US20220000543A1 - Bipolar tissue ablation in accordance with a predefined periodic set of time slots - Google Patents

Abstract

A method for applying bipolar ablation pulses, the method includes positioning multiple electrodes of a catheter in contact with tissue of an organ. The tissue is ablated using the multiple electrodes in accordance with a predefined pattern including a periodic set of time slots. Each of the time slots defines (i) an electrode-pair (EP), (ii) a waveform of one or more bipolar ablation pulses (BAPs) applied to the tissue by the EP, and (iii) a duration of the time slot. The time slots are applied sequentially, and the pattern further includes at least one time slot that is empty.

Description

FIELD OF THE INVENTION
• The present invention relates generally to medical devices, and particularly to methods and systems for bipolar tissue ablation.
BACKGROUND OF THE INVENTION
• Various techniques for ablating an extended area of heart tissue by applying irreversible electroporation (IRE) pulses are known in the art.
• For example, U.S. Pat. No. 10,470,822 describes a system for estimating a three-dimensional treatment volume for a device that applies treatment energy through a plurality of electrodes defining a treatment area, the system comprising a memory, a display device, a processor coupled to the memory and the display device, and a treatment planning module stored in the memory and executable by the processor.
• U.S. Patent Application Publication No. 2019/0336207 describes a system that includes a pulse waveform generator and an ablation device coupled to the pulse waveform generator. The ablation device includes at least one electrode configured for ablation pulse delivery to tissue during use. The pulse waveform generator is configured to deliver voltage pulses to the ablation device in the form of a pulsed waveform. The pulsed waveform can include multiple levels of hierarchy, and multiple sets of electrodes can be activated such that their pulsed delivery is interleaved with one another.
SUMMARY OF THE INVENTION
• An embodiment of the present invention that is described herein provides a method for applying bipolar ablation pulses, the method includes positioning multiple electrodes of a catheter in contact with tissue of an organ. The tissue is ablated using the multiple electrodes in accordance with a predefined pattern including a periodic set of time slots. Each of the time slots defines (i) an electrode-pair (EP), (ii) a waveform of one or more bipolar ablation pulses (BAPs) applied to the tissue by the EP, and (iii) a duration of the time slot. The time slots are applied sequentially, and the pattern further includes at least one time slot that is empty.
• In some embodiments, a first electrode of a first EP is positioned between second and third electrodes of a second EP. In other embodiments, each of the time slots includes a time gap scheduled before or after the one or more BAPs. In yet other embodiments, the BAPs include irreversible electroporation (IRE) BAPs.
• In an embodiment, the EPs of the time slots have a same inter-electrode distance. In another embodiment, a first EP of a first time slot of the predefined pattern includes a first electrode and a second electrode, and a second EP of a second time slot of the predefined pattern includes the first electrode and a third electrode.
• In some embodiments, the predefined pattern includes at least one time slot positioned between the first and second time slots. In other embodiments, positioning the catheter includes positioning a lasso catheter.
• There is additionally provided, in accordance with an embodiment of the present invention, a system including a catheter, a pulse generator, and a processor. The catheter including multiple electrodes, which are configured to make contact with tissue of an organ. The pulse generator is configured to generate one or more bipolar ablation pulses (BAPs). The processor is configured to ablate the tissue using the multiple electrodes in accordance with a predefined pattern including a periodic set of time slots that are applied to the tissue sequentially. Each of the time slots defines (i) an electrode-pair (EP) selected from the multiple electrodes, (ii) a waveform of the one or more BAPs applied to the tissue by the EP, and (iii) a duration of the time slot, and the pattern further includes at least one time slot that is empty.
BRIEF DESCRIPTION OF THE DRAWINGS
• The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:
• FIG. 1 is a schematic, pictorial illustration of a catheter-based position-tracking and irreversible electroporation (IRE) ablation system, in accordance with an exemplary embodiment of the present invention;
• FIG. 2 is a schematic pictorial illustration of a tip section of an IRE catheter having multiple electrodes, and architecture for applying IRE pulses to selected electrodes thereof, in accordance with an exemplary embodiment of the present invention; and
• FIG. 3 is a flow chart that schematically illustrates a method for applying bipolar IRE ablation pulses to tissue, in accordance with an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF EMBODIMENTSOverview
• Irreversible electroporation (IRE) may be used, for example, for treating arrhythmia by ablating tissue cells using high-voltage pulses applied to the tissue. Cellular destruction occurs when the transmembrane potential exceeds a threshold, leading to cell death and formation of a lesion. In IRE-based ablation procedures, also referred to herein as an IRE ablation for brevity, high-voltage bipolar electrical pulses are applied, for example, to pairs of electrodes in contact with tissue to be ablated, so as to form a lesion between the electrodes, and thereby to treat arrhythmia in a patient heart.
• Sometimes, a lasso-type catheter having multiple electrodes, may be used for performing IRE ablation over an extended area. Due to the lasso shape of the catheter, when applying bipolar IRE pulses to pairs of electrodes sequentially or simultaneously, one or more electrodes that are not intended to be energized, may undesirably touch an energized electrode, and consequently, may disrupt the outcome of the IRE ablation, and in severe cases, may be harmful to the patient.
• Embodiments of the present invention that are described hereinbelow provide improved techniques for applying the IRE bipolar pulses using an ablation protocol that improves the patient safety.
• In some embodiments, in an IRE ablation procedure using a lasso-type catheter, a physician positions multiple electrodes of the catheter in contact with a target tissue, such as pulmonary vein of a patient heart. Subsequently, the physician may use a processor that controls an IRE ablation system for ablating the tissue using the multiple electrodes in accordance with a predefined pattern comprising a periodic set of time slots.
• In some embodiments, the time slots are applied sequentially, and each of the time slots defines (i) an electrode-pair (EP) selected from among the multiple electrodes, (ii) a waveform of one or more bipolar ablation pulses (BAPs), also referred to herein as “IRE ablation pulses,” are applied to the tissue by the EP, and (iii) duration of the time slot. Note that the term “periodic” refers to one or more repetitions of the same predefined pattern. For example, a given predefined pattern may have three time slots, wherein one or more BAPs are applied sequentially to first, second and third EPs, during first second and third time slots, respectively. Subsequently, the given predefined pattern is repeated with applying the one or more BAPs to the first EP of the first time slot and so on.
• In some embodiments, the electrodes of different EPs are interleaved, such that a first electrode of a first EP is positioned between second and third electrodes of a second EP. Each of the time slots comprises a time gap scheduled before or after the one or more BAPs, so that during the time gap IRE ablation pulses are not applied to the target tissue.
• In some embodiments, the pattern further may comprise at least one time slot that is empty, in other words, IRE ablation pulses are not applied to any EP during the duration of the empty time slot.
• The disclosed techniques improve the safety in various bipolar ablation procedures applying bipolar pulses applied to a target tissue having a broad area, by controlling the position of the bipolar ablation pulses applied to the target tissue.
System Description
• FIG. 1 is a schematic, pictorial illustration of acatheter21 based position-tracking and irreversible electroporation (IRE)ablation system20, in accordance with an exemplary embodiment of the present invention.
• In some embodiments,system20 comprises adeflectable tip section40 that is fitted at adistal end22aof ashaft22 ofcatheter21 withtip section40 comprising multiple electrodes50 (inset25). In the present example,tip section40 comprises a Lasso® catheter, also referred to herein as “lasso” for brevity, produced by Biosense Webster Inc. (Irvine, Calif.). The lasso andelectrodes50 are described in detail with respect toFIG. 2 below.
• In other embodiments,tip section40 may comprise any other suitable type of deflectablecatheter having electrodes50.
• In the embodiment described herein,electrodes50 are configured to apply IRE ablation pulses to tissue of the left atrium of aheart26, such as IRE ablation of anostium51 of a pulmonary vein inheart26.Electrodes50 may also be used for sensing intra-cardiac electrocardiogram (ECG) signals. Note that the techniques disclosed herein are applicable, mutatis mutandis, to other sections (e.g., atrium or ventricle) ofheart26, and to other organs of apatient28.
• In some embodiments, the proximal end ofcatheter21 is connected to a control console24 (also referred to herein as a console24) comprising an ablative power source, in the present example an IRE pulse generator (IPG)45, which is configured to deliver peak power in the range of tens of kW.Console24 comprises aswitching box46, which is configured to switch the power applied by IPG45 to one or more selected pairs ofelectrodes50. A sequenced IRE ablation protocol, also referred to herein as an ablation plan or a predefined pattern, may be defined in advance byphysician30, or byprocessor41, or by a combination thereof, and stored in amemory48 ofconsole24.
• In some embodiments,processor41 and/orphysician30 may select, e.g., based on electrical mapping of activation pulses produced inheart26, the most suitable predefined pattern for obtaining the desired outcome of the IRE ablation procedure. The configuration oftip section40 with IPG45 andswitching box46 are described in detail with respect toFIG. 2 below, and the predefined pattern is described in detail inFIGS. 2 and 3 below.
• In some embodiments, aphysician30 insertsdistal end22aofshaft22 through asheath23 intoheart26 ofpatient28 lying on a table29.Physician30 navigatesdistal end22aofshaft22 to a target location inheart26 by manipulatingshaft22 using amanipulator32 located, for example, in close proximity to the proximal end ofcatheter21. During the insertion ofdistal end22a,deflectable tip section40 is maintained in a straightened configuration bysheath23. By containingtip section40 in a straightened configuration,sheath23 also serves to minimize vascular trauma whenphysician30 movescatheter21, through the vasculature ofpatient28, to the target location, such as an ablation site inheart26.
• Oncedistal end22aofshaft22 has reached the ablation site,physician30 retractssheath23 and manipulatesshaft22 to placeelectrodes50 disposed over the lasso oftip section40 to make contact with the walls ofostium51 at the ablation site. In the present example, the ablation site comprises a pulmonary vein, but in other embodiments,physician30 may select any other suitable ablation site.
• In some embodiments,electrodes50 are connected by wires running throughshaft22 to theprocessor41, which is configured to control switchingbox46 ofinterface circuits44 inconsole24.
• As further shown ininset25,distal end22acomprises aposition sensor39 of a position tracking system, which is coupled todistal end22a, e.g., attip section40. In the present example,position sensor39 comprises a magnetic position sensor, but in other embodiments, any other suitable type of position sensor (e.g., other than magnetic-based) may be used. During the navigation ofdistal end22ainheart26,processor41 ofconsole24 receives signals frommagnetic position sensor39 in response to magnetic fields fromexternal field generators36, for example, for the purpose of measuring the position oftip section40 inheart26 and, optionally, displays the tracked position overlaid on the image ofheart26, on adisplay27 ofconsole24.Magnetic field generators36 are placed at known positions external topatient28, e.g., below table29.Console24 also comprises adriver circuit34, configured to drivemagnetic field generators36.
• The method of position sensing using external magnetic fields is implemented in various medical applications, for example, in the CARTO™ system, produced by Biosense Webster Inc. (Irvine, Calif.) and is described in detail in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. Patent Application Publication Nos. 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1, whose disclosures are all incorporated herein by reference.
• Typically,processor41 ofconsole24 comprises a general-purpose processor of a general-purpose computer, with suitable front end andinterface circuits44 for receiving signals fromcatheter21, as well as for applying ablation energy viacatheter21 in a left atrium ofheart26 and for controlling the other components ofsystem20.Processor41 typically comprises software inmemory48 ofsystem20, which is programmed to carry out the functions described herein. The software may be downloaded to the computer in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory.
Applying Irreversible Electroporation Pulses to Tissue
• Irreversible electroporation (IRE), also referred to as Pulsed Field Ablation (PFA), may be used as a minimally invasive therapeutic modality for forming a lesion (e.g., killing tissue cells) at the ablation site by applying high-voltage pulses to the tissue. In the present example, IRE pulses may be used for killing myocardium tissue cells in order to treat cardiac arrhythmia in theheart26. Cellular destruction occurs when the transmembrane potential exceeds a threshold, leading to cell death and thus the development of a tissue lesion. Therefore, of particular interest is the use of high-voltage bipolar electrical pulses, e.g., using a pair ofelectrodes50 in contact with tissue at the ablation site, to generate high electric fields (e.g., above a certain threshold) to form a lesion by killing tissue cells located between the electrodes.
• In the context of this disclosure, “bipolar” voltage pulse means a voltage pulse applied between twoelectrodes50 of catheter21 (as opposed, for example, to unipolar pulses that are applied, e.g., during a radio-frequency ablation, by a catheter electrode relative to some common ground electrode not located on the catheter). Moreover, the terms “IRE pulse” and “bipolar ablation pulse” are used interchangeably and refer to one or more bipolar pulses applied byIPG45, via switchingbox46 and an electrode-pair (EP) selected fromelectrodes50, to the ablated tissue ofheart26.
• To implement IRE ablation over a relatively large tissue region ofheart26, such as a circumference of an ostium of a pulmonary vein (PV) or any other suitable organ, it is necessary to use multiple pairs ofelectrodes50 ofcatheter21 havingmulti electrodes50 intip section40. To make the generated electric field as spatially uniform as possible over a large tissue region it is best to have pairs ofelectrodes50 selected with overlapping fields, or at least fields adjacent to each other. However, there is a Joule heating component that occurs with the IRE generated fields, and this heating may cause uncontrolled damage to tissue and undesired damage to the electrodes when multiple pairs ofelectrodes50 are continuously used for applying the predefined the IRE pulses in accordance with a pattern of time slots.
• In some embodiments, based on pre-mapping of activation signals produced inheart26,processor41 is configured to assist thephysician30 in defining the IRE ablation plan. The pre-mapping may be carried out usingelectrodes50, and/or usingsurface electrodes38, shown in the example ofFIG. 1, as attached by wires running through acable37 to the chest and shoulder ofpatient28.
• In some embodiments,surface electrodes38 are configured to sense body-surface (BS) ECG signals in response to beats ofheart26. Acquisition of BS ECG signals may be carried out using conductive pads attached to the body surface or any other suitable technique. As shown inFIG. 1,surface electrodes38 are attached to the chest and shoulder ofpatient28, however,additional surface electrodes38 may be attached to other organs ofpatient28, such as limbs.
• In some embodiments,electrodes50 are configured to sense intra-cardiac (IC) ECG signals, and (e.g., at the same time)surface electrodes38 are sensing the BS ECG signals. In other embodiments, sensing the IC ECG signals may be sufficient for performing the IRE ablation, so thatsurface electrodes38 may be applied for other use cases.
• In some embodiments,physician30 may couplemultiple electrodes50 to a target tissue at the ablation site inheart26. The target tissue is intended to be ablated by applying one or more IRE pulses via pairs ofelectrodes50. Note that the IRE pulses may be applied to the target tissue multiple times, using any suitable pattern, during the IRE ablation procedure.
• This particular configuration ofsystem20 is simplified for the sake of conceptual clarity and is shown by way of example, in order to illustrate certain problems that are addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such an IRE ablation system. Embodiments of the present invention, however, are by no means limited to this specific sort of exemplary system, and the principles described herein may similarly be applied to other sorts of ablation systems.
Applying Irreversible Electroporation Pulses to Tissue in Accordance with a Predefined Pattern
• FIG. 2 is a schematic pictorial illustration oftip section40, and an architecture for applying IRE pulses to selectedelectrodes50, in accordance with an exemplary embodiment of the present invention.
• In the example ofFIG. 2,tip section40 comprises tenelectrodes50, referred to herein aselectrodes50A,50B,50C,50D,50E,50F,50G,50H,50I and50J, coupled totip section40 along the lasso described inFIG. 1 above.
• In some embodiments,IPG45 applies the BAPs to switchingbox46, which is electrically coupled to each ofelectrodes50A-50J via arespective wire55, or using any other suitable connection.
• In some embodiments, based on the aforementioned mapping ofheart26,processor41 and/orphysician30 may select from the aforementioned one or more predefined patterns of the IRE ablation protocol stored inmemory48, the most suitable predefined pattern for treating the arrhythmia detected inheart26.
• An example of a predefined pattern is shown in Table 1 below:

• TABLE 1
  Predefined pattern of EP by time slot

  	Time Slot	Energized EP

  	1	50E-50G
  	2	50F-50H
  	3	50A-50C
  	4	50B-50D
  	5	Empty
  	6	Empty
  	7	50G-50I
  	8	50H-50J
  	9	50C-50E
  	10	50D-50F

• As shown in Table 1, each time slot defines an electrode-pair (EP), which receives bipolar ablation pulses (BAPs) generated byIPG45 and routed to the respective EP via switchingbox46.
• In some embodiments, all EPs have the same inter-electrode distance. For example, the distance betweenelectrodes50E and50G of time slot1 is similar to the distance betweenelectrodes50F and50H of time slot2, and to the distance betweenelectrodes50C and50E of time slot9.
• In some embodiments, at least some ofelectrodes50 are used more than one time in different time slots of the same predefined pattern, but is paired with a different electrode in different time slots. For example,electrode50C is paired withelectrode50A in time slot1, and withelectrode50E in time slot9. Moreover, as shown in Table 1, at least one time slot is positioned, in the predefined pattern, between two time slots having a common electrode.
• In some embodiments, the time slots are applied sequentially to the ablated tissue, but in other embodiments, two or more time slots may be applied at the same time or with some overlap in timing.
• In some embodiments, each time slot defines a waveform of one or more BAPs that are applied in bursts, to the tissue by the respective EP. In the present example, the waveform comprises ten pulses of about 5 microseconds each, applied at 200 KHz, and the time slot is concluded by a time gap of about 0.5 millisecond (msec) typically but not necessarily scheduled after the tenth pulse. Moreover, all the time slots of Table 1 are using the same waveform described above.
• In the context of the present disclosure and in the claims, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein.
• In some embodiments, the predefined pattern comprises a periodic set of the time slots. In other words, after concluding time slot10 and the time gap, the predefined pattern is repeated one or more times, so as to complete the required amount of ablation energy applied to the ablated tissue. Note that the number of repetitions may be calculated based on the electrical mapping and the aforementioned ablation protocol. As described above, the total duration of each time slot is slightly longer than about 0.5 msec, and therefore, the total duration, also referred to herein as the cycle length, of the predefined pattern, is slightly longer than 5 msec.
• In such embodiments, each electrode-pair of the predefined pattern has a duration slightly longer than 5 milliseconds for cooling before receiving the next waveform of ten BAPs, thereby preventing overheating of the respective electrodes, and may also prevent uncontrolled damage to the section of tissue located between the electrodes of the respective pair.
• In some embodiments, the predefined pattern of Table 1 has time slots5 and6 that are empty. In the context of the present disclosure and in the claims, the term “empty” refers to not applying any BAP to any EP ofelectrodes50 ofcatheter tip40. Note that in the present example, the time gap of 0.5 msec is retained also in the empty time slots.
• Note that the EPs of the predefined pattern are interleaved between the time slots. For example,electrode50F of time slot2 is positioned (along catheter tip40) betweenelectrodes50E and50G of time slot1.
• In other embodiments, the ablation protocol may comprise a predefined pattern having all time slots filled with respective EPs receiving one or more BAPs fromIPG45. In other words, without empty time slots.
• In yet other embodiments,physician30 and/orprocessor41 may skip a time slot, e.g., by not energizing the EP defined in the time slot, and thereby may shorten the cycle length of the predefined pattern.
• In alternative embodiments, each time slot may comprise more than one waveform with a time gap between adjacent waveforms.
• This particular time slot configuration and order of the predefined pattern of Table 1 are shown by way of example, in order to illustrate certain problems that are addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such an IRE ablation protocol. Embodiments of the present invention, however, are by no means limited to this specific sort of example predefined pattern, and the principles described herein may similarly be applied to other sorts of predefined pattern and/or ablation protocols.
• FIG. 3 is a flow chart that schematically illustrates a method for applying bipolar IRE ablation pulses to ablated tissue, in accordance with an embodiment of the present invention. The method begins at an ablationprotocol definition step100, with defining a pattern of ablation protocol having a periodic set of time slots. Each time slot comprising an electrode-pair (EP), a waveform of one or more bipolar ablation pulses (BAPs), and duration of the time slot. As described inFIG. 2 above, the time slot may comprise a time gap scheduled before or after the one or more BAPs of the waveform.
• At a catheter insertion step102,physician30inserts catheter tip40 ofcatheter21 intoheart26 and positionsmultiple electrodes50 in contact with the target tissue, as described inFIG. 1 above.
• At atissue ablation step104 that concludes the method, irreversible electroporation (IRE) bipolar ablation pulses (BAPs) are applied to the target tissue in accordance with the predefined pattern of the ablation protocol described instep100 above, and in greater detail inFIG. 2 above. Note that the predefined pattern is periodic, such that the set of time slots repeats after concluding the cycle of time slots defined in the pattern. The number of repetitions is defined based on the ablation protocol and the electrical mapping ofheart26, such that, in case of multiple repetitions, the method terminates after concluding the last repetition, andphysician30 retractscatheter tip40 out ofpatient28.
• Although the embodiments described herein mainly address irreversible electroporation of patient heart, the methods and systems described herein can also be used in other applications, such as but not limited to renal ablation, liver ablation, treatment of lung cancer or in ablation of any other suitable organ.
• It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art. Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.

Claims (16)

1. A method for applying bipolar ablation pulses, the method comprising:

positioning multiple electrodes of a catheter in contact with tissue of an organ; and

ablating the tissue using the multiple electrodes in accordance with a predefined pattern comprising a periodic set of time slots, wherein each of the time slots defines (i) an electrode-pair (EP), (ii) a waveform of one or more bipolar ablation pulses (BAPs) applied to the tissue by the EP, and (iii) a duration of the time slot, wherein the time slots are applied sequentially, and wherein the pattern further comprises at least one time slot that is empty.

2. The method according toclaim 1, wherein a first electrode of a first EP is positioned between second and third electrodes of a second EP.

3. The method according toclaim 1, wherein each of the time slots comprises a time gap scheduled before or after the one or more BAPs.

4. The method according toclaim 1, wherein the BAPs comprise irreversible electroporation (IRE) BAPs.

5. The method according toclaim 1, wherein the EPs of the time slots have a same inter-electrode distance.

6. The method according toclaim 1, wherein a first EP of a first time slot of the predefined pattern comprises a first electrode and a second electrode, and wherein a second EP of a second time slot of the predefined pattern comprises the first electrode and a third electrode.

7. The method according toclaim 6, wherein the predefined pattern comprises at least one time slot positioned between the first and second time slots.

8. The method according toclaim 1, wherein positioning the catheter comprises positioning a lasso catheter.

9. A system for applying bipolar ablation pulses, comprising:

a catheter comprising multiple electrodes, which are configured to make contact with tissue of an organ;

a pulse generator, which is configured to generate one or more bipolar ablation pulses (BAPs); and

a processor, which is configured to ablate the tissue using the multiple electrodes in accordance with a predefined pattern comprising a periodic set of time slots that are applied to the tissue sequentially, wherein each of the time slots defines (i) an electrode-pair (EP) selected from the multiple electrodes, (ii) a waveform of the one or more BAPs applied to the tissue by the EP, and (iii) a duration of the time slot, and wherein the pattern further comprises at least one time slot that is empty.

10. The system according toclaim 9, wherein a first electrode of a first EP is positioned between second and third electrodes of a second EP.

11. The system according toclaim 9, wherein each of the time slots comprises a time gap scheduled before or after the one or more BAPs.

12. The system according toclaim 9, wherein the BAPs comprise irreversible electroporation (IRE) BAPs.

13. The system according toclaim 9, wherein the EPs have a same inter-electrode distance.

14. The system according toclaim 9, wherein a first EP of a first time slot of the predefined pattern comprises a first electrode and a second electrode, and wherein a second EP of a second time slot of the predefined pattern comprises the first electrode and a third electrode.

15. The system according toclaim 14, wherein the predefined pattern comprises at least one time slot positioned between the first and second time slots.

16. The system according toclaim 9, wherein the catheter comprises a lasso catheter.

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