Patent Publication Number: US-2022226041-A1

Title: Electrode assembly including inner and outer baskets and methods of forming same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional patent application Ser. No. 62/842,654, filed May 3, 2019, the disclosure of which is incorporated herein in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates to ablating tissue, and more particularly, this disclosure relates to an electrode assembly including inner and outer baskets for ablating tissue. 
     BACKGROUND 
     Catheter systems are well known in the art for use in medical procedures, such as diagnostic, therapeutic and ablative procedures. Typical catheter systems generally include an elongate catheter extending from a handle. A physician manipulates the catheter through the patient&#39;s vasculature to an intended site within the patient. The catheter typically carries one or more working components, such as electrodes and thermocouples, or other diagnostic, therapeutic, or ablative devices for carrying out the procedures. One or more controls or actuators may be provided on the handle for selectively adjusting one or more characteristics of the working components. 
     One particular example of a multi-electrode catheter system is an ablative catheter system in which the working component is a multi-electrode assembly carried at the distal end of a flexible catheter. A control wire generally extends within the catheter from the multi-electrode assembly to the handle to operatively connect the multi-electrode assembly to an actuator on the handle. Manipulating the actuator acts on the control wire to configure the multi-electrode assembly into a desired configuration for carrying out the ablative procedure. For example, in one such ablative catheter system made by Abbott Laboratories under the trade name EnligHTN, the multi-electrode assembly is an electrode assembly in the general form of an electrode basket. The electrode basket generally includes a number of struts, wherein each strut may include one or two electrodes. In at least some known catheter systems, however, the electrode basket is relatively long, and different struts may expand and collapse at different times, and by different amounts. The electrodes may not contact the tissue as desired, which may interfere with ablation processes. 
     Moreover, for “one-shot” ablation procedures, which reduce the number of ablations needed and therefore reduce an overall procedure duration, a complex current is applied to the multi-electrode ablation assembly. The spacing between electrodes on the multi-electrode assembly—specifically between cathode electrodes and anode electrodes, or between the multi-electrode assembly and an external “patch” electrode—may induce skeletal “jumping,” or spasms in the patient tissue, during such one-shot ablation procedures. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     In one embodiment, the present disclosure is directed to an electrode assembly for a catheter system. The electrode assembly includes an inner electrode basket including a first proximal end, a first distal end, and a first plurality of struts extending between the first proximal end and the first distal end. The electrode assembly also includes an outer electrode basket including a second proximal end, a second distal end, and a second plurality of struts extending between the second proximal end and the second distal end. The first proximal end is positioned within and coaxial with the second proximal end, and the first distal end is positioned within and coaxial with the second distal end such that the inner electrode basket is positioned within and coaxial with the outer electrode basket. The inner electrode basket is angularly offset from the outer electrode basket such that the first plurality of struts and the second plurality of struts alternate about a circumference of the electrode assembly. 
     In another embodiment, the present disclosure is directed to a method of forming an electrode assembly. The method includes forming an inner electrode basket including a first proximal end, a first distal end, and a first plurality of struts extending between the first proximal end and the first distal end. The method also includes forming an outer electrode basket including a second proximal end, a second distal end, and a second plurality of struts extending between the second proximal end and the second distal end. The method further includes positioning the first proximal end within and coaxial with the second proximal end, positioning the first distal end within and coaxial with the second distal end, and orienting the inner electrode basket relative to the outer electrode basket such that the first plurality of struts and the second plurality of struts alternate about a circumference of the electrode assembly. 
     In a further embodiment, the present disclosure is directed to a catheter system including a flexible catheter shaft, a handle coupled to a proximal end of the catheter shaft, and an electrode assembly sized for advancement through the catheter shaft to a distal end of the catheter shaft. The electrode assembly includes an inner electrode basket including a first proximal end, a first distal end, and a first plurality of struts extending between the first proximal end and the first distal end. The electrode assembly also includes an outer electrode basket including a second proximal end, a second distal end, and a second plurality of struts extending between the second proximal end and the second distal end. The first proximal end is positioned within and coaxial with the second proximal end, and the first distal end is positioned within and coaxial with the second distal end such that the inner electrode basket is positioned within and coaxial with the outer electrode basket. The inner electrode basket is angularly offset from the outer electrode basket such that the first plurality of struts and the second plurality of struts alternate about a circumference of the electrode assembly. 
     In yet another embodiment, the present disclosure is directed to a method of performing an ablation procedure. The method includes advancing an electrode assembly to a target location. The electrode assembly includes (i) an inner electrode basket including a first proximal end, a first distal end, and a first plurality of struts extending between the first proximal end and the first distal end, and (ii) an outer electrode basket including a second proximal end, a second distal end, and a second plurality of struts extending between the second proximal end and the second distal end, wherein the first proximal end is positioned within and coaxial with the second proximal end and the first distal end is positioned within and coaxial with the second distal end such that the inner electrode basket is positioned within and coaxial with the outer electrode basket. The inner electrode basket is angularly offset from the outer electrode basket such that the first plurality of struts and the second plurality of struts alternate about a circumference of the electrode assembly. The method also includes contacting tissue at the target location with the electrode assembly, and energizing the electrode assembly by energizing the inner electrode basket as one of a cathode with a positive charge or an anode with a negative charge, and energizing the outer electrode basket as the other of the cathode or the anode, such that the first plurality of struts and the second plurality of struts alternate charge about the circumference of the electrode assembly and ablate the tissue in a circumferential pattern. 
     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 perspective view of one embodiment of a catheter system including a handle, a catheter, and an electrode assembly. 
         FIGS. 2-4  depict one example embodiment of the electrode assembly shown in  FIG. 1 , including an inner electrode basket and an outer electrode basket. 
         FIG. 5  is a perspective view of a first embodiment of an inner electrode basket. 
         FIG. 6  is a perspective view of a first embodiment of an outer electrode basket. 
         FIG. 7  is a side view of a second embodiment of an inner electrode basket. 
         FIG. 8  is a side view of a second embodiment of an outer electrode basket. 
         FIG. 9  is a perspective view of the electrode assembly of  FIG. 2  illustrating the electrode assembly during a tissue ablation procedure. 
         FIGS. 10 and 11  illustrate the electrode assembly shown in  FIGS. 2-4  including electrically insulating material to insulate the inner electrode basket from the outer electrode basket. 
         FIG. 12  is another perspective view of the electrode assembly shown in  FIGS. 2-4  with the outer electrode basket depicted in phantom. 
         FIG. 13  is a side view of another embodiment of an electrode assembly suitable for use with the catheter system of  FIG. 1 . 
         FIGS. 14-16  illustrate the electrode assembly of  FIGS. 2-4  being deployed from the catheter shown in  FIG. 1 , from a collapsed configuration to an expanded configuration. 
         FIGS. 17 and 18  illustrate an alternative embodiment of an electrode assembly. 
         FIG. 19  is a simplified process diagram for a method of forming an electrode assembly. 
         FIG. 20  is a simplified process diagram for a method of performing an ablation procedure using an electrode assembly. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The disclosure provides systems and methods for electrode assemblies including an inner basket and an outer basket. Each basket includes a plurality of struts configured to be energized. One of the inner and the outer baskets functions as an anode or negative (−) electrode, and the other of the inner and outer baskets functions as a cathode or positive (+) electrode. When the electrode assembly is constructed, the struts of the inner and outer basket alternate with one another (e.g., in a +−+− pattern). Accordingly, when the electrode assembly is fully energized and advanced into contact with tissue, the electrode assembly functions as a plurality of bipolar electrode pairs (e.g., each pair of adjacent (+−) struts), and provides a full 360° circumferential ablation of the contacted tissue. 
     The electrode assembly described herein is particularly suitable for “one-shot” ablation procedures, also referred to as “irreversible electroporation (IRE)” procedures, in which it is desirable to complete the ablation procedure in a single ablation event (or in very few ablation events). Specifically, because the electrode assembly enables 360°, fully circumferential tissue contact, an entire circumferential ablation can be completed in a single ablation event (or in very few ablation events). 
     The electrode assembly may also reduce the occurrence and/or magnitude of skeletal jumping in the patient&#39;s tissue. Specifically, the spacing between electrodes is reduced by effectively doubling the number of struts (and therefore the number of adjacent electrodes). In addition, different currents may be applied to the electrode assembly to reduce the occurrence and/or magnitude of skeletal jumping in the patient&#39;s tissue. 
     Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views,  FIG. 1  illustrates a catheter system  100 . Catheter system  100  includes a flexible catheter  102 , a handle  104  to which flexible catheter  102  is connected, and a conductor assembly  106  for electrically connecting catheter system  100  to a suitable power supply, such as a generator  108 . 
     As one example, catheter system  100  illustrated and described herein is suitably constructed for use as an ablation system, such as a renal or heart ablation system, for ablation of tissue. General operation of a renal denervation system is known to those of skill in the art and is not described further herein except to the extent necessary to describe the present embodiments. In the exemplary embodiment, “tissue” includes heart or cardiac tissue within a human body. It should be understood, however, that catheter system  100  may find application in connection with a variety of other tissues within human and non-human bodies, and therefore, the present disclosure is not meant to be limited to the use of catheter system  100  in connection with only cardiac tissue and/or human bodies. 
     It is also understood that catheter system  100  may be used for any other suitable treatment or purpose without departing from the scope of this disclosure, such as mapping procedures. In such embodiments, catheter system  100  may include a display device (not shown) for visualization, navigation, and/or mapping of internal body structures within the patient. 
     Additionally, while catheter system  100  is illustrated and described herein as including flexible catheter  102 , such as, for example, an electrophysiology catheter, catheter system  100  may further include other components used, for example, to guide flexible catheter  102  into the patient—such as, without limitation, a relatively more rigid guide catheter or sheath (not shown) or guide wire (not shown). 
     Flexible catheter  102  includes an elongate, flexible hollow catheter shaft  110  connected to handle  104  at or near a proximal or rear end  112  of catheter shaft  110 , and an electrode assembly  114  disposed at or near a distal or front end  116  of catheter shaft  110 . Electrode assembly  114  includes a proximal end  118  and a distal end  120 . As used herein, the terms proximal and front, and distal and rear, are used with reference to the orientation of catheter system  100  illustrated in the various drawings and for the purpose of describing the various embodiments set forth herein, and are not intended as limiting the catheter system and related components to having any particular orientation upon assembly or during operation thereof. In particular, the terms proximal and rear refer to a longitudinal position that is relatively nearer to handle  104  while the terms distal and front refer to a longitudinal position that is relatively farther from handle  104 . 
     The illustrated electrode assembly  114  is in the form of what may be referred to as an electrode basket and includes struts  122 . Electrode assembly  114  is configurable between a collapsed configuration (see  FIG. 1 ) for maneuvering and positioning the electrode assembly in the patient&#39;s vasculature, and an expanded configuration (see  FIGS. 2-4 ) for operation of the electrode assembly to perform a desired procedure, such as an ablation procedure. Electrode assembly  114  may be delivered to a target site within the patient in the collapsed configuration within catheter shaft  110 . Handle  104  includes an actuator  124  operatively connected to electrode assembly  114  for selectively configuring electrode assembly  114  between its collapsed and expanded configurations and/or for maneuvering electrode assembly  114  proximally and distally within the patient&#39;s vasculature. Although actuator  124  is embodied as a rotation actuator in the illustrated embodiment, actuator  124  may include, for example, one or more of a slide actuator, a push button, a lever, and/or combinations thereof. In some embodiments, electrode assembly  114  may be selectively adjustable (e.g., using actuator  124 ) between an infinite number of configurations (e.g., degrees of expansion) between its collapsed and expanded configurations. Handle  104  provides a location for a user to hold catheter  102  and provides means for steering or guiding shaft  110  within the patient&#39;s body. In some embodiments, control of catheter  102  may be automated such as by being robotically driven or controlled, or driven and controlled by a magnetic-based guidance system. Accordingly, catheters controlled either manually or automatically are both within the scope of the present disclosure. 
     A control line, such as a suitable cable or pull wire  126  (shown in greater detail in  FIGS. 10 and 11 and 14-16 ) extends from electrode assembly  114  within hollow catheter shaft  110  and into handle  104  for operative connection with actuator  124  to thereby operatively connect actuator  124  with electrode assembly  114 . In some embodiments, two or more pull wires, cables, or other suitable control lines or tubes may be used for selectively configuring electrode assembly  114 . It is also understood that control line  126  may be any suitable control line other than a pull wire, such as a cable, string, tie, compression member or other suitable control to operatively connect electrode assembly  114  to actuator  124 . A suitable electrical wire bundle (not shown) also extends through hollow catheter shaft  110  from handle  104  to electrode assembly  114  to deliver power to, and receive feedback from, electrode assembly  114 , as described further herein. 
     In some embodiments, catheter  102  and/or electrode assembly  114  may further include other conventional components such as, for example and without limitation, steering wires and actuators, irrigation lumens and ports, pressure sensors, contact sensors, temperature sensors, and/or positioning sensors. 
     Turning now to  FIG. 2 , a perspective view of an exemplary electrode assembly  114  is illustrated.  FIGS. 3 and 4  depict a side view and a longitudinal view of electrode assembly  114  (i.e., a view taken along a longitudinal axis  127  of electrode assembly  114 ), respectively. Electrode assembly  114  extends from proximal end  118  to distal end  120  along longitudinal axis  127 , and has an overall assembly length L and an overall assembly diameter D. Assembly length L and assembly diameter D vary as electrode assembly  114  is transitioned between its collapsed configuration and its expanded configuration. More specifically, assembly length L decreases and assembly diameter D increases as electrode assembly  114  is transitioned between its collapsed configuration and its expanded configuration. In the exemplary embodiment, electrode assembly  114  includes two electrode baskets, specifically, an inner basket  204  and an outer basket  304 . Inner basket  204  is shown in greater detail in  FIG. 5 , and outer basket  304  is shown in greater detail in  FIG. 6 . 
     With reference to  FIG. 5 , inner basket  204  extends from a proximal end  208  to a distal end  210 . In the exemplary embodiment, proximal end  208  is generally defined by an annular or tubular proximal end portion or collar  212 , and distal end  210  is generally defined by an annular or tubular distal end portion or collar  214 . Annular proximal end portion  212  is an annular or tubular structure including a wall  216  that extends continuously about a circumference of proximal end  208  and has a diameter d i, p . Wall  216  has a plurality of through-holes  218  defined therein. In the illustrated embodiment, through-holes  218  are arranged in a regular pattern about wall  216 , in a plurality of rows and columns. In other embodiments, wall  216  includes any number of through-holes  218  arranged in any suitable regular and/or irregular pattern. 
     Likewise, annular distal end portion  214  is an annular or tubular structure including a wall  220  that extends continuously about a circumference of distal end  210  and has a diameter d i,d . Diameter d i,d  is the same as diameter d i, p , in the exemplary embodiment. Wall  220  has a plurality of through-holes  222  defined therein. In the illustrated embodiment, through-holes  222  are arranged in a regular pattern about wall  220 , in a plurality of rows and columns. In other embodiments, wall  220  includes any number of through-holes  222  arranged in any suitable regular and/or irregular pattern. 
     When inner basket  204  is coupled to outer basket  304  to form electrode assembly  114 , as described in greater detail herein, proximal end  208  of inner basket  204  (e.g., annular proximal end portion  212 ) partially defines proximal end  118  of electrode assembly  114 . Likewise, when inner basket  204  is coupled to outer basket  304  to form electrode assembly  114 , distal end  210  of inner basket  204  (e.g., annular distal end portion  214 ) partially defines distal end  120  of electrode assembly  114 . 
     Inner basket  204  further includes a plurality of struts  224  that extend from proximal end  208  to distal end  210  of inner basket  204 . Specifically, struts  224  have a strut length L, defined between annular proximal end portion  212  and annular distal end portion  214 . Inner basket  204  may include any number of struts  224 , including at least 8 struts, or at least 10 struts, or at least 12 struts. Struts  224  each have an inner surface  225  (which may also refer generally to an inner surface of inner basket  204 ) and an outer surface  227  (which may also refer generally to an outer surface of inner basket  204 ). As described further herein, struts  224  are formed from a shape memory material such that struts  224  tend to return to a particular shape or profile in the absence of any force thereon. In the illustrated embodiment, struts  224  have a generally arcuate and continuous profile that is symmetrical about longitudinal axis  127  and across a plane (not shown) bisecting inner basket  204 . In particular, the profile of each strut  224  is the same. In alternative embodiments, the profile of struts  224  may vary (e.g., each strut  224  may have a different profile, adjacent struts  224  may alternate between two profiles, etc.). 
     In the expanded configuration, inner basket  204  has a diameter D i . Additionally, in the exemplary embodiment, struts  224  are equally spaced from one another. More specifically, a distance between each pair of adjacent struts  224  is the same. Each strut includes a central portion  228 , a proximal portion  230  that extends between central portion  228  and annular proximal end portion  212 , and a distal portion  232  that extends between central portion  228  and annular distal end portion  214 . Proximal portion  230 , central portion  228 , and distal portion  232  extend continuously from one another, such that strut  224  is continuously curvilinear. In an alternative embodiment, proximal portion  230 , central portion  228 , and/or distal portion  232  are connected to one another via a hinge (e.g., a living hinge). 
     In the illustrated embodiment, the profile of struts  224 —specifically, the profile of struts  224  within central portion  228 —defines a radial maximum or outermost point  234  of each strut  224 . In the illustrated embodiment, each maximum  234  (of each strut  224 ) is the same distance m i  from longitudinal axis  127  when inner basket  204  is in an expanded configuration (corresponding to the expanded configuration of electrode assembly  114 ). Moreover, maximum  234  is located at a center of strut  224 , such that struts  224  are symmetrical across a plane bisecting inner basket  204 . Proximal and distal portions  230 ,  232  extend symmetrically inwardly from central portion  228  as they extend towards proximal and distal ends  208 ,  210 , respectively. Accordingly, inner basket  204  includes a proximal basket half  236  including proximal portions  230  and a proximal section of central portions  228  proximal to maximum  234 , as well as a distal basket half  238  including distal portions  232  and a distal section of central portions  228  distal from maximum  234 . 
     In alternative embodiments, struts  224  may include more than one maximum and/or may include a maximum located elsewhere along strut  224  (e.g., within proximal portion  230  or distal portion  232 , or at another, non-center position within central portion  228 ). In such embodiments, proximal basket half  236  may therefore represent less or more than a “half” of inner basket  204 , and distal basket half  238  may represent less or more than a “half” of inner basket  204 . More particularly, proximal basket half  236  may represent the portion of inner basket  204  proximal to the proximal-most maximum, and distal basket half  238  may represent the portion of inner basket  204  distal to the distal-most maximum (where the proximal-most and distal-most maxima may be the same or different maxima). 
     Another embodiment of inner basket  204  is shown in  FIG. 7 . In the illustrated embodiment, maximum  234  is not at a center of each strut  224 , but rather is distally offset, and inner basket  204  is not symmetrical across a plane  226  bisecting inner basket  204 . In addition, inner basket  204  includes a tab  240  extending from proximal end  208 . Tab  240  enables electrical connection between inner basket  204  and electrical cables (not shown) that provide power to inner basket  204  (e.g., from generator  108 , shown in  FIG. 1 ). Inner basket  204  may include only one tab  240 , a pair of tabs  240 , or additional/alternative tabs and/or suitable electrical connection points. 
     To form inner basket  204 , in one embodiment, a tube (not shown) of suitable material is provided. In the exemplary embodiment, the tube is formed of an electrically conductive shape memory material, such that inner basket  204  is electrically conductive and may be treated to retain a desired shape. Suitable materials may include, for example and without limitation, copper-aluminum-nickel alloys, nickel-titanium (NiTi) alloys, nitinol, alloys including zinc, copper, gold, and/or iron, polymers including any of the above materials, and/or combinations thereof. The tube is cut to a desired length, such as an overall length of inner basket  204  between proximal end  208  and distal end  210 . In some embodiments, the length of the tube further includes a length of one or more tabs  240 . Alternatively, tabs  240  may be coupled to the tube (e.g., by welding, bonding using a conductive adhesive, etc.). 
     Through-holes  218  and  222  are formed in the tube, for example, via laser-cutting, die-cutting, and/or any other suitable method. Subsequently, the tube is slit longitudinally (e.g., parallel to a longitudinal axis thereof) to form struts  224 , for example, via laser-cutting, die-cutting, and/or any other suitable method. This step also defines annular proximal end portion  212  and annular distal end portion  214 , specifically, as the portions of the tube that are not slit. In some embodiments, the tube is slit before the through-holes  218 ,  222  are formed. 
     Thereafter, the tube is positioned about a mandrel and heat-set to define the shape or profile of struts  224 . For example, the mandrel has an outer surface complementary to the desired shape of struts  224  and/or the desired shape of inner basket  204  in the expanded configuration. The resulting inner basket  204  is a unitary, single-piece basket having struts  224  that retain a desired shape or profile (such as that shown in  FIG. 5  and/or  FIG. 7 ) extending between annular proximal end portion  212  and annular distal end portion  214 , having through-holes  218  and  222 , respectively, defined therein. 
     Inner basket  204  may be formed using an alternative method, such as forming struts  224  and attaching annular proximal end portion  212  and annular distal end portion  214  thereto (e.g., via welding, bonding using a conductive adhesive, etc.). 
     Turning now to  FIG. 6 , in the illustrated embodiment, outer basket  304  is substantially similar to inner basket  204 , and similar components common to inner basket  204  and outer basket  304  will be referred to with reference numerals beginning with “3”. Outer basket  304  extends from a proximal end  308  to a distal end  310 . In the exemplary embodiment, proximal end  308  is generally defined by an annular or tubular proximal end portion or collar  312 , and distal end  310  is generally defined by an annular or tubular distal end portion or collar  314 . Annular proximal end portion  312  is an annular or tubular structure including a wall  316  that extends continuously about a circumference of proximal end  308  and has a diameter d o,p . Wall  316  has a plurality of through-holes  318  defined therein. In the illustrated embodiment, through-holes  318  are arranged in a regular pattern about wall  316 , in a plurality of rows and columns. In other embodiments, wall  316  includes any number of through-holes  318  arranged in any suitable regular and/or irregular pattern. 
     Likewise, annular distal end portion  314  is an annular or tubular structure including a wall  320  that extends continuously about a circumference of distal end  310  and has a diameter d o,d . Diameter d o,d  is the same as diameter d o,p , in the exemplary embodiment. Wall  320  has a plurality of through-holes  322  defined therein. In the illustrated embodiment, through-holes  322  are arranged in a regular pattern about wall  320 , in a plurality of rows and columns. In other embodiments, wall  320  includes any number of through-holes  322  arranged in any suitable regular and/or irregular pattern. 
     When inner basket  204  is coupled to outer basket  304  to form electrode assembly  114 , as described in greater detail herein, proximal end  308  of outer basket  304  (e.g., annular proximal end portion  312 ) partially defines proximal end  118  of electrode assembly  114 . Likewise, when inner basket  204  is coupled to outer basket  304  to form electrode assembly  114 , distal end  310  of outer basket  304  (e.g., annular distal end portion  314 ) partially defines distal end  120  of electrode assembly  114 . 
     Outer basket  304  further includes a plurality of struts  324  that extend from proximal end  308  to distal end  310  of outer basket  304 . Specifically, struts  324  have a strut length L o  defined between annular proximal end portion  312  and distal proximal end portion  314 . Outer basket  304  may include any number of struts  324 , including at least 8 struts, or at least 10 struts, or at least 12 struts. In the exemplary embodiment outer basket  304  includes the same number of struts  324  as the number of struts  224  of inner basket  204 . Struts  324  each have an inner surface  325  (which may also refer generally to an inner surface of outer basket  304 ) and an outer surface  327  (which may also refer generally to an outer surface of outer basket  304 ). As described further herein, struts  324  are formed from a shape memory material such that struts  324  tend to return to a particular shape or profile in the absence of any force thereon. In the illustrated embodiment, struts  324  have a generally arcuate and continuous profile that is symmetrical about longitudinal axis  127  and across a plane (not shown) bisecting outer basket  304 . In particular, the profile of each strut  324  is the same. In alternative embodiments, the profile of struts  324  may vary (e.g., each strut  224  may have a different profile, adjacent struts  224  may alternate between two profiles, etc.). 
     In the expanded configuration, outer basket  304  has a diameter D o . Additionally, in the exemplary embodiment, struts  324  are equally spaced from one another. More specifically, a distance between each pair of adjacent struts  324  is the same. Each strut includes a central portion  328 , a proximal portion  330  that extends between central portion  328  and annular proximal end portion  312 , and a distal portion  332  that extends between central portion  328  and annular distal end portion  314 . Proximal portion  330 , central portion  328 , and distal portion  332  extend continuously from one another, such that strut  324  is continuously curvilinear. In an alternative embodiment, proximal portion  330 , central portion  328 , and/or distal portion  332  are connected to one another via a hinge (e.g., a living hinge). 
     In the illustrated embodiment, the profile of struts  324 —specifically, the profile of struts  324  within central portion  328 —defines a radial maximum or outermost point  334  of each strut  324 . In the illustrated embodiment, each maximum  334  (of each strut  324 ) is the same distance m o  from longitudinal axis  127  when inner outer basket  304  is in an expanded configuration (corresponding to the expanded configuration of electrode assembly  114 ). Moreover, maximum  334  is located at a center of strut  324 , such that struts  324  are symmetrical across a plane bisecting outer basket  304 . Proximal and distal portions  330 ,  332  extend symmetrically inwardly from central portion  328  as they extend towards proximal and distal ends  308 ,  310 , respectively. Accordingly, outer basket  304  includes a proximal basket half  336  including proximal portions  330  and a proximal section of central portions  328  proximal to maximum  334 , as well as a distal basket half  338  including distal portions  332  and a distal section of central portions  328  distal from maximum  334 . 
     In alternative embodiments, struts  324  may include more than one maximum and/or may include a maximum located elsewhere along strut  324  (e.g., within proximal portion  330  or distal portion  332 , or at another, non-center position within central portion  328 ). In such embodiments, proximal basket half  336  may therefore represent less or more than a “half” of outer basket  304 , and distal basket half  338  may represent less or more than a “half” of outer basket  304 . More particularly, proximal basket half  336  may represent the portion of outer basket  304  proximal to the proximal-most maximum, and distal basket half  338  may represent the portion of outer basket  304  distal to the distal-most maximum (where the proximal-most and distal-most maxima may be the same or different maxima). 
     Another embodiment of outer basket  304  is shown in  FIG. 8 . In the illustrated embodiment, maximum  334  is not at a center of each strut  324 , but rather is distally offset, and outer basket  304  is not symmetrical across a plane  326  bisecting outer basket  304 . In addition, outer basket  304  includes a tab  340  extending from proximal end  308 . Tab  340  enables electrical connection between outer basket  304  and electrical cables (not shown) that provide power to outer basket  304  (e.g., from generator  108 , shown in  FIG. 1 ). Outer basket  304  may include only one tab  340 , a pair of tabs  340 , or additional/alternative tabs and/or suitable electrical connection points. 
     To form outer basket  304 , in one embodiment, a tube (not shown) of suitable material is provided. In the exemplary embodiment, the tube is formed of an electrically conductive shape memory material, such that outer basket  304  is electrically conductive and may be treated to retain a desired shape. Suitable materials may include, for example and without limitation, copper-aluminum-nickel alloys, nickel-titanium (NiTi) alloys, nitinol, alloys including zinc, copper, gold, and/or iron, polymers including any of the above materials, and/or combinations thereof. The tube is cut to a desired length, such as an overall length of outer basket  304  between proximal end  308  and distal end  310 . In some embodiments, the length of the tube further includes a length of one or more tabs  340 . Alternatively, tabs  340  may be coupled to the tube (e.g., by welding, bonding using a conductive adhesive, etc.). 
     Through-holes  318  and  322  are formed in the tube, for example, via laser-cutting, die-cutting, and/or any other suitable method. Subsequently, the tube is slit longitudinally (e.g., parallel to a longitudinal axis thereof) to form struts  324 , for example, via laser-cutting, die-cutting, and/or any other suitable method. This step also defines annular proximal end portion  312  and annular distal end portion  314 , specifically, as the portions of the tube that are not slit. In some embodiments, the tube is slit before the through-holes  318 ,  322  are formed. 
     Thereafter, the tube is positioned about a mandrel and heat-set to define the shape or profile of struts  324 . For example, the mandrel has an outer surface complementary to the desired shape of struts  324  and/or the desired shape of outer basket  304  in the expanded configuration. The resulting outer basket  304  is a unitary, single-piece basket having struts  324  that retain a desired shape or profile (such as that shown in  FIG. 6  and/or  FIG. 8 ) extending between annular proximal end portion  312  and annular distal end portion  314 , having through-holes  318  and  322 , respectively, defined therein. 
     Outer basket  304  may be formed using an alternative method, such as forming struts  324  and attaching annular proximal end portion  312  and annular distal end portion  314  thereto (e.g., via welding, bonding using a conductive adhesive, etc.). 
     To form electrode assembly  114 , as shown in  FIGS. 2-4 , inner basket  204  (shown in  FIG. 5 ) is positioned within and is co-axial with outer basket  304  (shown in  FIG. 6 ). Specifically, proximal ends  208  and  308  of inner and outer baskets  204  and  204 , respectively, are co-located to define proximal end  118  of electrode assembly  114 . Likewise, distal ends  210  and  310  of inner and outer baskets  204  and  304 , respectively, are co-located to define distal end  120  of electrode assembly  114 . 
     For example, inner basket  204  is transitioned into its collapsed configuration (e.g., such that inner basket  204  is substantially tubular), and inner basket  204  is moved longitudinally through annular proximal end portion  312  and/or annular distal end portion  314  of outer basket  304 . In the exemplary embodiment, diameters d i,p  and d i,d  of annular proximal end portion  212  and annular distal end portion  214 , respectively, of inner basket  204  are smaller than diameters d o,p  and d o,d  of annular proximal end portion  312  and annular distal end portion  314 , respectively, of outer basket  304 , such that inner basket  204  fits through annular proximal end portion  312  and/or annular distal end portion  314  of outer basket  304 . Put another way, proximal end portion  312  and annular distal end portion  314  of outer basket  304  are sized to receive annular proximal end portion  212  and annular distal end portion  214  of inner basket  204 . Accordingly, when electrode assembly  114  is formed from inner basket  204  and outer basket  304 , inner basket  204  and outer basket  304  are coaxial with one another. 
     Inner basket  204  is oriented with respect to outer basket  304  (e.g., by rotating or angularly displacing inner basket  204  relative to outer basket  304 ) such that struts  224  of inner basket  204  alternate with and are equally spaced from struts  324  of outer basket  304 . Accordingly, electrode assembly  114  includes struts  224  alternating with struts  324  about a circumference of the electrode assembly  114 . Struts  224  are equidistant from adjacent struts  324 . To facilitate spacing and positioning of struts  224  relative to adjacent struts  324 , inner basket  204  and/or outer basket  304  may include one or more alignment features. In some embodiments, through-holes  218 ,  222  and through-holes  318 ,  322  are the alignment feature. Specifically, through-holes  218  are arranged to align with through-holes  318 , and through-holes  222  are arranged to align with through-holes  322 , when inner basket  204  is properly angularly offset from outer basket  304  (i.e., such that struts  224  are equidistant from adjacent struts  324 ). Additionally or alternatively, the alignment feature may include a tab on one of inner basket  204  and outer basket  304  and a slot sized and located to receive the tab, on the other of inner basket  204  and outer basket  304 , when inner basket  204  is properly angularly offset from outer basket  304 . 
     In the exemplary embodiment, inner basket  204  functions as one of a cathode or negative (−) electrode and an anode or positive (+) electrode of electrode assembly  114 , and outer basket  304  functions as the other of the cathode and anode of electrode assembly  114 . Specifically, inner basket  204  is electrically coupled to generator  108  to receive a cathode or anode signal, and outer basket  304  is electrically coupled to generator  108  to receive the other of the cathode or anode signal. In one exemplary embodiment, inner basket  204  is the anode, and outer basket  304  is the cathode. 
     Accordingly, the alternating pattern of struts  224  and  324  corresponds to an alternating pattern of charge (+/−/+/−) about the circumference of electrode assembly  114 . Specifically, energized struts  224  and  324  define pairs of adjacent, opposite-charge electrodes (e.g., a negative (−) strut  224  adjacent to a positive (+) strut  324 ). When electrode assembly  114  is energized and advanced into contact with tissue, electrode assembly  114  generates a circumferential ablation pattern between each pair of adjacent struts  224 ,  324 , thereby creating a 360° ablation pattern in a single ablation event (e.g., between an initial contact of electrode assembly  114  and the tissue, and the removal of the electrode assembly  114  from the tissue or the termination of the energization of electrode assembly  114 ). 
       FIG. 9  depicts electrode assembly  114  being advanced into contact with exemplary tissue  115 . As shown, electrode assembly  114  is particularly suitable for complete, 360° contact with tissue  115 . When energized, electrode assembly  114  functions as a plurality of electrode pairs between adjacent struts  224 ,  324 , to generate an ablation pattern (not shown) about an entirety of the outer surface thereof that is in contact with tissue  115 . Accordingly, struts  224 ,  324  may be referred to generally as “electrodes” or “ablation electrodes” of electrode assembly  114 . 
     In the illustrated embodiment of  FIGS. 2-4 , electrode assembly  114  has diameter D that corresponds generally to diameter D o  of outer basket  304 . In one embodiment, diameter D i  is slightly less than D o , by an amount corresponding to the difference between d i, p  and d o,p , (e.g., the difference in diameter between the tubes used to form inner basket  204  and outer basket  304 ). In another embodiment, D i  is substantially the same as D o . For example, struts  224  may be slightly longer than struts  324  and may be particularly heat-set such that maxima  234  are circumferentially aligned with maxima  334 . Diameter D i  and diameter D o  are generally sufficiently similar such that, when electrode assembly  114  is advanced into contact with tissue  115 , struts  224  and  324  both sufficiently contact tissue  115  to ablate tissue  115 . 
     In addition, electrode assembly  114  is substantially symmetrical about longitudinal axis  127  and across a plane  129  bisecting electrode assembly  114 . Maxima  234  and maxima  334  are located at the same longitudinal or axial position on struts  224 ,  324  at plane  129 , or at the center of struts  224 ,  324 . 
     In the exemplary embodiment, to prevent electrical shorts between inner basket  204  and outer basket  304 , inner basket  204  is electrically insulated from outer basket  304 . Specifically, as electrode assembly  114  is formed, an electrically insulating material  128  (e.g., a dielectric coating, shown in  FIGS. 4, 10 and 11 ) is provided between inner basket  204  and outer basket  304 . In one embodiment, electrically insulating material  128  is re-flowed between inner basket  204  and outer basket  304 , via through-holes  218 ,  222 ,  318 , and/or  322 . More particularly, insulating material  128  is reflowed (e.g., via through-holes  218  and/or  318 ) between annular proximal end portion  212  and annular proximal end portion  312 , to prevent electrical contact therebetween. In addition, electrically insulating material  128  is reflowed (e.g., via through-holes  222  and/or  322 ) between annular distal end portion  214  and annular distal end portion  314 , to prevent electrical contact therebetween. In one embodiment, through-holes  218  and  318  may not be directly aligned and/or through-holes  222  and  322  may not be directly aligned, to improve reflow of electrically insulating material  128  between annular proximal end portions  212  and  312  and/or annular distal end portions  214  and  314  (as illustrated in  FIG. 12 , in which outer basket  304  is shown in phantom). In the exemplary embodiment, electrically insulating material  128  also facilitates adhering inner basket  204  to outer basket  304 , to prevent angular displacement of inner basket  204  with respect to outer basket  304 . Electrically insulating material  128  may be reflowed or otherwise provided on the sections of struts  224 ,  324  adjacent to annular end portions  212 ,  214 ,  312 ,  314 , which may be in such close proximity to each other that electrical shorts could occur therebetween. 
     In addition, insulating material  128  is provided over inner and/or outer surface(s)  225 ,  227 ,  325 ,  327  of struts  224  and/or  324  to define a conductive portion  130  and a non-conductive portion  132  of electrode assembly  114  (shown in  FIG. 10 ). In the illustrated embodiment of  FIGS. 10 and 11 , proximal portions  230  of struts  224  and proximal portions  330  of struts  324  are coated in insulating material  128 . Specifically, struts  224  and  324  are coated in insulating material  128  until just below (e.g., proximal of) maxima  234 ,  334  thereof. Accordingly, non-conductive portion  132  of electrode assembly  114  includes the portion(s) of struts  224 ,  324  coated in insulating material  128 , including proximal portions  230 ,  330  (and, in some embodiments, at least a section of central portions  228 ,  328  proximal of maxima  234 ,  334 ). For example, non-conductive portion  132  of electrode assembly  114  includes proximal basket half  236  of inner basket and proximal basket half  336  of outer basket  304 . Conductive portion  130  of electrode assembly  114  includes the portion(s) of struts  224 ,  324  that are free of insulating material  128 , including distal portions  232 ,  332  (and, in some embodiments, maxima  234 ,  334  and at least a second of central portions  228 ,  328  distal of maxima  234 ,  334 ). For example, conductive portion  130  includes distal basket half  238  of inner basket  204  and distal basket half  338  of outer basket  304 . 
     “Conductive portion  130 ” may refer to any of (i) the conductive (i.e., uninsulated) portion(s) of inner basket  204  and struts  224 , (ii) the conductive (i.e., uninsulated) portion(s) of outer basket  304  and struts  324 , and/or (iii) the conductive (i.e., uninsulated) portion(s) of formed electrode assembly  114 . Likewise, “non-conductive portion  132 ” may refer to any of (i) the non-conductive (i.e., insulated) portion(s) of inner basket  204  and struts  224 , (ii) the non-conductive (i.e., insulated) portion(s) of outer basket  304  and struts  324 , and/or (iii) the non-conductive (i.e., insulated) portion(s) of formed electrode assembly  114 . 
     When electrode assembly  114  is advanced into contact with tissue (e.g., tissue  115 , shown in  FIG. 9 ) and energized, conductive portion  130  of electrode assembly  114  transmits ablative energy into the tissue, whereas non-conductive portion  132  is insulated from the tissue. Accordingly, conductive portions  130  of struts  224  and conductive portions  130  of struts  324  may be referred to as the “electrodes” and/or “ablation electrodes” of electrode assembly  114 . 
     Varying configurations (e.g., locations, sizes, and/or orientations) of conductive portion  130  and non-conductive portion  132  are contemplated within the scope of the present disclosure. The specific configuration can be selected and created by selectively providing insulating material  128  on electrode assembly  114 . Insulating material  128  may be deposited on inner basket  204 , outer basket  304 , and/or the formed electrode assembly  114 . Additionally or alternatively, inner basket  204 , outer basket  304 , and/or the formed electrode assembly  114  may be dipped into insulating material  128  to coat struts  224 ,  324  (as well as, in some embodiments, proximal end(s)  208 ,  308 ,  118  and/or distal end(s)  210 ,  310 ,  120 ). 
       FIG. 13  illustrates an alternative embodiment of an electrode assembly, designated using the reference numeral  114 ′. Electrode assembly  114 ′ is symmetrical about longitudinal axis  127  and is asymmetrical about a plane  129  bisecting electrode assembly  114 ′. Maxima  234  and  334  are not located at the same longitudinal or axial position. Rather, maxima  234  and  334  are offset to define two maxima  150  and  152  of electrode assembly  114 ′. Electrode assembly  114 ′ may generate a 360° circumferential ablation pattern between maximum  150  and maximum  152 . Such a configuration may be suitable for ablation within a cylindrical vessel. 
     With reference to  FIGS. 10 and 14-16 , electrode assembly  114  may further include pull wire  126  coupled to distal end  120  thereof (e.g., coupled to distal end  210  of inner basket  204  and/or distal end  310  of outer basket  304 ). Pull wire  126  may be used to transition electrode assembly  114  from its collapsed configuration to its expanded configuration, or to vary the electrode assembly  114  between degrees of expansion within the expanded configuration. For example, as shown in  FIGS. 14-16 , electrode assembly  114  is maneuvered to its position within the patient&#39;s vasculature and advanced from catheter shaft  110  in a collapsed configuration. Pull wire  126  may be manipulated (e.g., using an actuator within handle  104 , shown in  FIG. 1 ) to transition electrode assembly  114  between the configurations shown in  FIGS. 14-16 . 
       FIGS. 17 and 18  illustrate another alternative embodiment of an outer basket, designated using the reference number  304 ′. Outer basket  304 ′ includes four tabs  340  extending from proximal end  308  thereof. In the illustrated embodiment, annular proximal end portion or collar  312  is separated or divided into sections  342 . Each section  342  has a respective tab  340  extending therefrom. Although annular proximal end portion  312  includes four sections  342 , annular proximal end portion  312  may include more than or fewer than four section  342 . Likewise, annular distal end portion or collar  314  is separated or divided into sections  344 . Although annular distal end portion  314  includes four sections  344 , annular distal end portion  314  may include more or fewer than four section  344 . 
     Sections  342  are electrically insulated from each adjacent section  342  by insulating material  128 . Likewise, sections  344  are electrically insulated from each adjacent section by insulating material  128 . Each section  344  corresponds to a section  342 . Each strut  324  extends from a section  342  to a corresponding section  344 . Each pair of corresponding sections  342 - 344  and the struts  324  extending therebetween define a “quadrant”  346  of outer basket  304 ′. For example, a first quadrant  346 A of outer basket  304 ′ includes a first (proximal) section  342 A, a first (distal) section  344 A, and struts  324 A,  324 B, and  324 C extending between first section  342 A and section  344 A. In the illustrated embodiment, each tab  340  corresponds to a respective quadrant  346 . As such, each quadrant  346  can be separately energized, as each quadrant  346  is insulated from each adjacent quadrant (e.g., by insulating material  128  at end portions  312 ,  314 ). 
     In some embodiments, an exemplary electrode assembly includes outer basket  304 ′ divided into quadrants  346 , and an inner basket divided into quadrants (not shown) in the same manner. In such embodiments, individual quadrants of the inner and outer basket may each be energized with a positive or negative charge, or individual quadrants may not be energized. This electrode assembly may be used during an ablation procedure to generate a 360° circumferential ablation pattern formed from quadrants energized with alternating charges, or to generate an ablation pattern over less than the entire circumference of the electrode assembly, such as two discrete ablation patterns of less than 180°. 
       FIG. 19  is a simplified process diagram for a method  1900  of forming an electrode assembly (e.g., electrode assembly  114 , shown, for example, in  FIGS. 1-4 ). Method  1900  includes forming  1902  an inner electrode basket (e.g., inner electrode basket  204 ) including a first proximal end (e.g., proximal end  208 ), a first distal end (e.g., distal end  210 ), and a first plurality of struts (e.g., struts  224 , all shown in  FIG. 5 ) extending between the first proximal end and the first distal end. 
     Method  1900  also includes forming  1904  an outer electrode basket (e.g., outer electrode basket  304 ) including a second proximal end (e.g., proximal end  308 ), a second distal end (e.g., distal end  310 ), and a second plurality of struts (e.g., struts  324 , all shown in  FIG. 6 ) extending between the second proximal end and the second distal end. 
     Method  1900  further includes positioning  1906  the first proximal end within and coaxial with the second proximal end, positioning  1908  the first distal end within and coaxial with the second distal end, and orienting  1910  the inner electrode basket relative to the outer electrode basket such that the first plurality of struts and the second plurality of struts alternate about a circumference of the electrode assembly. 
       FIG. 20  is a simplified process diagram for a method  2000  of performing an ablation procedure using an electrode assembly (e.g., electrode assembly  114 , shown, for example, in  FIGS. 1-4 ). Method  2000  includes advancing  2002  the electrode assembly to a target location. In the exemplary embodiment, the electrode assembly includes (i) an inner electrode basket (e.g., inner electrode basket  204 ) including a first proximal end (e.g., proximal end  208 ), a first distal end (e.g., distal end  210 ), and a first plurality of struts (e.g., struts  224 , all shown in  FIG. 5 ) extending between the first proximal end and the first distal end, and (ii) an outer electrode basket (e.g., outer electrode basket  304 ) including a second proximal end (e.g., proximal end  308 ), a second distal end (e.g., distal end  310 ), and a second plurality of struts (e.g., struts  324 , all shown in  FIG. 6 ) extending between the second proximal end and the second distal end. Additionally, the first proximal end is positioned within and coaxial with the second proximal end and the first distal end is positioned within and coaxial with the second distal end such that the inner electrode basket is positioned within and coaxial with the outer electrode basket, and the inner electrode basket is angularly offset from the outer electrode basket such that the first plurality of struts and the second plurality of struts alternate about a circumference of the electrode assembly. 
     Method  2000  also includes contacting  2004  tissue (e.g., tissue  115 , shown in  FIG. 9 ) at the target location with the electrode assembly, and energizing  2006  the electrode assembly (e.g., using a power supply such as generator  108 , shown in  FIG. 1 ) by energizing the inner electrode basket as one of a cathode with a positive charge or an anode with a negative charge, and energizing the outer electrode basket as the other of the cathode or the anode, such that the first plurality of struts and the second plurality of struts alternate charge about the circumference of the electrode assembly and ablate the tissue in a circumferential pattern. 
     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 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 scope 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.