Self-similar electrode for electrophysiology catheter

Abstract

An electrode for delivering electrical energy and / or sensing electrical signals in biological tissue is described. The electrode includes a conductive body that defines an electrode surface and a self-similar pattern formed in the electrode surface. For example, repeating geometric features may be arranged in at least two hierarchical levels such that a first-level geometry and a second-level geometry are geometrically similar. Example embodiments include conductive-member architectures with a core, first members, and sets of second (and optional third) members arranged in repeated patterns, and surface-pattern architectures in which the self-similar pattern is defined by negative space (grooves or recesses), raised conductive material, or dimples. The pattern may be contiguous and space-filling, including space-filling fractal patterns that increase effective edge length and geometric gradients relative to Euclidean shapes.

Description

Attorney Docket No.: 073777.00138SELF-SIMILAR ELECTRODE FOR ELECTROPHYSIOLOGY CATHETER Cross-Reference to Related Applications

[0001] This international patent application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 739,387, filed December 27, 2024, now pending, the entire contents of which are incorporated herein by reference.Field of the Disclosure

[0002] The present disclosure is related to the field of surgical electrodes, and more particularly to electrodes for use with ablation catheters, mapping catheters, and the like.Background of the Disclosure

[0003] Cardiac radiofrequency (RF) ablation delivers current from a catheter electrode into the heart muscle, creating a lesion of irreversible tissue injury. The depth and size of the lesion is dictated by the current density delivered to the tissue. A significant hurdle in the treatment of ventricular arrhythmias is the inability to create lesions that can extend into deeper layers of tissue where ventricular arrhythmias can originate from — this is reflected in failure rates that can approach 50%.

[0004] There is a clinical need for technology to target arrhythmias arising from mid-myocardial ventricular tissue. This is bom out in failure rates in this population that can approach 50%. Per year, in the U.S., over 21,000 people undergo ablations for ventricular arrhythmias. Ablation for ventricular arrhythmias account for 5% of the total ablation volume in the US, and the total number has steadily increased every year for more than a decade and will likely continue to increase.Brief Summary of the Disclosure

[0005] The present disclosure relates to electrodes for delivering ablation energy and / or sensing electrical signals in biological tissue, including electrodes configured for use with ablation catheters, mapping catheters, and related electrophysiology tools. The disclosure addresses limitations of conventional Euclidean electrode geometries by providing electrode surfaces that present increased effective edge length, local curvature, and geometric gradients at the tissue interface for a given footprint, thereby shaping electric potential and current density7Attorney Docket No.: 073777.00138distributions in tissue and supporting deeper or more efficient energy delivery, including in thick ventricular substrates where lesion depth and transmurality can be difficult to achieve.

[0006] In one aspect, an electrode includes a conductive body that defines an electrode surface and a self-similar pattern formed in the electrode surface. The self-similar pattern has repeating geometric features arranged in at least two hierarchical levels such that a first-level arrangement defines a first geometry and a second-level arrangement defines a second geometry that is geometrically similar to the first geometry. The repeating geometric features may be implemented as conductive members in a “positive space” architecture that propagates from a conductive core through first members, sets of second members at distal ends, and optionally sets of third members, with symmetrical arrangements and consistent member counts across hierarchical levels in certain embodiments.

[0007] In another aspect, the self-similar pattern is implemented through surface topography, including negative-space patterns defined by grooves or recesses, raised conductive material above a reference surface, or arrays of dimples, where irrigation apertures may be positioned within grooves or within dimples for fluid delivery during energy application. The self-similar pattern may be contiguous and space-filling across a region of the electrode surface, and may be expressed as a space-filling fractal pattern that repeats upon itself across multiple levels of magnification and that defines boundaries with vertices and curved segments that increase edge length relative to a circular boundary of equal projected area. The conductive body may be formed from a metal sheet, may have example thicknesses around 0.5 mm in certain implementations, and may carry a plating layer such as gold over part or all of the conductive body.

[0008] The electrode may be configured as an end cap at a distal tip of an ablation catheter or a mapping catheter, may be configured as an expandable array deploy able from a sheath with distinct insertion and deployed configurations, and may be foldable and / or stretchable in the deployed configuration while maintaining the self-similar pattern. The electrode may also be configured as a return electrode for bipolar ablation, including arrangements where the return electrode is positioned on an opposite side of tissue relative to an active electrode positioned by a catheter. The disclosed electrode geometries are suitable for radiofrequency ablation in bipolar or unipolar modes and are also suitable for pulsed field ablation, including unipolar pulsed field ablation between the electrode and a grounding patch,Attorney Docket No.: 073777.00138among other applications. Experimental and benchtop evaluations described herein support that space-filling fractal electrode geometries can increase lesion depth or lesion area relative to circular electrodes under comparable conditions.Description of the Drawings

[0009] For a fuller understanding of the nature and objects of the disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.

[0010] Figure 1 A is an electrode according to an embodiment of the present disclosure.

[0011] Figure IB is an end-view of the electrode of Figure 1A.

[0012] Figure 2A is an electrode according to another embodiment of the present disclosure.

[0013] Figure 2B is an end- view of the electrode of Figure 2A.

[0014] Figure 2C is an elevation view of the electrode of Figures 2A and 2B.

[0015] Figure 3 is a photograph of a prototype self-similar electrode according to another embodiment of the present disclosure. The experimental electrode was made from a copper sheet (0.25 mm thickness) and the floret has a diameter of 16 mm.

[0016] Figure 4A is a photograph of a transmural lesion (lighter shading) created with bipolar RF using a self-similar return electrode according to an embodiment of the present disclosure (the ruler is delineated in major units of cm).

[0017] Figure 4B is a photograph of a non-transmural lesion created with bipolar RF using a conventional return electrode.

[0018] Figure 5 is a perspective view rendering of an electrode of another embodiment, wherein the electrode includes grooves forming a self-similar pattern.

[0019] Figure 6 is a perspective view rendering of an electrode of another embodiment, wherein the electrode is configured as an endcap of an ablation catheter.Attorney Docket No.: 073777.00138

[0020] Figure 7 is a series of drawings showing the self-similar nature of an example pattern which may be used for an electrode according to the present disclosure, such as, for example, a groove pattern of an electrode.

[0021] Figure 8 is a series of drawings showing the self-similar nature of another example pattern which may be used for an electrode according to the present disclosure.

[0022] Figure 9 is a perspective view showing a self-similar dimpled pattern according to another embodiment of the present disclosure. Here again the electrode is configured as an end cap for a catheter.

[0023] Figure 10 is a series of drawings showing the self-similar nature of an example dimpled pattern which may be used for an electrode according to the present disclosure.

[0024] Figures 11A and 1 IB depict a model of electrical potential propagation of a traditional electrode (shown as isosurfaces).

[0025] Figures 12A and 12B depict a model of electrical potential propagation of a selfsimilar electrode according to an embodiment of the present disclosure (shown as isosurfaces).

[0026] Figure 13A shows three gold plated copper return electrodes. (Left): Fractal electrode; (middle): circle with matching surface area; (right) circle with matched diameter.

[0027] Figure 13B shows corresponding lesions created in a potato model dyed on 1% TTC solution.

[0028] Figure 14: Top panel (A): three gold plated copper return electrodes. (Left): Fractal electrode; (middle): circle with same surface area; (right) circle with same diameter. Middle panel (B): Corresponding lesions created in the gel phantom. Note the areas of relative overheating (>90°C; (arrows)). Bottom panel (C): Infrared camera image of a fractal electrode (left) and circular electrode (right) directly after RF delivery. Note the areas of heating at the edges of the electrodes (arrows).

[0029] Figure 15 depicts a method according to another embodiment of the present disclosure.Attorney Docket No.: 073777.00138Detailed Description of the Disclosure

[0030] The present disclosure relates to electrodes for delivering energy to tissue and / or sensing electrical signals in tissue, including electrodes used with electrophysiology catheters for cardiac ablation, mapping, pacing, and other applications. In cardiac radiofrequency (RF) ablation, current delivered from an electrode into myocardium creates a lesion of irreversible tissue injury. Lesion depth and size are strongly influenced by current density at the electrodetissue interface and within the tissue volume. A persistent clinical challenge, particularly in ventricular substrates, is achieving effective energy del i \ ery to deeper tissue layers where arrhythmogenic foci may reside. In thicker myocardium, conventional electrode shapes and conventional bipolar configurations may fail to create confluent transmural lesions at practical power levels and durations. The present disclosure addresses these challenges through electrode geometries that increase effective edge length, local curvature, and geometric gradients at the tissue interface for a given footprint, thereby shaping the distribution of electric potential and current density in tissue.

[0031] As used herein, “self-similar pattern" refers to a geometry that repeats at different scales such that a pattern observed at one scale resembles, in a geometric sense, a pattern obser ed at another scale. This resemblance may be exact in idealized form or approximate in manufactured form. “Repeating geometric features” refers to recurring elements of the geometry that may be formed as conductive projections, conductive boundaries, raised portions of the electrode surface, recessed portions of the electrode surface, or combinations of these.“Hierarchical levels” refers to at least two distinct scales at which the repeating features are present. A first-level arrangement of repeating features defines a first geometry, and a second-level arrangement defines a second geometry that is geometrically similar to the first geometry. “Geometrically similar” indicates that the second geometry preserves shape relationships of the first geometry' under scaling, rotation, reflection, or combinations of these; the term allows practical manufacturing tolerances, rounding, radiusing, and minor deviations due to material constraints, electrode finishing, or coating thickness. In some embodiments, the relationship between levels is characterized by a substantially constant scale factor from one level to the next, meaning that a characteristic dimension of the repeating features at one level (such as length, width, radius, spacing, or feature pitch) is proportional to a corresponding characteristic dimension at an adjacent level within typical engineering tolerances.Attorney Docket No.: 073777.00138

[0032] A “contiguous, space-filling pattern” refers to a self-similar pattern that is continuous across a region of the electrode surface rather than being limited to discrete, separated islands. In such embodiments, the pattern may form a continuous groove network, a continuous boundary, or a continuous raised ridge network that traverses the electrode surface and, in some cases, substantially fills a designated region of the surface. A “space-filling fractal pattern” refers to a space-filling pattern that repeats across multiple levels of magnification, often producing high perimeter length relative to enclosed area and multiple vertices and curved or angled segments. Use of “fractal” in this disclosure describes self-similar and space-filling characteristics and does not require a strict mathematical fractal dimension or an infinite number of levels. Practical embodiments may include two, three, four, or more hierarchical levels as appropriate for the electrode size and manufacturing limits.

[0033] “Negative space not occupied by conductive material” refers to patterns formed by removal or absence of conductive material, such as grooves, channels, recesses, dimples, apertures, or combinations thereof, where the boundary of the conductive region defines the selfsimilar geometry. "Raised conductive material above a surface” refers to patterns formed by conductive ridges, mesas, protrusions, or members that extend above a reference surface of the conductive body, where the raised portion forms the self-similar geometry. “Irrigation apertures” refers to openings that permit fluid delivery7through the electrode body to the electrode-tissue interface, including apertures positioned within grooves or within dimples. “Return electrode for bipolar ablation” refers to an electrode configured to serve as the return pole in a bipolar energy delivery circuit, including configurations where the return electrode is positioned on an opposite side of tissue relative to an active electrode delivered by a catheter.

[0034] With reference to Figures 1A and IB, the present disclosure may be embodied as an electrode for delivering electrical energy and / or sensing electrical signals in biological tissue, such as surgical electrode 10. The electrode has a conductive body 12 defining an electrode surface 14. The electrode surface has a self-similar pattern. The self-similar pattern may include repeating geometric features arranged in at least two hierarchical levels such that a first-level arrangement of the repeating geometric features defines a first geometry and a second-level arrangement of the repeating geometric features defines a second geometry that is geometrically similar to the first geometry7. In some embodiments, the repeating geometric features are made up of a plurality of conductive members arranged in a self-similar pattern. For example, the electrode may have a plurality of conductive members arranged in a self-similar pattern (i.e.. aAttorney Docket No.: 073777.00138self-similar geometry ). In some embodiments, the electrode 10 includes a core 20 and at least two conductive first members 22. The at least two first members 22 extend from the core 20. The first members 22 may be symmetrically arranged around the core. The first members 22 have at least one distal end 24. In some embodiments, such as that depicted in Figures 2A and 2B, the electrode 100 has a conductive body 110 where first members 122 are attached to the core 120 at a location along its longitudinal length other than at an end. For example, in Figures 2A and 2B, the first members 122 are attached to the core 120 at a midpoint 121. In such cases, each first member has two distal ends 124 (i.e., distal with respect to the core).

[0035] The electrode has a shape which is referred to as self-similar — i.e., a shape that replicates at different scales. As such, the electrode 10 has a plurality of sets 30 of second members 32. The number of sets of second members corresponds to the number of distal ends 24 of the first members 22. Each set 30 of second members includes a at least two second members 32, where the number of second members corresponds to the number of first members. The second members making up each set of second members is arranged in a similar geometry to the arrangement of first members. In this way. the electrode has a self-similar configuration.

[0036] In some embodiments, the electrode may have a plurality of sets of third members (see, e.g., second members 132 and third members 142 in Figure 2A). The number of sets of third members corresponds to the number of distal ends of the second members. Each set of third members includes a at least two third members, where the number of third members corresponds to the number of first members. The third members making up each set of third members is arranged in a similar geometry to the arrangement of each set of second members and the first members.

[0037] In some embodiments, the self-similar geometry of the surgical electrode has a contiguous, self-similar pattern — a “space-filling shape.” In some embodiments, a surgical electrode has a self-similar geometry formed by space not occupied by conductive members — i.e.. the self-similar geometry is in the negative (unoccupied) space. For example, the electrode may have one or more grooves with a self-similar geometry (see Figures 5 and 6). The electrode 200 of Figure 6 is configured as an end cap of an ablation catheter, with a self-similar pattern of the grooves 220 formed in the conductive body 210 and the electrode surface 212. The self-similar nature of the groove pattern is also shown in Figures 7 and 8. It can be seen that atAttorney Docket No.: 073777.00138every scaling up, the groove pattern remains the same. In some embodiments, one or more irrigation holes are located within the groove(s).

[0038] In some embodiments, the electrode may have a self-similar shape raised above a surface of the metal. For example, the raised self-similar shape of the electrode material may form the positive space of the electrode. In another example, the electrode may include grooves in the electrode material resulting in a self-similar shape formed in the raised (i.e., un-grooved) portion.

[0039] In some embodiments, a surgical electrode has a plurality7of dimples arranged in a self-similar geometry. For example, Figure 9 depicts an electrode 300 configured as an end cap for a distal tip of a catheter, such as an ablation catheter, a mapping catheter, a pacing catheter, etc. The electrode 300 has a plurality7of dimples 320 arranged in a self-similar pattern on the electrode surface 310. The repeating pattern of the self-similar dimple geometry7is shown in the diagrams of Figures 10(a)-10(d). In some embodiments, at least one of the dimples may include an irrigation aperture 330.

[0040] Embodiments of an electrode of the present disclosure may be used for RF ablation of any ty pe, including conventional unipolar ablation and bipolar ablation. Significantly, the physical properties of a self-similar electrode design that lends itself to bipolar RF ablation could also benefit unipolar RF ablation. Various embodiments of the electrode may be used with a pulsed field ablation system.

[0041] Conductive-member (“positive space”) self-similar electrodes

[0042] In some embodiments, an electrode includes a conductive body with conductive members arranged in a self-similar geometry7in which the conductive members themselves define the repeating pattern. One example embodiment uses a conductive core and at least two conductive first members that extend outward from the core. The first members may be arranged symmetrically about the core, for example with two, three, four, five, six, or more first members distributed around the core. Each first member has at least one distal end. In configurations where the first members attach to an end of the core, a given first member may have a single distal end distal relative to the core. In other configurations, the first members attach to the core at a position along a longitudinal length of the core other than at an end, such as at or near aAttorney Docket No.: 073777.00138midpoint, such that each first member has two distal ends that are distal relative to the attachment location on the core.

[0043] From each distal end of each first member, a corresponding set of at least two conductive second members extends. The set of second members at a given distal end may be arranged in a geometry similar to the arrangement of first members about the core. For example, if the first-level arrangement uses three first members spaced approximately 120 degrees apart around the core, each second-level set may likewise use three second members spaced approximately 120 degrees apart around that distal end. In some embodiments, the number of second members in a set equals the number of first members, supporting a repeated motif that propagates across hierarchical levels. In further embodiments, a third hierarchical level is formed by sets of conductive third members extending from distal ends of the second members, where each set is arranged in a geometry similar to the arrangement of first members about the core and / or similar to the arrangement of second members about the distal ends of the first members. Additional levels bey ond a third may be used, subject to electrode size and manufacturability'.

[0044] Conductive-member embodiments may be planar, substantially planar, or three-dimensional. In planar embodiments, members lie in a plane suitable for placement against tissue. In three-dimensional embodiments, members may be curved, bent, or contoured to conform to an anatomical surface or to distribute contact forces more evenly. The conductive members may be integral with the core and formed from a unitary piece of conductive material, or may be assembled from multiple conductive components electrically' bonded by welding, brazing, soldering, conductive adhesives, mechanical fasteners, crimping, swaging, or combinations thereof.

[0045] Surface-pattern (“negative space” and “raised”) self-similar electrodes

[0046] In other embodiments, the conductive body defines an electrode surface, and a self-similar pattern is formed in that surface through recesses, grooves, channels, or dimples, or through raised features such as ridges or mesas. In negative-space embodiments, the self-similar geometry' is defined by regions not occupied by conductive material, such as grooves cut into the surface, such that the boundary of the conductive regions forms a self-similar pattern. A groove network may be continuous across a region of the electrode surface and may be arranged as a contiguous, space-filling pattern. In such embodiments, when the groove pattern is viewed at increasing magnification, the pattern retains similar structure, with repeating motifs occurring atAttorney Docket No.: 073777.00138multiple hierarchical levels. The groove depth and width may be selected to balance electrical, thermal, and mechanical goals. For example, groove depths may fall in a range from about 0.01 mm to about 2 mm, and groove widths may fall in a range from about 0.01 mm to about 2 mm, with larger or smaller values used depending on electrode size and manufacturing. Where the electrode is intended for catheter-tip use, groove dimensions may be selected so that the surface retains sufficient mechanical integrity and avoids excessive stress concentration.

[0047] In raised-feature embodiments, the self-similar pattern is formed by raised conductive material above a reference surface of the conductive body. Raised ridges, mesas, protrusions, or embossed patterns may define repeating geometric features at multiple hierarchical levels. In some embodiments, grooves are formed in the electrode surface such that the un-grooved portions become raised relative to groove bottoms; in this way, negative-space and raised-feature concepts may coexist, and either the groove network or the raised land network may be treated as the self-similar pattern for design and claim support.

[0048] Dimples may also be used to form a self-similar pattern. In such embodiments, the electrode surface includes a plurality of dimples arranged in a repeating, multi-scale geometry. Dimples may be circular, oval, polygonal, or irregular in plan view, and may be concave with rounded bottoms or may be formed with a conical or faceted profile. Dimple diameters or characteristic widths may be selected across hierarchical levels using a scale factor, with smaller dimples nested within larger dimple arrangements or arranged in a repeating pattern that is geometrically similar across scales. Dimple depths may be selected in a range from about 0.01 mm to about 2 mm, with deeper dimples used in larger electrodes and shallower dimples used in smaller catheter-tip electrodes.

[0049] Irrigation apertures and fluid delivery

[0050] In embodiments that use irrigation, one or more irrigation apertures are located within grooves, within dimples, or at intersections of groove networks. Irrigation apertures may provide saline or other biocompatible fluids to reduce char formation, manage electrode temperature, improve lesion uniformity, and reduce impedance rise. Aperture diameters may be selected based on desired flow and clog resistance, for example from about 0.05 mm to about 1.0 mm, with multiple apertures distributed across the patterned region. In some embodiments, irrigation apertures open to groove bottoms so that delivered fluid spreads along the groove network and exits near boundaries where current density is elevated. In other embodiments,Attorney Docket No.: 073777.00138irrigation apertures open within dimples so that fluid pools and then spreads to adjacent surface regions. Irrigation flow rates may be selected to match clinical practice and electrode size, for example from about 1 mL / min to about 60 mL / min, with lower rates used for mapping and higher rates used for high-power RF ablation.

[0051] Materials, coatings, and construction

[0052] The conductive body may be formed from materials suitable for ablation, pacing, and / or mapping electrodes, including nickel alloys, nickel-platinum alloys, platinum and platinum alloys, platinum-iridium alloys, stainless steel, titanium, cobalt-chromium alloys, tantalum, conductive ceramics, or combinations thereof. Shape-memory alloys such as nitinol may be used for expandable or deployable embodiments that transition between insertion and deployed configurations. In sheet-formed embodiments, the conductive body is formed from a metal sheet, such as a copper sheet, or a clinically suitable metal or alloy for in vivo use. For example, electrodes may be cut or etched from a metal sheet with thickness around 0.5 mm. Some embodiments may use thicknesses selected for mechanical robustness and electrical performance, such as about 0.05 mm to about 2.0 mm, with thicker sections used for larger return electrodes and thinner sections used for foldable or deployable structures.

[0053] In embodiments where the conductive body is formed from a metal sheet, sheet thickness may be selected based on mechanical robustness, manufacturability of the self-similar pattern, flexibility for deployment, and electrical / thermal performance. By way of example, sheet thickness may be in a range from 0.05 mm to 2.0 mm, such as from 0.10 mm to 1.0 mm, such as from 0.20 mm to 0.80 mm. In certain implementations, the sheet thickness is 0.5 mm. In certain implementations, the sheet thickness is within a range of 0.3 mm to 0.7 mm, or within a range of 0.4 mm to 0.6 mm. The disclosure also contemplates thickness expressed as a tolerance around a nominal value, such as 0.5 mm ± 0.05 mm, 0.5 mm ± 0.10 mm, or 0.5 mm ± 0.20 mm.

[0054] A plating layer may be disposed over part or all of the conductive body to improve corrosion resistance, biocompatibility, and electrical stability. Gold plating is one example coating used in such electrodes. Other coatings include, but are not limited to, platinum, iridium, titanium nitride, diamond-like carbon, or oxide layers selected for clinical compatibility. Coating thickness may be selected to preserve fine geometric features while providing continuous coverage, for example from tens of nanometers to tens of micrometers depending on the process used.Attorney Docket No.: 073777.00138

[0055] Electrode surfaces and patterns may be formed through machining, micromachining, laser ablation, laser cutting, stamping, chemical etching, photolithographic patterning, electrical discharge machining, additive manufacturing followed by finishing, or combinations thereof. For groove and dimple embodiments, subtractive techniques such as milling, laser ablation, or etching may be used. For raised-feature embodiments, embossing, stamping, additive deposition, or selective etching may be used. Edges may be radiused to avoid tissue trauma while maintaining high geometric gradients; radii may be chosen in ranges such as about 0.01 mm to about 1.0 mm depending on electrode scale.

[0056] Electrodes described herein may be sized for catheter-tip use, for mapping arrays, for epicardial or endocardial placement, or for return electrode use. For ablation catheter tips, an electrode may have a diameter around 4 mm and length around 8 mm, with other sizes used based on catheter platform and intended lesion characteristics. Mapping catheter embodiments may use widths around 1 cm and lengths around 2 cm to 3 cm, with larger or smaller arrays used depending on mapping resolution requirements. In some embodiments, electrodes may have maximum transverse dimensions around 10 mm, including electrodes designed as space-filling fractal patterns with a nominal 10 mm diameter footprint. More generally, maximum transverse dimensions may fall in a range from about 1 mm to about 30 mm for catheter-associated electrodes, and larger sizes may be used for external return electrodes or patches.

[0057] In some embodiments, an electrode is configured as an end cap at a distal tip of an ablation catheter, a mapping catheter, or a pacing catheter. The end cap may be bonded to the catheter shaft through welding, brazing, adhesive bonding, overmolding, or mechanical retention features. Electrical connection may be made through welded conductors, crimped joints, conductive adhesives, or integral conductive pathways. In bipolar ablation systems, a first electrode may be positioned on one surface of tissue via a catheter, and a return electrode may be positioned on an opposite surface of tissue. The return electrode may be delivered by a second catheter, by a sheath-based device, or by an external or internal platform suitable for placing an electrode on an opposing tissue surface. This configuration supports energy delivery through the tissue volume and is particularly relevant for thick ventricular substrates.

[0058] In some embodiments, an electrode is configured as an expandable array such as, for example, an expandable array deployable from a sheath. The electrode may have a first configuration suitable for insertion and a second configuration suitable for deployment. ForAttorney Docket No.: 073777.00138example, Figure 2C shows the electrode 100 of Figure 2A in a first configuration (rolled up), while Figure 2A shows the electrode in the second configuration (unfurled). A diameter of the electrode in the first configuration may be less than a diameter in the second configuration. The electrode may be biased toward the deployed configuration through elastic properties of the material or through shape-memory behavior. Nitinol and other shape-memory alloys may be trained to assume the deployed shape at body temperature. Expandable embodiments may be implemented as telescoping frameworks, fold-out petals, rolled sheets that unfurl, or lattice structures that expand radially. In foldable and / or stretchable embodiments, the electrode in the deployed state maintains the self-similar pattern while allowing deformation. This may be achieved by forming the pattern in a thin sheet that folds along designated hinge lines, by using serpentine traces that stretch without plastic deformation, by using segmented conductive islands connected by flexible conductive bridges, or by using an elastomeric substrate with embedded conductive features. The self-similar pattern may be preserved in the sense that repeating geometric features remain present at multiple hierarchical levels even when the overall footprint deforms.

[0059] Electrical and physical basis for enhanced energy delivery

[0060] Self-similar and fractal-like electrode patterns tend to increase the ratio of boundary length to surface area relative to conventional Euclidean shapes such as circles.Electric field and current density in conductive media concentrate near boundaries and regions with high geometric gradients, often referred to as edge effects. By increasing effective edge length and incorporating multiple vertices and curved segments, the electrode-tissue interface may exhibit a larger fraction of high-gradient regions for a given projected area. This can increase local current density during RF delivery and can increase the volume of tissue exceeding an electroporation threshold during pulsed field ablation. The disclosure also contemplates that the pattern may influence impedance and heat distribution, potentially improving lesion depth while controlling excessive overheating by distributing the interface into many small high-gradient regions rather than a single sharp point.

[0061] Embodiments of the present electrode may be configured for use with conventional ablation catheters (e.g., 4 mm catheter diameter), where the self-similar electrodes are located at the catheter tip (e.g., end cap configuration shown in Figures 6 and 9). In someAttorney Docket No.: 073777.00138embodiments, the electrode may be configured for use with a mapping catheter. The electrode may be configured for use as a grounded return electrode for a bipolar configuration.

[0062] Embodiments of the electrode may have dimensions suitable to the particular use. For example, as an electrode for an ablation catheter, an electrode may have a diameter of 4 mm and a length of 8 mm. Other dimensions may be used and are within the scope of the present disclosure. Some embodiments of the present disclosure may be used with a mapping catheter. Such embodiments may have a width of 1 cm and a length of between 2 cm and 3 cm, although other lengths and widths may be used.

[0063] For most cardiac electrophysiological procedures, it is possible to target the tissue underpinning a cardiac arrhythmia with radiofrequency (RF) energy delivered from an ablation catheter. This is effective if the targeted tissue is at or near the heart’s surface. However, if the arrhythmia resides deep within the heart tissue it can be difficult or impossible to deliver adequate RF energy to penetrate the deeper layers. This is a particular problem in the low er heart chambers, termed the “ventricles,” where the heart tissue is thicker.

[0064] Conventional bipolar RF ablation is able to target arrhythmias by creating a transmural ablation that spans the cross section of the heart muscle; this configuration delivers energy from an electrode at the end of a catheter that is positioned on a surface of the heart, with a grounded electrode at the end of a different catheter positioned on an opposite tissue surface. RF energy is a medium frequency alternating current (e.g., 350-500 kHz), and when applied there is resistive heating at the electrode-tissue interfaces, with conductive heating of the tissues in between — ideally forming a confluent lesion whereby there is irreversible cell injury at 50 degrees Celsius. The size and confluence of the ablation lesion created is directly related to the current density applied w ith RF. In a significant proportion of patients, particularly those with hy pertrophied or thickened tissue, bipolar ablation fails to achieve transmurality and is associated with recurrence of arrhythmias.

[0065] The present disclosure provides an electrode design that can more effectively target deeper layers tissue, for example, heart tissue. Compared to conventional electrodes with Euclidean or near-Euclidean shapes, an ablation electrode with a self-similar design according to an embodiment of the present disclosure will enhance current density and be better able to create a transmural lesion in thick (> 20 mm) regions of the heart muscle. Self-similar electrode shapes provide an increased edge length on the boundary of the electrode compared to conventionalAttorney Docket No.: 073777.00138Euclidean shapes (Figure 3). Described by the Laplace formula, with a radiating field source there is a higher current density at areas of a high geometric gradient on a conductor such as the edges of electrodes (termed the "edge effecf '). A higher proportion of electrode edge length can therefore increase circuit density and thermal injury, and lead to a larger lesion.

[0066] In head-to-head comparisons using an experimental embodiment of a self-similar electrode (Figure 3), the self-similar electrode that is the return electrode of a bipolar ablation configuration was able to create a transmural lesion in tissue to a depth of greater than 20 mm (Figure 4A). A conventional circular electrode, having the same surface area as the self-similar electrode, was not able to create a transmural lesion with same ablation parameters, as shown in Figure 4B.

[0067] Modeling data shows similar results. For example, Figures 11A and 1 IB depict the electric potential radiated from a convention circular electrode at various penetration depths. Figures 12A and 12B show the modeled electric potential for an electrode having a self-similar geometry according to an embodiment of the present disclosure (similar to that depicted in Figures 1 A and IB). The comparison shows that the depth of penetration is improved (i.e., greater depth) using the self-similar electrode design.

[0068] Use in RF ablation, including bipolar and unipolar modes

[0069] Embodiments described herein may be suitable for conventional unipolar RF ablation and bipolar RF ablation. RF energy may use medium-frequency alternating current, for example in a range from about 200 kHz to about 1 MHz, and in many clinical systems around 350 kHz to 500 kHz. In unipolar operation, current flows between an active catheter electrode and a distant return, such as a grounding patch. In bipolar operation, current flows between two electrodes positioned in proximity, including configurations with an active catheter electrode on one tissue surface and a return electrode on an opposite tissue surface. Energy’ delivery parameters may be selected based on the clinical goal and electrode geometry-, such as powers from about 5 W to about 100 W and durations from about 1 s to about 300 s, with irrigated delivery used where desired to manage interface temperature and impedance rise. Lesion formation may be associated with tissue heating to temperatures that cause irreversible injury-, such as around 50 °C in many contexts, with additional heating and conductive spread shaping lesion geometry.Attorney Docket No.: 073777.00138

[0070] Use in pulsed field ablation (PF A)

[0071] The disclosure also supports use of self-similar, space-filling, and fractal-pattern electrodes in pulsed field ablation systems. PFA uses high-voltage pulses to create reversible or irreversible electroporation in tissue, with tissue selectivity and reduced collateral thermal injury in some contexts compared with purely thermal modalities. Electrode geometry influences electric field distribution and the region exceeding electroporation thresholds. Space-filling fractal patterns may increase effective edge length and local curvature, thereby expanding and deepening regions of elevated electric field at a given applied voltage. In unipolar PFA configurations, energy7may be delivered between the electrode and a grounding patch. Peak voltages may range, for example, from about 200 V to about 3000 V, and in certain embodiments around 1000 V, with waveform characteristics selected by the PFA generator. The disclosure contemplates PFA delivery in catheter systems that also support mapping, RF ablation, or both, and contemplates electrodes that serve as active electrodes or return electrodes depending on system design.

[0072] In some embodiments, a pulse generator may apply a train of pulses having a selected peak voltage and waveform parameters suitable to produce reversible or irreversible electroporation in the target tissue. In some embodiments, peak voltage is in a range from 200 V to 3000 V, such as from 400 V to 2000 V, such as from 600 V to 1500 V. In certain implementations, peak voltage is 1000 V. In some embodiments, peak voltage is within a range of 800 V to 1200 V, or within a range of 900 V to 1100 V. Peak voltage may be specified as a nominal value with an allowable tolerance, such as 1000 V ± 50 V, 1000 V ± 100 V, or 1000 V ± 200 V, depending on generator regulation accuracy and load conditions.

[0073] Illustrative experimental and modeling support

[0074] Benchtop evaluations have been performed to assess the influence of fractal geometry on lesion characteristics. In one study using a potato model with saline bath conductivity selected to approximate blood conductivity7, three return electrodes were manufactured from metal sheet stock, including a space-filling fractal electrode w ith a nominal 10 mm diameter footprint, a circular electrode w ith matching diameter, and a circular electrode with matching surface area (smaller diameter). Unipolar PFA delivery at a peak voltage around 1000 V produced lesions that, when dyed and cross-sectioned, exhibited greater depth for the fractal electrode relative to circular controls, with lesion width comparable across testedAttorney Docket No.: 073777.00138conditions. These observations support the proposition that a space-filling fractal geometry' may deepen the region exceeding electroporation threshold at a given applied voltage.

[0075] In a benchtop evaluation of pulsed field ablation, three return electrodes were fabricated from approximately 0.5-mm copper sheet stock, including a nominal 10-mm diameter space-filling fractal electrode, a circular electrode with a matched diameter, and a circular electrode with a matched surface area (nominal diameter about 5.5 mm). Unipolar pulsed field ablation was delivered between a grounding patch and the electrode prototypes at a peak voltage of about 1000 V using a commercial generator, with approximately 2-cm thick potato samples (Solanum tuberosum) placed in a saline bath adjusted to match blood conductivity. The samples were dyed using about 1% TTC solution, cross-sectioned, and lesion depth and width were quantified. Under these conditions, cross-sectioned lesion depth was greater for the fractal electrode (about 7.1 ± 1.2 mm, n = 5) than for the surface-area-matched circular electrode (about 4.0 ± 1.9 mm, p = 0.02, n = 5) and the diameter-matched circular electrode (about 5.7 ± 0.4 mm, p = 0.02, n = 5), while cross-sectioned lesion width for the fractal electrode (about 22.9 ± 1.8 mm) was similar to the area-matched circular electrode (about 22.3 ± 1.9 mm, p = 0.4) and the diameter-matched circular electrode (about 19.1 ± 3.7 mm, p = 0.55).

[0076] In another evaluation using a validated ventricular gel phantom model with approximately 20 mm thickness and thermochromic dyes, bipolar RF ablations were performed with an irrigated catheter positioned with controlled contact force on one surface of the gel and a return electrode positioned on the opposite surface. Three return electrodes included a spacefilling fractal electrode with a nominal 10 mm diameter footprint, a circular electrode with matching diameter, and a circular electrode with matching surface area. Measured electrical parameters included impedance and total delivered current. The fractal return electrode increased current density at the interface relative to circular controls and increased cross-sectioned lesion area defined by thermochromic response, while avoiding significant overheating relative to controls. Infrared thermography after RF delivery indicated heating concentrated at electrode edges, consistent with edge-effect mechanisms. These observations align with the theoretical basis described herein and support use of self-similar and fractal patterns to enhance lesion formation in thick substrates.

[0077] In the ventricular phantom evaluation of bipolar radiofrequency ablation, three return electrodes were fabricated from approximately 0.5-mm copper sheet stock, including aAttorney Docket No.: 073777.00138nominal 10-mm diameter space-filling fractal electrode, a circular electrode w ith a matched diameter, and a circular electrode with a matched surface area (nominal diameter about 5.5 mm). Bipolar ablations were delivered at approximately 30 W for about 60 s in a validated 20-mm thick ventricular gel phantom that incorporated thermochromic dyes having activation thresholds near 60 °C (magenta) and 90 °C (black). An irrigated ablation catheter was positioned on one gel surface with approximately 10 g of contact force in an irrigated saline bath held near 37 °C, with the return electrode on the opposite surface. Impedance and delivered current were recorded, lesion area was measured from cross-sections using the visible magenta region (> 60 °C) as the lesion boundary, and in a subset the electrodes were imaged after RF delivery using infrared thermography. Average starting impedances were reported as about 177 ± 34 Q (n = 9) for the fractal electrode, about 193 ± 22 Q (n = 5) for the area-matched circle, and about 167 ± 23 Q (n = 13) for the diameter-matched circle. Mean delivered current was about 371.9 ± 38.0 mA for the fractal electrode, similar to the diameter-matched circle at about 373.4 ± 42.0 mA (p = 0.93) and greater than the area-matched circle at about 328.2 ± 44.5 mA (p = 0.037), with the fractal electrode also producing increased current density and greater cross-sectioned lesion area relative to the circular controls, while infrared thermography showed heating concentrated at electrode edges consistent with geometric edge effects.

[0078] The disclosure further contemplates numerical modeling of electric potential propagation in tissue for conventional circular electrodes and for self-similar electrodes.Modeling results may be visualized as isosurfaces of electric potential at various penetration depths and times. In representative modeling comparisons, the self-similar electrode geometry exhibited deeper penetration of electric potential relative to a conventional circular electrode under otherwise comparable conditions, supporting the practical expectation of improved lesion depth and / or more favorable electric field distribution.

[0079] Catheter systems and methods

[0080] An ablation catheter may include any electrode described herein, including catheter tip end-cap embodiments, expandable array embodiments, and return electrode embodiments configured for bipolar operation. A mapping catheter may include any electrode described herein, including embodiments tailored to sensing electrical signals with high spatial resolution and embodiments that integrate irrigation apertures when desired for combined mapping and ablation workflows. A pacing catheter may include any electrode described herein,Attorney Docket No.: 073777.00138including embodiments configured to deliver pacing stimulation pulses to biological tissue and embodiments configured to sense electrical signals during pacing and capture verification. With reference to Figure 15, in an aspect, a method 400 of performing bipolar RF ablation includes positioning 403 a first electrode at tissue, positioning 406 a return electrode at tissue where the return electrode includes a self-similar patterned electrode as described herein, and delivering 409 RF energy between the first electrode and the return electrode. The same electrode architectures may be used as active electrodes for unipolar RF ablation. Methods may further include delivering 412 pulsed-field ablation energy using an electrode described herein, including unipolar PF A delivery between the electrode and a grounding patch, and in some embodiments applying peak voltages around 1000 V. Methods may also include irrigating fluid through one or more irrigation apertures during RF delivery to manage interface temperature and lesion characteristics, and may aim to form transmural lesions in cardiac tissue where clinically appropriate.

[0081] In this disclosure, the term “about’' when used with a numerical value indicates a range that accounts for ordinary manufacturing tolerances, measurement uncertainty, and clinically or experimentally acceptable variation for the stated parameter. In some embodiments, “about” indicates ±1%, ±2%, ±5%, ±10%, or ±20% of the stated value, depending on the parameter and the measurement technique. In each case, the disclosure also expressly contemplates the stated numerical value without the term “about,” and also contemplates explicit endpoint ranges that include the stated value.

[0082] The embodiments described herein are illustrative and are not intended to limit the scope of the disclosure. Variations in, for example, geometry, scale factor between hierarchical levels, pattern topology, manufacturing method, material selection, coating selection, and integration with catheter platforms may be implemented while retaining the principles described herein, including formation of self-similar patterns with repeating geometric features at multiple hierarchical levels and the resulting influence on electric field and current density distribution in tissue.

[0083] Although the present disclosure has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present disclosure may be made without departing from the spirit and scope of the present disclosure.

Claims

Attorney Docket No.: 073777.00138What is claimed is:

1. An electrode for delivering electrical energy and / or sensing electrical signals in biological tissue, comprising:a conductive body defining an electrode surface; anda self-similar pattern formed in the electrode surface, wherein the self-similar pattern comprises repeating geometric features arranged in at least two hierarchical levels such that a first-level arrangement of the repeating geometric features defines a first geometry and a second-level arrangement of the repeating geometric features defines a second geometry that is geometrically similar to the first geometry.

2. The electrode of claim 1, wherein the repeating geometric features comprise a plurality of conductive members arranged in the self-similar pattern.

3. The electrode of claim 2, wherein the electrode comprises:a conductive core;at least two conductive first members extending from the core, each first member having at least one distal end; andfor each distal end of each first member, a corresponding set of at least two conductive second members extending from that distal end, wherein the second members in each set are arranged in a geometry similar to an arrangement of the first members about the core.

4. The electrode of claim 3, wherein the first members are symmetrically arranged about the core.

5. The electrode of claim 3, wherein the first members are attached to the core at a location along a longitudinal length of the core other than at an end such that each first member has two distal ends distal with respect to the core.

6. The electrode of claim 3, wherein, for each distal end of each first member, a number of second members in the corresponding set is the same as a number of the first members.

7. The electrode of claim 3, further comprising, for each distal end of each second member, a corresponding set of conductive third members extending from that distal end, wherein the third members in each set are arranged in a geometry similar to the arrangement of the first members about the core.Attorney Docket No.: 073777.001388. The electrode of claim 1, wherein the self-similar pattern is formed by negative space not occupied by conductive material.

9. The electrode of claim 8, wherein the repeating geometric features comprise one or more grooves formed in the conductive body and arranged in the self-similar pattern.

10. The electrode of claim 9. further comprising one or more irrigation apertures located within at least one groove.

11. The electrode of claim 1, wherein the self-similar pattern is formed by raised conductive material above a surface of the conductive body.

12. The electrode of claim 1, wherein the self-similar pattern comprises a contiguous, space-filling pattern fonned in the electrode surface.

13. The electrode of claim 1, wherein the repeating geometric features comprise a plurality of dimples arranged in the self-similar pattern on the electrode surface.

14. The electrode of claim 13, wherein at least one of the dimples includes an irrigation aperture.

15. The electrode of claim 1, wherein the electrode is configured as an end cap for a distal tip of an ablation catheter or a mapping catheter.

16. The electrode of claim 1, wherein the electrode is configured as an expandable array deployable from a sheath, the electrode having a first configuration for insertion and a second configuration when deployed, wherein a diameter of the electrode in the first configuration is less than a diameter of the electrode in the second configuration, and wherein the electrode is biased toward the second configuration.

17. The electrode of claim 16, wherein the electrode in the second configuration is configured to be foldable and / or stretchable while maintaining the self-similar pattern.

18. The electrode of claim 1, wherein the self-similar pattern comprises a space-filling fractal pattern.

19. The electrode of claim 18, wherein the space-filling fractal pattern comprises a pattern that repeats upon itself at a plurality of levels of magnification.Attorney Docket No.: 073777.0013820. The electrode of claim 1 , wherein the repeating geometric features define a boundary including a plurality of vertices and curved segments that increase edge length at the electrodetissue interface relative to a circular boundary having an equal projected area.

21. The electrode of claim 1, wherein the electrode is configured as a return electrode for bipolar ablation.

22. The electrode of claim 21, wherein the return electrode is configured to be positioned on an opposite side of tissue relative to an active electrode positioned by a catheter.

23. The electrode of claim 1. wherein the conductive body is formed from a metal sheet.

24. The electrode of claim 23, wherein the metal sheet has a thickness of about 0.5 mm.

25. The electrode of claim 1. further comprising a plating layer disposed over at least a portion of the conductive body.

26. The electrode of claim 25, wherein the plating layer comprises gold.

27. The electrode of claim 1, wherein the electrode has a maximum transverse dimension of about 10 mm.

28. The electrode of claim 1. wherein the electrode is configured to deliver pulsed field ablation (PF A) energy.

29. The electrode of claim 1, wherein the electrode is configured to deliver unipolar PFA between the electrode and a grounding patch.

30. The electrode of claim 1, wherein the electrode is configured to deliver pacing stimulation pulses to biological tissue.

31. The electrode of claim 1, wherein the electrode is configured to deliver ablation energy to biological tissue.Attorney Docket No.: 073777.0013832. A method of performing bipolar radiofrequency ablation, comprising:positioning a first electrode at a tissue;positioning a return electrode at the tissue, the return electrode comprising an electrode of claim 1; anddelivering radiofrequency energy between the first electrode and the return electrode.

33. The method of claim 32, wherein the electrode is used as an active electrode for unipolar radiofrequency ablation.

34. The method of claim 32, further comprising delivering pulsed-field ablation energy using the electrode.

35. The method of claim 34, wherein delivering pulsed-field ablation energy comprises applying a peak voltage of about 1000 V.

36. The method of claim 32, wherein the electrode includes at least one irrigation aperture, and the method further comprises irrigating fluid through the irrigation aperture while delivering the radiofrequency energy.

37. The method of claim 32, wherein the radiofrequency energy is delivered to form a transmural lesion in cardiac tissue.

38. An ablation catheter comprising an electrode according to any one of claims 1-29.

39. A mapping catheter comprising an electrode according to any one of claims 1-29.

40. An electrophysiology catheter comprising an electrode according to any one of claims 1-29, wherein the catheter is configured to apply pacing stimulation pulses and record intracardiac electrograms.

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