Ablation Catheter for Pulsed-Field Ablation and Method for Electrode Position Assessment for Such Catheter

Abstract

A system for treatment of patient tissue by delivery of high-voltage pulses comprising an ablation catheter, a measurement unit and an electronic control unit (ECU). The measurement unit is configured to perform measurements using an energy source, whereby the impedance and/or current measurement values are determined as response to an alternating voltage and/or at least one voltage pulse. The ECU is configured to receive and analyze said measurement values provided by the measurement unit and determine arcing risk (AR) indexes for said electrode pairs and/or a contact uniformity (CU) value based on said impedance measurement values and/or impedances for said electrodes and/or an impedance uniformity (IU) value based on said current measurement values.

Claims

1. A system for treatment of patient tissue by delivery of high-voltage pulses, comprising: an ablation catheter, a measurement unit, and an electronic control unit (ECU), wherein the catheter comprises 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 each of the plurality of electrodes is electrically connected to the measurement unit through the catheter shaft, wherein the measurement unit is configured to perform measurements using an energy source thereby determining measurement values of a subgroup of the plurality of electrodes, wherein said subgroup is formed by all or a part of the plurality of electrodes, wherein the ECU is configured to receive and analyze said measurement values provided by the measurement unit and determine arcing risk (AR) and/or a contact uniformity (CU) and/or impedance uniformity (IU) value indexes for said subgroup of the plurality of electrodes.

2. The system of claim 1, wherein said measurement values are bipolar impedance measurement values of electrode pairs of a subgroup of the plurality of electrodes and/or quasi-unipolar impedance measurement values of a subgroup of the plurality of electrodes and/or current measurement values of a subgroup of the plurality of electrodes.

3. The system of claim 2, wherein the impedance and/or current measurement values are determined as response to an alternating voltage and/or at least one voltage pulse.

4. The system of claim 1, wherein the determined arcing risk (AR) and/or a contact uniformity (CU) indexes are based on said impedance measurement values

5. The system of claim 1, wherein the impedance uniformity (IU) indexes are based on said current measurement values.

6. The system of claim 1, wherein the electronic control unit is arranged proximal to or at the proximal end of the catheter, and wherein the measurement unit is connected to or integrated within the ECU

7. The system of claim 1, wherein the measurement unit is configured to determine at least one current measurement value for each of the subgroup of the plurality of electrodes by measuring the respective current value of one or several of rectangular, sinusoidal, tooth or similar shaped voltage pulses, wherein one impedance value is determined from said determined current measurement values for each of the subgroup of electrodes.

8. The system of claim 2, wherein the ECU is configured to determine an impedance uniformity (IU) of two groups of the subgroup of electrodes, wherein $\mathrm{IU}=1-\frac{1}{2}\left(\frac{\sigma \left(\left\{Z_d\right\}\right)}{\mu \left(\left\{Z_d\right\}\right)}+\frac{\sigma \left(\left\{Z_p\right\}\right)}{\mu \left(\left\{Z_p\right\}\right)}\right)$ wherein σ({Z.sub.d,p}) is the standard deviation and μ({Z.sub.d,p}) the mean value of the determined impedances of the electrodes of the respective group.

9. The system of claim 1, wherein the ECU is configured to determine the AR index for a particular electrode pair x,y from the bipolar impedance measurement values of the particular electrode pair x,y from the subgroup of electrodes scaled by the minimum of bipolar impedance measurement values of the respective electrodes with their adjoining electrodes of the subgroup.

10. The system of claim 1, wherein the ECU is configured to determine the CU value for the subgroup of electrodes based on the standard deviation of the bipolar impedance measurement values of the pairs of adjoining electrodes of said subgroup or based on the minimum and the maximum of the bipolar impedance measurement values of the pairs adjoining electrodes of said subgroup and/or to determine the CU value for the subgroup of electrodes based on the standard deviation of a quasi-unipolar impedance measurement values of all electrodes of said subgroup or based on the minimum and the maximum of the quasi-unipolar impedance measurement values of all electrodes of said subgroup.

11. The system of claim 1, wherein the ECU is configured to determine an overall risk for arcing for all electrodes of the subgroup based on a maximum of the AR index of all electrode pairs of the subgroup.

12. The system of claim 1, wherein the measurement unit is configured such that the frequency for determination of quasi-unipolar or bipolar impedance measurement values of the subgroup of electrodes is between 1 kHz and 1 MHz and/or such that the voltage amplitude of the pulses is between 1V and 1 kV, in particular between 10V and 700V, in particular between 100V and 500V

13. A method for assessment of positions and/or configuration of a plurality of electrodes of an ablation catheter for treatment of patient tissue by delivery of high-voltage pulses comprising a catheter shaft and an ablation portion, wherein the ablation portion is arranged at a distal end of the catheter shaft with the plurality of electrodes accommodated along the ablation portion, wherein each of the plurality of electrodes is electrically connected to a measurement unit through the catheter shaft, wherein the measurement unit performs measurements using an energy source thereby determining measurement values of a subgroup of the plurality of electrodes, wherein the subgroup is formed by all electrodes or a part of the plurality of electrodes, respectively, wherein said measurement values are transmitted to the ECU which receives and analyzes said measurement values as well as determines arcing risk (AR) and/or a contact uniformity (CU) and/or an impedance uniformity (IU) indexes based on said current measurement values.

14. The method of claim 13, wherein said measurement values are bipolar impedance measurement values of electrode pairs of a subgroup of the plurality of electrodes and/or quasi-unipolar impedance measurement values of a subgroup of the plurality of electrodes and/or current measurement values of a subgroup of the plurality of electrodes.

15. The method of claim 14, wherein the impedance and/or current measurement values are determined as response to an alternating voltage and/or at least one voltage pulse.

16. The method of claim 13, wherein the determined arcing risk (AR) and/or a contact uniformity (CU) indexes are based on said impedance measurement values

17. The method of claim 13, wherein the impedance uniformity (IU) indexes are based on said current measurement values.

18. The method of claim 13, wherein the electronic control unit is arranged proximal to or at the proximal end of the catheter, and wherein the measurement unit is connected to or integrated within the ECU

19. The method of claim 13, wherein the electronic control unit is arranged separate from catheter, and wherein the measurement unit is connected to or integrated within the ECU

20. The method of claim 13, wherein the measurement unit determines at least one current measurement value for each of the subgroup of the plurality of electrodes by measuring the respective current value of one or several of rectangular, sinusoidal, tooth or similar shaped voltage pulses, wherein one impedance value is determined from said determined current measurement values for each electrode of the subgroup of electrodes.

21. The method of claim 20, wherein the ECU determines an impedance uniformity (IU) of two groups of the subgroup of electrodes, wherein $\mathrm{IU}=1-\frac{1}{2}\left(\frac{\sigma \left(\left\{Z_d\right\}\right)}{\mu \left(\left\{Z_d\right\}\right)}+\frac{\sigma \left(\left\{Z_p\right\}\right)}{\mu \left(\left\{Z_p\right\}\right)}\right).Math.,$ wherein ({Z.sub.d,p}) is the standard deviation and μ({Z.sub.d,p}) the mean value of the determined impedances of the electrodes of the respective group.

22. The method of claim 13, wherein the ECU determines the AR index for a particular electrode pair x,y from the bipolar impedance measurement values of the particular electrode pair x,y from the subgroup of electrodes scaled by the minimum of bipolar impedance measurement values of the respective electrodes with their adjoining electrodes of the subgroup.

23. The method of claim 13, wherein the ECU determines the CU value for the subgroup of electrodes based on the standard deviation of the bipolar impedance measurement values of the pairs of adjoining electrodes of said subgroup or based on the minimum and the maximum of the bipolar impedance measurement values of the pairs adjoining electrodes of said subgroup and/or determines the CU value for the subgroup of electrodes based on the standard deviation of the quasi-unipolar impedance measurement values of all electrodes of said subgroup or based on the minimum and the maximum of the quasi-unipolar impedance measurement values of all electrodes of said subgroup.

24. The method of claim 13, wherein ECU determines an overall risk for arcing for all electrodes of the subgroup based on a maximum of the AR index of all electrode pairs of the subgroup.

25. A computer program product comprising instructions which, when executed by a processor, cause the processor to perform the steps of the method according to claim 13.

26. A computer readable data carrier storing a computer program product according to claim 25.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] 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,

[0075] FIG. 1 depicts a distal end of a first embodiment of an ablation catheter in a perspective side view;

[0076] FIG. 2 illustrates a delivery path for an ablation catheter leading to a pulmonary vein ostium of a human heart;

[0077] FIGS. 3-3A show part of the electric control of the electrode leads for the embodiment of the ablation catheter of FIG. 1;

[0078] FIG. 4 depicts the distal end of the ablation catheter of FIG. 1 with electrode numbering in a top view;

[0079] FIGS. 5 and 6 show matrices containing AR indexes for each electrode pair and the impedance values of the ablation catheter of FIG. 1 for a saline position of the ablation portion;

[0080] FIG. 7 shows the ablation portion of the ablation catheter of FIG. 1 pressed to chicken heart tissue in a top view;

[0081] FIGS. 8 and 9 show matrices containing AR indexes for each electrode pair and the CU value of the ablation catheter of FIG. 1 in the position shown in FIG. 7;

[0082] FIG. 10 shows another position of the ablation portion of the ablation catheter of FIG. 1 pressed to chicken heart tissue in a top view;

[0083] FIGS. 11-12 show matrices containing AR indexes for each electrode pair and the CU value of the ablation catheter of FIG. 1 in the position shown in FIG. 10;

[0084] FIG. 13 depicts a schematic example of an applicable PFA waveform;

[0085] FIG. 14 shows another position of the ablation portion of the ablation catheter of FIG. 1 pressed to a chicken heart tissue in a top view;

[0086] FIG. 15 shows a matrix containing impedance values and an AR index (flagged) for the electrode pairs 1,2; 2,3; 2,9; 8,9; 9,10, respectively of the ablation catheter of FIG. 1 in the position shown in FIG. 14;

[0087] FIG. 16 shows another position of the ablation portion of the ablation catheter of FIG. 1 pressed to a chicken heart tissue in a top view;

[0088] FIG. 17 shows a matrix containing impedance values and an AR index (flagged) for the electrode pairs 1,2; 2,3; 2,9; 8,9; 9,10, respectively of the ablation catheter of FIG. 1 in the position shown in FIG. 16;

[0089] FIG. 18 shows another position of the ablation portion of the ablation catheter of FIG. 1 pressed to a chicken heart tissue in a top view;

[0090] FIG. 19 shows a matrix containing impedance values and an AR index (flagged) for the electrode pairs 1,2; 2,3; 2,9; 8,9; 9,10, respectively of the ablation catheter of FIG. 1 in the position shown in FIG. 18;

[0091] FIG. 20 shows another position of the ablation portion of the ablation catheter of FIG. 1 pressed to a chicken heart tissue in a top view;

[0092] FIG. 20A shows another position of the ablation portion of the ablation catheter of FIG. 1 pressed to a chicken heart tissue in a top view;

[0093] FIG. 21 shows a matrix containing impedance values for the adjoining electrode pairs derived from a bipolar measurement and a CU value of the ablation catheter of FIG. 1 in the position shown in FIG. 20 calculated from these impedance values;

[0094] FIG. 21A shows a matrix containing impedance values for the adjoining electrode pairs derived from a bipolar measurement and a CU value of the ablation catheter of FIG. 1 in the position shown in FIG. 20A calculated from these impedance values;

[0095] FIG. 22 shows a table containing impedance values derived from a quasi-unipolar measurement at 500 kHz and a CU value calculated from these impedance values of the ablation catheter of FIG. 1 in the position shown in FIG. 20;

[0096] FIG. 22A shows a table containing impedance values derived from a quasi-unipolar measurement at 500 kHz and a CU value calculated from these impedance values of the ablation catheter of FIG. 1 in the position shown in FIG. 20A;

[0097] FIGS. 23-25 visualize three different pulse shapes for current measurements at each individual electrode;

[0098] FIGS. 26-29 show four different positions of the ablation catheter of FIG. 1, partly with respect to a chicken heart tissue in saline;

[0099] FIG. 30 shows a bar diagram containing impedance values determined for the four positions of FIGS. 26 to 29 with respect to each electrode of the ablation portion of the ablation catheter of FIG. 1;

[0100] FIG. 31 shows a position of the ablation catheter of FIG. 1 within a heart of an 80 kg pig;

[0101] FIG. 32 shows a bar diagram containing impedance values determined for the position of the catheter depicted in FIG. 31 with respect to each electrode of the ablation portion of the catheter;

[0102] FIG. 33 visualizes a flowchart for the use of a PFA catheter including PFA precheck determining AR indexes and CU value in order to treat paroxysmal atrial fibrillation; and

[0103] FIGS. 34-35 show examples of visualization of impedance values for electrodes of an ablation section of an ablation catheter similar to the one of FIG. 1.

DETAILED DESCRIPTION

[0104] FIGS. 1 and 4 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.

[0105] 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. 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. However, dependent on the form of the patient's tissue and the position of the ablation portion 12, electrodes of opposite polarities may collide when the spiral catheter is compressed thereby causing arcing and/or the contact of the electrodes with the patient's tissue may not be uniform. 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.

[0106] In order to address measurement values to the different electrodes 120, the electrodes are consecutively numbered as shown in FIG. 4 (see numbers at the electrodes). The most distal electrode has the number 1, whereas the most proximal electrode is denoted with number 14. Different numbering is possible, as well.

[0107] The loop sections 121, 122 may further exhibit a plurality of mapping electrodes, which are configured for receiving electrical signals from tissue.

[0108] 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 or any other suitable 3-dimensional configuration (not shown).

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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, transeptally 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).

[0113] Reliable full ablation along a whole circumference is achieved with the first embodiment of the ablation catheter shown in FIGS. 1 and 4 at their respective position within the heart or the vein to which the form is adapted. A small compression of the ablation portion 12 of the respective catheter 1 may be possible during ablation into the direction of the longitudinal axis of the spiral.

[0114] The ablation procedure using one of the ablation catheters 1 may start after the ablation portion 12 is in the correct position relative to the targeted tissue, for example at a PVO. The assessment of the position and/or configuration of the ablation electrodes 120 is provided prior and/or between two ablation steps (if applicable) and is explained in more detail below. The ablation electrodes 120 will provide pulsed electric RF field in a unipolar 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.

[0115] 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 and produced by a waveform generator 50 (see FIG. 3). FIG. 3A also shows connectivity that can be used to generate unipolar or bipolar electric fields. ECUs in FIGS. 3 and 3A may control application of PFA fields. FIG. 3A illustrates a catheter 1401 (such was the one with reference number 1 from FIGS. 1 and 4) 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, the AR index may be determined. In order to provide quasi-unipolar measurements, the PFA generator may be connected to one of the electrodes as the reference electrode instead of to the grounding pad 1404.

[0116] In order to assess the positions and/or configuration of the electrodes 120 with regard to each other and the targeted tissue, the ablation catheter further comprises a measurement unit 68 which is connected to the ECU 70 and a switch unit 60 with the waveform generator 50. The measurement unit 68 is configured to measure peak current and peak voltage as well as impedance at the respective electrode lead 61 and transmit these data to the ECU for further analysis. Further, the measurement unit 68 provides the electrodes 120 at the respective lead(s) 61 with pre-defined measurement signals (current or voltage pulses) via the waveform generator 50 in order to measure the above-mentioned parameter.

[0117] In the bipolar arrangement neighboring (adjoining) electrodes 120 may be paired along the loop sections 121, 122, across two neighboring loop sections 121 and 122 or any other pre-defined pair combination, in particular for impedance determination for AR value and/or CU value. Further, the electrodes 120 may be used in a unipolar arrangement. In this case, a ground pad 1404 may be provided at the surface of the patient's body. Alternatively, one of the non-adjacent electrodes 120 may be used as reference electrode thereby forming a quasi-unipolar arrangement.

[0118] In order to switch between different bipolar arrangements or between unipolar and bipolar arrangement, the ablation catheter 1 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 wherein each electrode lead 61 is electrically connected to one particular electrode 120 at the ablation portion 12. 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, across the loop sections and any other electrodes are paired. 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 the electrodes of ablation catheter 1. As indicated above mapping electrodes located in the ablation portions 12 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 may be switched into the mapping mode and back into the ablation mode.

[0119] As indicated in the general description, prior ablation treatment and/or between ablation treatment steps the AR value and CU value are determined in order to assess the positions of the electrodes 120 and/or their configuration with regard to each other and/or with regard to the tissue under treatment.

[0120] In the first example, the ablation catheter of FIGS. 1 and 4 is measured with regard to the impedance of all pairs of the 14 electrodes in saline (for comparison), a first position axially pressed to a chicken heart tissue (see FIG. 7) and in a second position axially pressed to a chicken heart tissue wherein black rubber bands keep the electrodes 4 and 12 close to each other (see FIG. 10). The matrices of FIGS. 5 and 6 belong to the saline configuration, the matrices of FIGS. 8 and 9 to the position shown in FIG. 7 and the matrices of FIGS. 11 and 12 to the position shown in FIG. 10.

[0121] For example, AC voltage signals with a frequency of 500 kHz with a peak voltage (amplitude) of 1 V are chosen. The matrices of FIGS. 5, 8 and 11 show the AR index calculated from the bipolar impedance measurement values Z.sub.x,y of the electrode pair x,y. The number of the electrodes of the particular electrode pair can be found in the respective header line and the first row. The value at the row-line-intersection contains the AR index of the respective electrode pair x,y determined from the impedance measurement values for 500 kHz. The AR index is calculated using the formula

[00009]${\mathrm{AR}}_{x,y}=1-\frac{Z_{x,y}}{\min \left(Z_{x-1,x},Z_{x,x+1},Z_{y-1,y},Z_{y,y+1}\right)}.$

[0122] All AR index values are zero or close to zero for the saline configuration. No risk or arcing exists since all electrodes have a sufficient distance to each other.

[0123] In contrast, with regard to the ablation portion position of FIG. 7 it is apparent that the AR index of the electrode pair 5, 14 is considerable higher than the other AR indexes. In FIG. 7 it appears, that these electrodes are the only ones which are close to each other—there is an arcing risk with regard to these electrodes and repositioning is needed.

[0124] The matrix of FIG. 11 contains the AR index values calculated in a similar way for the configuration of FIG. 10 and a frequency of 500 kHz. It is apparent that in particular the electrode pairs 3, 11 and 4, 12 show considerable higher AR index values than any other AR index value of this matrix. For these pairs a risk for arcing exists, if the electrodes of these pairs would be at different polarities.

[0125] In another representation shown in FIGS. 6, 9 and 12 the calculated AR indexes of the respective electrode pairs (electrode numbers are shown in the header line and in the first row, formula see above) are provided for all electrode pairs but the adjoining electrode pairs (marked in the diagonal) for the respective ablation portion position. In the diagonal line the impedances of the adjoining electrode pairs are provided. In the matrix of FIG. 9 the AR index of the electrode pair 5 and 14 is highlighted since it indicates a high arcing risk (AR index >0.25). With regard to the third position (FIG. 10), in particular, the electrode pair 2, 9 has a higher arcing risk. Just for clarification, in this position the AR index values for the electrode pairs 4, 12 and 5, 13 are neglected since these electrodes share the same polarity and therefore no risk for arcing exists.

[0126] Further, the diagrams of FIGS. 6, 9 and 12 contain the CU value for the respective position in the upper left corner calculated from the following formula (see explanation above) and the measured bipolar impedances of the adjoining electrodes

[00010]$\mathrm{CU}=1-\frac{\sigma \left(\left\{Z_{n,n+1}\right\}\right)}{\mu \left(\left\{Z_{n,n+1}\right\}\right)}.$

[0127] It appears from the matrices in FIGS. 6, 9 and 12 that the contact uniformity of the position shown in FIG. 7 is better than of the position shown in FIG. 10 as the CU value is greater (0.92>0.86). The contact uniformity is best in the saline position (0.99)—if all electrodes without contact, i.e. all electrodes are floating in saline.

[0128] Further examples of ablation catheter positions pressed to a chicken heart are shown in the following FIGS. 14 to 19, wherein a profile shown in FIG. 13 is used as PFA protocol, wherein V=2.5 kV, P=3 μs, I.sub.1=25 μs, and I.sub.2=2 ms. Further, a pulse number PN=20 were chosen intentionally to provoke arcing.

[0129] FIG. 14 shows a position of the ablation portion of the ablation catheter of FIGS. 1 and 4 in which the electrodes 2, 9 are in close proximity (see encircled area). Accordingly, the AR index of these electrodes is 0.455 indicating the high arcing risk (see matrix shown in FIG. 15). The arcing threshold was determined as 0.9 kV confirming the calculated AR index. FIG. 16 shows a position of the ablation portion of the ablation catheter of FIGS. 1 and 4 where electrodes 2, 9 do not overlap (see marked area, so-called edge-edge position). Accordingly, the AR index shown in FIG. 17 is lower than the one of FIG. 15. The lowest AR index may be found for the position of these electrodes 2,9 shown in FIG. 18 in which these electrodes are sufficiently far away thereby having a low arcing risk (see marked area). Accordingly, the AR index of this electrode pair 2, 9 is close to zero (see FIG. 19).

[0130] In another example, the CU value for two positions of the ablation catheter of FIGS. 1 and 4 is determined, in particular the CU value determined from bipolar impedance measurements of adjoining electrodes using formula (n=1 . . . 13)

[00011]$\mathrm{CU}=1-\frac{\sigma \left(\left\{Z_{n,n+1}\right\}\right)}{\mu \left(\left\{Z_{n,n+1}\right\}\right)}$

is compared with the CU value determined from quasi-unipolar impedance measurement values. For determination of the CU value for the quasi-unipolar impedance measurement values Z.sub.n in the above formula the parameter Z.sub.n,n+1 is replaced by Z.sub.n for the standard deviation and the mean value. In this case n=1 . . . 14. The quasi-unipolar impedance one electrode (e.g. electrode 1) is measured against all electrodes of opposing polarity (e.g. against all even electrodes, and electrode 2 against all odd electrodes).

[0131] FIG. 20 shows a position in which three electrodes (2, 8, 9) are floating in saline while the others are in contact with the heart tissue. The CU value (bipolar, see FIG. 21) is 0.89 and the CU value (quasi-unipolar) is determined as 0.86 (see FIG. 22) which is comparably low thereby indicating bad contact uniformity. In contrast the position shown in FIG. 20A has all electrodes in contact with the chicken heart's tissue. Accordingly, CU value (bipolar, see FIG. 21A) is 0.92 and the CU value (quasi-unipolar) is determined as 0.91 (see FIG. 22A).

[0132] FIGS. 23 and 24 show the current measurements using a single pulse for each of the electrodes in order to determine CU, namely a rectangular pulse. FIG. 23 represents a rectangular current waveform as response to the rectangular voltage pulse. The tooth shaped waveform shown in FIG. 24 represents the measured current in the case of a short circuit. Even in this case a current measurement and thereby impedance measurement is possible. Current measurements (all even electrodes, 16 single electrodes) have been performed with a current transformer (Magnelab CT-C0.5) while a 500 V rectangular biphasic pulse (4 μs pulse length, 25 μs interphase delay) was applied. The impedances determined from the peak current measurement values are displayed as bars for each electrode (electrode number at x-axis) and impedance (in Ω at y-axis). The first (dark blue) bars refer to the position shown in FIG. 26 (ablation portion in saline), the second (orange) bars refer to the position shown in FIG. 27, the third (grey) bars refer to the position shown in FIG. 28, and the fourth (yellow) bars refer to the position shown in FIG. 29.

[0133] The impedance values shown for the saline configuration are low because of the higher conductivity of saline (˜0.7 S/m, which is matched to human blood in this experiment) compared to the chicken heart tissue. For the position shown in FIG. 27 the electrodes 2 to 5 and 11 to 13 have lesser contact, whereas the other electrodes have better contact. Regarding the position shown in FIG. 28 the electrodes 6 and 15 are short circuited and the position of the ablation portion needs to be corrected (impedance close to zero). The position shown in FIG. 29 provides impedance values similar to the position of FIG. 27.

[0134] FIG. 31 shows an animal setup. For this test a corkscrew-type catheter (25 mm outer diameter) with 16 electrodes with a spacing of 6 mm (first group of 8 electrodes) and 3 mm (second group of 8 electrodes) was positioned at the right ventricular outflow tract of an 80 kg pig. Rectangular pulses with an amplitude of 500 V were used. For calculating impedance, the maximal values of voltage and current were used. FIG. 32 shows the impedance values (in Ω) determined from current measurements as bars in relation to the respective electrode (see x-axis). It can be shown that the electrodes 9 to 16 have a quite good contact uniformity, whereas with regard to the electrodes 1 to 8 the contact uniformity can be considered mediocre. However, the impedance values of the first group of electrodes 1 to 8 is higher as the electrodes are at a greater distance compared to the second group of electrodes. Accordingly, if one calculates the IU value for the electrodes, the two groups of electrodes should be differentiated. If one applies the above formula for IU and IU*, one derives IU=0.84 and IU*=0.58. It can be seen that IU* appears to be too low as it does not take the two groups of electrodes into account.

[0135] In the following the usage of an inventive catheter as described with regard to FIGS. 1 and 4 is explained in detail referring to the flowchart of FIG. 33. In the first step 201, the catheter 1 is manipulated to targeted PV antrum in the usual way. During advancement of the catheter the ablation portion 12 is covered by the delivery sheath 15 until the distal end of the catheter reaches the targeted region. In the next step 202, the catheter provides quality EGMs to confirm placement near PV and to assess pre-PFA amplitudes and/or an electro-anatomical mapping system displays the 3-dimensional shape and location of the catheter 1. Then, in the next step 203, and after release of the ablation portion 12 from the delivery sheath 15 by retracting the delivery sheath into proximal direction, the AC index and/or CU value measurement is started by short pressing a food pedal of the catheter 1. Then, in step 204, accurate current or impedance measurements between electrodes 120 of the catheter are provided as explained above in detail by the measurement unit 68, the waveform generator 50 and the ECU 70. In one embodiment, the measurement may be provided to all electrodes 120 of the ablation portion 12 or, alternatively, electrodes at positions at risk are measured. Afterwards, the current or impedance measurement values are processed by the ECU 70 and the impedance values for all ablation electrodes, AR indexes of electrode pairs, IU value and/or the CU value for all ablation electrodes of the ablation portion 12 are determined in the following step 205. In step 206, the GUI connected with the ECU 70 colors catheter electrodes or a respective bar diagram at risk of arcing in easy-to-see colors as shown in FIGS. 34 and 35. FIG. 34 depicts the ablation portion 12 with 16 numbered electrodes 120 and a respective bar diagram 230, wherein the height of a bar shown with reference to the electrode number represents the impedance value. The bar diagram shows a low impedance for electrodes number 7 and 10. Electrodes 13 and 14 are mapping electrodes and therefore not measured. FIG. 15 indicates the calculated impedance values directly at the electrode location of electrodes 7 and 10 at the ablation portion 12 with different colors, wherein each color represents the deviation from the target impedance value. The red color of electrode number 10 visualizes a greater deviation from the target impedance value than the yellow color of electrode number 7.

[0136] If a risk of arcing is identified and visualized by the GUI (step 207), the electrodes are grouped such that the critical electrodes are split into separate energy-delivery groups (step 208). Now, in step 209, the GUI displays impedances, AR indexes, IU value and/or CU value of electrodes that are in an acceptable range. If there is no risk of arcing identified step 209 can be directly reached from step 206. Then, in step 210, a PFA treatment is initiated by, e.g. a food pedal of the ablation catheter is continued to be pressed (e.g. by some seconds) by the HCP to the patient if an acceptable positioning of the ablation catheter is shown. Then, in step 211, the procedure continues with step 204 if there was no PFA precheck measurement, with step 212 if the PFA precheck measurement is OK, and with step 213 if the PFA precheck measurement failed. Step 213 contains a repositioning of the catheter, in particular of its ablation portion 12 with respect to the targeted PV antrum. After step 213 the procedure continues with step 202 (see above).

[0137] Then, if PFA delivery is aborted by the user in step 212, the procedure continues with step 213 (see explanation of step 213 above). If the PFA delivery is not aborted during treatment, the procedure continues with step 214 the PFA generator provides accurate delivery of ablation energy according to pulse protocol to the user by the electrodes 120 of the ablation portion 12.

[0138] According to above procedure, the PFA arcing risk and/or contact uniformity is checked prior PFA ablation in order to guarantee the catheter position with the highest contact uniformity and lowest arcing risk for all electrodes taking part in the PFA. Accordingly, dangerous arcing can be avoided and the electrodes have a uniform contact to the targeted tissue in order to provide high-quality PFA realizing a moat of electrical isolation in one shot.

[0139] 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.