above may be performed while ablative energy or power (for example, ablative radiofrequency energy or power) is being delivered because the frequencies being used for contact sensing are outside of the range (either above or below, or both) of the ablation frequency(ies).

(241) FIG. 27 schematically illustrates a system 4600 comprising a high-resolution, combination electrode, or split-tip, electrode catheter, the system being configured to perform ablation procedures and contact sensing or determination procedures simultaneously. The high resolution (e.g., split-tip) electrode assembly 4615 may comprise two electrodes or two electrode members or portions 4630A, 4630B separated by a gap. A separator is positioned within the gap G, between the electrodes or electrode portions 4630A, 4630B. The split-tip electrode assembly 4615 may comprise any of the features of the split-tip electrode assemblies described above in connection with FIG. 2 and and/or as otherwise disclosed herein. An energy delivery module (not shown, such as energy delivery module 40 of FIG. 1) or other signal source 4605 may be configured to generate, deliver and/or apply signals in an ablative range (for example, radiofrequency energy 200 kHz-800 kHz, and nominally 460 kHz) while a contact sensing subsystem 4650 (such as the contact sensing subsystem shown in FIG. 25D) delivers low-power signal(s) 4607 (such as excitation signals) in a different frequency range (for example, between 5 kHz and 1000 kHz) to be used to perform the contact sensing or determination assessments to a split-tip electrode assembly 4615. The low-power signal(s) 4607 may comprise a multi-tone signal or waveform or separate signals having different frequencies. The contact sensing subsystem 4650 may comprise the elements shown in FIG. 25D, as well as notch filter circuits to block the ablation frequency (for example, a 460 kHz notch filter if a 460 kHz ablation frequency is used). In this configuration, a filter 4684 is utilized to separate the contact sensing frequencies and the ablation frequency(ies).

(242) The filter 4684 may comprise, for example, an LC circuit element, or one or more capacitors without an inductor. The elements and values of the components of the filter 4684 may be selected to center the minimum impedance at the center frequency of the ablative frequencies delivered by the energy delivery module to effect ablation of targeted tissue. In some embodiments, the filtering element 4684 comprises a single capacitor that electrically couples the two electrodes or electrode portions 4630A, 4630B when radiofrequency current is applied to the system. In one embodiment, the capacitor comprises a 100 nF capacitor that introduces a series impedance lower than about 4Ω at 460 kHz, which, according to some arrangements, is a target frequency for ablation (for example, RF ablation). However, in other embodiments, the capacitance of the capacitor(s) or other band-pass filtering elements that are incorporated into the system can be greater or less than 100 nF, for example, 5 nF to 300 nF, according to the operating ablation frequency, as desired or required. In this case, the contact sensing impedance frequencies would all be below the ablation frequency range; however, in other implementations, at least some of the contact sensing impedance frequencies are within or above the ablation frequency range.

(243) FIG. 28 illustrates a plot of impedance of an LC circuit element comprising the filter 4684, for example. As shown, the minimum impedance is centered at the center frequency of the ablative RF frequencies (460 kHz as one example) and the impedance is high at the frequencies in the EGM spectrum so as not to affect EGM signals or the contact sensing measurements. Additionally, the contact impedance measurements are performed at frequencies that exist above and/or below the RF frequency (and above the EGM spectrum). For example, two frequencies f.sub.1 and f.sub.2 may be utilized where f.sub.1=20 kHz and f.sub.2=800 kHz. At these frequencies, the LC circuit would have a large impedance in parallel with the electrodes, thereby allowing the impedance to be measured. In one embodiment, the inductor L has an inductance value of 240 μH and the capacitor C has a capacitance value of 5 nF. However, in other embodiments, the inductor L can range from 30 μH to 1000 μH (for example, 30 to 200 μH, 200 to 300 μH, 250 to 500 μH, 300 to 600 μH, 400 to 800 μH, 500 to 1000 μH, or overlapping ranges thereof) and the capacitor C can range from 0.12 nF to 3.3 μF (for example, 0.12 to 0.90 nF, 0.50 to 1.50 nF, 1 nF to 3 nF, 3 nF to 10 nF, 5 nF to 100 nF, 100 nF to 1 μF, 500 nF to 2 μF, 1 μF to 3.3 μF, or overlapping ranges thereof). In various embodiments, f.sub.1 is between 10 kHz and 100 kHz and f.sub.2 is between 400 kHz and 1000 kHz.

(244) In accordance with several embodiments, the same hardware and implementation as used for contact sensing may be used to determine tissue type (for example, viable tissue vs. ablated tissue), so as to confirm whether ablation has been successful or not. FIG. 29 is a plot illustrating resistance, or impedance magnitude, values for ablated tissue, viable tissue and blood across a range of frequencies. As can be seen, the resistance of ablated tissue starts at a high resistance value (200Ω) and remains substantially flat or stable, decreasing slightly over the range of frequencies. The resistance of blood starts at a lower resistance (125Ω) and also remains substantially flat or stable, decreasing slightly over the range of frequencies. The resistance of viable tissue, however, starts at a high resistance value (250Ω) and significantly decreases across the range of frequencies, roughly forming an “s-shaped” curve. The reason for the different resistance responses between ablated and viable tissue is due, at least partially, to the fact that the viable cells (for example, cardiac cells) are surrounded by a membrane that acts as a high-pass capacitor, blocking low-frequency signals and allowing the higher-frequency signals to pass, whereas the cells of the ablated tissue no longer have such membranes as a result of being ablated. The reason for the substantially flat response for blood resistance is that most of the blood is comprised of plasma, which is more or less just electrolytes having low impedance. The red blood cells do provide some variance, because they have similar membranes acting as capacitors as the viable cardiac cells. However, because the red blood cells constitute such a small percentage of the blood composition, the effect of the red blood cells is not substantial.

(245) Similar to the contact sensing assessments described above, resistance, or impedance magnitude, values may be obtained at two or more frequencies (for example, 20 kHz and 800 kHz) and the values may be compared to each other to determine a ratio. In some embodiments, if the ratio of the impedance magnitude value at the higher frequency f.sub.2 to the impedance magnitude value at the lower frequency f.sub.1 is less than a threshold, then the processing device (for example, processing device 4624, which may execute a tissue type determination module stored in memory) determines that the contacted tissue is viable tissue and if the ratio of the impedance magnitude value at the higher frequency f.sub.2 to the impedance magnitude value at the lower frequency f.sub.1 is greater than a threshold, then the processing device 4624 determines that the contacted tissue is ablated tissue. In various embodiments, the predetermined threshold has a value between 0.5 and 0.8 (for example, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80).

(246) In some embodiments, a combination of impedance magnitude differences and differences in the ratio of impedance magnitudes at frequencies f.sub.2 and f.sub.1 are utilized to determine both contact state (for example, contact vs. in blood) as well as tissue type (for example, viable tissue vs. ablated tissue). In some embodiments, contact state and tissue type determinations are not performed during energy delivery or other treatment procedures. In other embodiments, contact state and/or tissue type determinations are performed during energy delivery or other treatment procedures using filters and/or other signal processing techniques and mechanisms to separate out the different frequency signals.

(247) In addition to the impedance magnitude, the same hardware and implementation used for contact sensing (for example, contact sensing subsystem 50, 4650) may be utilized to compute the phase of the impedance (for example, complex impedance) across electrode portions. In one embodiment, the phase of the impedance may be added to algorithms for determining different contact states (for example, contact vs. in blood) as well as different tissue states (for example, viable tissue vs. ablated tissue). FIG. 30 shows an example of the phase of the impedance across electrode portions versus frequency for viable tissue, ablated tissue and blood. The phase tends to be larger (closer to 0 degrees) for blood and smaller for viable (unablated) tissue. For ablated tissue the phase may be in between blood and viable tissue. In one embodiment, a negative phase shift at a single frequency indicates contact with tissue (either viable or ablated). A larger negative phase shift may indicate contact with viable tissue. In one embodiment, a phase of less than −10 degrees at 800 kHz indicates contact with tissue (either viable or ablated). In one embodiment, a phase of less than −20.5 degrees at 800 kHz indicates contact with viable tissue. In other embodiments, the phase at other frequencies or combinations of frequencies are utilized to determine contact state and tissue type. In some embodiments, the impedance magnitude and phase are utilized together as vector quantities, and differences in the vectors for different frequencies are utilized to determine contact state and tissue type.

(248) In some embodiments, a combination of impedance magnitude differences, differences in the ratio of impedance magnitude values at frequencies f.sub.2 and f.sub.1, and differences in the phase of the impedance are utilized together to determine both contact state (for example, contact vs. in blood) as well as tissue type (for example, viable tissue vs. ablated tissue). In one embodiment, the determination process 5000 illustrated in FIG. 31 is utilized to determine both contact state as well as tissue type. In this embodiment, an impedance magnitude threshold of 150Ω at 20 kHz is utilized to delineate between no contact and tissue contact (with a larger value indicating contact) at block 5005. Once contact is determined at block 5005, the ratio of the impedance magnitude at f.sub.2=800 kHz and f.sub.1=20 kHz is computed at block 5010, with a value of less than 0.6 indicating contact with unablated, or viable, tissue. If the aforementioned ratio is greater than 0.6, then the impedance phase at 800 kHz is utilized at block 5015, and an (absolute) value greater than 20.5 degrees indicates contact with ablated tissue. An (absolute) value of less than 20.5 degrees indicates contact with unablated, or viable, tissue.

(249) In some embodiments, the contact sensing subsystem 50 or system 10 (for example, a processing device thereof) analyzes the time-domain response to the waveform described in FIG. 25B, or to an equivalent waveform. In accordance with several embodiments, contact sensing or tissue type determinations are based on processing the response to a signal applied to a pair of electrodes or electrode portions (for example electrode pair 4630A, 4630B), the signal either including multiple frequencies or several frequencies applied sequentially. In some embodiments, processing device 4624 may process the response in time domain or frequency domain. For example, given that blood is mostly resistive, with little capacitive characteristics, it is expected that time-domain features such as rise or fall times, lag or lead times, or delays between applied signal 4402 (for example, I in FIG. 25D) and processed response 4404 (for example, V2 in FIG. 25D) will exhibit low values. Conversely, if the electrode pair 4630A, 4630B of FIG. 27 is in contact with tissue, given that tissue exhibits increased capacitive characteristics, it is expected that time-domain features such as rise or fall times, lag or lead times, or delays between applied signal 4402 (for example, I in FIG. 25D) and processed response 4404 (for example, V2 in FIG. 25D) will exhibit higher values. An algorithm that processes parameters such as, but not limited to, rise or fall times, lag or lead times, or delays between applied signal 4402 and processed response 4404 may indicate or declare contact with tissue when the parameters exceed a threshold, or, conversely, it may indicate or declare no contact with tissue when the parameters have values below a threshold. For example, assuming the signal 4402 is represented by a sinusoidal current of 800 kHz frequency, the algorithm could declare contact with tissue if the response 4404 lags by more than 0.035 μs. Conversely, the algorithm could declare lack of tissue contact if the response 4404 lags by less than 0.035 μs. Similarly, if the frequency of signal 4402 were 400 kHz, the algorithm may decide:

(250) no tissue contact, when the lag time is less than 0.07 μs;

(251) contact with ablated tissue, when the lag time is between 0.07 μs and 0.13 μs;

(252) contact with viable or unablated tissue, when the lag time is greater than 0.13 μs.

(253) The decision thresholds or criteria depend on the waveform of signal 4402. Thresholds or decision criteria for other types of waveforms may also be derived or determined.

(254) In some embodiments, multiple inputs may be combined by a contact sensing or contact indication module or subsystem executable by a processor (for example, processor of the contact sensing subsystems 50, 4650) to create a contact function that may be used to provide an indication of contact vs. no contact, an indication of the amount of contact (for example, qualitative or quantitative indication of the level of contact, contact state or contact force), and/or an indication of tissue type (for example, ablated vs. viable (non-ablated) tissue). For example, a combination of (i) impedance magnitude at a first frequency f.sub.1, (ii) the ratio of impedance magnitudes at two frequencies f.sub.2 and f.sub.1 (defined as the slope) or the delta, or change, in impedance magnitudes at the two frequencies, and/or (iii) the phase of the complex impedance at the second frequency f.sub.2 are utilized together to create a contact function that is indicative of contact state (for example, tissue contact vs. in blood). Alternatively, instead of slope, a derivative of impedance with respect to frequency may be used.

(255) In one embodiment, a minimum threshold |Z|.sub.min is defined for the impedance magnitude at f.sub.1, and a maximum threshold |Z|.sub.max is defined for the impedance at f.sub.1. The impedance magnitude measured by the contact sensing subsystem 50, 650 at f.sub.1 can be normalized such that the impedance magnitude is 0 if the measured result is equal to |Z|.sub.min or below, and the impedance magnitude is 1 if the measured result is equal to |Z|.sub.max or above. Results in-between |Z|.sub.min and |Z|.sub.max may be linearly mapped to a value between 0 and 1. Similarly, a minimum threshold S.sub.min and a maximum threshold S.sub.max may be defined for the slope (ratio of impedance magnitude between f.sub.2 and f.sub.1). If a derivative of impedance with respect to frequency is used, then similar minimum and maximum thresholds may be defined. The slope measured by the contact sensing subsystem 50 may be normalized such that the slope is 0 if the measured result is equal to or above S.sub.min and the slope is 1 if the measured result is equal to or below S.sub.max. Results in between S.sub.min and S.sub.max may be linearly mapped to a value between 0 and 1. A minimum threshold P.sub.min and a maximum threshold P.sub.max may also be defined for the phase of the complex impedance at f.sub.2. The phase measured by the contact sensing subsystem 50 at f.sub.2 may be normalized such that the phase is 0 if the measured result is equal to or greater than P.sub.min and 1 if the measured result is equal to or less than P.sub.max.

(256) In accordance with several embodiments, the resulting three normalized terms for magnitude, slope and phase are combined utilizing a weighting factor for each. The sum of the weighting factors may be equal to 1 such that the resulting addition of the three terms is a contact indicator that goes from a zero to 1 scale. The weighted contact function (CF) can thus be described by the below equation:

(257) $\mathrm{CF}=\mathrm{WF}1\frac{{.Math.Z.Math.}_{f1}-{.Math.Z.Math.}_{\min }}{{.Math.Z.Math.}_{\max }-{.Math.Z.Math.}_{\min }}+\mathrm{WF}2\frac{S-S_{\min }}{S_{\max }-S_{\min }}+\mathrm{WF}3\frac{P_{f2}-P_{\min }}{P_{\max }-P_{\min }}$

(258) where |Z|.sub.f1 is the measured impedance magnitude at a first frequency f.sub.1, clipped to a minimum value of |Z|.sub.min and a maximum value of |Z|.sub.max as described above; S is the ratio of the impedance magnitude at a second frequency f.sub.2 to the magnitude at f.sub.1, clipped to a minimum value of S.sub.min and a maximum value of S.sub.max as described above; and P.sub.f2 is the phase of the impedance at frequency f.sub.2, clipped to a minimum value of P.sub.min and a maximum value of P.sub.max as described above. The weighting factors WF1, WF2 and WF3 may be applied to the magnitude, slope and phase measurements, respectively. As previously stated, the weighting factors WF1+WF2+WF3 may sum to 1, such that the output of the contact function always provides a value ranging from 0 to 1. Alternatively, values greater than 1 may be allowed to facilitate generation of alerts to a user about circumstances when more tissue-electrode contact may become unsafe for patients. Such alerts may be helpful in preventing application of unsafe levels of contact force. For example, CF values in the range of 1 to 1.25 may be flagged as a “contact alert” and may cause the contact sensing subsystem to generate an alert for display or other output to a user. The alert may be visual, tactile, and/or audible. The weighting factors may vary based on catheter design, connection cables, physical patient parameters, and/or the like. The weighting factors may be stored in memory and may be adjusted or modified (for example, offset) depending on various parameters. In some embodiments, the weighting factors may be adjusted based on initial impedance measurements and/or patient parameter measurements.

(259) The contact function described above can be optimized (for example, enhanced or improved) to provide a reliable indicator of the amount of contact with tissue (for example, cardiac tissue, such as atrial tissue or ventricular tissue). The optimization may be achieved by defining minimum thresholds Z.sub.min, S.sub.min and P.sub.min that correspond with no to minimal tissue contact, as well as thresholds Z.sub.max, S.sub.max and P.sub.max that correspond with maximal tissue contact. Weighting terms may also be optimized (for example, enhanced or improved) for robust responsiveness to contact. In some embodiments, windowed averaging or other smoothing techniques may be applied to the contact function to reduce measurement noise.

(260) As one example, at a frequency f.sub.1=46 kHz and f.sub.2=800 kHz, the values Z.sub.min=115 ohms, Z.sub.max=175 ohms, S.sub.min=0.9, S.sub.max=0.8, P.sub.min=−5.1 degrees, P.sub.max=−9 degrees, WF1=0.75, WF2=0.15, and WF3=0.1 are desirable (for example, optimal) for representing the amount of tissue contact (for example, for cardiac tissue of the atria or ventricles). In other embodiments, Z.sub.min may range from 90 ohms to 140 ohms (for example, 90 ohms to 100 ohms, 95 ohms to 115 ohms, 100 ohms to 120 ohms, 110 ohms to 130 ohms, 115 ohms to 130 ohms, 130 ohms to 140 ohms, overlapping ranges thereof, or any value between 90 ohms and 140 ohms), Z.sub.max may range from 150 ohms up to 320 ohms (for example, 150 ohms to 180 ohms, 160 ohms to 195 ohms, 180 ohms to 240 ohms, 200 ohms to 250 ohms, 225 ohms to 260 ohms, 240 ohms to 300 ohms, 250 ohms to 280 ohms, 270 ohms to 320 ohms, overlapping ranges thereof, or any value between 150 ohms and 320 ohms), S.sub.min may range from 0.95 to 0.80 (for example, 0.95 to 0.90, 0.90 to 0.85, 0.85 to 0.80, overlapping ranges thereof, or any value between 0.95 and 0.80), S.sub.max may range from 0.85 to 0.45 (for example, 0.85 to 0.75, 0.80 to 0.70, 0.75 to 0.65, 0.70 to 0.60, 0.65 to 0.55, 0.60 to 0.50, 0.55 to 0.45, overlapping ranges thereof, or any value between 0.85 and 0.45), P.sub.min may range from 0 to −10 degrees (for example, 0, −1, −2, −3, −4, −5, −6, −7, −8, −9, −10 or any combinations of ranges between, such as 0 to −5, −2 to −6, −4 to −8, −5 to −10), and P.sub.max may range from −5 to −25 degrees (for example, −5 to −10, −7.5 to −15, −10 to −20, −15 to −25, overlapping ranges thereof or any value between −5 and −25 degrees). The weighting factors WF1, WF2 and WF3 may cover the range from 0 to 1. In some embodiments, values above or below the ranges provided may be used as desired and/or required. Appropriate values for these parameters may be dependent on the electrode geometry and frequencies f.sub.1 and f.sub.2 used for the measurements. Changes in the electrode geometry, physical patient parameters, connection cables, and frequencies may require different ranges for the above values.

(261) In some embodiments, a contact function, or contact criterion, can be determined based, at least in part, on an if-then case conditional criterion. One example if-then case criterion is reproduced here:

(262) CC=IF(|Z.sub.MAG|>Z.sub.THR1, Best, IF(AND(Z.sub.THR1>|Z.sub.MAG|, |Z.sub.MAG|≥Z.sub.THR2), Good, IF(AND(Z.sub.THR2>|Z.sub.MAG|, |Z.sub.MAG|≥Z.sub.THR3), Medium, IF(AND(Z.sub.THR3>|Z.sub.MAG, |Z.sub.MAG|≥Z.sub.THR4), Low, No_Contact))))+IF(|Z.sub.MAG|>Z.sub.THR1, 0, IF(AND(SLOPE≤S.sub.THR1), Good, IF(AND(S.sub.THR1<SLOPE, SLOPE≤S.sub.THR2), Medium, IF(AND(S.sub.THR2<SLOPE, SLOPE≤S.sub.THR3), Low, No_Contact))))+IF(|Z.sub.MAG|>Z.sub.THR1, 0, IF(AND(PHASE≤P.sub.THR1), Good, IF(AND(P.sub.THR1<PHASE, PHASE≤P.sub.THR2), Medium, IF(AND(P.sub.THR2<PHASE, PHASE≤P.sub.THR3), Low, No_Contact))))

(263) FIG. 32 illustrates an embodiment of a contact criterion process 5100 corresponding to the above if-then case conditional criterion. The contact criterion process 5100 may be executed by a processor upon execution of instructions stored in memory or a non-transitory computer-readable storage medium. At decision block 5105, a measured or calculated impedance magnitude value (for example, based on direct impedance measurements or based on voltage and/or current measurements obtained by a combination electrode assembly comprising two electrode portions) is compared to a predetermined threshold impedance. If the measured or calculated impedance magnitude value |Z.sub.MAG| is greater than a first threshold Z.sub.THR1 (for example, 350Ω), then the Contact Criterion (CC) is assigned a “best” or highest value. If, however, the measured or calculated impedance magnitude value |Z.sub.MAG| is less than the threshold Z.sub.THR1, then the process 5100 proceeds to block 5110, where individual subvalues for impedance magnitude, slope and phase are determined. At block 5115, the individual subvalues are combined (for example summed) into an overall value indicative of contact state. In some embodiments, the combination is a sum of a weighted combination, as described above.

(264) The process 5100 may optionally generate output at block 5120. For example, if at decision block 5105, the measured or calculated impedance magnitude value |Z.sub.MAG| is greater than the first threshold Z.sub.THR1, the process can generate an alert to a user that further manipulation of the catheter or other medical instrument may not further improve tissue contact, but may instead compromise patient safety. For example, if the user pushes too hard on the catheter or other medical instrument, the additional pressure may achieve little improvement in tissue contact but may increase the risk of tissue perforation (for example, heart wall perforation). The output may comprise a qualitative or quantitative output as described in further detail herein (for example in connection with FIG. 33).

(265) FIG. 32A illustrates an embodiment of the individual subvalue subprocess 5110 of process 5100 performed when the measured or calculated impedance magnitude value |Z.sub.MAG| is less than the first threshold Z.sub.THR1. The Contact Criterion (CC) overall value may be calculated by bracketing the impedance magnitude (|Z.sub.MAG|), the slope (S) and the phase (P) into intervals corresponding to good, medium, low and no contact levels. Subvalues corresponding to either good, medium, low or not contact are determined for each of the impedance magnitude, slope and phase components depending on comparisons to various predetermined threshold values. The subvalues may be combined to determine an overall contact state value. In the example case conditional criterion above, the CC is a sum of the individual values received by each of the three parameters (|Z.sub.MAG|, S, P) according to their corresponding level of contact (for example, good, medium, low or no contact). For example, if Good=3, Medium=2, Low=1 and No_Contact=0 then the overall CC could be between 0-2 for no or low contact, between 3-4 for poor contact, between 5-6 for medium contact and 7-9 for good contact. In one embodiment, when |Z.sub.MAG| exceeds the first threshold Z.sub.THR1, then CC=10, as an indication that a “best,” or “optimal” level of tissue contact was achieved.

(266) In some embodiments, more than two frequencies are used (for example, three or four frequencies) for tissue contact or tissue type detection. Although the computations described above were presented using impedance magnitude, slope and phase, other characteristics of the complex impedance may be used in other embodiments. For example, analyses of the real and imaginary components of impedance may be used. Analyses of admittance parameters or scattering parameters may also be used. In some embodiments, direct analyses of the voltages and currents described in FIGS. 25A-27 (for example, processing of voltage or current magnitudes, frequency changes or relative phase) may be used. Analyses of voltages or currents may be performed in time domain or frequency domain. Impedance measurements, or values, may be calculated based on voltage and current measurements or may be directly measured. For example, phase measurements may comprise a difference in phase between measured voltage and measured current or may be actual impedance phase measurements.

(267) In some embodiments, the contact indicator or contact function is associated with output via an input/output interface or device. The output may be presented for display on a graphical user interface or display device communicatively coupled to the contact sensing subsystem 50 (FIG. 1). The output may be qualitative (for example, comparative level of contact as represented by a color, scale or gauge) and/or quantitative (for example, represented by graphs, scrolling waveforms or numerical values) as shown in FIG. 33.

(268) FIG. 33 illustrates an embodiment of a screen display 5200 of a graphical user interface of a display device communicatively coupled to the contact sensing subsystem 50 (FIG. 1). The screen display 5200 includes a graph or waveform 5210 illustrating impedance magnitude at frequency f.sub.1 over time, as well as a box 5211 indicating the real-time numerical value of the impedance magnitude. The screen display 5100 also includes a graph or waveform 5220 of slope (from f.sub.2 to f.sub.1) over time, as well as a box 5221 indicating the real-time numerical value of the slope. The screen display 5200 further includes a graph or waveform 5230 illustrating phase at frequency f.sub.2 over time, as well as a box 5231 indicating the real-time numerical value of the phase. The three measurements (magnitude, slope and phase) are combined into a contact function as described above and may be represented as a contact function or indicator over time, as displayed on graph or waveform 5240. The real-time or instantaneous numerical value of the contact function may also be displayed (Box 5241).

(269) In some embodiments, as shown in FIG. 33, the contact function or indicator may be represented as a virtual gauge 5250 that provides a qualitative assessment (either alone or in addition to a quantitative assessment) of contact state or level of contact in a manner that is easily discernable by a clinician. The gauge 5250 may be segmented into, for example, four segments, or regions, that represent different classifications or characterizations of contact quality or contact state. For example, a first segment (for example, from contact function values of 0 to 0.25) may be red in color and represent no contact, a second segment (for example, from contact function values of 0.25 to 0.5) may be orange in color and represent “light” contact, a third segment (for example, from contact function values of 0.5 to 0.75) may be yellow in color and represent “medium” or “moderate” contact, and a fourth segment (for example, from contact function values of 0.75 to 1) may be green in color and represent “good”, or “firm”, contact. In other embodiments, fewer than four segments or more than four segments may be used (for example, two segments, three segments, five segments, six segments). In one embodiment, three segments are provided, one segment for no contact or poor contact, one segment for moderate contact and one segment for good, or firm, contact. The segments may be divided equally or otherwise as desired and/or required. Other colors, patterns, graduations and/or other visual indicators may be used as desired. Additionally, a “contact alert” color or gauge graduation may be provided to alert the user about engaging the catheter or other medical instrument with too much force (for example, contact function values greater than 1). The gauge 5250 may include a pointer member that is used to indicate the real-time or instantaneous value of the contact function on the gauge 5250.

(270) In some embodiments, a qualitative indicator 5260 indicates whether or not contact is sufficient to begin a treatment (for example, ablation) procedure, the level of contact, tissue type, and/or whether contact is greater than desired for safety. The qualitative indicator 5260 may provide a binary indication (for example, sufficient contact vs. insufficient contact, contact or no contact, ablated tissue or viable tissue) or a multi-level qualitative indication, such as that provided by the gauge 5250. In one embodiment, the qualitative indicator 5260 displays the color on the gauge 5250 corresponding to the current contact function value. Other types of indicators, such as horizontal or vertical bars, other meters, beacons, color-shifting indicators or other types of indicators may also be utilized with the contact function to convey contact quality to the user. Indicators may include one or more light-emitting diodes (LEDs) adapted to be activated upon contact (or a sufficient level of contact) or loss of contact. The LEDs may be different colors, with each color representing a different level of contact (for example, red for no contact, orange for poor contact, yellow for medium contact and green for good contact). The LED(s) may be positioned on the catheter handle, on a display or patient monitor, or any other separate device communicatively coupled to the system.

(271) In one embodiment involving delivery of radiofrequency energy using a radiofrequency ablation catheter having a plurality of temperature-measurement devices (such as the ablation catheters and temperature-measurement devices described herein), the criterion for detecting a loss of tissue contact during delivery of radiofrequency energy may be implemented as:
ΔT.sub.i/Δt<−Threshold1  (Condition 1)
or
ΔT.sub.comp/ΔP<Threshold2  (Condition 2)
where ΔT.sub.i is the change in the temperature of any of the plurality of temperature-measurement devices (for example, sensors, thermocouples, thermistors) positioned along the catheter or other medical instrument; Δt is the interval of time over which the temperature change is measured; ΔT.sub.comp is the change in the maximum of the temperatures of the temperature-measurement devices and ΔP is the change in applied power.

(272) Condition 1 may signal that the temperature measurements obtained by the temperature-measurement devices have dropped rapidly in a short period of time, which may be indicative of a loss of contact or an insufficient or inadequate level of contact. For example, if ΔT.sub.i is −10 degrees Celsius over a Δt of 1 second and Threshold1 is −5 degrees Celsius/second, then the contact loss condition is met (because −10 degrees Celsius/second<−5 degrees Celsius/second).

(273) Condition 2 may signal that the temperature of the temperature-measurement devices is not increasing even though sufficient power is being applied, which may be indicative of a loss of contact or an insufficient or inadequate level of contact. For example, if ΔT.sub.comp=5 degrees Celsius and ΔP=30 Watts and if Threshold2 is 1 degree Celsius/Watt, then the contact loss condition is met (because 5 degrees Celsius/30 Watts<1 degree Celsius/Watt).

(274) In accordance with several embodiments, systems and methods for de-embedding, removing, or compensating for the effects caused by variations in cables, generators, wires and/or any other component of an ablation system (and/or components operatively coupled to an ablation system) or by the presence or absence of a catheter interface unit or other hardware component in an energy delivery and mapping system are provided. In some embodiments, the systems and methods disclosed herein advantageously result in contact indication values that are based on network parameter values (for example, impedance values) that more closely represent the actual network parameter value (for example, impedance) across the electrodes of the high resolution electrode assembly. Accordingly, as a result of the compensation or calibration systems and methods described herein, a clinician may be more confident that the contact indication values are accurate and are not affected by variations in the hardware or equipment being used in or connected to the system or network parameter circuit. In some arrangements, the network parameter values (for example, impedance measurements) obtained by the system using the compensation or calibration embodiments disclosed herein can be within ±10% (for example, within ±10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%) of the actual network parameter values (for example, impedance values) across the electrode members of the combination electrode assembly. For example, the impedance magnitude, the impedance slope (ratio of impedance magnitudes at two frequencies) and phase of the impedance may each individually be measured to within +/−10% or better using this approach. As a result, the contact function or contact indicator can advantageously provide an accurate representation of tissue contact, with an accuracy of +/−10% or greater.

(275) FIG. 34A illustrates a schematic block diagram of an embodiment of a network parameter measurement circuit 5400 (for example, tissue contact impedance measurement circuit). The network parameter measurement circuit 5400 includes a contact sensing signal source 5405, a load 5410 between two electrodes D1, D2 of a high-resolution electrode assembly at a distal end portion of an ablation catheter, and a chain of multiple two-port networks representative of a generator 5415, catheter interface unit cables 5420A, 5420B, a catheter interface unit 5425, a generator cable 5430 and catheter wires 5435. Because in some arrangements the network parameter values (for example, scattering parameter or electrical measurement such as voltage, current or impedance measurements) are obtained at the beginning of the chain at the level of the generator 5415, the measured network parameter values (for example, impedance values obtained directly or from voltage and/or current values) may differ significantly from the actual network parameter values (for example, impedance values) between the two spaced-apart electrode members D1, D2 due to effects of the components of the network parameter circuit between the signal source 5405 and the electrode members D1, D2. The impedance values may comprise impedance magnitude, slope between impedance magnitude at different frequencies, and/or impedance phase values. For example, detected impedance magnitude at a frequency f.sub.1 can be as much as ±25% different than the actual impedance magnitude at a frequency f.sub.1. Similarly, a detected slope (ratio of impedance magnitudes at frequencies f.sub.2 and f.sub.1) can be as much as ±50% different than the actual slope. Additionally, the detected phase may be as much as ±−30 degrees different than the actual phase. As a result of these combined inaccuracies, a contact function (CF) or contact indication values may be as much as −100% or +150% different than the intended contact function or contact indication values, thereby rendering the contact function ineffective in determining tissue contact. In accordance with several embodiments, the compensation or calibration embodiments disclosed herein can advantageously improve the accuracy of the contact function or contact indication values.

(276) The network parameters of each of the multi-port (for example, two-port) networks in the network parameter measurement circuit 5400 can be obtained (for example, measured) and utilized to convert the measured network parameter value (for example, scattering parameter or electrical parameter such as impedance) to a corrected (actual) value (for example, impedance value). In some embodiments, a two-port network analyzer is used to directly measure the scattering parameters (S-parameters) at the input and output of each of the two-port networks. In other embodiments, multiple components of the network parameter measurement circuit 5400 can be combined into groups of components and measured together. The network parameters of the individual components or groups of components can be combined to determine an aggregate effect of the chain of two-port networks on the network parameter value(s). In some implementations, the scattering parameters of at least some of the components may be hard-coded into a software program (for example, using an average value based on a few measurement samples) so as to reduce the number of measurements to be taken or obtained.

(277) According to one implementation, S-parameter matrices for each of the two-port networks or groups of two-port networks can be transformed to an overall transmission matrix. The overall transmission matrix may then be transformed back into S-parameters (or some other parameters) to generate an S-parameter (or another type of) matrix for the total network. The S-parameters from the total S-parameter matrix can then be used to de-embed, calibrate or compensate for the S-parameters from the measured input reflection coefficient to result in a corrected (actual) reflection coefficient. The actual reflection coefficient may then be converted into a corrected impedance value that is more closely indicative of the actual impedance between the two electrode portions D1, D2 of a high-resolution electrode assembly. In several embodiments, the corrected impedance values are used as the inputs for the Contact Function (CF) or other contact indication or level of contact assessment algorithm or function, as described above. For example, the corrected impedance values can be used to determine the Z, S and P values in the weighted contact function (CF) described above.

(278) The effects of the hardware components of the network parameter measurement circuit (for example, impedance measurement circuit) 5400 can be compensated for, de-embedded from, or calibrated so as to reduce or remove the effects of the hardware components or differences in the hardware components of a particular system (for example, impedance measurement circuit) setup prior to first use; however, the components of the network parameter circuit may differ across different procedures as different hardware components (for example, generators, cables, catheters and/or the like) are used or as a catheter interface unit or other hardware component to facilitate electroanatomical mapping is plugged in or removed, thereby resulting in inconsistency if not compensated for. In some embodiments, the total system S-parameter matrix may only be updated when the connections within the network parameter measurement circuit 5400 change (for example, when a catheter interface is plugged in or removed from the electrical path, when a cable is switched, etc.).

(279) In some embodiments, instead of requiring a manual de-embedding of the effects on impedance of certain circuit components when connections change (which can be time-consuming and result in increased likelihood of user error), the network parameters of a subset of the various components (for example, the generator 5415, the catheter interface unit cables 5420A, 5420B and the catheter interface unit 5425) are automatically measured to enable the effects of these elements to be de-embedded from the network parameters (for example, scattering parameters or impedance measurements) or otherwise compensated for or calibrated. FIG. 34B illustrates an embodiment of a circuit 5450 that can be used to automatically de-embed or compensate for the effects of certain hardware components in the network parameter circuit 5400. In one embodiment, the auto-calibration circuit 5450 is positioned at a distal end of the catheter interface unit cable before the generator cable 5430 and catheter wires 5435. The circuit 5450 may advantageously provide the ability to disconnect the electrode members D1, D2 of the high-resolution electrode assembly from the generator cable 5430 and catheter 5435 and to connect a known load between D1 and D2.

(280) In this embodiment, the auto-calibration circuit 5450 can assume that the network parameters of the generator cable 5430 and catheter wire 5435 components are known and can be assumed to be constant. However, if the generator cable 5430 and/or catheter wires 5435 are determined to vary significantly from part to part, the circuit 5450 could be implemented at the distal end of the generator cable 5430, in the catheter tip or at any other location, as desired or required. In some embodiments, the known load of the auto-calibration circuit 5450 includes a calibration resistor R.sub.cal and a calibration capacitor C.sub.cal. Switches may be used to connect R.sub.cal as the load, C.sub.cal as the load and both R.sub.cal and C.sub.cal in parallel as the load. Other elements (such as inductors, combinations of resistors, inductors and/or capacitors, or shorts or open circuits can be utilized as the known load). As shown in FIG. 34B, the combined network parameters of the generator 5415, catheter interface unit cables 5420A, 5420B and the catheter interface unit 5425 are represented as a single combined network (Network 1).

(281) In this embodiment, the network parameters (for example S-parameters) of Network 1 are measured directly using the network parameter circuit and an S-parameter matrix is created from the network parameters. Each of the elements in the S-parameter matrix is a complex number and is frequency dependent. The S-parameters may be measured at multiple different frequencies (for example, 3 different frequencies in the kHz range, such as a first frequency from 5-20 kHz a second frequency from 25-100 kHz and a third frequency from 500-1000 kHz). In one embodiment, the complex impedance is measured with the resistor R.sub.cal connected and the capacitor C.sub.cal disconnected, with the capacitor C.sub.cal connected and the resistor R.sub.cal disconnected and with both the resistor R.sub.cal and the capacitor C.sub.cal connected in parallel. The relationship between the measured complex impedance, the S-parameters of Network 1 and the known load can be expressed as three equations, which can then be used to solve for the S-parameters of Network 1. Once the S-parameters are characterized, they can be combined (for example, using a transmission matrix approach) with the known network parameters of the generator cable 5430 and catheter wires 5435 to provide corrected (actual) impedance measurements at the distal end portion of the catheter (for example, across two spaced-apart electrode portions of a combination electrode assembly).

(282) The automatic calibration techniques and systems described herein advantageously allow for increased confidence in the contact indication values regardless of the generator, cables, catheter or other equipment being used and regardless of whether a hardware component to facilitate simultaneous electroanatomical mapping (for example, a catheter interface unit) is connected. The various measurements may be performed automatically upon execution of instructions stored on a computer-readable storage medium executed by a processor or may be performed manually.

(283) The automatic calibration systems and methods described herein may also be implemented using an equivalent circuit model for one or more hardware components of the system (for example, the generator circuitry, cable and catheter wiring). In such implementations, the equivalent circuit model comprises one or more resistors, one or more capacitors and/or one or more inductors that approximate an actual response of the one or more hardware components being represented. As one example, a generator cable component 5430 can be represented by a transmission-line equivalent RLC model as shown in FIG. 34C, where the measurement of the impedance Z.sub.meas would be performed at Port 1 with the actual (corrected) impedance Z.sub.act desired being at Port 2. In this example, if the impedance measurement circuit is measuring an impedance Z.sub.meas, the actual impedance measurement Z.sub.act can be extracted by using circuit analysis techniques. The equation relating the two impedances is given by:

(284) $Z_{\mathrm{meas}}=R+j\omega L+\frac{Z_{\mathrm{act}}}{1+j\omega C.Math.Z_{\mathrm{act}}}$

(285) The actual values for R, L and C may be extracted from network parameter measurements. For example if we measure the impedance (Z) parameters of this network, we can derive the following relationships:

(286) $Z_{11}=\frac{V_1}{I_1}{.Math.}_{\left(I2=0\right)}=R+j\omega L+\frac{1}{j\omega C}$$Z_{21}=\frac{V_2}{I_2}{.Math.}_{\left(I2=0\right)}=\frac{1}{j\omega C}$$Z_{11}-Z_{21}=R+j\omega L$

(287) where 1 and 2 denote the port numbers of the circuit, and V.sub.1, I.sub.1, V.sub.2 and I.sub.2 represent the voltages and currents at each of the respective ports. The values for R, L and C may also be measured utilizing measurement tools (for example, a multimeter). The equivalent circuit model approach described above is an example of this concept. In other implementations, more complex circuit models may be utilized to represent the various elements of the system.

(288) In some embodiments, the system comprises one or more of the following: means for tissue modulation (for example, an ablation or other type of modulation catheter or delivery device), means for generating energy (for example, a generator or other energy delivery module), means for connecting the means for generating energy to the means for tissue modulation (for example, an interface or input/output connector or other coupling member), means for performing tissue contact sensing and/or tissue type determination, means for displaying output generated by the means for performing tissue contact sensing and/or tissue type determination, means for determining a level of contact with tissue, means for calibrating network parameter measurements in connection with contact sensing means, etc.

(289) In some embodiments, the system comprises various features that are present as single features (as opposed to multiple features). For example, in one embodiment, the system includes a single ablation catheter with a single high-resolution (e.g., split-tip) electrode and one or more temperature sensors (e.g., thermocouples) to help determine the temperature of tissue at a depth. The system may comprise an impedance transformation network. In some embodiments, the system includes a single ablation catheter with a heat shunt network for the transfer of heat away from the electrode and/or tissue being treated. In some embodiments, the system includes a single contact sensing subsystem for determining whether there is and to what extent there is contact between the electrode and targeted tissue of a subject. Multiple features or components are provided in alternate embodiments.

(290) In one embodiment, the system comprises one or more of the following: means for tissue modulation (e.g., an ablation or other type of modulation catheter or delivery device), means for generating energy (e.g., a generator or other energy delivery module), means for connecting the means for generating energy to the means for tissue modulation (e.g., an interface or input/output connector or other coupling member), etc.

(291) In some embodiments, the system comprises one or more of the following: means for tissue modulation (e.g., an ablation or other type of modulation catheter or delivery device), means for measuring tissue temperature at a depth (e.g., using multiple temperature sensors (e.g., thermocouples) that are thermally insulated from the electrode and that are located along two different longitudinal portions of the catheter), means for effectively transferring heat away from the electrode and/or the tissue being treated (e.g., using heat shunting materials and components) and means for determining whether and to what extent there is contact between the electrode and adjacent tissue (e.g., using impedance measurements obtained from a high-resolution electrode that is also configured to ablate the tissue).

(292) In some embodiments, the system comprises one or more of the following: an ablation system consists essentially of a catheter, an ablation member (e.g., a RF electrode, a split-tip electrode, another type of high-resolution electrode, etc.), an irrigation conduit extending through an interior of the catheter to or near the ablation member, at least one electrical conductor (e.g., wire, cable, etc.) to selectively activate the ablation member and at least one heat transfer member that places at least a portion of the ablation member (e.g., a proximal portion of the ablation member) in thermal communication with the irrigation conduit, at least one heat shunt member configured to effectively transfer heat away from the electrode and/or tissue being treated, a plurality of temperature sensors (e.g., thermocouples) located along two different longitudinal locations of the catheter, wherein the temperature sensors are thermally isolated from the electrode and configured to detect temperature of tissue at a depth, contact detection subsystem for determining whether and to what extent there is contact between the electrode and adjacent tissue (e.g., using impedance measurements obtained from a high-resolution electrode that is also configured to ablate the tissue), etc.

(293) In the embodiments disclosed above, a heat transfer member is disclosed. Alternatively, a heat retention sink is used instead of or in addition to the heat transfer member in some embodiments.

(294) According to some embodiments, an ablation system consists essentially of a catheter, an ablation member (e.g., a RF electrode, a split-tip electrode, another type of high-resolution electrode, etc.), an irrigation conduit extending through an interior of the catheter to or near the ablation member, at least one electrical conductor (e.g., wire, cable, etc.) to selectively activate the ablation member and at least one heat transfer member that places at least a portion of the ablation member (e.g., a proximal portion of the ablation member) in thermal communication with the irrigation conduit, at least one heat shunt member configured to effectively transfer heat away from the electrode and/or tissue being treated and a plurality of temperature sensors (e.g., thermocouples) located along two different longitudinal locations of the catheter, wherein the temperature sensors are thermally isolated from the electrode and configured to detect temperature of tissue at a depth.

(295) Any methods described herein may be embodied in, and partially or fully automated via, software code modules executed by one or more processors or other computing devices. The methods may be executed on the computing devices in response to execution of software instructions or other executable code read from a tangible computer readable medium. A tangible computer readable medium is a data storage device that can store data that is readable by a computer system. Examples of computer readable mediums include read-only memory, random-access memory, other volatile or non-volatile memory devices, CD-ROMs, magnetic tape, flash drives, and optical data storage devices.

(296) In addition, embodiments may be implemented as computer-executable instructions stored in one or more tangible computer storage media. As will be appreciated by a person of ordinary skill in the art, such computer-executable instructions stored in tangible computer storage media define specific functions to be performed by computer hardware such as computer processors. In general, in such an implementation, the computer-executable instructions are loaded into memory accessible by at least one computer processor. The at least one computer processor then executes the instructions, causing computer hardware to perform the specific functions defined by the computer-executable instructions. As will be appreciated by a person of ordinary skill in the art, computer execution of computer-executable instructions is equivalent to the performance of the same functions by electronic hardware that includes hardware circuits that are hardwired to perform the specific functions. As such, while embodiments illustrated herein are typically implemented as some combination of computer hardware and computer-executable instructions, the embodiments illustrated herein could also be implemented as one or more electronic circuits hardwired to perform the specific functions illustrated herein.

(297) The various systems, devices and/or related methods disclosed herein can be used to at least partially ablate and/or otherwise ablate, heat or otherwise thermally treat one or more portions of a subject's anatomy, including without limitation, cardiac tissue (e.g., myocardium, atrial tissue, ventricular tissue, valves, etc.), a bodily lumen (e.g., vein, artery, airway, esophagus or other digestive tract lumen, urethra and/or other urinary tract vessels or lumens, other lumens, etc.), sphincters, other organs, tumors and/or other growths, nerve tissue and/or any other portion of the anatomy. The selective ablation and/or other heating of such anatomical locations can be used to treat one or more diseases or conditions, including, for example, atrial fibrillation, mitral valve regurgitation, other cardiac diseases, asthma, chronic obstructive pulmonary disease (COPD), other pulmonary or respiratory diseases, including benign or cancerous lung nodules, hypertension, heart failure, denervation, renal failure, obesity, diabetes, gastroesophageal reflux disease (GERD), other gastroenterological disorders, other nerve-related disease, tumors or other growths, pain and/or any other disease, condition or ailment.

(298) In any of the embodiments disclosed herein, one or more components, including a processor, computer-readable medium or other memory, controllers (for example, dials, switches, knobs, etc.), displays (for example, temperature displays, timers, etc.) and/or the like are incorporated into and/or coupled with (for example, reversibly or irreversibly) one or more modules of the generator, the irrigation system (for example, irrigant pump, reservoir, etc.) and/or any other portion of an ablation or other modulation system.

(299) Although several embodiments and examples are disclosed herein, the present application extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the inventions and modifications and equivalents thereof. It is also contemplated that various combinations or subcombinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combine with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.

(300) While the embodiments disclosed herein are susceptible to various modifications, and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the inventions are not to be limited to the particular forms or methods disclosed, but, to the contrary, the inventions are to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the various embodiments described and the appended claims. Any methods disclosed herein need not be performed in the order recited. The methods disclosed herein include certain actions taken by a practitioner; however, they can also include any third-party instruction of those actions, either expressly or by implication. For example, actions such as “advancing a catheter” or “delivering energy to an ablation member” include “instructing advancing a catheter” or “instructing delivering energy to an ablation member,” respectively. The ranges disclosed herein also encompass any and all overlap, sub-ranges, and combinations thereof. Language such as “up to,” “at least,” “greater than,” “less than,” “between,” and the like includes the number recited. Numbers preceded by a term such as “about” or “approximately” include the recited numbers. For example, “about 10 mm” includes “10 mm.” Terms or phrases preceded by a term such as “substantially” include the recited term or phrase. For example, “substantially parallel” includes “parallel.”