Ablation Catheter and Operation Method of Same

Abstract

The invention relates to an ablation catheter for treatment of a patient's tissue, for example for a PVI procedure on a patient's heart, comprising an elongated catheter shaft and an ablation portion being arranged at a distal end of the catheter shaft with a plurality of electrodes accommodated along the ablation portion, wherein the ablation portion comprises at least two loop sections forming a three-dimensional spiral. In order to increase safety of ablation treatment, spare adjacent tissue (e.g. nerves, vessels, esophagus) and shorten ablation time, a pitch, or clearance of two neighboring loop sections is greater than an ionization threshold of the medium around the distal section, for example blood or gases resulted from electrolysis. The invention further relates to an operation method of such ablation catheter.

Claims

1. An ablation catheter for treatment of patient tissue by delivery of high-voltage pulses comprising: a catheter shaft and an ablation portion being arranged at a distal end of the catheter shaft with a plurality of electrodes accommodated along the ablation portion, wherein the ablation portion comprises at least two loop sections forming a three-dimensional spiral, wherein a pitch and/or clearance of two neighboring loop sections is greater than an ionization threshold of a respective medium around the plurality of electrodes, the medium comprising blood or gases resulted from electrolysis.

2. The catheter of claim 1, wherein the pitch and/or clearance of two neighboring loop sections is further less than a therapeutic threshold of the respective tissue.

3. The catheter of claim 1, wherein the diameters of two neighboring loop sections increase into the direction of the distal end of ablation portion or the diameters of two neighboring loop sections decrease into the direction of the distal end of the ablation portion.

4. The catheter of claim 1, wherein at least two of the plurality of electrodes of the ablation portion are adapted to deliver to tissue high voltage monopolar pulsed field ablating (PFA) energy or bipolar PFA energy or a combination of monopolar and bipolar PFA energy.

5. The catheter of claim 1, wherein at least two of the electrodes are controlled by an electronic control unit, wherein the electronic control unit is adapted to connect at least two of the plurality of electrodes with a high-voltage pulse generator and to pair these at least two electrodes in a pre-defined manner.

6. The catheter of claim 1, wherein the catheter shaft comprises at least two lumens separated by a material with a dielectric strength greater than a threshold required to withstand high-voltage pulses.

7. The catheter of claim 1, wherein the first lumen of the at least two lumens is configured to retain at least two electrode leads which are connected with electrodes providing the same first polarity and wherein the second lumen of the at last two lumens different from the first lumen is configured to retain at least two electrode leads which are connected with electrodes providing the same second polarity different from the first polarity.

8. The catheter of claim 1, wherein the ablation portion comprises an inner support structure and/or a center wire connected with the distal tip of the ablation portion.

9. The catheter of claim 1, wherein the electrodes are distributed along the at least two loops in a way, that the angular separation between the most distal and the most proximal electrode is at least 2*360°, or at least 720°.

10. The catheter of claim 1, wherein the catheter further comprises at least one irrigation lumen configured to apply an irrigation fluid at the treatment site via at least one individual irrigation opening at the ablation section, preferably multiple irrigation openings at the individual electrodes, in between the electrodes or proximal and/or distal to the most proximal and most distal electrode at the ablation section

11. A method to operate an ablation catheter for treatment of patient tissue as for a PVI procedure on a patient's heart, comprising an elongated catheter shaft and an ablation portion being arranged at a distal end of the catheter shaft with a plurality of electrodes accommodated along the ablation portion, wherein the ablation portion comprises at least two loop sections forming a three-dimensional spiral, wherein the plurality of electrodes is energized with high-voltage charge-balanced pulsed electric fields which are delivered in a monopolar arrangement or in a bipolar arrangement or in a combination of a monopolar arrangement and a bipolar arrangement.

12. The method of claim 11, wherein two neighboring electrodes along a loop section or two neighboring electrodes of different loop sections are energized with said pulsed electric fields in a bipolar arrangement.

13. The method of claim 11, wherein the voltage amplitude of pulses delivered to said catheter electrodes is greater than 1 kV, preferably greater than 2.5 kV, more preferably between 2.5 kV and 3.5 kV.

14. The method of claim 11, wherein the pulse width is greater than 0.5 μs, preferably between 0.5 μs and 30 μs.

15. The method of claim 11, wherein a sterile irrigation fluid is applied at the treatment site, whereby preferably distilled water or a physiological saline solution having a low salinity, preferably of no more than 0.1%, is used as irrigation fluid.

16. The method of claim 11, wherein an impedance of the medium around said plurality of electrodes is measured using electrodes from the plurality of electrodes.

17. The method of claim 11, wherein biopotentials are acquired from the surrounding tissue using at least two mapping electrodes located on the ablation portion or the plurality of electrodes for ablation used in a mapping mode.

18. The method of claim 11, wherein impedance values are measured over a frequency range using said plurality of electrodes.

19. The method of claim 11, for operating an ablation catheter according to claim 1.

20. A system to achieve a moat of cardiac conduction block in a tissue of a human or animal, comprising: a catheter comprising a catheter shaft and an ablation portion being arranged at a distal end of the catheter shaft with a plurality of electrodes accommodated along the ablation portion, a high-voltage generator configured to deliver positive and negative high-voltage pulses comprising a pulse peak and a pulse width, the catheter being adapted to connect with the generator and to deliver the pulses to a plurality of electrodes accommodated along the ablation portion, whereby the pulse peak and pulse width are configured to generate electric field intensities between the ionization threshold and the therapeutic threshold.

21. The system of claim 20, wherein generator is configured to provide charge-balanced pulses having a positive and negative pulse peaks and corresponding pulse widths.

22. The system of claim 21, wherein the generator is configured to provide biphasic pulses in the shape of a sine wave, a square wave, a triangle wave, exponential-decay or a sawtooth wave.

23. The system of claim 21, wherein the generator is configured to generate pulse trains comprising at least one pulse, preferably at least two pulses.

24. The system of claim 23, wherein pulses having a pulse width between 0.5 μs and 30 μs, an interpulse delay between 0.1 ms and 100 ms and an interphase delay within the range of 1 μs to 100 μs.

25. The system of claim 20, wherein the generator is configured to generate pulse trains comprising at least one pulse, preferably at least two pulses, wherein a pulse train could comprise biphasic pulses and/or monophasic pulses, and wherein the length of the pulse train is between 5 ms and 100 ms.

26. The system of claim 25, wherein the generator is configured to deliver up to 500 pulse trains in a time frame of at least 1 second, preferably less than 2 minutes.

27. The system of claim 20, further comprise an apparatus to measure an electrocardiogram and detect the characteristic peaks of the QRS cycle, the P-wave and/or T-wave.

28. The system of claim 27, wherein the apparatus is configured to be connected with and/or to communicate with the generator.

29. The system of claim 28, wherein the apparatus is configured to provide a trigger signal corresponding to the detection of at least one of the following: the QRS cycle, the P-wave and/or T-wave.

30. The system of claim 29, wherein the generator is configured to start at least one pulse or a pulse train in connection with the trigger signal.

31. The system of claim 28, wherein the generator is configured to analyze the electrocardiogram and start at least one pulse or a pulse train in connection with the QRS cycle, the P-wave and/or T-wave.

32. The system of claim 20 comprising an ablation catheter of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The various features and advantages of the present invention may be more readily understood with reference to the following detailed description and the embodiments shown in the drawings. Herein schematically and exemplarily,

[0067] FIG. 1 depicts a distal end of a first embodiment of an ablation catheter in a perspective side view;

[0068] FIG. 2 illustrates a delivery path for an ablation catheter leading to a pulmonary vein ostium of a human heart;

[0069] FIGS. 3 and 4 show the distal end of the embodiment of FIG. 1 in a perspective front view and in a side view;

[0070] FIGS. 5 to 7 depict a distal end of a second embodiment of an ablation catheter in a side view, a front view and in a perspective front view;

[0071] FIGS. 8 to 11 depict a distal end of a third embodiment of an ablation catheter in a side views and a front view;

[0072] FIG. 12 shows the distal end of the embodiment of FIG. 1 in a perspective side view with some marked dimensions;

[0073] FIG. 13 shows part of the electric control of the electrode leads for the embodiment of FIG. 1;

[0074] FIG. 14 shows electrical field vector distribution electronically steered to achieve a moat of conduction bloc;

[0075] FIGS. 15A-B illustrate exemplary waveforms that are charge balanced. Waveform in FIG. 15A is of exponential decay type. Waveform in FIG. 15B is of rectangular type;

[0076] FIGS. 16A-C illustrate the concept of QRS gating. FIG. 16A shows the QRS detector signal (top trace), the PFA trigger signal (middle trace) and the ECG (bottom trace) over several heart beats. FIG. 16B shows a detail into one heartbeat. The PFA trigger signal (middle trace) falls within the refractory period of the cardiac cycle. FIG. 16C shows the PFA pulse artifact, as recorded during a preclinical study;

[0077] FIG. 17 shows an actual histology slide identifying the moat of conduction block (or electrical isolation) around the right superior pulmonary vein (RSPV);

[0078] FIGS. 18A-C further exemplify a possible electrode distribution on a spiral distal section.

[0079] FIG. 18A shows the catheter of this invention facing a PV. FIG. 18B shows the catheter of this invention deployed when pressed against PV wall. Note the clearance between spiral arms. FIG. 18C shows an alternative split-tip electrode construction;

[0080] FIG. 19 shows three schematic impedance curves measured over frequency between two electrodes; and

[0081] FIGS. 20A-B show two examples of measured impedance over frequency

DETAILED DESCRIPTION

[0082] FIGS. 1, 3, 4 and 12 schematically and exemplarily illustrate a distal portion of an ablation catheter 1 in accordance with a first embodiment. The ablation catheter may be used for PFA, when used with the PFA generator and accessories, and is indicated for use in cardiac electrophysiological mapping (stimulation and recording) and in high-voltage, pulsed-field cardiac ablation. Peak voltages are, for example, without limitation, +/−1 kV to 3 kV with a pulse width of up to 30 μs. Higher peak voltages (e.g. up to 10 kV) may be used provided the pulse duration is correspondingly shorter (e.g. 0.5 μs). The catheter 1 has an elongated circular catheter shaft 10, which may connect with a handle comprising a steering mechanism at a proximal end (not illustrated). As a result, the catheter may control deflections of the depicted distal section carrying the ablation electrodes.

[0083] At the illustrated distal end of the catheter shaft 10 an ablation portion 12 is arranged, which comprises a plurality of loop sections 121, 122. The concept of loop sections includes embodiments that use continuous loops or spirals configurations. The catheter shaft may have an effective length of approximately 115 cm from the distal tip of the ablation portion 12. Each of a first loop section 121 and a neighboring second loop section 122 exhibits ablation electrodes 120 (altogether, for example, 14 electrodes), which are configured for delivering energy to tissue. Although two loops are illustrated in FIG. 1, more can be used. It is preferred that at least a partial third loop is used in order to provide sufficient overlap among resulting ablation zones. Said overlap would increase chances of achieving a conduction block moat without drops in lesion continuity, contiguity or transmurality. As an example, see catheter illustration in FIG. 14. The distal section comprises at least 45° of overlap of a 3.sup.rd loop section with the previous two sections. In particular, the ablation catheter 1 may be configured for delivering an electrical high voltage PFA signal to tissue via the ablation electrodes 120. For example, the ablation electrodes 120 may consist of or comprise gold and/or a platinum/iridium alloy. Alternatively, electrodes 120 from different loop sections may be positioned so that electrodes of same polarity are aligned. Either the staggering or the polarity-based approach ensures that electrodes of opposite polarities would not collide when the spiral catheter is compressed.

[0084] In the exemplary embodiment illustrated in FIG. 1, the ablation electrodes 120 of the second loop section 122 are arranged partly in a staggered manner with respect to the ablation electrodes 120 of the first loop section 121.

[0085] The loop sections 121, 122 may further exhibit a plurality of mapping electrodes, which are configured for receiving electrical signals from tissue.

[0086] Together, the loop sections 121, 122 form a three-dimensional spiral, which form a corkscrew-similar form. Alternatively, they may form a plunger-like configuration, as shown in FIGS. 5-7. It should be noted that respective diameters of the loop sections 121, 122 are such that the first, more proximal loop section 121 has a greater inner diameter D1 (for example 30 mm, see FIG. 12) than the second, more distal loop section 122 (inner diameter D2, for example 24 mm). At the furthest distal tip of the ablation portion 12 the inner diameter D3 is even lower (for example 18 mm). In general, the diameters of loop sections may be, for example, between 10 mm and 40 mm. More specifically, if used in the left atrium, the widest loop section may have a diameter between 20-35 mm, preferably between 25-32 mm. The smallest diameter can be 12-22 mm, preferably 15-20 mm.

[0087] The loop sections 121, 122 may comprise a shape memory material, for example, in the form of an inner structural support wire (not illustrated), for example a Nitinol wire as described above. In particular, the loop sections 121, 122 may have super-elastic properties.

[0088] The ablation portion 12 may be constrained into an essentially elongate shape for the purpose of delivery to a target region in the human body by means of a (fixed or steerable) delivery sheath 15, which may also be referred to as an introducer sheath. At the target position, upon exiting a distal end of the delivery sheath 15, the ablation portion 12 may then recoil to its original (biased) shape.

[0089] The length of each electrode 120 along the respective loop section 121, 122 is, for example, 4 mm. In general, the electrode length is in the range 1-10 mm, preferably 3-5 mm. The catheter shaft 10 size may be compatible with an 8.5 F ID sheath and may consist of radiopaque extrudable polymer and, if applicable, a polymer-reinforcing braid. In general, the size of the catheter shaft 10 may be compatible with a 7 F to 14 F ID sheath. The width between neighboring electrodes along the respective loop section may be chosen between 1 mm and 10 mm, preferably 3-6 mm, in order to provide a contiguous ablated area at the patient's tissue.

[0090] FIG. 2 schematically and exemplarily illustrates a delivery path for an ablation catheter 1 leading to a pulmonary vein ostium (PVO) of a human heart. For orientation, the inferior vena cava (IVC), the right atrium (RA), the right ventricle (RV), the left atrium (LA), the left ventricle (LV), as well as pulmonary veins (PV), each with a PVO, are shown. The large black arrows indicate a delivery path passing through the IVC, the RA, transseptally through the septal wall (SW), and into the LA. Finally, using appropriate deflection means, catheter 1 is steered to PVO regions. There, the corkscrew type ablation catheter may be used for ablation in the area of the atrial end of the pulmonary vein close to PVO. The form of the ablation portion 12 is configured such that it fits to the dimensions of the targeted PVO. Alternatively, corkscrew-type catheters may be used to ablate at the SVC or at Appendages, such as the left or right atrial appendages (LAA or RAA).

[0091] The second embodiment of an ablation catheter 2 shown in FIGS. 5 to 7 is adapted to the use for ablation in the atrial area of the left atrium LA surrounding the PVOs, or located between PVOs (e.g. posterior LA wall). Alternatively, catheter 2 may be well suited for ablations on ventricular (RV or LV) walls, or in the RA (e.g. free RA wall, Tricuspid Valve annulus, etc.). The ablation portion 22 comprises two loop sections 221 and 222 with a plurality of ablation electrodes 220 (and, if applicable also with mapping electrodes) analogous to the first embodiment. However, the ablation portion 22 is formed like a three-dimensional spiral having the form of a plunger, where the more proximal first loop section 221 has a lower diameter than the second, more distal loop section 222.

[0092] There is a third embodiment shown in FIGS. 8 to 11 similar to the first embodiment. Without limitations though, elements of this embodiment (e.g. center wire 31, for spiral expandability or compression) may be used with other type of spiral catheter. Additional to the construction of the first embodiment the third embodiment of an ablation catheter 3 comprises a center wire 31, used to facilitate expandability or compression of the distal section. Center wire 31 is connected with the distal tip of the ablation portion 32. Ablation portion 32 carries ablation electrodes 320. Center wire 31 is running approximately along the longitudinal axis of the spiral formed by the ablation portion and its two loop sections 321, 322. Center wire 31 enters and runs inside catheter shaft 30. At the proximal end of the catheter, center wire 31 connects with actuating element associated with or integrated in the catheter handle. The center wire 31 may be manipulated such that a longitudinal length of the ablation portion 32 (i.e. its length along the longitudinal axis of the three-dimensional spiral of the ablation portion 32) and, accordingly the diameters of the loop sections 321, 322 may be changed and adapted to the therapeutic needs and the local situation. In the drawing of FIG. 8 the longitudinal length of the ablation portion is greatest compared with the drawings of FIGS. 9 and 10 because the center wire pushes the distal tip of the ablation portion 32 in distal direction. Accordingly, the diameter of the loop sections 321, 322 is smallest. FIG. 10 shows the shortest longitudinal length of the ablation portion 32 of the ablation catheter 3. This is achieved by pulling the center wire 31. The ablation catheter 3 shown in FIG. 9 has a nominal longitudinal length of the ablation portion 32, which is between those of FIGS. 8 and 10. Hence, the diameter of the loop sections 321, 322 is greatest in FIG. 10 and smallest in FIG. 8.

[0093] Reliable full ablation along a whole circumference is achieved with the first and the second embodiment at their respective position within the heart or the vein to which the form is adapted. A small compression of the ablation portion 12, 22 of the respective catheter 1, 2 may be possible during ablation into the direction of the longitudinal axis of the spiral, but the distance of the loop sections 121, 122 or 221, 222 is still in the region limited by the therapeutic threshold and the ionization threshold.

[0094] In order to cause IRE, spare adjacent tissue and shorten ablation time, the pitch of neighboring loop sections is chosen between the ionization threshold and the therapeutic threshold as explained in detail above. Referring to the first embodiment shown in FIG. 12, the first pitch, or clearance, s1 of the first loop section 121 and the second loop section 122 is approximately 5 mm and the second pitch, or clearance, s2 of the second loop section 122 and the furthest distal end of the ablation portion 12 is approximately 5 mm, as well. In general, the pitch, or clearance, should be between the ionization (2 mm) and therapeutic thresholds (up to 8 mm). As presented above, it is important that the angular offset between most distal and most proximal electrodes on any of the catheters #1, #2 or #3, exceeds 2*360°, preferably it is 2*360°+45° (i.e. two full loops plus ⅛.sup.th of a third loop).

[0095] The ablation procedure using one of the ablation catheters 1, 2, 3 may start after the ablation portion 12, 22, or 32 is in the correct position relative to the targeted tissue, for example at a PVO. The ablation electrodes 120, 220, 320 will provide pulsed electric RF field in a monopolar or bipolar arrangement. Peak voltages are, for example, without limitation, +/−1 kV to 3 kV with a pulse width of up to 30 μs. Higher peak voltages (e.g. up to 10 kV) may be used provided the pulse duration is correspondingly shorter (e.g. 0.5 μs). The pulse width may be 12 μs (between 0.5-30 μs) forming a pulse train comprising up to 500 pulses/train. Any of the waveforms illustrated in FIG. 15 may be used.

[0096] Without limitations, as an example, waveform in FIG. 15A shows biphasic exponentially decaying voltage pulses suitable for PFA treatment. Over the entire waveform complex, the exponential decays achieve a charge-balanced goal, needed to minimize chances of bubbling, arcing or undesired tissue stimulation. Such waveforms may be achieved by using high-voltage output stages which are AC-coupled to the ablation electrodes 120, 220 or 320. The two biphasic pulses shown in FIG. 15A form a pulse train, which could be repeated N-times. The biphasic pulses consist of a positive section PP and a negative section PN. As shown in FIG. 15A a positive biphasic pulse is followed by an inverse negative biphasic pulse. The interphase delay I.sub.1 is the time between the end of the negative section PN of the first biphasic pulse and the start of the positive section of the following pulse. As defined above the pulse width P corresponds to the length of the positive/negative section PP/PN, if biphasic pulses are used. The next pulse train starts after the interpulse delay I.sub.2.

[0097] Similarly, FIG. 15B shows an example of suitable PFA waveforms which have rectangular shapes. The rectangular pulses as shown in FIG. 15B are characterized by the voltage peak V and the pulse width P. A positive rectangular pulse is followed by a negative rectangular pulse after the interphase delay I.sub.1. The two pulses shown in FIG. 15B form a pulse train, which is repeated N-times. The next pulse train starts after the interpulse delay I.sub.2. These waveforms are also charge balanced. Such charge-balanced rectangular waveforms may be achieved by using DC-coupled high-voltage output stages with reasonably accurate control of the positive and negative phase amplitude and duration. As a result, the net charge (current amplitude*pulse width) can be controlled to achieve net balancing.

[0098] FIGS. 16A-C show QRS-gated output waveforms. A typical lead-I ECG waveform 1601a is shown in FIG. 16A. The output of the QRS detector is illustrated as signal 1602A. The trigger of the PFA waveform is shown as signal 1603a. FIG. 16B provides a zoomed-in view of FIG. 16A. The ECG waveform 1601b is represented over one cardiac cycle. Its R-wave 1604 is detected by the QRS detector output 1602b. After a programmed delay 1605, the PFA waveform trigger 1603b is turned on. In this embodiment, delay 1605 is shown to be about 70 ms. Delay 1605 may be between 20-150 ms, depending on the heart rate. It is important to make sure PFA pulses are applied within the refractory period of the heart. As FIG. 16B shows, in this particular example the train of pulse ends before the beginning of T wave 1606. FIG. 16C shows an example of PFA pulses artifacts, as recorded with a standard cardiac recording system. R wave 1604c is seen being followed by artifacts 1607 caused by delivery of PFA pulses. Artifacts 1607 safely end before the beginning of T waves 1606c. The process described above delivers one train of pulses within one cardiac cycle. In the above example, 10 pulses/train were delivered using waveform 1501 from FIG. 15A. Persons of skill in the art may modify the above approach by using other known parameters without departing from the essence of this invention. For example up to 500 pulse trains may be provided. However, although not required, it is preferable to select a number of trains so that to keep the PFA application time to greater than 1 s (to allow of cell membrane poration) but less than 2 min (to avoid long procedures). The interphase delay may be 1-100 μs. The interpulse delay may be 0.1 ms or 100 ms.

[0099] The electric field generation (in particular voltage, current and impedance) is monitored by an electronic control unit (ECU) 70 which is connected to the leads 61 of the electrodes 120, 220, 320 and produced by a waveform generator 50 (see FIG. 13). FIG. 14 also shows connectivity that can be used to generate monopolar or bipolar electric fields. ECUs in FIGS. 13 and 14 may control application of PFA fields with a goal of achieving wide coverage of the tissue space in between catheter loops or spirals. FIG. 14 illustrates a catheter 1401 (such was #1, #2 or #3 from FIGS. 1-10) with its electrodes driven by ECU 1403. ECU 1403 can be controlled to deliver field vectors 1402 that cover the tissue zone in between catheter 1401 spiral arms/loops. By doing so, a moat of conduction block/electrical isolation is more likely to be achieved.

[0100] In the bipolar arrangement neighboring (adjacent) electrodes 120, 220, 320 may be paired along the loop sections 121, 122, 212, 222, 321, 322 or across two neighboring loop sections 121 and 122; 221 and 222; 321 and 322. Further, the electrodes 120, 220, 320 may be used in monopolar arrangement. In this case, a ground pad 1404 may be provided at the surface of the patient's body. Alternatively, reference electrodes associated with the catheter shaft may be used.

[0101] In order to switch between different bipolar arrangements or between monopolar and bipolar arrangement, the ablation catheter 1, 2, 3 may comprise a switch unit 60 connected to and controlled by the ECU 70. The switch unit 60 provides the respective phase of the pulsed electric field provided by the waveform generator 50 to the predefined electrode lead 61 and thereby to the predefined electrode 120, 220, 320, wherein each electrode lead 61 is electrically connected to one particular electrode 120, 220, 320 at the ablation portion 12, 22, 32. The switch unit 60 comprises a switch matrix and may realize any configuration of phase distribution, for example, such that two neighboring electrodes along the loop sections or across the loop sections are paired to achieve the aforementioned uniform moat of conduction block. Any other configuration is possible. The switching signal and configuration information is provided by the ECU 70. ECU 70 further may provide data processing of electrical or biopotential data or impedance data acquired by mapping electrodes of ablation catheters 1, 2, 3. As indicated above mapping electrodes located in the ablation portions 12, 22, 32 may comprise mapping electrodes for determining the electrical potential of the surrounding tissue in order to observe the ablation progress at pre-defined time points during ablation procedure. Alternatively, the ablation electrodes 120, 220, 320 may be switched into the mapping mode and back into the ablation mode. Further, the impedance between neighboring electrodes or across two different, neighboring loop segments may be determined prior to delivery of PFA energy. Thereby impedance (monopolar or bipolar) is monitored whether the neighboring loop segments and hence the electrodes of these segments are located in a sufficient distance to the other loop segment or electrode, respectively. By monitoring impedance, ECU 70 or 1403 may alert the user when any two electrodes are too close, with respective inter electrode distance falling below the ionization threshold. Conversely, users may be alerted when impedance measurements indicate that the inter electrode distance exceeds the therapeutic threshold.

[0102] As indicated above, the catheter shaft 10, 20, 30 may comprise two lumens separated by a material, e.g. Kapton®, with a dielectric strength greater than a dielectric threshold for high-voltage PFA pulses. The first lumen may retain, for example, 7 electrode leads 61 providing the first polarity and the second lumen may retain, for example, 7 electrode leads 61 providing a second polarity thereby reducing the overall diameter of the catheter shaft.

[0103] The above explained embodiments of ablation catheters realize IRE in order to prevent spread of electrical signals (i.e. achieve conduction block) that gives rise to the cardiac arrhythmia along a contiguous area with improved safety, as it is believed to spare adjacent tissues (e.g. nerves, vessels, esophagus), and with shorter ablation time. FIG. 17 illustrates such moat of conduction block, or electrical isolation. The right superior pulmonary vein 1701 is seen at the center of the picture. After application of PFA pulses according to this invention (totaling cumulative PFA application time of about 90 s/PV), a continuous, contiguous and transmural lesion was achieved. The lesion perimeter 1402 is illustrated. The moat of conduction block, or electrical isolation, 1403 completely covers the cardiac tissue zone between RSPV 1401 and the lesion border 1402. Electroanatomic mapping confirmed lasting chronic isolation of pulmonary veins. FIG. 18A shows the catheter of this invention facing a pulmonary vein atrium. FIG. 18B shows the catheter of this invention deployed when pressed against pulmonary vein wall. As indicated by line c1 and c2 the angular separation between the most distal electrode 1802 and the most proximal electrode 1801 exceeds 2*360°, or 720°. FIG. 18C shows an alternative split-tip electrode construction with an inner electrode facing the blood and an outer electrode facing the tissue.

[0104] FIG. 19 shows three schematic impedance curves measured over frequency between two electrodes. The impedance could be measured starting with a low frequency f.sub.low of 10 kHz up to a frequency f.sub.high of 500 kHz. A pronounced impedance curve as the topmost curve ranging from Z.sub.1 to Z.sub.4 indicates a good tissue contact between the two electrodes. A flat lowermost impedance curve in the lower range of Z.sub.3 to Z.sub.5 indicates contact between the two electrodes. The flat impedance curve in the middle ranging from Z.sub.2 to Z.sub.4 indicates bad tissue contact between the two electrodes. For example, without limitation, following thresholds may be used: [0105] 1. Good tissue contact—at F.sub.LOW (e.g. 10 kHz) Z.sub.1 is in the range 100-500 ohm, depending on electrode size and tissue properties. At f.sub.HIGH (e.g. 500 kHz) Z.sub.4 is at least 20% lower than Z.sub.1 (S-curve). [0106] 2. Poor contact—at f.sub.LOW (e.g. 10 kHz) Z.sub.2 is in the range of 80-400 ohm, depending on electrode size and blood properties. At f.sub.HIGH (e.g. 500 kHz) Z.sub.4 is at most 20% lower than Z.sub.2, typically only 10% or less lower (flat curve). As shown in FIG. 20A, under poor electrical contact conditions, the bipolar impedance decreases from about 113 ohm at 10 kHz to about 110 ohm at 500 kHz. The phase varies only slightly, increasing from about −4° to 2°. [0107] 3. Electrodes in contact—at f.sub.LOW (e.g. 10 kHz) Z.sub.3 is in the range 0-300 ohm, depending on the amount of contact, electrode size, blood properties. At f.sub.HIGH (e.g. 500 kHz) Z.sub.5 is at most 20% lower than Z.sub.3, typically only 10% or less lower (flat curve). As shown in FIG. 20B, when electrodes collide and make good electrical contact, Z.sub.5 is low, between 4-9 ohm, while phase increases with frequency. At 500 kHz, the phase is approximately 66°, indicating a mostly inductive electrical characteristic given by the electrode wires.

[0108] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points.