Patent Publication Number: US-2023149070-A1

Title: Systems and methods for energizing electroporation catheters using quadripolar arrays

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to provisional application Ser. No. 63/278,605, filed Nov. 12, 2021, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to tissue ablation systems. In particular, the present disclosure relates to applying electroporation therapy using a catheter including a plurality of electrodes defining at least one quadripolar array. 
     BACKGROUND 
     It is generally known that ablation therapy may be used to treat various conditions afflicting the human anatomy. For example, ablation therapy may be used in the treatment of atrial arrhythmias. When tissue is ablated, or at least subjected to ablative energy generated by an ablation generator and delivered by an ablation catheter, lesions form in the tissue. Electrodes mounted on or in ablation catheters are used to create tissue necrosis in cardiac tissue to correct conditions such as atrial arrhythmia (including, but not limited to, ectopic atrial tachycardia, atrial fibrillation, and atrial flutter). 
     Arrhythmia (i.e., irregular heart rhythm) can create a variety of dangerous conditions including loss of synchronous atrioventricular contractions and stasis of blood flow which can lead to a variety of ailments and even death. It is believed that the primary cause of atrial arrhythmia is stray electrical signals within the left or right atrium of the heart. The ablation catheter imparts ablative energy (e.g., radiofrequency energy, cryoablation, lasers, chemicals, high-intensity focused ultrasound, etc.) to cardiac tissue to create a lesion in the cardiac tissue. This lesion disrupts undesirable electrical pathways and thereby limits or prevents stray electrical signals that lead to arrhythmias. 
     Electroporation is a non-thermal ablation technique that involves applying strong electric-fields that induce pore formation in the cellular membrane. The electric field may be induced by applying a relatively short duration pulse which may last, for instance, from a nanosecond to several milliseconds. Such a pulse may be repeated to form a pulse train. When such an electric field is applied to tissue in an in vivo setting, the cells in the tissue are subjected to trans-membrane potential, which opens the pores on the cell wall. Electroporation may be reversible (i.e., the temporally-opened pores will reseal) or irreversible (i.e., the pores will remain open). For example, in the field of gene therapy, reversible electroporation (i.e., temporarily open pores) is used to transfect high molecular weight therapeutic vectors into the cells. In other therapeutic applications, a suitably configured pulse train alone may be used to cause cell destruction, for instance by causing irreversible electroporation. 
     For example, pulsed field ablation (PFA) may be used to perform instantaneous pulmonary vein isolation (PVI). PFA generally involves delivering high voltage pulses from electrodes disposed on a catheter. For example, voltage pulses may range from less than about 500 volts to about 2400 volts or higher. These fields may be applied between pairs of electrodes (bipolar therapy) or between one or more electrodes and a return patch (monopolar therapy). 
     BRIEF SUMMARY OF THE DISCLOSURE 
     In one aspect, an apparatus for controlling an electroporation catheter is provided. The electroporation catheter includes a distal end, a proximal end, a plurality of splines extending from the distal end to the proximal end, and a plurality of electrodes arranged on the plurality of splines and defining at least one quadripolar array, each quadripolar array defined by four electrodes of the plurality of electrodes. The apparatus includes a pulse generator coupled to the electroporation catheter, and a computing device coupled to the pulse generator, the computing device operable to control the pulse generator to selectively energize the electrodes defining the at least one quadripolar array according to a first energization pattern, and selectively energize the electrodes defining the at least one quadripolar array according to a second energization pattern, wherein the first and second energization patterns are different from one another. 
     In another aspect, a method for controlling a system including an electroporation catheter, a pulse generator coupled to the electroporation catheter, and a computing device coupled to the pulse generator is provided. The electroporation catheter includes a distal end, a proximal end, a plurality of splines extending from the distal end to the proximal end, and a plurality of electrodes arranged on the plurality of splines and defining at least one quadripolar array, each quadripolar array defined by four electrodes of the plurality of electrodes. The method includes selectively energizing, using the computing device and the pulse generator, the electrodes defining the at least one quadripolar array according to a first energization pattern, and selectively energizing, using the computing device and the pulse generator, the electrodes defining the at least one quadripolar array according to a second energization pattern, wherein the first and second energization patterns are different from one another. 
     In yet another aspect, a system is provided. The system includes an electroporation catheter including a distal end, a proximal end, a plurality of splines extending from the distal end to the proximal end, and a plurality of electrodes arranged on the plurality of splines and defining at least one quadripolar array, each quadripolar array defined by four electrodes of the plurality of electrodes. The system further includes a pulse generator coupled to the electroporation catheter, and a computing device coupled to the pulse generator, the computing device operable to control the pulse generator to selectively energize the electrodes defining the at least one quadripolar array according to a first energization pattern, and selectively energize the electrodes defining the at least one quadripolar array according to a second energization pattern, wherein the first and second energization patterns are different from one another. 
     The foregoing and other aspects, features, details, utilities and advantages of the present disclosure will be apparent from reading the following description and claims, and from reviewing the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic and block diagram view of a system for electroporation therapy. 
         FIG.  2    is a side view of one embodiment of a grid assembly that may be used with the catheter shown in  FIG.  1   . 
         FIG.  3    is an image showing the grid assembly of  FIG.  2    positioned within a patient&#39;s heart. 
         FIGS.  4 A- 4 C  illustrate a plurality of example energization patterns using the grid assembly shown in  FIG.  2   . 
         FIGS.  5 A  illustrates an example energization pattern using the grid assembly shown in  FIG.  2   . 
         FIG.  5 B  is a diagram simulating an electric field strength for the energization pattern shown in  FIG.  5 A . 
         FIG.  5 C  is a diagram simulating a potential field for the energization pattern shown in  FIG.  5 A . 
         FIG.  6    is a diagram simulating an electric field strength for an energization pattern that corresponds to the energization pattern  FIG.  4 B . 
         FIG.  7    is a diagram simulating an electric field strength for an energization pattern that corresponds to the energization pattern  FIG.  4 C . 
         FIGS.  8 A- 8 C  are representations of the diagram shown in  FIGS.  5 B,  6 , and  7   . 
         FIG.  9    is a diagram showing the representations of  FIGS.  8 A- 8 C  superimposed on one another. 
         FIG.  10 A- 10 D  illustrate a plurality of additional example energization patterns using the grid assembly shown in  FIG.  2   . 
         FIGS.  11 A and  11 B  are perspective views of one embodiment of a basket assembly that may be used with the catheter shown in  FIG.  1   . 
         FIGS.  12 A- 12 C  are views of another embodiment of a basket assembly that may be used with the catheter shown in  FIG.  1   . 
         FIG.  13    is a schematic diagram of one embodiment of a switching architecture that may be used with the system shown in  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The systems and methods described herein are directed to an apparatus for controlling an electroporation catheter. The electroporation catheter includes a distal end, a proximal end, a plurality of splines extending from the distal end to the proximal end, and a plurality of electrodes arranged on the plurality of splines and defining at least one quadripolar array, each quadripolar array defined by four electrodes of the plurality of electrodes. The apparatus includes a pulse generator coupled to the electroporation catheter, and a computing device coupled to the pulse generator, the computing device operable to control the pulse generator to selectively energize the electrodes defining the at least one quadripolar array according to a first energization pattern, and selectively energize the electrodes defining the at least one quadripolar array according to a second energization pattern, wherein the first and second energization patterns are different from one another. 
       FIG.  1    is a schematic and block diagram view of a system  10  for electroporation therapy. In general, system  10  includes a catheter electrode assembly  12  disposed at a distal end  48  of a catheter  14 . As used herein, “proximal” refers to a direction toward the end of the catheter near the clinician and “distal” refers to a direction away from the clinician and (generally) inside the body of a patient. The electrode assembly includes one or more individual, electrically-isolated electrode elements. Each electrode element, also referred to herein as a catheter electrode, is individually wired such that it can be selectively paired or combined with any other electrode element to act as a bipolar or a multi-polar electrode. 
     System  10  may be used for irreversible electroporation (IRE) to destroy tissue. In particular, system  10  may be used for electroporation-induced therapy that includes delivering electrical current in such a manner as to directly cause an irreversible loss of plasma membrane (cell wall) integrity leading to its breakdown and cell necrosis. This mechanism of cell death may be viewed as an “outside-in” process, meaning that the disruption of the outside wall of the cell causes detrimental effects to the inside of the cell. Typically, for classical plasma membrane electroporation, electric current is delivered as a pulsed electric field in the form of short-duration pulses (e.g., having a 100 nanosecond (ns) to 100 microsecond (μs) duration) between closely spaced electrodes capable of delivering an electric field strength of about 0.1 to 10.0 kilovolts/centimeter (kV/cm). System  10  may be used with a grid catheter such as that depicted in  FIG.  2   , for example, for high output (e.g., high voltage and/or high current) electroporation procedures. Alternatively, system  10  may be used with any suitable catheter configuration. 
     In one embodiment, all electrodes of the catheter deliver an electric current simultaneously. Alternatively, in other embodiments, stimulation is delivered selectively (e.g., between pairs of electrodes) on the catheter. For example, in some embodiments, the catheter includes a plurality of splines, each spline including a plurality of electrodes. In such embodiments, electrodes on one spline may be selectively activated, and electrodes on an adjacent (or other) spline function as an energy return (or sink). Further, in the embodiments described herein, the electrodes may be switchable between being connected to a 3D mapping system and being connected to an electroporation generator. 
     Irreversible electroporation through a multi-electrode catheter may enable pulmonary vein isolation in as few as one shock per vein, which may produce much shorter procedure times compared to sequentially positioning a radiofrequency (RF) ablation tip around a vein. 
     It should be understood that while the energization strategies are described as involving DC pulses, embodiments may use variations and remain within the spirit and scope of the disclosure. For example, exponentially-decaying pulses, exponentially-increasing pulses, and combinations may be used. 
     Further, it should be understood that the mechanism of cell destruction in electroporation is not primarily due to heating effects, but rather to cell membrane disruption through application of a high-voltage electric field. Thus, electroporation may avoid some possible thermal effects that may occur when using radio frequency (RF) energy. This “cold therapy” thus has desirable characteristics. 
     With this background, and now referring again to  FIG.  1   , system  10  includes a catheter electrode assembly  12  including at least one catheter electrode. Electrode assembly  12  is incorporated as part of a medical device such as a catheter  14  for electroporation therapy of tissue  16  in a body  17  of a patient. In the illustrative embodiment, tissue  16  includes heart or cardiac tissue. It should be understood, however, that embodiments may be used to conduct electroporation therapy with respect to a variety of other body tissues. 
       FIG.  1    further shows a plurality of return electrodes designated  18 ,  20 , and  21 , which are diagrammatic of the body connections that may be used by the various sub-systems included in overall system  10 , such as an electroporation generator  26 , an electrophysiology (EP) monitor such as an ECG monitor  28 , and a localization and navigation system  30  for visualization, mapping, and navigation of internal body structures. In the illustrated embodiment, return electrodes  18 ,  20 , and  21  are patch electrodes. It should be understood that the illustration of a single patch electrode is diagrammatic only (for clarity) and that such sub-systems to which these patch electrodes are connected may, and typically will, include more than one patch (body surface) electrode, and may include split patch electrodes (as described herein). In other embodiments, return electrodes  18 ,  20 , and  21  may be any other type of electrode suitable for use as a return electrode including, for example, one or more catheter electrodes. Return electrodes that are catheter electrodes may be part of electrode assembly  12  or part of a separate catheter or device (not shown). System  10  may further include a main computer system  32  (including an electronic control unit  50  and data storage-memory  52 ), which may be integrated with localization and navigation system  30  in certain embodiments. System  32  may further include conventional interface components, such as various user input/output mechanisms  34 A and a display  34 B, among other components. 
     Electroporation generator  26  is configured to energize the electrode element(s) in accordance with an electroporation energization strategy, which may be predetermined or may be user-selectable. For electroporation-induced primary necrosis therapy, generator  26  may be configured to produce an electric current that is delivered via electrode assembly  12  as a pulsed electric field in the form of short-duration DC pulses (e.g., a nanoseconds to several milliseconds duration, or any duration suitable for electroporation) between closely spaced electrodes capable of delivering an electric field strength (i.e., at the tissue site) of about 0.1 to 1.0 kV/cm. The amplitude and pulse duration needed for irreversible electroporation are inversely related. 
     Electroporation generator  26 , sometimes also referred to herein as a DC energy source, is a biphasic electroporation generator  26  configured to generate a series of DC energy pulses that all produce current in two directions. In other embodiments, electroporation generator is a monophasic or polyphasic electroporation generator. In some embodiments, electroporation generator  26  is configured to output energy in DC pulses at selectable energy levels, such as fifty joules, one hundred joules, two hundred joules, and the like. Other embodiments may have more or fewer energy settings and the values of the available setting may be the same or different. For successful electroporation, some embodiments utilize the two hundred joule output level. For example, electroporation generator  26  may output a DC pulse having a peak magnitude from about 300 Volts (V) to about 3,200 V at the two hundred joule output level. Other embodiments may output any other suitable positive or negative voltage. 
     In some embodiments, a variable impedance  27  allows the impedance of system  10  to be varied to limit arcing. Moreover, variable impedance  27  may be used to change one or more characteristics, such as amplitude, duration, pulse shape, and the like, of an output of electroporation generator  26 . Although illustrated as a separate component, variable impedance  27  may be incorporated in catheter  14  or generator  26 . 
     With continued reference to  FIG.  1   , as noted above, catheter  14  may include functionality for electroporation and in certain embodiments also additional ablation functions (e.g., RF ablation). It should be understood, however, that in those embodiments, variations are possible as to the type of ablation energy provided (e.g., cryoablation, ultrasound, etc.). 
     In the illustrative embodiment, catheter  14  includes a cable connector or interface  40 , a handle  42 , and a shaft  44  having a proximal end  46  and a distal  48  end. Catheter  14  may also include other conventional components not illustrated herein such as a temperature sensor, additional electrodes, and corresponding conductors or leads. Connector  40  provides mechanical and electrical connection(s) for cable  56  extending from generator  26 . Connector  40  may include conventional components known in the art and as shown is disposed at the proximal end of catheter  14 . 
     Handle  42  provides a location for the clinician to hold catheter  14  and may further provide means for steering or the guiding shaft  44  within body  17 . For example, handle  42  may include means to change the length of a guidewire extending through catheter  14  to distal end  48  of shaft  44  or means to steer shaft  44 . Moreover, in some embodiments, handle  42  may be configured to vary the shape, size, and/or orientation of a portion of the catheter, and it will be understood that the construction of handle  42  may vary. In an alternate embodiment, catheter  14  may be robotically driven or controlled. Accordingly, rather than a clinician manipulating a handle to advance/retract and/or steer or guide catheter  14  (and shaft  44  thereof in particular), a robot is used to manipulate catheter  14 . Shaft  44  is an elongated, tubular, flexible member configured for movement within body  17 . Shaft  44  is configured to support electrode assembly  12  as well as contain associated conductors, and possibly additional electronics used for signal processing or conditioning. Shaft  44  may also permit transport, delivery and/or removal of fluids (including irrigation fluids and bodily fluids), medicines, and/or surgical tools or instruments. Shaft  44  may be made from conventional materials such as polyurethane and defines one or more lumens configured to house and/or transport electrical conductors, fluids or surgical tools, as described herein. Shaft  44  may be introduced into a blood vessel or other structure within body  17  through a conventional introducer. Shaft  44  may then be advanced/retracted and/or steered or guided through body  17  to a desired location such as the site of tissue  16 , including through the use of guidewires or other means known in the art. 
     In some embodiments, catheter  14  is a grid catheter having catheter electrodes (not shown in  FIG.  1   ) distributed at the distal end of shaft  44 . In some embodiments, catheter  14  has sixteen catheter electrodes. In other embodiments, catheter  14  includes ten catheter electrodes, twenty catheter electrodes, or any other suitable number of electrodes for performing electroporation. In some embodiments, the catheter electrodes are ring electrodes, such as platinum ring electrodes. Alternatively, the catheter electrodes may be any other suitable type of electrodes, such as partial ring electrodes or electrodes printed on a flex material. In various embodiments, the catheter electrodes have lengths of 1.0 mm, 2.0 mm, 2.5 mm, and/or any other suitable length for electroporation. 
     Localization and navigation system  30  may be provided for visualization, mapping and navigation of internal body structures. Localization and navigation system  30  may include conventional apparatus known generally in the art. For example, localization and navigation system  30  may be substantially similar to the EnSite Precision™ System, commercially available from Abbott Laboratories, and as generally shown in commonly assigned U.S. Pat. No. 7,263,397 titled “Method and Apparatus for Catheter Navigation and Location and Mapping in the Heart”, the entire disclosure of which is incorporated herein by reference. In another example, localization and navigation system  30  may be substantially similar to the EnSite X™ System, as generally shown in U.S. Pat. App. Pub. No. 2020/0138334 titled “Method for Medical Device Localization Based on Magnetic and Impedance Sensors”, the entire disclosure of which is incorporated herein by reference. It should be understood, however, that localization and navigation system  30  is an example only, and is not limiting in nature. Other technologies for locating/navigating a catheter in space (and for visualization) are known, including for example, the CARTO navigation and location system of Biosense Webster, Inc., the Rhythmia® system of Boston Scientific Scimed, Inc., the KODEX® system of Koninklijke Philips N. V., the AURORA® system of Northern Digital Inc., commonly available fluoroscopy systems, or a magnetic location system such as the gMPS system from Mediguide Ltd. In this regard, some of the localization, navigation and/or visualization system would involve a sensor be provided for producing signals indicative of catheter location information, and may include, for example one or more electrodes in the case of an impedance-based localization system, or alternatively, one or more coils (i.e., wire windings) configured to detect one or more characteristics of a magnetic field, for example in the case of a magnetic-field based localization system. As yet another example, system  10  may utilize a combination electric field-based and magnetic field-based system as generally shown with reference to U.S. Pat. No. 7,536,218 entitled “Hybrid Magnetic-Based and Impedance Based Position Sensing,” the disclosure of which is incorporated herein by reference in its entirety. 
     In at least some of the embodiments described herein, a catheter includes an array of electrodes that define one or more pixels. The array of electrodes may be arranged, for example, on a grid catheter (e.g., as shown in  FIGS.  2 - 5 B ) or on a basket catheter (e.g., as shown in  FIGS.  6 A- 7 C ). Alternatively, the array of electrodes may be arranged on any suitable catheter assembly. 
       FIG.  2    is a side view of one embodiment of a grid assembly  200  that may be used with catheter  14  in system  10 . Those of skill in the art will appreciate that, in other embodiments, any suitable catheter may be used. In addition, those of skill in the art will appreciate that, although the embodiments disclosed herein are discussed in the context of a grid catheter, the methods and systems described herein may be implemented using any suitable catheter (e.g., basket catheters, etc.). As shown in  FIG.  2   , grid assembly  200  is coupled to a distal section  202  of shaft  44 . 
     Grid assembly  200  includes a plurality of splines  204  extending from a proximal end  206  to a distal end  208 . Each spline  204  includes a plurality of electrodes  210 . In the embodiment shown in  FIG.  2   , grid assembly  200  includes four splines  204 , and each spline  204  includes four electrodes  210 , such that electrodes  210  form a grid configuration. Accordingly, grid assembly  200  provides a four by four grid of electrodes  210 . In one embodiment, the spacing between each pair of adjacent electrodes  210  is approximately 4 millimeters (mm) such that the dimensions of the grid of electrodes  210  are approximately 12 mm×12 mm. Alternatively, grid assembly  200  may include any suitable number of splines  204 , any suitable number of electrodes  210 , and/or any suitable arrangement of electrodes  210 . For example, in some embodiments, the spacing between each pair of adjacent electrodes is approximately 2 millimeters (mm). Further, in some embodiments, grid assembly  200  may include, for example, fifty-six electrodes arranged in a 7×8 grid. 
     Using grid assembly  200 , lesions may be generated at individual electrodes  210  using a monopolar approach (e.g., by applying a voltage between individual electrodes  210  and a return patch), or generated between pairs of electrodes  210  using a bipolar approach. Lesions may be generating within an anatomy by selectively energizing electrodes in a particular configuration and/or pattern (e.g., including energizing individual electrodes  210  independent of one another, or energizing multiple electrodes  210  simultaneously). 
       FIG.  3    is an image  300  showing grid assembly  200  positioned within a left atrium  302  of a patient&#39;s heart. As shown in  FIG.  3   , grid assembly  200  covers a relatively wide area of the heart. The width of this area is generally larger than that needed to perform pulmonary vein isolation (PVI). Accordingly, to perform a successful PVI ablation, it may be possible to only energize a portion of grid assembly  200 . 
     Using bipolar delivery patterns, a plurality of different energization patterns are available using grid assembly  200 . For example, each electrode  210  may selectively function as a positive electrode, a negative electrode, or an inactive electrode. If all electrodes  210  are energized at the same polarity, then an indifferent electrode (e.g., one of surface electrodes  18 ,  20 , and  21  (shown in  FIG.  1   )) functions as a return electrode. If some electrodes  210  are energized at a positive polarity, and other electrodes  210  are energized at a negative polarity, no indifferent electrode is required, as there are current paths between electrodes  210 . 
     In the embodiments described herein, energy is delivered uniformly using quadripolar arrays (i.e., 2×2 arrays) of electrodes  210 . In this embodiment, grid assembly  200  includes four quadripolar arrays  220 , as shown in  FIG.  2   . As will be appreciated by those of skill in the art, a plurality of different energization schemes are possible for a quadripolar array  220  of electrodes  210 . For example, in some embodiments, different quadripolar arrays  220  may share at least one electrode  210 . 
     For example,  FIGS.  4 A,  4 B, and  4 C  illustrate a first energization pattern  402 , a second energization pattern  404 , and a third energization pattern  406 , respectively. 
     In first energization pattern  402 , a first electrode  410  is positive, a second electrode  412  is negative, a third electrode  414  is negative, and a fourth electrode  416  is positive. In second energization pattern  404 , first electrode  410  is positive, second electrode  412  is positive, third electrode  414  is negative, and fourth electrode  416  is negative. In third energization pattern  406 , first electrode  410  is positive, second electrode  412  is negative, third electrode  414  is positive, and fourth electrode  416  is negative. 
     Those of skill in the art will appreciate that other energization patterns are possible. Notably, other energization patterns are redundant to those shown in  FIGS.  4 A- 4 C  (i.e., with the polarity of each electrode  210  switched), degenerate (i.e., with all electrodes  210  having the same polarity), or unequal (i.e., having a different number of positive and negative electrodes  210 ). 
       FIG.  5 A  is an example energization pattern  502  for all sixteen electrodes  210  of catheter assembly  200 . Specifically, energization pattern  502  corresponds to each quadripolar array  220  using first energization pattern  402  (shown in  FIG.  4 A ). 
       FIG.  5 B  is a diagram  510  simulating an electric field strength (e.g., in Volts/centimeter (V/cm)) when energization pattern  502  is implemented. As shown in diagram  510 , the electric field strength is highest around each electrode  210 . In contrast, the electric field strength is low at low field spots  512 . Low field spots  512  are generally located at a midpoint between adjacent electrodes  210  having the same polarity. Accordingly, with energization pattern  502 , low field spots  512  occur at approximately the center of each quadripolar array  220 . The low electric field strength occurs because the gradient of the electric field is at or near zero at low field spots  512 . 
       FIG.  5 C  is a diagram  520  simulating the potential field when energization pattern  502  is implemented. As shown in  FIG.  5 C , saddle points  522  correspond to the location of low field spots  512  in diagram  510 . At saddle points  522 , there is no slope, and thus no gradient (i.e., corresponding to zero electric field strength). 
     Notably, different energization patterns generally result in different low field spots. For example,  FIG.  6    is a diagram  600  simulating an electric field strength for an energization pattern that corresponds to using second energization pattern  404  (shown in  FIG.  4 B ) for each quadripolar array  220 . Again, the electric field strength is highest around each electrode  210 . However, in diagram  600 , low field spots  602  occur between electrodes  210  that are located in the same row. Accordingly, low field spots  602  are located at different positions than low field spots  512  (shown in  FIG.  5 B ). Further, in diagram  600 , at the locations corresponding to low field spots  512  from diagram  510 , the electric field strength is relatively high. 
     As another example,  FIG.  7    is a diagram  700  simulating an electric field strength for an energization pattern that corresponds to using third energization pattern  406  (shown in  FIG.  4 C ) for each quadripolar array  220 . In diagram  700 , low field spots  702  occur between electrodes  210  that are located in the same column. Again, low field spots  702  are located at different positions that low field spots  512  (shown in  FIG.  5 B ) and low field spots  602  (shown in  FIG.  6   ). Further, in diagram  700 , at the locations corresponding to low field spots  512  from diagram  510  and the locations corresponding to low field spots  602  from diagram  600 , the electric field strength is relatively high. 
     Accordingly, by applying combinations of energization patterns, a relatively uniform electric field strength can be achieved (as the low field spots in a particular energization pattern will be compensated for in other energization patterns). Thus, by cycling through multiple energization patterns, the overall ablation area generated will be relatively uniform. 
     For example,  FIG.  8 A  is a representation  802  of diagram  510  (shown in  FIG.  5 B ),  FIG.  8 B  is a representation  804  of diagram  600  (shown in  FIG.  6   ), and  FIG.  8 C  is a representation  806  of diagram  700  (shown in  FIG.  7   ).  FIG.  9    is a diagram  900  showing representations  802 ,  804 , and  806  superimposed on one another. As demonstrated by diagram  900 , when representations  802 ,  804 , and  806  are superimposed on one another (corresponds to cycling through all three energization patterns), the ablation area generated is relatively uniform, with holes in one energization pattern being filled by other energization patterns. 
     Those of skill in the art will appreciate that other energization patterns (i.e., other than those shown in  FIGS.  4 A- 4 C ) may be used for each quadripolar array  220 . For example,  FIGS.  10 A- 10 D  illustrate a fourth energization pattern  1002 , a fifth energization pattern  1004 , a sixth energization pattern  1006 , and a seventh energization pattern  1008 . These energization patterns  1002 ,  1004 ,  1006 , and  1008  are unbalanced (i.e., with an unequal number of positive and negative electrodes). 
     In fourth energization pattern  1002 , a first electrode  1010  is negative, a second electrode  1012  is negative, a third electrode  1014  is negative, and a fourth electrode  1016  is positive. In fifth energization pattern  1004 , first electrode  1010  is negative, second electrode  1012  is negative, third electrode  1014  is positive, and fourth electrode  1016  is negative. In sixth energization pattern  1006 , first electrode  1010  is negative, second electrode  1012  is positive, third electrode  1014  is negative, and fourth electrode  1016  is negative. In seventh energization pattern  1008 , first electrode  1010  is negative, second electrode  1012  is positive, third electrode  1014  is positive, and fourth electrode  1016  is positive. 
     Although the embodiments described herein are discussed in the context of IRE/PFA, those of skill in the art will appreciate that the methods and systems described herein may also be utilized for RF ablation applications. 
     Further, those of skill in the art will appreciate that the techniques described herein may be implemented with catheter configurations other than grid assembly  200 . For example,  FIGS.  11 A and  11 B  are perspective views of one embodiment of a basket assembly  1100  including a plurality of splines  1102  that form a basket, each spline including a plurality of electrodes  1104 . Similar to grid assembly  200 , quadripolar arrays can be defined by sets of electrodes  1104 . For example, a first electrode  1110 , second electrode  1112 , third electrode  1114 , and fourth electrode  1116  define a quadripolar array  1120  (shown in  FIG.  11 B ). Other catheter configurations may also utilize similar implementations. 
       FIGS.  12 A- 12 C  are views of another embodiment of a basket assembly  1250  that may be used with the electrode energization techniques described herein. Specifically,  FIG.  12 A  is a perspective view of basket assembly  1250 , and  FIGS.  12 B and  12 C  are side views of basket assembly  1250  positioned within a pulmonary vein  1252 . 
     Basket assembly  1250  includes a plurality of splines  1254  that form a basket. In this embodiment, each spline  1254  has a generally sigmoidal shape. The sigmoidal shape of splines  1254  results in adjacent splines  1254  maintaining roughly the same distance between one another along the length of splines  1254 , which may improve lesion quality. In this embodiment, basket assembly  1250  includes eight splines  1254 . Alternatively, basket assembly  1250  may include any suitable number of splines  1254 . 
     As shown in  FIG.  12 A , basket assembly  1250  may include a selectively inflatable balloon  1256  positioned in an interior of the basket. Balloon  1256  may facilitate supporting splines  1254  (e.g., when splines are pressed against tissue). In some embodiments, balloon  1256  is omitted. Additional detail regarding basket assemblies with sigmoidal-shaped splines may be found in International Application No. PCT/US20/36410 entitled ELECTRODE BASKET HAVING HIGH-DENSITY CIRCUMFERENTIAL BAND OF ELECTRODES, filed on Jun. 5, 2020, and U.S. Provisional Patent Application No. 62/861,135, entitled ELECTRODE BASKET HAVING HIGH-DENSITY CIRCUMFERENTIAL BAND OF ELECTRODES, filed on Jun. 13, 2019, the disclosures of which are incorporated herein by reference in their entirety. 
     Each spline  1254  include at least one electrode  1270  that is selectively energizable using the systems and methods disclosed herein. For example,  FIG.  7 B  shows one elongated electrode  1272  on each spline  1254 , whereas  FIG.  7 C  shows a plurality of individual electrodes  1274  on each spline  1254 . Electrodes  1270  are generally located on a distal portion of basket assembly  1250 , to facilitate contacting tissue of pulmonary vein  1252 . Alternatively, any suitable configuration of electrodes  1270  may be used. Similar to the embodiments described previously, sets of individual electrodes  1274  on basket assembly  1250  may define quadripolar arrays, and energization schemes similar to those described above may be suitably implemented. 
     As described herein, electrodes on a catheter are selectively energized to generate different patterns.  FIG.  13    is a schematic diagram of one embodiment of a switching architecture  1300  that may be used to selectively energize electrodes on a catheter  1302 . Specifically, switching architecture includes a catheter  1302 , a pulse source  1304 , and a switching unit  1306  coupled between catheter  1302  and pulse source  1304 . 
     Pulse source  1304  generates energy pulses to be applied by the electrodes (not shown) on catheter  1302 . Further, switching unit  1306  includes a plurality of switching circuits  1310  for selectively delivering energy pulses from pulse source  1304  to the electrodes. In this embodiment, switching unit  1306  includes a switching circuit  1310  (and corresponding channel) for each electrode. Each switching circuit  1310  receives an energy pulse from pulse source  1304  and, depending on a configuration of switches within switching circuit  1310 , delivers a positive pulse, a negative pulse, or no pulse to the corresponding electrode. Accordingly, by controlling switching circuits  1310 , the electrodes on catheter  1302  are selectively energizable. 
     The embodiments described herein are directed to an apparatus for controlling an electroporation catheter. The electroporation catheter includes a distal end, a proximal end, a plurality of splines extending from the distal end to the proximal end, and a plurality of electrodes arranged on the plurality of splines and defining at least one quadripolar array, each quadripolar array defined by four electrodes of the plurality of electrodes. The apparatus includes a pulse generator coupled to the electroporation catheter, and a computing device coupled to the pulse generator, the computing device operable to control the pulse generator to selectively energize the electrodes defining the at least one quadripolar array according to a first energization pattern, and selectively energize the electrodes defining the at least one quadripolar array according to a second energization pattern, wherein the first and second energization patterns are different from one another. 
     Although certain embodiments of this disclosure have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this disclosure. All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the present disclosure, and do not create limitations, particularly as to the position, orientation, or use of the disclosure. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the disclosure as defined in the appended claims. 
     When introducing elements of the present disclosure or the preferred embodiment(s) thereof, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     As various changes could be made in the above constructions without departing from the scope of the disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.