Patent Publication Number: US-2021169421-A1

Title: Catheter with Plurality of Sensing Electrodes Used as Ablation Electrode

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to medical probes, and particularly to cardiac multi-electrode electrophysiological (EP) sensing and ablation catheters. 
     BACKGROUND OF THE INVENTION 
     Multi electrode catheters for tissue sensing and ablation were previously proposed in the patent literature. For example, U.S. Patent Application Publication 2010/0168548 describes cardiac catheters, including a lasso catheter, for use in a system for electrical mapping of the heart has an array of raised, perforated electrodes, which are in fluid communication with an irrigating lumen. There are position sensors on a distal loop section and on a proximal base section of the catheter. The electrodes are sensing electrodes that may be adapted for pacing or ablation. The raised electrodes securely contact cardiac tissue, forming electrical connections having little resistance. 
     As another example, U.S. Pat. No. 5,562,720 describes an endometrial ablation device and a method of manufacturing and using the device. An electroconductive expandable member, such as a balloon, is used as a medium for passing RF current through endometrium tissue to heat the endometrium tissue. The power delivered from a power source to the balloon is selectively provided to a plurality of electrode area segments on the balloon with each of the segments having a thermistor associated with it, whereby temperature is monitored and controlled by a feedback arrangement from the thermistors. The selective application of power is provided on the basis of a switching arrangement which provides either monopolar or bipolar energy to the electrodes. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention provides a system including a switching assembly and a processor. The switching assembly is connected to multiple electrodes that are disposed on an expandable distal end of a catheter, and is configured to switch the electrodes between a position tracking system, an electrophysiological (EP) sensing module and a generator of an ablative power. The processor is configured to control the switching assembly to switch the electrodes. 
     In some embodiments, the ablative power includes at least one of a radiofrequency (RF) power outputted by an RF generator and irreversible electroporation (IRE) pulses outputted by an IRE pulse generator. 
     In some embodiments, each of the electrodes includes a plurality of electrode segments. 
     In an embodiment, when connecting a given electrode to the position tracking system or to the EP sensing module, the switching assembly and the processor are configured to connect each of the electrode segments of the given electrode individually. When connecting the given electrode to the generator of the ablative power, the switching assembly and the processor are configured to jointly connect all the electrode segments of the given electrode. 
     In another embodiment, the processor is configured to control whether to use the electrode as a position sensor, as an EP sensor, or as an ablation electrode, by evaluating a preset impedance criterion. 
     In some embodiments, the processor is configured to evaluate the impedance criterion by assessing whether a frequency-dependence of the impedance indicates that the electrode is in contact with blood or with tissue. 
     There is additionally provided, in accordance with an embodiment of the present invention, a method including, using a switching assembly, interchangeably switching multiple electrodes, which are disposed on an expandable distal end of a catheter, between a position tracking system, an electrophysiological (EP) sensing module and a generator of an ablative power. Using a processor, the switching assembly is controlled to switch the electrodes. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, pictorial illustration of a balloon-catheter based position-tracking, electrophysiological (EP) sensing, and ablation system, in accordance with an embodiment of the present invention; 
         FIG. 2  is a schematic, pictorial side view of a distal end of the balloon catheter of  FIG. 1  deployed in a region of a pulmonary vein (PV) and its ostium, in accordance with an embodiment of the invention; 
         FIG. 3  is a block diagram that schematically describes the functionality of the processor-controlled switching box of  FIG. 1 , in accordance with an embodiment of the invention; and 
         FIG. 4  is a flow chart that schematically illustrates a method for interchangeably using segmented electrodes of the balloon catheter of  FIG. 2  for position sensing, electrophysiological (EP) sensing, and ablation, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     For efficient sensing and ablation with a medical probe, such as an intra-cardiac radiofrequency (RF) and/or an irreversible electroporation (IRE) catheter with a distal end disposed with multiple electrodes, it is important that (a) the distal end is accurately navigated to a tissue location most suitable for electrophysiological (EP) sensing and ablation, and (b) the electrodes disposed over the distal can effectively acquire EP signals from tissue and/or ablate tissue. For example, when a balloon catheter with multiple electrodes is used for treating cardiac arrhythmia, the balloon has to be brought to a cardiac location, such as an ostium of a pulmonary ventricle (PV), acquire EP signals to verify an arrhythmia, and ablate arrhythmogenic tissue, all using the multiple electrodes. 
     Similarly, other multi-electrode catheters, such as the Lasso catheter (made by Biosense Webster, Irvine, Calif.) or a basket catheter, also need to have their electrodes capable of such sensing and ablation. 
     Embodiments of the present invention that are described hereinafter provide techniques to interchangeably use electrodes disposed over the distal end for sensing and for ablation. In some embodiments, the electrodes are initially used as sensors, to track a position of the distal end, so as to navigate it to a cardiac tissue location inside the heart. Subsequently, the electrodes are used for EP sensing. Finally, RF and/or IRE ablation is applied using the electrodes. Typically, the electrodes can be used in a spatially selectable manner, in which at any given time any subset of the electrodes can be switched to be used for any of the above applications. For example, electrodes that have insufficient contact with tissue can be used for position tracking, while others for EP sensing and subsequent ablation. 
     In the context of the present patent application, the term “applying ablation” covers both applying RF power and applying IRE pulses. Typically, the ablative power comprises either a radiofrequency (RF) power outputted by an RF generator or irreversible electroporation (IRE) pulses outputted by an IRE pulse generator. However, a single generator may be configured to interchangeably output RF power and IRE pulses. 
     In some embodiments, an expandable multi-electrode catheter (e.g., an inflatable balloon catheter, which is used by way of example hereinafter) is provided that comprises electrodes divided into segments (i.e., into electrode segments). In some embodiments, a balloon catheter is provided with ten electrodes disposed on a membrane of the balloon. Each of the ten electrodes is divided into four segments with one or more temperature sensors, such as thermocouples, located on each electrode segment. 
     Further provided is a processor-controlled switching box (also referred to as a switching assembly). During navigation of the distal end of a catheter (e.g., a balloon catheter) to a target location for ablation, the disclosed system uses the electrode segments as position sensors of an electrical-impedance-based position tracking sub-system, as described below. Once the balloon is determined to be at the target location (using the position tracking sub-system), the processor controlling the switching box switches an EP sensing module or ablative power to at least part of the electrode segments. 
     In an embodiment, once catheter is placed in target position, the processor analyzes a characteristic of the measured impedance, such as, for example, the different frequency-dependence of the impedance of blood and tissue, and, using the outcome of the analysis, provides an independent assessment for each electrode segment as to whether the electrode segment is in direct electrical contact with (i.e., touches) cardiac tissue or is not in contact (e.g., the electrode segment is mostly immersed in blood). 
     The impedance of an electrode can be determined in any of the modes that the electrodes are used in (i.e., position tracking, EP sensing and ablation). Each electrode having a frequency-dependent impedance indicative of tissue is subsequently switched to the EP sensing module or the ablative power source by the processor, using the switching box. An electrode segment with a frequency-dependent impedance indicative of blood is kept as a position sensing electrode by the processor. 
     In some embodiments, the balloon direction in space is measured using a magnetic sensor on the catheter in vicinity of the balloon, as described below, to further assist a best placement of the balloon against the ostium, e.g., to achieve sufficient electrode contact over an entire circumference of the balloon. 
     Typically, the processor is programmed in software containing a particular algorithm that enables the processor to conduct each of the processor-related steps and functions outlined above. 
     By providing electrode segments that are switchable according to navigational tasks, EP sensing tasks, and ablation tasks, the disclosed segmented-electrode sensing and ablation technique can provide safer and more effective diagnostics and treatment. This, in turn, may improve the clinical outcome of, for example, cardiac balloon ablation treatments, such as of PV isolation for treatment of arrhythmia. 
     System Description 
       FIG. 1  is a schematic, pictorial illustration of a balloon-catheter based position-tracking, electrophysiological (EP) sensing, and ablation system  20 , in accordance with an embodiment of the present invention. System  20  comprises a catheter  21  that is fitted at a distal end  22   a  of a shaft  22  of the catheter with an RF ablation expandable balloon  40  comprising segmented electrodes  50  (seen in inset  25 ). In the embodiment described herein, segmented electrodes  50  are used for ablating tissue of an ostium  51  of a PV in a heart  26 . 
     The proximal end of catheter  21  is connected to a control console  24  comprising an ablative power source  45  that can deliver IRE and/or RF power. Console  24  includes a processor  41  that controls a switching box  46  (also referred to as a switching assembly) to switch any segment of a segmented electrode  50  between acting as a position sensing electrode and acting as an ablation electrode. An ablation protocol comprising ablation parameters including impedance criteria is stored in a memory  48  of console  24 . 
     Physician  30  inserts distal end  22   a  of shaft  22  through a sheath  23  into heart  26  of a patient  28  lying on a table  29 . Physician  30  advances the distal end of shaft  22  to a target location in heart  26  by manipulating shaft  22  using a manipulator  32  near the proximal end of the catheter and/or deflection from the sheath  23 . During the insertion of distal end  22   a , balloon  40  is maintained in a collapsed configuration by sheath  23 . By containing balloon  40  in a collapsed configuration, sheath  23  also serves to minimize vascular trauma along the way to target location. 
     Once distal end  22   a  of shaft  22  has reached heart  26 , physician  30  retracts sheath  23  and partially inflates balloon  40 , and further manipulates shaft  22  to navigate balloon  40  to an ostium  51  the pulmonary vein. 
     In an embodiment, physician  30  navigates the distal end of shaft  22  to the target location by tracking a position of balloon  40  using impedances measured between segmented electrodes  50  and surface electrodes  38 . 
     To perform its functions, processor  41  includes an electrode-impedance-sensing module  47 . In the exemplified system, impedance-sensing module  47  receives electrical impedance signals measured between segmented electrodes  50  and surface electrodes  38 , which are seen as attached by wires running through a cable  37  to the chest of patient  28 . Electrodes  50  are connected by wires running through shaft  22  to processor  41  controlling switching box  46  of interface circuits  44  in a console  24 . 
     A method for tracking the positions of electrodes, such as electrodes  50 , using the aforementioned measured impedances is implemented in various medical applications, for example in the CARTO™ system, produced by Biosense-Webster (Irvine, Calif.) and is described in detail in U.S. Pat. Nos. 7,756,576, 7,869,865, 7,848,787, and 8,456,182, whose disclosures are all incorporated herein by reference with a copy provided in the Appendix. This method is sometimes called Advanced Catheter Location (ACL). In an embodiment, console  24  drives a display  27 , which shows the tracked position of balloon  40  inside heart  26 . 
     When at target position (e.g., at ostium  51 ), physician  30  fully inflates balloon  40  and places segmented electrodes  50  disposed over a perimeter of balloon  40  in contact with ostium  51  tissue. Next, physician  30  measures, e.g., using impedance sensing module  47 , the impedance of each of segmented electrode segments, as described above. Processor  41  compares the measured impedance of each segment with a preset threshold impedance. If segment impedance is below or equals the preset impedance threshold, which means that the electrode segment is in contact with blood rather than being in good contact with tissue, processor  41  controls switching box  46  to keep the segment operating as a position sensing electrode. If, on the other hand, the segment impedance is above the preset threshold, which means that the electrode segment is in good contact with tissue, the processor controls switching box  46  to operate the segment as an ablation electrode. 
     As further shown in inset  25 , distal end  22   a  comprises a magnetic position sensor  39  contained within distal end  22   a  just proximally to expandable balloon  40 . During navigation of distal end  22   a  in heart  26 , console  24  receives signals from magnetic sensor  39  in response to magnetic fields from external field generators  36 , for example, for the purpose of measuring the direction of ablation balloon  40  in the heart and, optionally, presenting the tracked direction on a display  27 , e.g., relative to an orientation of an axis of approximate symmetry of ostium  51 . Magnetic field generators  36  are placed at known positions external to patient  28 , e.g., below patient table  29 . Console  24  also comprises a driver circuit  34 , configured to drive magnetic field generators  36 . 
     The method of direction sensing using external magnetic fields is implemented in various medical applications, for example, in the CARTO™ system, produced by Biosense-Webster, 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 Publications 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1, whose disclosures are all incorporated herein by reference as if set forth in full into this application with a copy provided in the Appendix. 
     In an embodiment, signals from sensor  39  are further used for position sensing using the aforementioned CARTO™ system. 
     Processor  41  is typically a general-purpose computer, with suitable front end and interface circuits  44  for receiving signals from catheter  21 , as well as for applying RF energy treatment via catheter  21  in a left atrium of heart  26  and for controlling the other components of system  20 . Processor  41  typically comprises software in a memory of system  20  that 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. In particular, processor  41  runs a dedicated algorithm as disclosed herein, included in  FIG. 4 , that enables processor  41  to perform the disclosed steps, as further described below. 
     While  FIG. 1  describes a multi-electrode balloon catheter, the principles of the present technique apply to any catheter having a distal end fitted with multiple electrodes, such as the aforementioned Lasso and basket catheters. 
     Catheter with Plurality of Sensing Electrodes as Ablation Electrodes 
       FIG. 2  is a schematic, pictorial side view of the balloon catheter of  FIG. 1  deployed in a region of a pulmonary vein (PV) and its ostium  51 , in accordance with an embodiment of the invention. The balloon catheter is used to sense EP signals from ostium  51  tissue, to determine an arrhythmia, and to ablate ostium  51  tissue to isolate a source of arrhythmia. Balloon  40  has ten segmented electrodes  50  disposed over a membrane  71  of the balloon. IRE and/or RF power can be delivered from ablative power source  45  independently to each of the four electrode segments  55  of each of the ten electrodes, depending, for example, on the level of physical contact of each segment  55  with tissue during ablation. 
     As seen in  FIG. 2 , an electrode segment  55   a  is not in good contact with tissue. Based on impedance readings from electrode segment  55   a  as below or equal to the preset impedance value, processor  41  determines the insufficient physical contact of electrode segment  55   a . In response, processor  41  controls switching box  46  to maintain electrode segment  55   a  as a position-sensing electrode. 
     An electrode segment  55   b , on the other hand, is in good contact with tissue. Based on impedance readings from electrode segment  55   b  as above the preset threshold impedance value, processor  41  determines the sufficient physical contact of electrode segment  55   a . In response, processor  41  controls switching box  46  to switch electrode segment  55   b  to be used as an EP-sensing electrode or as an ablation electrode. 
     In some embodiments, to determine sufficiency of contact with tissue, the impedance of each electrode segment is monitored by the processor that receives impedance readings sensed by the electrode segment. The processor uses a preset impedance criterion, such as a relation of the impedance readings with respect to a preset threshold impedance, to determine whether a physical contact between any of the electrodes and tissue meets a predefined contact quality with tissue. For example, if the impedance of an electrode segment does not rise above the threshold impedance, the processor determines that the level of contact of the electrode segment with tissue is insufficient (meaning that EP-sensing is of blood signals, or that ablative energy would mainly heat blood). In this case the processor controls the switching box to maintain the electrode segment as a position-sensing electrode. If, on the other hand, an impedance reading from an electrode segment is above the preset threshold impedance (e.g., above a threshold determined by previous experimentation), the processor determines that the contact of the electrode segment with the tissue is good, i.e., meets a predefined contact quality criterion, and that tissue can be either EP sensed, or ablated with the electrode segment. In this case the switching box switches the electrode segment to connect the electrode segment to either an EP sensing module, or the ablative power source. 
     A technique for sensing electrode-tissue physical contact using analysis of frequency response of tissue is described in U.S. patent application Ser. No. 15/991,291, filed May 29, 2018, entitled “Touch Detection by Different Frequency Response of Tissue,” which is assigned to the assignee of the present patent application and whose disclosure is incorporated herein by reference as if set forth in full into this application with a copy in the Appendix. In an embodiment, the processor may use this method to analyze the acquired intra-cardiac signals. However, other techniques to asses level of contact with tissue that utilize electrical measurements provided by segmented electrodes may be used. 
     The pictorial side view shown in  FIG. 2  is chosen by way of example, where other embodiments are possible. For example, in another embodiment, cooling fluid sprays via irrigation holes (not shown) in electrodes  50  to cool ablated tissue. As another example, tissue temperature is measured using temperature sensors (not shown) fitted on electrodes  50 . 
       FIG. 3  is a block diagram that schematically describes the functionality of processor-controlled switching box  46  of  FIG. 1 , in accordance with an embodiment of the invention. As seen, in response to a command by processor  41 , switching box  46  either connects an electrode segment to the aforementioned ACL position-sensing sub-system of system  20  to provide position signals to be used with the ACL position tracking method, or connects the electrode segment to an EP sensing module, or connects the electrode segment to an RF power supply to be used as an ablation electrode. 
     In another embodiment, when connecting a given electrode to the position tracking system or to the EP sensing module, the switching assembly and the processor are configured to connect each of the electrode segments of the given electrode individually, whereas when connecting the given electrode to the generator of the ablative power, the switching assembly and the processor are configured to jointly connect all the electrode segments of the given electrode. 
     The block diagram of  FIG. 3  is highly simplified to maintain clarity of presentation. Information from other system elements, such as temperature sensors on balloon  40 , which do not contribute directly to the clarity presentation, are thus omitted. 
       FIG. 4  is a flow chart that schematically illustrates a method for interchangeably using segmented electrodes of the balloon catheter of  FIG. 2  for position sensing, electrophysiological (EP) sensing, and ablation, in accordance with an embodiment of the invention. The algorithm, according to the presented embodiment, carries out a process that begins when physician  30  navigates the balloon catheter to a target location within a lumen of a patient, such as at ostium  51 , using electrode segments  55  as ACL-sensing electrodes, at a balloon catheter navigation step  80 . 
     Next, physician  30  positions the balloon catheter at ostium  51 , at a balloon catheter positioning step  82 . Next, physician  30  fully inflates balloon  40  to contact the lumen wall with electrode segments  55  over an entire circumference of the lumen, at a balloon inflation step  84 . 
     Next, using impedance reading by module  47 , the impedance of each of electrode segments  55 , typically to one of surface electrodes  38 , is measured, and based on an impedance criterion, processor  41  switches part or all electrode segments  55  for use as EP sensing electrodes. 
     After using the electrodes as EP sensors, to verify an arrythmia, the processor controls switching box  46  to operate the segment as an ablation electrode (e.g., to connect the electrode to ablative power source  45 ), at a switching step  88 . At a switching step  90 , physician  30  re-switches part or all electrode segments  55  for use as EP sensing electrodes, to verify arrhythmia was eliminated. 
     The example flow chart shown in  FIG. 4  is chosen purely for the sake of conceptual clarity. In alternative embodiments, additional steps may be performed, such as processor  41  monitoring measured contact force of segments, and acting according to measured contact forces. 
     While  FIG. 4  describes a multi-electrode balloon catheter, the principles of the present technique apply to any catheter having a distal end fitted with multiple electrodes, such as the aforementioned Lasso and basket catheters. 
     Although the embodiments described herein mainly address pulmonary vein isolation, the methods and systems described herein can also be used in other applications that require a determination of occlusion, such as, for example, in renal denervation, and generally, in ablating other organs. 
     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.