Electrode design for directional lithotripsy catheters.

Abstract

The present disclosure provides a catheter for treating lesions in a body lumen, such as calcified lesions and occlusions in a vessel. The catheter can include a dual-layer electrode assembly having a first conductive sheath and a second conductive sheath circumferentially disposed therearound. In some implementations, the first conductive sheath can be a flat coil. When a voltage is applied across the conductive sheath, current flows across an arcing region, for example, from a distal end of the first sheath to a distal end of the second sheath, creating shock waves and / or cavitation bubbles. As treatment continues, the sheath slowly erodes in the arcing region where current flows between the sheaths. To increase the life of the electrode assembly, the distal end of the sheath can be shaped to promote sheath erosion in a predetermined or semi-controlled pattern.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 63 / 284,582, filed November 30, 2021, entitled "DUAL-LAYER ELECTRODE DESIGN FOR LITHOTRIPSY CATHETERS," and U.S. Provisional Patent Application No. 63 / 349,994, filed June 7, 2022, entitled "HELICAL ELECTRODE DESIGN FOR LITHOTRIPSY CATHETERS," which are incorporated by reference in their entireties herein.

[0002] FIELD OF THE DISCLOSURE The present disclosure relates generally to the field of medical devices and methods, and more specifically to an electrode assembly for inclusion in a catheter device used to treat lesions in body lumens, such as calcified lesions and obstructions in blood vessels, and kidney stones in the urinary system. [Background technology]

[0003] Calcified lesions in body lumens can adversely affect the health of patients. For example, when calcium accumulates in the walls of coronary arteries, calcification of the arteries can restrict blood flow to the heart muscle, which can eventually lead to a heart attack. Catheter devices are one type of device that can be used to treat calcified lesions in body lumens, such as arteries. When treating lesions with catheter devices, it is important to minimize damage to surrounding soft tissues while still crushing as much of the lesion as possible.

[0004] A wide variety of catheters have been developed to treat lesions such as calcified lesions and plaques in vessels associated with arterial disease. For example, treatment systems for percutaneous coronary or peripheral angioplasty use angioplasty balloons to widen calcified lesions and restore normal blood flow in the vessel. In these types of procedures, a catheter carrying a balloon is advanced into the vessel along a guidewire until the balloon is aligned with the calcified plaque. The balloon is then pressurized, which causes the balloon to expand within the vessel and push the calcified plaque back into the vessel wall, widening the blocked area of ​​the vessel. Balloons with different diameters and lengths appropriate for coronary vessels or different types of peripheral vessels (e.g., above the knee, below the knee, brachial artery disease, etc.) can be used to access different anatomical structures.

[0005] More recently, catheters have been developed that include one or more electrode pairs for generating shock waves inside an angioplasty balloon. Such shock wave devices can be particularly effective for treating calcified lesions, as the acoustic pressure from the shock waves can fragment and disintegrate the lesion in the vicinity of the angioplasty balloon without harming the surrounding tissue. This therapy has become known as intravascular lithotripsy (IVL), although the principle of using shock wave devices is not limited to systems that include balloons. In these devices, a catheter is advanced over a guidewire through the patient's vasculature until it is positioned proximal to the lesion in the body lumen. The balloon is then inflated with a conductive fluid, which causes the balloon to expand and contact the lesion. A shock wave emitter can then be activated to create acoustic shock waves (transformation of electrical energy into mechanical energy) that propagate through the wall of the angioplasty balloon and into the lesion. Once the lesion has been fragmented by the acoustic shock waves, the balloon can be further expanded to increase the cross-sectional area of ​​the lumen and improve blood flow through the vessel.

[0006] Catheters including electrode pairs for generating directed cavitation bubbles for the treatment of calcified lesions in vessels have also been developed. In these devices, an open-ended catheter is advanced into a patient's vessel using a guidewire until it is proximal to the lesion. A relatively lower voltage is applied across the electrode pair at a relatively higher repetition rate, causing gas cavitation bubbles to form on the surface of the electrodes. The cavitation bubbles begin to accumulate on the electrodes until fluid flow through the open distal tip of the catheter causes the cavitation bubbles to flow into the target lesion in the body lumen. Once the lesion has been sufficiently reduced by the cavitation bubbles, debris can be aspirated from the treatment site and the catheter can be removed from the vessel. The implementation of such open-ended catheters allows for a degree of directional control, directing where the cavitation bubbles form and how they progress and evolve outward from the catheter.

[0007] Efforts have been made to improve the design of the electrode assemblies contained within shock wave and directed cavitation catheters. For example, low-profile electrode assemblies have been developed that reduce the transverse profile of the catheter, allowing the catheter to more easily navigate calcified blood vessels and deliver shock waves in more severely blocked areas of the vessel. Examples of low-profile electrode designs can be found in U.S. Patent Nos. 8,888,788 and 10,709,462, both of which are incorporated herein by reference. Other catheter designs have improved the delivery of shock waves, for example, by specific electrode structures and configurations, thereby directing the shock waves in a forward direction to break up tighter, more difficult to cross blockages in the vessel. Examples of forward-launched catheter designs can be found in U.S. Patent No. 10,966,737 (Patent Document 2) and U.S. Publication Nos. 2019 / 0388110 and 2021 / 085348 (all of which are incorporated by reference into this specification).

[0008] Despite these advances in electrode assembly design, the duration of treatment with shockwave or cavitation catheters is limited by the lifespan of the electrode pairs contained within the catheter, which slowly erode and deteriorate as shockwaves and / or cavitation bubbles are generated across the electrodes. Many currently available catheter designs include electrodes formed from conductive wires or other thin conductive materials that have a relatively small conductive surface area and deteriorate rapidly during the procedure. Other electrode assemblies deteriorate in random or unfavorable patterns that reduce the lifespan of the electrodes. Thus, many catheters cannot be used for more than an hour before the electrodes become too eroded to continue treatment. As a result, many currently available designs lack the necessary lifespan for longer shockwave procedures, such as procedures to remove resistant lesions and treat more chronically occluded areas of the vessel. Thus, electrode structure and design variations are provided herein to address unmet needs for shockwave and cavitation catheter designs, which incorporate electrode assemblies with increased lifespans and more favorable deterioration patterns. In particular, the electrode structures and designs herein also provide a significant degree of directional control for the formation of shock waves and cavitation bubbles emanating from the electrode assembly. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Pat. No. 8,888,788 [Patent Document 2] U.S. Pat. No. 10,966,737 Summary of the Invention [Means for solving the problem]

[0010] A catheter having an electrode pair configured to generate shock waves and / or cavitation bubbles can be useful for treating calcified lesions in a body lumen (such as a vessel) without damaging the surrounding soft tissue. When used to treat a lesion, a voltage can be applied across the electrodes, which causes shock waves and / or cavitation bubbles to form. The shock waves and / or cavitation bubbles can then be caused to flow outward, such as from the distal end of the open-ended catheter to the treatment site. Once the lesion has been sufficiently reduced, debris can be aspirated from the treatment site.

[0011] When using such catheter devices to treat and remove calcified lesions, the electrodes of the electrode pair may erode. Electrode erosion (also referred to as deterioration) may then limit the duration of treatment, as if the erosion progresses too far, the electrodes will no longer generate shock waves and / or cavitation bubbles capable of treating the lesion. Thus, extending the life of the electrodes is a major concern for electrode assemblies used in catheters to calcified occlusions (e.g., lesions). Additionally, ensuring that erosion proceeds in a relatively controlled manner is also a major concern, as largely asymmetric erosion can significantly shorten the usable duration of the electrodes.

[0012] In one embodiment, the above goals are realized in a catheter that includes an electrode assembly formed from concentric conductive metal sheaths separated by an insulating layer. Shock waves and / or cavitation bubbles are formed across the distal end of the conductive sheath, which serves as an electrode of an electrode pair, slowly degrading the distal end over time. The distal end of the conductive sheath is shaped such that degradation proceeds in a semi-controlled manner and is more evenly distributed around the circumference of the conductive sheath. This increases the maximum life of the electrode assembly and allows for longer duration treatments with the catheter.

[0013] An exemplary embodiment provides a catheter for treating an occlusion in a body lumen. The catheter includes an elongated tube and a cylindrical inner conductive sheath mounted within the elongated tube. The inner conductive sheath has a distal end. A cylindrical outer conductive sheath is mounted circumferentially around the inner conductive sheath within the elongated tube. The outer conductive sheath has a distal end proximal to the distal end of the inner conductive sheath. An insulating sheath is mounted within the elongated tube between the outer conductive sheath and the inner conductive sheath. When a voltage pulse is applied across the inner conductive sheath and the outer conductive sheath, current flows across an arcing region between the inner conductive sheath and the outer conductive sheath, generating cavitation bubbles and / or shock waves that can be used to treat an occlusion in a body lumen.

[0014] In a further embodiment, a catheter system is provided herein that includes an electrode assembly including a conductive sheath mounted within the catheter, an insulating sheath mounted circumferentially within the conductive sheath, and a flat coil disposed on the inner surface of the insulating sheath. In one or more examples, the conductive sheath and the flat coil can form an electrode of an electrode pair such that when a voltage is applied to the electrode assembly, a current travels between the flat coil and the conductive sheath. As the current travels, an arc discharge region can appear at the shortest distance between the flat coil and the conductive sheath. In the arc discharge region, shock waves and / or cavitation bubbles can be generated. Thus, in one or more examples, when a voltage pulse is applied across the flat coil and the conductive sheath of the electrode assembly, cavitation bubbles and / or shock waves can be generated that can be used to treat an obstruction in a body lumen.

[0015] An embodiment of the present disclosure may have a catheter for treating an occlusion in a body lumen, the catheter including an elongated tube, a cylindrical inner conductive sheath mounted within the elongated tube, the inner conductive sheath having a distal end, a cylindrical outer conductive sheath mounted circumferentially within the elongated tube around the inner conductive sheath, the outer conductive sheath having a distal end proximal to the distal end of the inner conductive sheath, and an insulating sheath mounted within the elongated tube between the outer conductive sheath and the inner conductive sheath, wherein when a voltage pulse is applied across the inner conductive sheath and the outer conductive sheath, current flows across an arcing region between the inner conductive sheath and the outer conductive sheath, generating cavitation bubbles and / or shock waves. In some aspects, the elongated tube includes a fluid lumen for flowing a conductive fluid along the catheter and through a fluid outlet port at the distal end of the catheter. In such aspects, the outer conductive sheath, the insulating sheath, and the inner conductive sheath are mounted within the fluid lumen such that fluid flowing through the fluid lumen flows through the inner conductive sheath. In other aspects, the elongate tube includes an aspiration lumen for removing debris from the body lumen, and in optional aspects also includes a guidewire lumen sized to receive a guidewire. In further aspects, the arcing region is located where the distal end of the outer conductive sheath is closest to the distal end of the inner conductive sheath. In such aspects, generating cavitation bubbles and / or shock waves causes the distal end of the inner conductive sheath to erode proximate to the arcing region, and the erosion of the inner conductive sheath causes current to flow across a secondary arcing region between the distal end of the inner conductive sheath and the distal end of the outer conductive sheath. In a similar aspect, generating cavitation bubbles and / or shock waves causes a distal end of the outer conductive sheath to erode proximate to the arc discharge region, and the erosion of the outer conductive sheath causes current to flow across a secondary arc discharge region between the distal end of the outer conductive sheath and the distal end of the inner conductive sheath.In some aspects, when a voltage pulse is applied, a positive pressure spike is generated followed by a negative pressure spike.

[0016] Another embodiment of the present disclosure may have a catheter for treating an occlusion in a body lumen, the catheter including an elongated tube, a cylindrical conductive sheath mounted within the elongated tube, the conductive sheath having a distal end, an insulating sheath mounted circumferentially within the conductive sheath, the insulating sheath having a distal end proximal to the distal end of the conductive sheath, and a flat coil disposed on an inner surface of the insulating sheath, the flat coil having a distal end proximal to the distal end of the conductive sheath and the distal end of the insulating sheath, wherein when a voltage pulse is applied across the flat coil and the conductive sheath, current flows across an arcing region between the flat coil and the conductive sheath generating cavitation bubbles and / or shock waves. In some aspects, the flat coil has a rectangular cross-section with a planar inner surface opposite the inner surface of the insulating sheath. In another aspect, the elongate tube includes a fluid lumen for flowing a conductive fluid along the catheter and through a fluid outlet port at the distal end of the catheter, and the conductive sheath, insulating sheath, and flat coil can all be mounted within the fluid lumen such that fluid flowing through the fluid lumen flows through the flat coil. In a further aspect, the arcing region is located where the distal end of the conductive sheath is closest to the distal end of the flat coil. In such an aspect, generating cavitation bubbles and / or shock waves causes the insulating sheath to erode proximate to the arcing region, the erosion of the insulating sheath exposing the outer surface of the flat coil and causing current to flow across a secondary arcing region between the outer surface of the flat coil and the distal end of the conductive sheath. Similarly, generating cavitation bubbles and / or shock waves causes the distal end of the conductive sheath to erode proximate to the arcing region, and the erosion of the conductive sheath begins before erosion of the insulating sheath begins. In some aspects, the elongate tube includes an aspiration lumen for removing debris from the body lumen, and in optional aspects, the elongate tube includes a guidewire lumen sized to receive a guidewire.In an alternative aspect, the flat coil is constructed with one or more cross ties extending along the length of the flat coil between each coil of the flat coil. In another aspect, an adhesive is disposed in the areas between the coils of the flat coil on the inner surface of the insulating sheath, the adhesive filling the areas between the coils and securing the flat coil to the insulating sheath. In a further aspect, when a voltage pulse is applied, a positive pressure spike is generated followed by a negative pressure spike. [Brief description of the drawings]

[0017] Exemplary aspects of the present disclosure are described in detail below with reference to the following drawing figures: It is intended that the embodiments and figures disclosed herein be considered illustrative, not restrictive.

[0018] [Figure 1] 1A-1G illustrate a mode of operation for generating forward-firing cavitation bubbles using an electrode assembly according to an aspect of the present disclosure.

[0019] [Diagram 2] FIG. 2 illustrates an exemplary erosion pattern for the degradation of a cylindrical electrode.

[0020] [Diagram 3] FIG. 3 illustrates a perspective view of an exemplary electrode assembly of a catheter according to an aspect of the present disclosure.

[0021] [Figure 4A] FIG. 4A illustrates a side view of an exemplary inner conductive sheath of an electrode assembly, such as the electrode assembly of FIG. 3, in accordance with an aspect of the present disclosure.

[0022] [Figure 4B] FIG. 4B illustrates a perspective view of an exemplary inner conductive sheath of an electrode assembly, such as the electrode assembly of FIG. 3, in accordance with an aspect of the present disclosure.

[0023] [Figure 5A]FIG. 5A illustrates a left side cross-sectional view of an exemplary electrode assembly of a catheter in accordance with an aspect of the present disclosure.

[0024] [Figure 5B] FIG. 5B illustrates a front view of the exemplary electrode assembly of FIG. 4A in accordance with an aspect of the present disclosure.

[0025] [Figure 6] FIG. 6 illustrates a perspective view of the example electrode assembly of FIG. 3 after the inner conductive sheath according to aspects of the present disclosure has been degraded by the generation of a series of shock waves or cavitation bubbles.

[0026] [Figure 7A] FIG. 7A illustrates a front side view of an exemplary inner conductive sheath of an electrode assembly, such as the electrode assembly of FIG. 6, in accordance with an aspect of the present disclosure.

[0027] [Figure 7B] FIG. 7B illustrates a perspective view of an exemplary inner conductive sheath of an electrode assembly, such as the electrode assembly of FIG. 6, in accordance with an aspect of the present disclosure.

[0028] [Figure 8A] FIG. 8A illustrates a left side cross-sectional view of an exemplary electrode assembly of a catheter, such as the electrode assembly of FIG. 6, in accordance with an aspect of the present disclosure.

[0029] [Figure 8B] FIG. 8B illustrates a front view of an exemplary electrode assembly of a catheter, such as the electrode assembly of FIG. 6, in accordance with an aspect of the present disclosure.

[0030] [Figure 8C] FIG. 8C illustrates an enlarged, more detailed cross-sectional view of a deteriorated distal end of the exemplary electrode assembly of FIG. 8A in accordance with an aspect of the present disclosure.

[0031] [Figure 9A] FIG. 9A illustrates a perspective view of an exemplary electrode assembly of a catheter according to an aspect of the present disclosure.

[0032] [Figure 9B] FIG. 9B illustrates a left side cross-sectional view of an exemplary electrode assembly of the catheter shown in FIG. 9A in accordance with an aspect of the present disclosure.

[0033] [Figure 10] FIG. 10 illustrates a perspective view of the example electrode assembly of FIG. 9A after the outer conductive sheath according to aspects of the present disclosure has been degraded by the generation of a series of shock waves or cavitation bubbles.

[0034] [Figure 11A] FIG. 11A illustrates a left side cross-sectional view of an exemplary electrode assembly of the catheter shown in FIG. 10 in accordance with an aspect of the present disclosure.

[0035] [Figure 11B] FIG. 11B illustrates a front view of an exemplary electrode assembly of the catheter shown in FIG. 10 in accordance with an aspect of the present disclosure.

[0036] [Figure 11C] FIG. 11C illustrates an enlarged, more detailed cross-sectional view of a deteriorated distal end of the exemplary electrode assembly of FIG. 11A in accordance with an aspect of the present disclosure.

[0037] [Figure 12] FIG. 12 illustrates a perspective view of a distal end of an exemplary catheter according to an aspect of the present disclosure.

[0038] [Figure 13A] FIG. 13A illustrates a top side cross-sectional view of the distal end of the exemplary catheter shown in FIG. 12 in accordance with an aspect of the present disclosure.

[0039] [Figure 13B] 13B illustrates a left side view of the distal end of the exemplary catheter shown in FIG. 12 in accordance with an aspect of the present disclosure.

[0040] [Figure 13C] FIG. 13C illustrates a front view of the distal end of the exemplary catheter shown in FIG. 12 in accordance with an aspect of the present disclosure.

[0041] [Figure 14A] FIG. 14A illustrates a perspective view of a distal end of an exemplary catheter having a guidewire lumen in accordance with an aspect of the present disclosure.

[0042] [Figure 14B] FIG. 14B illustrates a perspective view of a distal end of an exemplary catheter having a guidewire lumen in accordance with an aspect of the present disclosure.

[0043] [Figure 15A] FIG. 15A illustrates a top side cross-sectional view of the distal end of the exemplary catheter shown in FIG. 14B in accordance with an aspect of the present disclosure.

[0044] [Figure 15B] FIG. 15B illustrates a left side view of the distal end of the exemplary catheter shown in FIG. 14B in accordance with an aspect of the present disclosure.

[0045] [Figure 15C] FIG. 15C illustrates a front view of the distal end of the exemplary catheter shown in FIG. 14B in accordance with an aspect of the present disclosure.

[0046] [Figure 16] FIG. 16 is a graph showing measurements of pressure generated by a device constructed in accordance with FIGS. 3-5.

[0047] [Figure 17] FIG. 17 illustrates a perspective view of an exemplary electrode assembly of a catheter according to an aspect of the present disclosure.

[0048] [Figure 18] FIG. 18 illustrates a perspective view of an exemplary flat coil of an electrode assembly according to an aspect of the present disclosure.

[0049] [Figure 19] FIG. 19 illustrates a perspective view of an exemplary flat coil with cross-tie electrode assemblies in accordance with an aspect of the present disclosure.

[0050] [Figure 20] FIG. 20 illustrates a perspective cross-sectional view of an exemplary electrode assembly of a cathode according to an aspect of the present disclosure.

[0051] [Figure 21A] FIG. 21A illustrates a left side cross-sectional view of an exemplary electrode assembly of a catheter in accordance with an aspect of the present disclosure.

[0052] [Figure 21B] FIG. 21B illustrates a front view of the exemplary electrode assembly of FIG. 21A in accordance with an aspect of the present disclosure.

[0053] [Figure 22] FIG. 22 is a graph showing measurements of pressure generated by a device constructed in accordance with FIG.

[0054] [Diagram 23] FIG. 23 illustrates a perspective view of the example electrode assembly of FIG. 17 prior to any erosion in accordance with an aspect of the present disclosure.

[0055] [Figure 24A] FIG. 24A illustrates an enlarged detailed view of the eroded distal end of the exemplary electrode assembly of FIG. 17 in accordance with an aspect of the present disclosure.

[0056] [Figure 24B] FIG. 24B illustrates an enlarged detailed view of the eroded distal end of the example electrode assembly of FIG. 17 as erosion in accordance with an aspect of the present disclosure expands.

[0057] [Figure 25A] FIG. 25A illustrates a perspective view of the example electrode assembly of FIG. 17 after initial erosion caused by the generation of a series of shock waves and / or cavitation bubbles in accordance with aspects of the present disclosure.

[0058] [Figure 25B] FIG. 25B illustrates a perspective view of the example electrode assembly of FIG. 17 after extensive erosion caused by the generation of a series of shock waves and / or cavitation bubbles in accordance with aspects of the present disclosure.

[0059] [Figure 26] FIG. 26 illustrates a perspective view of a distal end of an exemplary catheter in accordance with an aspect of the present disclosure.

[0060] [Figure 27A] FIG. 27A illustrates a left side cross-sectional view of a distal end of an exemplary catheter in accordance with an aspect of the present disclosure.

[0061] [Figure 27B] FIG. 27B illustrates a front view of a distal end of an exemplary catheter in accordance with an aspect of the present disclosure.

[0062] [Figure 28] 28A and 28B illustrate perspective views of an exemplary electrode assembly having an internal coiled electrode with a curved distal tip in accordance with an aspect of the present disclosure.

[0063] [Figure 29] FIG. 29 illustrates a perspective view of an exemplary electrode assembly having an outer coiled electrode and a solid tube inner electrode in accordance with aspects of the present disclosure.

[0064] [Diagram 30] FIG. 30 illustrates a perspective view of an exemplary electrode assembly having an outer clockwise coiled electrode and an inner counterclockwise coiled electrode in accordance with aspects of the present disclosure.

[0065] [Figure 31-1] FIG. 31A illustrates a perspective view of an exemplary electrode assembly having an external electrode with cutout patterning in accordance with an aspect of the present disclosure.

[0066] [Figure 31-2] 31B-31E illustrate an exemplary progression of electrode degradation for an electrode having cutout patterning as shown in FIG. 31A in accordance with aspects of the present disclosure.

[0067] [Figure 32-1] 32A-32H are images captured from a high speed video showing an exemplary electrode assembly generating a forward-directed vapor bubble in accordance with an aspect of the present disclosure. [Figure 32-2] 32A-32H are images captured from a high speed video showing an exemplary electrode assembly generating a forward-directed vapor bubble in accordance with an aspect of the present disclosure. [Figure 32-3] 32A-32H are images captured from a high speed video showing an exemplary electrode assembly generating a forward-directed vapor bubble in accordance with an aspect of the present disclosure. [Figure 32-4] 32A-32H are images captured from a high speed video showing an exemplary electrode assembly generating a forward-directed vapor bubble in accordance with an aspect of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0068] The following description is presented to enable those skilled in the art to make and use the various embodiments disclosed herein. Descriptions of specific devices, assemblies, techniques, and applications are provided only as examples. Various modifications of the examples described herein will be readily apparent to those skilled in the art, and the general principles described herein may be applied to other examples and applications without departing from the spirit and scope of the various embodiments. Thus, the various embodiments are not intended to be limited to the examples described and shown herein, but rather are to be accorded the scope consistent with the claims.

[0069] Described herein is a catheter that incorporates design elements that improve the lifespan of the electrode assembly, allowing for longer duration shockwave and cavitation therapy. As shockwaves and / or cavitation bubbles are generated across the electrode pair, the electrode surface slowly erodes where current flows between the electrodes (i.e., in the "arcing region" between the pair of electrodes). As the initial arcing region erodes and the distance between the electrodes in the initial arcing region increases, current may begin to flow from undesirable secondary arcing regions or may cease to flow completely, and thus shockwaves and / or cavitation bubbles are no longer generated. Over the course of treatment, the electrodes may erode and deteriorate in a non-uniform manner, which limits the usable lifespan of the electrode assembly. For example, when the electrodes are formed from insulated wire or other thin conductive material with a relatively small conductive surface area, electrode erosion may proceed rapidly, resulting in premature termination of the shockwave procedure. Other catheter designs may include electrodes spaced a uniform distance apart across the surface of the electrode, thereby causing degradation to proceed in a stochastic manner, which results in uncontrolled, uneven degradation across the electrode surface. Another electrode design may be formed from two cylindrical conductive metal sheaths mounted concentrically within the catheter, which may demonstrate a longer life than insulated wire electrode designs. However, since the life of an electrode design directly impacts treatment duration, it is desirable to increase the life of the electrodes.

[0070] To increase the lifespan of the electrode assembly, in some of the implementations described herein, the electrode assembly is shaped so that degradation progresses in a predictable or semi-controlled manner across the surface area of ​​the electrodes. In particular, the electrode pairs of the assembly are shaped so that some portions of the electrode surface are closer in distance and other portions are farther apart. Thus, when a voltage is applied across the electrode pair, current initially flows across the initial arcing region where the electrodes are closest in distance. As the electrode surface erodes in the initial arcing region, current begins to flow across the secondary arcing region that provides a new least resistance (i.e., closest distance) path between the electrodes. As treatment continues, successively more distant portions will begin to degrade as the arcing region moves across the remaining surface area of ​​the electrodes.

[0071] To increase the lifespan of the electrode assembly, in other implementations described herein, the assembly can incorporate a flat non-insulated spiral electrode. The flat spiral electrode can have a larger cross-sectional area relative to the round wire, which can ensure that the flat spiral electrode has a lower resistance and therefore provides a higher current flow to the arcing region. Relative to an electrode pair with two concentric conductive sheaths, the flat spiral electrode can generate usable cavitation for a longer duration, thereby enabling longer shock wave and cavitation therapy. Furthermore, the use of a flat spiral electrode can improve the manufacturability of the electrode assembly.

[0072] Depending on the geometry of the electrodes, the location of the initial and further arcing regions can be configured to be relatively predictable or predetermined. For example, by providing a gradual slope along the surface of the electrode, or by providing a series of notches, waves, or other shapes along the electrode surface, a portion of the electrode surface can be located at a predetermined distance from the corresponding electrode of the pair. Throughout the course of the procedure, the surface of the electrode degrades in a semi-controlled manner according to the relative distance between the electrodes of the pair, starting from the closest distant portion of the electrode surface (i.e., the initial arcing region) and proceeding to successively more distant portions of the electrode surface. This results in more even erosion across the electrode surface and an increased maximum lifespan of the electrode assembly, allowing for longer duration shock wave and / or cavitation treatments.

[0073] The catheter designs described herein may be similar to current shockwave catheters in that they include at least one electrode pair within the working length of the catheter that delivers acoustic shock waves and / or cavitation bubbles to a treatment site proximate the distal tip of the catheter. For example, as described in U.S. Pat. No. 10,709,462 (incorporated herein by reference), the first electrode of the catheter can be formed from the side end of a conductive metal sheath mounted within the catheter. The electrode pair can be formed by positioning a second conductive material a controlled distance (i.e., gap) away from the conductive sheath to allow a reproducible arc across the electrodes for a given current and voltage. In some examples, as described in the above references, the second electrode of the electrode pair can be formed from a conductive portion (e.g., insulation removed portion) of a wire extending along the length of the catheter. Additionally or alternatively, an exemplary electrode pair can be formed from two cylindrical conductive metal sheaths mounted concentrically within the catheter, as described herein. Such an electrode assembly may have a relatively smaller cross-sectional profile compared to existing electrode assembly designs, for example, with a cross-sectional profile of 0.8 mm to 1.2 mm in diameter. Such an electrode assembly design may also facilitate manufacturing of the catheter by simplifying the process for constructing the electrode assembly.

[0074] As provided herein, any disclosure of a numerical range describing a dimension or measurement, such as thickness, length, weight, time, frequency, temperature, voltage, current, angle, etc., should be understood to include any numerical increment or gradient within the stated range for the given dimension or measurement.

[0075] 1A-1G illustrate a mode of operation for generating forward-firing cavitation bubbles using an electrode assembly. An exemplary electrode assembly 10 having an outer electrode 12 and an inner electrode 14 is illustrated in a perspective view in FIG. 1A and understood to be immersed in a conductive fluid. It should be understood that in other implementations and variations, the electrodes of the electrode assembly may be configured in different orientations, different shapes relative to one another, and may provide different profiles. FIG. 1B illustrates the electrode assembly 10 in a front view, and FIG. 1C illustrates the electrode assembly in a cross-sectional side profile view. Both FIGS. 1B and 1C further illustrate the location of an electrical spark 16, which may be generated in the gap between the outer electrode 12 and the inner electrode 14 when energy is applied across the paired electrodes of the electrode assembly 10. Depending on the polarity of the power source, the current driven into the electrode assembly 10 may travel from the inner electrode 14 across to the outer electrode 12, or vice versa. An electrical spark 16 created by the electrode assembly causes vapor bubbles 18 to form within the conductive fluid.

[0076] 1D-1G illustrate the expansion and collapse of a vapor bubble 18 generated by an electrical spark 16. In FIG. 1D, approximately 250-280 μsec after the generation of the electrical spark 16, a vapor bubble 18 forms and expands from the location of the electrical spark 16. Due at least in part to the arrangement of the inner electrode 12 and the outer electrode 14 relative to one another, the expansion of the vapor bubble 18 is directed distally from the open end of the electrode assembly 10. In particular, as shown in this example, the cylindrical wall of the electrode assembly 10 and the outer electrode 14 limit the initial expansion space of the vapor bubble 18, directing the vapor bubble 18 outward and distally (relatively forward) away from the electrode assembly 10. Additionally, the location of the inner electrode 12 within the structure of the electrode assembly 10 centers the origin for the expansion of the vapor bubble 18, reducing any bias away from the longitudinal centerline of the electrode assembly 10. In other words, the vapor bubble 18 begins to expand in the center of the electrode assembly cylinder and continues to expand in a relatively outward and distal (forward) direction from the end of the electrode assembly.

[0077] The progression of the change in shape of the vapor bubble 18, its expansion and collapse, further illustrates the mode of action for implementation of the present disclosure. In FIG. 1D, the vapor bubble 18 expands outward from the origin of the vapor bubble 18 (i.e., where the electrical spark 16 occurred). In FIG. 1E, the vapor bubble 18 has a relatively more spherical shape and is moving forward away from its origin. In FIG. 1F, the vapor bubble 18 has moved further forward and is beginning to collapse, having a relatively elliptical shape, with the vapor bubble 18 penetrating inward at its trailing edge and extending to a focal point at its leading edge. In FIG. 1G, the vapor bubble 18 has moved even further forward away from its origin and is collapsing with further penetration at its trailing edge, having a wishbone shape. At this point, the leading edge of the vapor bubble 18 is approximately one millimeter (1 mm) before the distal end of the electrode assembly. The leading edge of the vapor bubble 18 as shown in FIG. 1G has a focal point that extends significantly forward, and, without being bound by this theory, it is at this extended focal point that the maximum force (approximately 0.5-1.0 N) is exerted by the vapor bubble 18. Thus, a surface located at the distance where the maximum force is exerted by the vapor bubble 18 can be ablated by the force of the vapor bubble 18. With respect to the clinical applications contemplated by the present disclosure, such surfaces may be fibrous tissue, calcified tissue, lesions, or other tissue within the patient's body.

[0078] A cycle of flowing energy across the electrodes to generate electrical sparks and subsequent vapor bubbles may be approximately 30 seconds (30 seconds). Thus, in some embodiments, 20 cycles over a total execution time of 10 minutes may be performed to repeatedly and rapidly ablate the target tissue, and the ablation may be characterized as a "scrape-off" mode of operation. In other embodiments, the frequency of electrical spark generation may be relatively greater, within the range of approximately 100-200 Hz (e.g., 125 Hz, 150 Hz, 175 Hz, and other increments of frequency within this range), and the ablation may be characterized as a "woodpecker" mode of operation. It should be understood that other exemplary numbers of cycles and total execution times may be used to achieve similar ablation effects.

[0079] FIG. 2 illustrates an exemplary erosion pattern for degradation of a cylindrical electrode 20. As illustrated, the cylindrical electrode 20 is formed from a conductive sheet 22 (e.g., a metal or alloy) that is rolled into a cylindrical shape. In such structures, there will often be a seam 24 (shown in dashed lines in FIG. 2) where the edges of the conductive sheet 22 meet to form a cylindrical tube. It is generally observed that current will tend to arc at locations on the electrode where there are sharp edges or corners, and in the context of the cylindrical electrode 20, the seam 24 thus presents a relatively sharp edge, and current will preferentially arc toward the sharp edge, thus damaging the conductive sheet 22 primarily at the sharp edge. Erosion region 26 illustrates an exemplary erosion pattern that extends longitudinally along the seam 24 along the length of the cylindrical electrode 20, gradually widening and degrading the distal end of the cylindrical electrode 20, but ultimately producing an uneven and irregularly shaped electrode edge. Without mitigation, such irregularly shaped electrodes can lead to misfiring of the electrodes and, in the context of a shock wave generating device, failure to generate shock waves and cavitation bubbles.

[0080] There are several differences compared to traditional lithotripsy regarding the mode of action of both previously implemented IVL applications and the present disclosure. In contrast to traditional histotripsy, IVL leads to substantially different decisions to deliver shock waves in an intravascular environment rather than an extracorporeal treatment. Furthermore, histotripsy uses focused ultrasound that can deliver high intensity short pulses with energies in the range of 30-50 MPa at frequencies of 500-800 kHz. Furthermore, histotripsy typically targets soft tissues, which are not typical target tissues for IVL applications.

[0081] In contrast to previously implemented IVL applications, the present disclosure does not generate shock waves within a balloon or other sealed volume. Thus, there is great flexibility in the pressures used and the types of tissue that can be treated. In further contrast to previously implemented IVL applications, the structures of the present disclosure have different acoustic properties. The embodiments of the present disclosure generate lower peak positive pressures, similar peak negative pressures at higher frequencies (100-200 Hz in the present disclosure versus 1-2 Hz for conventional IVL). In addition, the present disclosure aims to fragment the lesion and aspirate the debris compared to IVL, which destroys the lesion remaining in situ. Furthermore, conventional IVL relies on an initial shock wave, which has a high peak positive value to destroy calcified lesions and a lower peak negative value that helps prevent soft tissue damage. As will be appreciated from the present disclosure, directional lithotripsy can utilize initial and subsequent shock waves generated to destroy calcified lesions while still avoiding soft tissue damage.

[0082] FIG. 3 illustrates an exemplary electrode assembly 100 of a catheter. The assembly 100 includes a first cylindrical conductive sheath configured as an inner conductive sheath 120 and a second cylindrical conductive sheath configured as an outer conductive sheath 122. The outer conductive sheath 122 is circumferentially mounted concentrically around the inner conductive sheath 120, whereby the inner and outer conductive sheaths form respective inner and outer electrodes of an electrode pair. The conductive sheaths 120, 122 are formed from a conductive material, such as a conductive metal or alloy, formed into an elongated tubular or cylindrical shape. In some examples, the inner conductive sheath 120 and / or the outer conductive sheath 122 are formed from erosion-resistant metal tubing, such as stainless steel, platinum, palladium, iridium, molybdenum, tungsten, or copper tubing. The inner conductive sheath 120 can be of any desired thickness, for example, between 0.002 and 0.003 inches thick. The outer conductive sheath 122 can be relatively thicker than the inner conductive sheath. For example, the outer conductive sheath 122 can be about 0.004 to 0.006 inches thick. However, in other examples, the inner conductive sheath 120 is thicker than the outer conductive sheath 122. For example, the inner conductive sheath 122 can be 0.004 to 0.006 inches thick and the outer conductive sheath 122 can be relatively thinner, for example, between 0.002 to 0.003 inches thick.

[0083] The inner conductive sheath 120 and the outer conductive sheath 122 each include a respective distal end 121, 123. The distal end 121 of the inner conductive sheath 120 is positioned proximate to the distal end 123 of the outer conductive sheath 122 to provide an arcing region between the sheaths across which current may flow to generate shock waves inside the catheter. Together, the distal end 121 of the inner conductive sheath 120 and the distal end 123 of the outer conductive sheath 122 form an electrode pair of an electrode assembly. As will be described in more detail below, the distal end 121 of the inner conductive sheath 120 may be shaped such that a particular portion of the distal end 121 (e.g., portion 125) is closer to the outer conductive sheath 122 than the remainder of the distal end (i.e., to provide a predetermined initial arcing region between the conductive sheaths).

[0084] As seen in FIG. 3, the inner conductive sheath 120 and the outer conductive sheath 122 are separated by a cylindrical insulating layer 140 mounted concentrically between the conductive sheaths 120, 122, for example by an insulating sheath. The insulating layer 140 is formed from a non-conductive insulating material that prevents unintended current flow between the inner surface of the outer conductive sheath 122 and the outer surface of the inner conductive sheath 120. In some examples, the insulating layer 140 is formed from a polymeric material, for example, polyimide, molded into an elongated tubular or cylindrical shape. In some examples, the insulating layer 140 is about 0.002 to 0.004 inches thick. As seen in FIG. 3, the insulating layer 140 has a distal end 141 that is adjacent (e.g., flush with) the distal ends 121, 123 of the respective inner and outer conductive sheaths 120, 122. The proximal end of the insulating layer 140 extends beyond the proximal end of at least one of the inner conductive sheath 120 and / or the outer conductive sheath 122 to prevent unintended current flow between the proximal ends of the conductive sheaths 120, 122. The shape and position of the insulating layer 140 ensures that the initial arcing region (i.e., the path of least resistance for current flow, which is usually the location of the closest distance between the sheaths) between the inner conductive sheath 120 and the outer conductive sheath 122 is between the respective distal ends 121, 123, and more specifically, at the coplanar portion 125 of the inner conductive sheath 120.

[0085] 4A-4B illustrate an exemplary cylindrical inner conductive sheath 120 of an electrode assembly, such as the electrode assembly 100 of FIG. 3. FIG. 4A shows a side view of the exemplary inner conductive sheath 120, and FIG. 4B shows a perspective view of the exemplary inner conductive sheath 120. In some examples, the distal end 121 of the inner conductive sheath 120 is shaped to have various regions closer to or farther from the paired distal end 123 of the outer conductive sheath 122, which can promote degradation in a predetermined or semi-controlled manner. For example, the distal end 121 of the inner conductive sheath 120 can be shaped such that a portion 125 of the distal end 121 is closest to the distal end 123 of the outer conductive sheath 122 to provide a predetermined initial arcing region for current flow between the conductive sheaths 120, 122. Second and further arcing regions may be provided by shaping additional portions of distal end 121 next closest to distal end 123, and so on.

[0086] 5A-5B provide more detailed views of the electrode assembly 100 shown in FIG. 3. FIG. 5A illustrates a left side cross-sectional view of the electrode assembly 100. FIG. 5B illustrates a front view of the exemplary electrode assembly 100 showing the cutting plane used to generate the cross-sectional view of FIG. 5A. As seen in FIG. 5A, at least a portion of the distal end 121 of the inner conductive sheath 120 is angled relative to the distal end 123 of the outer conductive sheath 122. At least a further portion (i.e., portion 125) of the distal end 121 is substantially flush with the distal end 123 of the outer conductive sheath 122 and the distal end 141 of the insulating layer 140, providing an initial arcing region a relatively short distance away from the distal end 123 of the outer conductive sheath 122. The angled portion of the distal edge 121 is angled proximally relative to the distal end 123 of the outer conductive sheath 122 such that the angled portion is farther away from the distal end 123 of the outer conductive sheath 122 than the coplanar portion 125. In some examples, the angled portion is angled a relatively small amount, e.g., 2 to 4 degrees or less than 2 degrees. However, in other examples, the angled portion of the distal edge 121 is angled a relatively larger amount, e.g., 4 to 10 degrees, 10 to 20 degrees, 20 to 45 degrees, or more than 45 degrees, relative to the distal end 123 of the outer conductive sheath 122. It should be understood that the angled portion of the distal edge 121 can be in any increment or gradient of degrees within the ranges described above.

[0087] 3, the electrode assembly 100 also includes two insulated wires 130, 132 that extend along the length of the catheter. More specifically, the first insulated wire 130 is electrically connected to the inner conductive sheath 120, and the second insulated wire 132 is electrically connected to the outer conductive sheath 122. The insulated wires 130, 132 provide an electrical connection between the conductive sheaths 120, 122 and an external voltage source, such as a high-voltage pulse generator (not depicted). In some examples, the inner conductive sheath 120 is connected to the positive terminal of the voltage source, and the outer conductive sheath 122 is connected to the negative terminal of the voltage source or to ground. However, the reverse connection is also contemplated (i.e., the outer conductive sheath 122 is connected to the positive terminal and the inner conductive sheath is connected to the negative terminal or ground). In some examples, the conductive portions of the wires 130, 132 are heat sealed or otherwise secured to the conductive sheaths 120, 122 to provide a direct electrical connection. The insulated wires 130, 132 extend into the fluid lumen of the catheter and may be secured, for example, to a sidewall of the lumen or disposed in a groove extending along the lumen. In other examples, the wires 130, 132 extend through a separate lumen of the catheter, for example, the wire lumen.

[0088] A series of high voltage pulses can be delivered across the wires 130, 132 by an external voltage source, e.g., a pulsed high voltage source, to generate a series of shock waves and / or cavitation bubbles in the electrode assembly 100. The negative and positive terminals of the external voltage source are connected to the proximal ends of the first and second insulated wires 132, 132, and when high voltage pulses are delivered across the wires 130, 132, a potential difference is generated across the inner and outer conductive sheaths 120, 122 (i.e., the electrode pairs of the electrode assembly). The potential difference causes current to flow through the electrode pairs, generating shock waves and / or cavitation bubbles. The direction of current flow depends on the polarity of the electrodes, with current flowing from the more positively charged electrode (i.e., the electrode connected to the positive terminal of the voltage source) to the more negatively charged electrode (i.e., the electrode connected to the negative terminal of the voltage source). The duration and magnitude of the voltage pulse is sufficient to generate gas bubbles and / or shock waves on the surface of the electrodes (ie, on the distal ends 121, 123 of the conductive sheaths 120, 122).

[0089] The size and other characteristics of the cavitation bubbles and / or shock waves can be controlled by adjusting the magnitude and duration of the applied voltage pulse. For example, delivering a relatively lower voltage at a higher repetition rate (e.g., a voltage of about 800V-2,000V and a repetition rate of about 20Hz-200Hz) generally produces cavitation bubbles on the electrode. When a series of relatively lower voltage and higher repetition rate voltage pulses are applied across the wires 130, 132, multiple gas cavitation bubbles accumulate on the surface of the electrode. The cavitation bubbles can be forced to flow through the open tip of the catheter and into the treatment site to pulverize calcified lesions. Applying a higher voltage pulse at a lower repetition rate (e.g., a voltage of about 2,500V-6,000V and a repetition rate of about 1Hz-4Hz) produces higher amplitude acoustic shock waves within the catheter. When a series of relatively higher voltage pulses are applied across the wires 130, 132, a plasma arc of current eventually forms across the bubble in the arcing region 125 between the inner conductive sheath 120 and the outer conductive sheath 122. The current traverses the bubble, creating a rapidly expanding and collapsing bubble that creates an acoustic shock wave that propagates toward the target lesion. The characteristics of the cavitation bubble and / or shock wave can also be controlled by adjusting aspects of the electrode assembly, such as by adjusting the distance between the electrodes of the electrode pair, the surface area of ​​the electrodes, and the shape of the electrodes.

[0090] FIG. 16 is a graph showing measurements of pressure generated by a device fabricated according to FIGS. 3-5. Measurements were taken with a hydrophone located approximately ten millimeters (10 mm) from the emitter location, where in the context of this disclosure, the emitter broadly refers to the area of ​​the electrode assembly where current travels across the electrode pair, generating shock waves and propagating the resulting bubbles. The measurements in FIG. 16 are in megapascals (MPa), and as a general estimate, the pressure close to the emitter at one millimeter (1 mm) in front of the emitter (i.e., the distance of cavitation bubble and subsequent shock wave formation) is approximately an order of magnitude higher than the pressure measured at the hydrophone 10 mm away. As can be seen in FIG. 16, there is a large positive spike at the beginning of the shock wave pulse of approximately 1.32 MPa. Based on the measurements at the hydrophone, the estimated pressure close to the emitter (1 mm) would be approximately 13.2 MPa. A smaller, but still significant, negative spike is recorded near the end of the pulse, approximately nine microseconds (9 μsec) after the initial positive spike. The negative pressure spike is caused by the collapse of a vapor bubble. At a distance of ten millimeters (10 mm) from the emitter, the hydrophone measures 0.19 MPa, which corresponds to an estimated negative pressure near the emitter of approximately 1.9 MPa. Thus, the peak-to-peak difference in pressure at one millimeter (1 mm) from the emitter would be approximately 15 MPa. As described herein, this type of pressure amplitude can improve clearance of lesions from the treatment site.

[0091] The magnitude and frequency of the voltage pulse can also be controlled to improve the characteristics of the acoustic pressure wave resulting from the generation of shock waves or cavitation bubbles at the electrode pair. Delivering a voltage pulse with a relatively short pulse width, e.g., below 50 microseconds (<50 μsec), can produce an acoustic pressure wave with a relatively high amplitude negative pressure. The increased negative pressure can improve the mechanism of action of the shock wave or cavitation catheter by providing a negative suction-like force that promotes the clearing of lesions and debris from the treatment site. In some examples, voltage pulses are delivered across the electrode pair at a relatively low frequency, e.g., 30-40 Hz, 40-50 Hz, or greater than 50 Hz, and a relatively short pulse width, e.g., about 10 microseconds (10 μsec) or less than 10 microseconds, to produce an acoustic pressure wave with a high negative pressure. In one example, the electrode pair of the catheter can produce an acoustic pressure wave with a peak negative pressure of about 3 MPa with a peak-to-peak pressure of about 10 MPa. However, in other examples, the electrode pairs may produce acoustic pressure waves having even greater peak pressures, for example, peak pressures of 10 MPa to 20 MPa, 20 MPa to 40 MPa, or up to 50 MPa.

[0092] When a voltage pulse is applied during shock wave and / or cavitation therapy, current flows across the path of least resistance between the electrodes of an electrode pair, which path of least resistance is generally where the electrodes are closest in distance. Thus, the initial arcing region is located where the distal end 121 of the inner conductive sheath 120 is closest to the distal end 123 of the outer conductive sheath 122. Repeated generation of cavitation bubbles and / or shock waves will cause the electrodes to erode proximate to the initial arcing region. For example, in the example shown in FIG. 3, generating cavitation bubbles and / or shock waves will cause the distal end 121 of the inner conductive sheath 120 to erode proximate to the portion 125 of the distal end 121 that is flush with and closest to the distal end 123 of the outer conductive sheath 122. Throughout the course of treatment, the distal end 121 of the inner conductive sheath 120 will continue to erode proximate to the initial arcing region. When the initial arcing region erodes far enough away that it is no longer the shortest distance between the inner conductive sheath 120 and the outer conductive sheath 122, current will begin to flow across the secondary arcing region, which provides the shortest distance path between the distal end 123 of the outer conductive sheath 122 and the partially depleted distal end 121 of the inner conductive sheath 120. As the shockwave treatment continues, the angled shape of the inner conductive sheath 120 promotes degradation in a semi-controlled pattern around the distal end 121 of the inner conductive sheath, beginning at the flush portion 125 and progressing along portions of the distal end 121 successively more distant from the outer conductive sheath 122. In other words, the structure of the constituent electrodes directs the location of the electric arc, thereby partially controlling the pattern of electrode erosion throughout use of the electrode assembly.

[0093] FIG. 6 illustrates an exemplary partially eroded electrode assembly 100, such as the assembly 100 shown in FIGS. 3 and 5A-5B, after the inner conductive sheath 120 has been at least partially eroded by the generation of a series of shock waves and / or cavitation bubbles. FIG. 7A illustrates a side view of the exemplary eroded inner conductive sheath 120, and FIG. 7B illustrates a perspective view of the exemplary eroded inner conductive sheath 120. FIGS. 8A-8B provide a more detailed view of the partially eroded electrode assembly 100 shown in FIG. 6. FIG. 8A illustrates a left side cross-sectional view of the exemplary eroded electrode assembly 100. FIG. 8B illustrates a front view of the exemplary electrode assembly 100 showing the cutting plane used to generate the cross-sectional view of FIG. 8A. FIG. 8C illustrates an enlarged left side cross-sectional view of the exemplary electrode assembly 100 shown in FIG. 8A, providing a more detailed view of the degraded distal end of the inner conductive sheath 100.

[0094] 6, 7A-7B, and 8A-8C, the repeated occurrence of shock waves and cavitation bubbles causes distal end 121 of inner conductive sheath 120 to erode proximate the initial arcing region, creating one or more depressions in distal end 121. The deterioration of the electrode surface in the initial arcing region increases the distance between portion 125 and distal end 123 of outer conductive sheath 122, causing a distinct portion 126 of the electrode surface to be closer in distance to distal end 123 (thus portion 125 is no longer coplanar as shown in FIGS. 4B, 5A, and 5B). As additional voltage pulses are applied across the sheaths 120, 122, erosion of the inner conductive sheath 120 in the initial arcing region will cause current to flow across a secondary arcing region between the distal end 121 of the inner conductive sheath 120 and the distal end 123 of the outer conductive sheath 122 (e.g., the region adjacent the nearest portion 126 at the new distance).

[0095] 6 and 8A-8C, the secondary arcing region is proximate to the initial arcing region around the circumference of the distal end 121. The gradually tapering angle of the distal end 121 causes degradation to progress outward from the initial arcing region (e.g., the region proximate portion 125) to portions of the distal end 121 that are progressively more distant from the distal end 123 of the outer conductive sheath 122 (e.g., portion 126, then to more distant portions at subsequent distances of the distal end 121). Eventually, when the entire circumference of the distal end 121 has eroded to an approximately equal distance from the distal end 123 of the outer conductive sheath 122, degradation may progress in a stochastic manner as current flows across the relatively least resistance (i.e., closest distance) path between the sheaths 120, 122.

[0096] In the embodiment shown in Figures 6, 7A-7B, and 8A-8C, erosion is shown as primarily affecting the distal end 121 of the inner conductive sheath 120. This is the pattern observed, particularly when the inner conductive sheath 120 is connected to the positive terminal of the voltage source. Note that the distal end 123 of the outer conductive sheath 122 may also erode in a similar manner, particularly if the polarity of the power supply relative to the sheaths is reversed such that the outer conductive sheath 122 is connected to the positive terminal of the voltage source. When the polarity of the electrode assembly is reversed, current flows in the opposite direction across the arcing region between the sheaths 120, 122, causing erosion that primarily affects the distal end 123 of the outer conductive sheath 122. An electrode assembly design in which erosion occurs primarily on the outer conductive sheath 122 may provide increased electrode life compared to an assembly in which erosion occurs primarily at the inner conductive sheath 120 due to the relatively larger circumference and larger electrode surface area of ​​the distal end 123 of the outer conductive sheath.

[0097] In these exemplary embodiments, the distal end 123 of the outer conductive sheath 122 is shaped to promote degradation in a predetermined or semi-controlled manner, and may be shaped, for example, similar to the distal end 121 of the inner conductive sheath 120 shown in Figures 6, 7A-7B, and 8A-8C. As previously described in connection with the inner conductive sheath 120, the outer conductive sheath 122 may be shaped such that various regions of the distal end 123 are closer to or further from the paired distal end 121 of the inner conductive sheath 120. For example, the distal end 123 of the outer conductive sheath 122 may be shaped such that a portion 125 of the distal end 121 is closest to the distal end 121 of the inner conductive sheath 120 to provide a predetermined initial arcing region. Second and further arcing regions may be provided by shaping additional portions of distal end 123 next closest to distal end 121, and so on.

[0098] 9A and 9B illustrate an exemplary electrode assembly in which the distal end 123 of the outer conductive sheath 122 is angled relative to the distal end 121 of the inner conductive sheath 120. At least a portion of the distal end 123, here portion 127, is substantially flush with the distal end 121 of the inner conductive sheath 120 and the distal end of the insulating layer 140, providing an initial arcing region that is a relatively short distance away from the distal end 121 of the inner conductive sheath 120. As seen in FIGS. 9A-9B, the surface of the distal end 123 gradually slopes away from the distal end 121 of the inner conductive sheath 120 in the proximal direction relative to the distal end 121. In some examples, the distal end 123 is angled a relatively small amount, for example, between 2 degrees and 4 degrees or less than 2 degrees. However, in other examples, the distal edge 123 is angled a relatively greater amount, such as between 4 and 10 degrees, between 10 and 20 degrees, between 20 and 45 degrees, or greater than 45 degrees, relative to the distal end 121 of the inner conductive sheath 120. It should be understood that the angled portion of the distal edge 123 can be at any degree increment or gradient within the ranges described above.

[0099] FIG. 10 illustrates the electrode assembly of FIGS. 9A-9B after the outer conductive sheath 122 has been at least partially eroded by the generation of a series of shock waves and / or cavitation bubbles. FIGS. 11A-11C provide a more detailed view of the partially eroded electrode assembly 100 shown in FIG. 10. FIG. 11A illustrates a left side cross-sectional view of the partially eroded electrode assembly 100. FIG. 11B illustrates a front view of the partial electrode assembly 100 showing the cutting plane used to generate the cross-sectional view of FIG. 11A. FIG. 11C shows an enlarged left side cross-sectional view of the exemplary electrode assembly 100 shown in FIG. 11A, providing a more detailed view of the degraded distal end of the inner conductive sheath 100. 10 and 11A-11C, the repeated generation of shock waves and / or cavitation bubbles causes the distal end 123 of the outer conductive sheath 122 to erode proximate to the initial arcing region, increasing the distance between portion 127 and the distal end 121 of the inner conductive sheath 120. Eventually, the erosion of the outer conductive sheath 122 in the initial arcing region causes a distinct portion 128 of the distal end 123 to become closer in distance to the distal end 121 of the inner conductive sheath 120. As additional voltage pulses are applied across the sheaths 120, 122, current will begin to flow across the secondary arcing region between the distal end 123 of the outer conductive sheath 122 and the distal end 121 of the inner conductive sheath 120, providing the closest path at the new distance between the sheaths. In the particular embodiment shown in Figures 10 and 11A-11C, the gradually tapering angle of distal end 123 causes degradation to progress outward from the initial arcing region (e.g., the region proximate portion 127) to portions of distal end 123 that are progressively more distant from distal end 121 of inner conductive sheath 120 (e.g., portion 128 and then to more distant portions at subsequent distances of distal end 123).

[0100] 3, 5A-5B, 6, 8A-8C, 9A-9B, 10, and 11A-11C illustrate an exemplary electrode assembly formed from concentric conductive sheaths 120, 122 that are molded with angled distal ends 121, 123, although other electrode configurations may result in advantageous degradation patterns. For example, in some instances, one or more of the distal ends 121, 123 are molded with a different pattern that places various portions of the edges at different predetermined distances from the other conductive sheath, such as with undulating waves, notches, differently angled portions, or some other surface configuration. Additionally, while the exemplary electrode assemblies described above include only one molded conductive sheath, in some instances, both the inner conductive sheath 120 and the outer conductive sheath 122 include molded distal ends 121, 123. Additionally or alternatively, the insulating layer 140 may be shaped to promote erosion in a desired pattern across the conductive sheaths 120, 122. For example, the insulating layer 140 may have a shaped (e.g., angled) distal end or one or more openings through the insulating layer that define various arcing regions between the inner conductive sheath 120 and the outer conductive sheath 122.

[0101] To still further increase the usable life of the electrode assembly contained within the catheter, the polarity of the electrode assembly can be switched one or more times during a shock wave or cavitation procedure. For example, U.S. Patent No. 10,226,265 (incorporated herein by reference) describes switching the polarity of the voltage pulses applied across the electrode pair during the procedure to change the direction of current flow. As previously described, the electrode connected to the positive terminal of the voltage source generally experiences increased erosion compared to the electrode connected to the negative terminal or ground. Thus, switching the polarity of the electrode assembly during the procedure can allow the user to control the relative deterioration at the surface of each electrode of the electrode pair. Over the course of the shock wave or cavitation procedure, polarity switching can be used to distribute the deterioration more evenly across both electrodes of the electrode pair, increasing the usable life of the electrode assembly. It is noted that electrode polarity switching can be implemented in any electrode assembly design, including but not limited to the assemblies shown throughout this disclosure.

[0102] Polarity switching can be performed using a controller, e.g., a polarity switching circuit and / or a multiplexing device, in electrical communication with the external voltage source and the electrode assembly. As previously described, the external voltage source is configured to selectively deliver a series of high voltage pulses across the wires 130, 132 of the electrode assembly to generate shock waves and / or cavitation bubbles at the electrode pairs of the assembly. The direction of current flow across the electrode pairs is determined by the polarity of the electrodes, i.e., the relative negative and positive charges of the electrodes. The polarity can be modified by selectively connecting the positive and negative terminals of a voltage source across the first and second insulated wires 130, 132 to cause current to flow in a particular direction (i.e., from the positive electrode to the negative electrode) across the electrodes of the electrode pairs. Thus, the controller is configured to control the direction of current flow through the electrode pairs by selectively delivering high voltage pulses with a desired polarity across the electrode assembly.

[0103] When a series of voltage pulses is delivered across the electrode assembly, the polarity can be controlled by the controller such that a certain number of consecutive pulses cause the current to flow in a first direction, and the remaining number of consecutive pulses cause the current to flow in a second direction opposite the first direction. In a particular example, the polarity of the assembly can be switched at periodic intervals during the procedure, for example, with the controller causing a polarity switch after every voltage pulse or after a certain number of voltage pulses (e.g., switching polarity after every two, three, four, or more consecutive pulses). In another example, the controller can be configured to control the polarity such that a certain percentage of the voltage pulses cause the current to flow in a first direction, and the remaining percentage of the voltage pulses cause the current to flow in a second direction opposite the first direction. For example, the polarity of the assembly can be controlled such that the current flows in a first direction for one-half, one-third, or one-quarter of the consecutive voltage pulses, and in the opposite direction for the remaining consecutive pulses.

[0104] To selectively promote erosion of the outer conductive sheath 122, the controller may cause a relatively greater number of the series of voltage pulses to be delivered with the outer conductive sheath connected to the positive terminal of the voltage source. For example, the controller may cause current to flow from the inner conductive sheath 120 to the outer conductive sheath 122 for one-fifth (1 / 5), one-quarter (1 / 4), one-third (1 / 3), two-fifths (2 / 5), one-half (1 / 2), three-fifths (3 / 5), two-thirds (2 / 3), three-quarters (3 / 4), four-fifths (4 / 5), or some other percentage or ratio of the series of voltage pulses. However, the controller may be configured to switch the polarity of the electrode assembly so that current flows in a particular direction across the assembly for any desired percentage of the series of voltage pulses.

[0105] Additionally, the controller can be configured with a progression of voltage pulsing sequences such that the number of pulses in a given direction (e.g., from the inner conductive sheath 120 to the outer conductive sheath) can increase or decrease over the course of use. For a decreasing example, in a given treatment procedure with 300 pulses, the first half of the voltage pulsing sequence (150 pulses) can have a four-fifths (4 / 5) ratio with 120 pulses where the current goes in an inner to outer direction and 30 pulses where the current goes in an outer to inner direction, and the second half of the voltage pulsing sequence (the remaining 150 pulses) can have a one-half (1 / 2) ratio with 75 pulses for the current in each direction. It should be understood that further variations of pulse sequence control can be extrapolated from this example.

[0106] In some examples, the controller automatically initiates a polarity switch based on a reading at a sensor in electrical communication with the controller. For example, the sensor may be configured to measure an operating parameter of the electrode assembly, such as the current flow through the assembly, the voltage pulse width, the time from delivery of the voltage pulse to the initiation of a shock wave across the electrode pair, the temperature of one or more of the electrodes, or some other parameter. If the parameter is above or below a predefined polarity switch threshold, the controller changes the direction of the current flow across the electrode pair by modifying the polarity of the voltage pulse. In some examples, the sensor is configured to measure a parameter that correlates with the relative erosion of the electrodes of the electrode pair, such that the controller may automatically initiate a polarity switch to balance the erosion between the electrodes of the pair. In a particular example, the sensor measures the current flow across the electrode pair, and the controller automatically initiates a polarity switch when the current falls below a predefined polarity switch threshold (e.g., a threshold indicating that the current flow is being adversely affected by electrode degradation). In another example, the sensor measures the voltage pulse width or the duration of the time between delivery of the voltage pulse and the initiation of a shock wave or cavitation bubble at the electrode pair. If the voltage pulse width or time duration measured by the sensor exceeds a predefined polarity switching threshold (e.g., a threshold indicating that shock wave / cavitation bubble formation is being adversely affected by electrode degradation), the controller automatically initiates a polarity switch and changes the direction of current flow through the electrode pair.

[0107] In some examples, the controller is configured to terminate delivery of the voltage pulse when the parameter measured by the sensor is above or below a termination threshold (e.g., to terminate the shock wave or cavitation procedure in response to an error mode or undesirable operating condition detected by the sensor). In such examples, the threshold for polarity switching may be a function of the termination threshold. For example, polarity switching may be performed when the measured parameter is above or below about 70% of the termination threshold. In a particular example, the termination threshold is one hundred milliseconds (100 ms) between delivery of the voltage pulse and the initiation of shock waves or cavitation bubbles at the electrode pair, and the polarity switching threshold is about seventy milliseconds (70 ms) between delivery of the pulse and the occurrence of shock waves or cavitation bubbles. In other examples, polarity switching may be initiated when the measured parameter is 50-70%, 70-90%, or 90-100% of the termination threshold.

[0108] FIG. 12 illustrates a perspective view of the distal end of an exemplary catheter 101 including a dual layer electrode assembly, such as any of the exemplary electrode assemblies 100 shown and described throughout this disclosure. FIGS. 13A-13C provide additional views of the distal end of the exemplary catheter 101 shown in FIG. 12, specifically illustrating the fluid lumen 152 and the suction lumen 154. FIG. 13A provides a top side cross-sectional view of the exemplary catheter 101 depicting the flow of fluid through the catheter body. FIG. 13B provides a left side view of the exemplary catheter 101 showing the cutting plane used to generate the cross-sectional view of FIG. 13A. FIG. 13C provides a front view of the exemplary catheter 101 depicting the fluid lumen 152 and the suction lumen 154.

[0109] 14A-14B illustrate perspective views of an alternative embodiment of catheter 101 further featuring guidewire lumen 156. FIG. 14A provides an example including an electrode assembly (e.g., one of the exemplary electrode assemblies throughout this disclosure) having a shaped inner conductive sheath 120. FIG. 14B provides an example of a similar catheter design including an electrode assembly having a shaped outer conductive sheath 122. FIGs. 15A-15C provide additional views of the distal end of exemplary catheter 101 shown in FIG. 14B including a top side cross-sectional view of FIG. 15A, a left side view of FIG. 15B showing the cutting plane used to generate the cross-sectional view of FIG. 15A, and a front view of FIG. 15C depicting fluid lumen 152, aspiration lumen 154, and guidewire lumen 156.

[0110] As seen in FIGS. 12 and 14A-14B, the exemplary catheter 101 includes a circular catheter body, i.e., an elongated tube 160, that terminates at a distal end (i.e., the end of the catheter 101 shown in FIGS. 12 and 14A-14B that is introduced into a body lumen). The elongated tube 160 is formed from a rigid or semi-rigid material, such as a molded polymeric material. The elongated tube 160 includes several lumens, e.g., a fluid lumen 152, an aspiration lumen 154, and optionally, a guidewire lumen 156. The fluid lumen 152 is configured for flowing a fluid, e.g., a conductive fluid such as saline, along the length of the catheter body and through a fluid outlet port 162 at the distal end of the elongated tube 160. The aspiration lumen 154 is configured to receive debris from a treatment site through a fluid inlet port 164 and flow the debris through the lumen 154 to a proximal portion of the catheter 101. In some examples, the catheter 101 includes one or more suction ports 166 extending through a sidewall of the elongate tube 160 so that debris can be aspirated through the sidewall and into the suction lumen 154. In some examples, as seen in FIGS. 14A-14B , the catheter 101 includes a guidewire lumen 156 sized to receive a guidewire. To facilitate positioning of the catheter 101 with the body lumen, a guidewire can be inserted through the guidewire lumen, and the catheter can be maneuvered through the lumen and over the guidewire to a treatment site proximate the lesion.

[0111] As seen in Figures 12, 13A, 14A-14B, and 15A, an electrode assembly is mounted within an elongated tube 160 proximate the distal tip of the catheter 101 such that shock waves can be generated within the catheter body. In some examples, the electrode assembly is mounted within the fluid lumen 152 such that fluid flowing through the lumen flows across the electrode assembly. The outer conductive sheath 122 is mounted inside the fluid lumen 152 adjacent to the wall of the fluid lumen 152 such that the outer surface of the outer conductive sheath 122 contacts the inner surface of the fluid lumen 152. The insulating sheath 140 is mounted within the fluid lumen 152 concentrically with the outer conductive sheath 122 such that the outer surface of the insulating sheath 140 contacts the inner surface of the outer conductive sheath 122. The inner conductive sheath 120 is also mounted within the fluid lumen 152, inside and concentric with the outer conductive sheath 122 and the insulating sheath 140, with the outer surface of the inner conductive sheath 120 contacting the inner surface of the insulating sheath 140. In other words, the outer conductive sheath 122 is mounted within the fluid lumen 152 circumferentially around the inner conductive sheath 120, with the insulating layer 140 positioned therebetween.

[0112] Both Figures 13A and 15A depict the flow of fluid, e.g., conductive fluid, through the distal end of an exemplary catheter 101. As seen in Figures 13A-13C and 15A-15C, the electrode assembly is mounted within the fluid lumen 152 of the catheter 101 such that the fluid flowing through the fluid lumen 152 flows through the inner conductive sheath 120 before exiting the fluid outlet port 162 (see, e.g., upper horizontal arrow F1 in Figures 13A and 15A, which represents the flow of fluid through the fluid lumen 152). The conductive fluid within the catheter 101 provides a path for electrical current to flow between the inner conductive sheath 120 and the outer conductive sheath 122, i.e., allowing for the generation of cavitation bubbles and / or shock waves during treatment. Fluid flow through the inner conductive sheath 120 can also cause cavitation bubbles generated by the electrode assembly to flow out of the distal end of the catheter 101 and into the lesion to assist in fracturing and disintegrating the lesion. In addition, fluid flow through the inner conductive sheath 120 can be used to clear debris from the surface of the electrodes (e.g., debris generated from erosion of the surface of the inner conductive sheath 120 and / or the outer conductive sheath 122) and to regulate the temperature of the electrode assembly (e.g., by cooling the electrode assembly). Fluid can be received into the catheter 101 through a fluid inlet port 164 located at the distal end of the aspiration lumen 154. In some examples, fluid can also be received through an aspiration port 166 that penetrates the outer surface of the elongated tube 160. Inward suction through the suction lumen 154 allows the catheter 101 to circulate fluid through the treatment site, aspirating the site and removing any air bubbles and debris created during treatment (see, e.g., the lower horizontal arrow F2 and the three vertical arrows F3 in Figures 13A and 15A, which represent the flow of fluid into the suction lumen 154).

[0113] FIG. 17 illustrates a perspective view of an exemplary electrode assembly 200 of a catheter. In one or more examples, the electrode assembly 200 can be used to generate shock waves and / or cavitation bubbles to treat calcified lesions in a patient's vasculature using acoustic pressure without harming surrounding tissue. As shown in FIG. 17, the electrode assembly 200 includes a flat helical wire configured as a flat coil 220 separated by an insulating sheath 240 and a cylindrical conductive sheath configured as a conductive sheath 222. The insulating sheath 240 is circumferentially mounted within the conductive sheath 222 such that the flat coil 220 and the conductive sheath 222 form respective electrodes of an electrode pair, and the flat coil 220 is disposed on an inner surface of the insulating sheath 222.

[0114] The conductive sheath 222 and the flat coil 220 can be formed from a conductive material, such as a conductive metal or alloy. In one or more examples, the conductive sheath 222 can be formed from an erosion-resistant metal tubing, such as stainless steel, platinum, palladium, iridium, molybdenum, tungsten, or copper tubing formed into an elongated tubular or cylindrical shape. The flat coil 220 can similarly be formed from an erosion-resistant metal material, such as stainless steel, platinum, palladium, iridium, molybdenum, tungsten, or copper tubing formed into a flat helical coil. The flat coil 220 can be of any desired thickness, for example, between 0.002 and 0.003 inches thick. In one or more examples, the conductive sheath 222 can be relatively thicker than the flat coil 220. For example, the conductive sheath 222 can be about 0.004 to 0.006 inches thick. Alternatively, the flat coil 220 can be thicker than the conductive sheath 222. For example, the flat coil 220 can be 0.004-0.006 inches thick, while the conductive sheath 222 can be relatively thinner, for example, 0.002-0.003 inches thick.

[0115] In one or more examples, the flat coil 220 and the conductive sheath 222 form an electrode pair of an electrode assembly for the catheter. As shown in FIG. 17, the flat coil 220 has a distal end 221 and the conductive sheath has a distal end 223. The distal end 221 of the flat coil 220 is positioned proximate to the distal end 223 of the (relatively outer) conductive sheath 222 to generate an arcing region, and current can flow across the arcing region between the flat coil 220 and the conductive sheath 222. In one or more examples, the current flowing across the arcing region can generate shock waves and / or cavitation bubbles inside the catheter.

[0116] As seen in FIG. 17, the flat coil 220 and the conductive sheath 222 are separated by an insulator sheath 240. The insulator sheath 240 can be formed from a non-conductive insulating material that prevents unintended current flow between certain regions of the flat coil 220 and the conductive sheath 222. In one or more examples, the insulator sheath 240 can block any flow of current between the flat coil 220 and the conductive sheath 222 along the length of the insulator sheath 240. Because current is prevented from flowing between the flat coil 220 and the conductive sheath 222 along the length of the insulator sheath 240, current can only flow across the arcing region between the distal end 223 of the conductive sheath 222 and the distal end 221 of the flat coil 220. In one or more examples, the insulator sheath 240 can be formed from a polymeric material, such as polyimide, molded into an elongated tubular or cylindrical shape. In one or more examples, the insulator sheath 240 can be approximately 0.002 to 0.004 inches thick.

[0117] 17, the insulator sheath 240 has a distal end 241. In one or more examples, the distal end 241 of the insulator sheath 240 may be proximate (e.g., flush with) the distal end of the conductive sheath 222 and / or the flat coil 220. The proximal end of the insulator sheath 240 may extend beyond the proximal end of at least one of the conductive sheath 222 and the flat coil 220 to prevent unintended current flow between the proximal ends of the conductive sheath 222 and the flat coil 220. The shape and position of the insulator sheath 240 may ensure that the arcing region between the flat coil 220 and the conductive sheath 222 (e.g., the path of least resistance for current flow, which is usually the closest distance between the flat coil and the sheath) is between the distal end 221 of the flat coil 220 and the distal end 223 of the conductive sheath 222. In one or more examples, the arcing region will begin first, more specifically at the distal end 221 of the flat coil 220 located at the very end of the coil.

[0118] FIG. 18 illustrates a perspective view of an exemplary flat coil 220 of an electrode assembly, such as the electrode assembly 200 of FIG. 17. As shown in FIG. 18, the flat coil 220 is formed as a flat wire with a rectangular cross-section that is looped around a central axis in a series of coils. In one or more examples, the flat coil 220 can be disposed on an inner surface of an insulating sheath 240 of the electrode assembly 200, as will be discussed below. In such a configuration, the flat coil 220 can include a flat planar inner surface near a distal end 221 of the flat coil 220, the flat planar inner surface being on the opposite side from the inner surface of the insulating sheath 240. In one or more examples, the flat coil 220 can be manufactured via laser cutting the shape of the flat coil 220 from erosion resistant metal tubing, such as stainless steel, platinum, palladium, iridium, molybdenum, tungsten, or copper tubing.

[0119] FIG. 19 illustrates a perspective view of an exemplary flat coil 320 with cross ties of an electrode assembly, which may also be used in devices such as the electrode assembly 200 of FIG. 17. As shown, the flat coil 320 is shaped similarly to the flat coil 220 of FIG. 18 with a rectangular cross section that loops around a central axis in a series of coils. However, unlike the flat coil 220 of FIG. 18, the flat coil 320 has several cross ties 323 that extend between successive turns of the flat coil 320. That is, the cross ties 323 bridge the gaps between each turn of the coil. Similar to the flat coil 220 of FIG. 18, the flat coil 320 may be disposed on an inner surface of an insulating sheath, such as the insulating sheath 240, such that the flat coil 320 includes a flat, planar inner surface near the distal end 321 of the flat coil 320 opposite the inner surface of the insulating sheath 240. In one or more examples, the cross ties 323 can provide improved structural stability for the flat coil 320. In one or more examples, the flat coil 320 can be manufactured via laser cutting the shape of the flat coil 320 from erosion resistant metal tubing, such as stainless steel, platinum, palladium, iridium, molybdenum, tungsten, or copper tubing.

[0120] 20 illustrates a perspective cross-sectional view of an exemplary electrode assembly 200 of a cathode. As shown in FIG. 20, the flat coil 220 has several individual coils 225 (i.e., "turns" of the flat coil 220) each disposed on the inner surface 243 of the insulating sheath 240. In one or more examples, the flat coil 220 can be bonded to the insulating sheath 240 by an adhesive. An adhesive (not shown) can be applied between the coils 225 of the flat coil 220 and allowed to permeate around the inner surface 243 of the insulating sheath 240, such that the adhesive fills the area between each adjacent coil 225 and secures the flat coil 220 to the insulating sheath 240.

[0121] FIG. 21A illustrates a left side cross-sectional view of an exemplary electrode assembly 200 of a catheter, and FIG. 21B illustrates a front view of the exemplary electrode assembly 200 of FIG. 21A showing the cutting plane used to generate the cross-sectional view of FIG. 21A. As discussed above, the flat coil 220 of the electrode assembly 200 has a rectangular cross-section and can include a flat, planar inner surface opposite the inner surface of the insulating sheath 240. This is shown more clearly in FIG. 21A, which illustrates that the flat coil 220 has a rectangular cross-section disposed on the inner surface of the insulating sheath 240. As can be seen near the distal end 221 of the flat coil 220, the flat coil has a planar inner surface opposite the inner surface of the insulating sheath 240.

[0122] 17, the electrode assembly 200 can also include two insulated wires 230, 232 extending along the length of the catheter. In particular, the first insulated wire 230 can be electrically connected to the flat coil 220, and the second insulated wire 232 can be electrically connected to the conductive sheath 222. In one or more examples, the insulated wires 230, 232 can provide electrical connections between the flat coil 220, the conductive sheath 222, and an external voltage source, such as a high voltage pulse generator (not depicted). In one or more examples, the flat coil 220 can be connected to the positive terminal of the voltage source, and the conductive sheath 222 can be connected to the negative terminal of the voltage source or to ground. Alternatively, the flat coil 220 can be connected to the negative terminal of the voltage source or to ground, while the conductive sheath is connected to the positive terminal of the voltage source. The conductive portions of the wires 230, 232 can be heat sealed or otherwise secured to the conductive sheath 222 and the flat coil 220 to provide a direct electrical connection. In one or more examples, the insulated wires 230, 232 extend into the fluid lumen of the catheter, for example, secured to a sidewall of the lumen or disposed in a groove extending along the lumen. The wires 230, 232 can also extend through a separate lumen of the catheter, for example, a wire lumen. In one or more examples, the wires 230, 232 can be insulated copper wires.

[0123] In one or more examples, a series of high voltage pulses can be transmitted across the wires 230, 232 by an external voltage source, e.g., a pulsed high voltage source, to generate a series of shock waves and / or cavitation bubbles in the electrode assembly 200. The negative and positive terminals of the external voltage source can be connected to the proximal ends of the first insulated wire 230 and the second insulated wire 232, such that a potential difference can be created across the flat coil 220 and the conductive sheath 222 (i.e., the electrode pair of the electrode assembly) when the high voltage pulses are delivered across the wires 230, 232. The potential difference can cause a current to flow between the electrode pair, generating shock waves and / or cavitation bubbles. In one or more examples, the direction of current flow depends on the polarity of the electrodes, and current can flow from the more positively charged electrode (i.e., the electrode connected to the positive terminal of the voltage source via one of the wires 230, 232) to the more negatively charged electrode (i.e., the electrode connected to the negative terminal of the voltage source via one of the wires 230, 232). The duration and magnitude of each of the voltage pulses can be sufficient to generate gas bubbles (e.g., cavitation bubbles) on the surface of the electrodes (i.e., on the distal end 221 of the flat coil 220 and the distal end 223 of the conductive sheath 222).

[0124] In one or more examples, the size and other characteristics of the generated shock waves and / or cavitation bubbles can be controlled by adjusting the magnitude and duration of the applied voltage pulse. For example, delivering a relatively lower voltage at a high repetition rate (e.g., a voltage of about 800V to 2,000V and a repetition rate of about 20Hz to 200Hz) can generally generate cavitation bubbles on the electrode. Delivering a relatively higher voltage pulse at a lower repetition rate (e.g., a voltage of about 2,500V to 6,000V and a repetition rate of about 1Hz to 4Hz) can generally generate acoustic shock waves with higher magnitudes for the cavitation bubbles. For directional lithotripsy electrode assemblies and emitters as contemplated herein, implementations using lower voltages at high repetition rates have been found to be advantageous for achieving the desired ablation mode of action. Thus, embodiments of the present disclosure can be implemented using voltages of about 200V to about 10,000V, and more specifically, about 1,500V to 2,000V and voltage increments and gradients within these ranges (e.g., 1.60kV, 1.70kV, 1.80kV, 1.90kV). Similarly, electrode assemblies and emitters as contemplated herein can be implemented using frequencies such as about 50Hz to 500Hz, about 100Hz to 200Hz, about 125Hz to 175Hz, and frequency increments and gradients within these ranges. In one or more examples, the characteristics of the shock waves and / or cavitation bubbles can also be controlled by adjusting structural aspects of the electrode assembly, such as the distance between the electrodes of an electrode pair, the surface area of ​​the electrodes, the shape of the electrodes, etc.

[0125] When a series of relatively lower voltages at a high repetition rate are transmitted across the wires 230, 232, multiple gas cavitation bubbles can accumulate on the surfaces of the electrodes of the electrode assembly 200 (e.g., at the distal end 221 of the flat coil 220 and the distal end 223 of the conductive sheet 222). In one or more examples, the cavitation bubbles formed on the surfaces of the electrodes can flow out through the open tip of the catheter and into the treatment site to pulverize calcified lesions. When a series of relatively higher voltages at a low repetition rate are transmitted across the wires 230, 232, a plasma arc of current can form across the generated bubbles in the arcing region between the electrodes (i.e., at the closest distance between the distal end 221 of the flat coil 220 and the distal end 223 of the conductive sheath 222). An electric current can be passed across the bubble, thereby creating a rapidly expanding and collapsing bubble that generates acoustic shock waves that propagate outward from the catheter toward the treatment site, disrupting the calcified lesion.

[0126] In contrast to a solid cylindrical conductive element used as an electrode, the flat coil 220 provides a guide for controlled erosion. While a simple cylinder (as part of an electrode pair) would degrade in a somewhat random pattern as the current travels across the electrode pair, the flat coil 220 takes advantage of the tendency of current to traverse the shortest path from one electrode of the electrode pair across to the other. Thus, the distal end 221 of the flat coil will generally be along the path of least resistance, in other words, the shortest distance between the flat coil 22 and the conductive sheath 222. Erosion of the flat coil 220 will tend to occur at the distal end 221, causing it to recede consistently as the flat coil 220 shortens (which in the example of FIG. 17 would be in a clockwise direction). Although the location of the distal end 221 will move as erosion progresses, the consistency of the spark gap location at the distal end 221 is relatively less random than that which would be observed along the edge of a solid cylinder. Thus, the flat coil 220 can provide a series of shock waves and cavitation bubbles with a more consistent origin and less potential for interference over the course of a treatment regimen.

[0127] FIG. 22 is a graph showing estimated measurements of pressure generated by a device fabricated according to FIG. 17, focusing on the initial period of spark generation before cavitation bubbles form. The estimated measurements depicted in FIG. 22 are depicted in megapascals (MPa) and were based on measurements with a hydrophone located approximately 10 mm from the emitter location. As shown, there is a large positive spike of approximately 4.2 MPa, followed by a negative spike to a magnitude of -2.03 MPa, resulting in a peak-to-peak magnitude of 6.23 MPa. The 6.23 MPa peak-to-peak magnitude may improve disruption of lesions at the treatment site.

[0128] In one or more examples, the rise time can be correlated with the efficacy of a catheter incorporating an electrode design such as the electrode assembly 200 of FIG. 17. That is, a fast rise time can improve the performance of the catheter when attempting to drill through a calcified lesion. As shown in FIG. 22, the positive peak has a relatively fast rise time with a narrow crest before dropping off, and thus a device fabricated according to FIG. 17 can perform better than other devices with slower rise times and / or broader peaks (which may indicate a slower pressure difference). As shown here, the positive and negative spikes in pressure are caused by the spark generation itself. In the subsequent cycle of firing the electrode assembly, the positive spike can be caused by the initial burst of the vapor bubble and the negative spike can be caused by the collapse of that bubble.

[0129] In one or more examples, the magnitude and frequency of the pressure resulting from the voltage pulse can be controlled to improve the characteristics of the acoustic pressure wave. Delivering a voltage pulse with a relatively short pulse width, e.g., below 50 microseconds, can produce an acoustic pressure wave with a relatively high amplitude negative pressure. The increased negative pressure can provide a force such as a negative suction force that can facilitate the clearing of lesions and debris from the treatment site. In one or more examples, the voltage pulse can be delivered across the electrode pair at a relatively low frequency, e.g., 30-40 Hz, 40-50 Hz, or greater than 50 Hz. Similarly, in one or more examples, the voltage pulse can have a relatively short pulse width, e.g., a pulse width of 2-20 microseconds, a pulse width of about 5 microseconds, a pulse width of about 10 microseconds, or less than 2 microseconds, to produce an acoustic pressure wave with a high negative pressure.

[0130] As discussed above, as shock waves and / or cavitation bubbles are generated by the voltage pulse transmitted across the electrode pair, the electrode surface may slowly erode in the arcing region between the electrodes. FIG. 23 illustrates a perspective view of the exemplary electrode assembly 200 of FIG. 17 prior to any erosion. As mentioned above, the initial arcing region may generally be located in the path of least resistance between the electrodes of the electrode pair. With reference to FIG. 23, the path of least resistance between the flat coil 220 and the conductive sheath 222 (i.e., the electrodes) would be where the gap between the flat coil 220 and the conductive sheath 222 is shortest and is not impeded by the insulating sheath 240. As shown in FIG. 23, the initial arcing region may thus be located between the distal end 221 of the flat coil 220 and the distal end 223 of the conductive sheath 222.

[0131] The repeated generation of shock waves and / or cavitation bubbles from applying a voltage to the electrode assembly 200 can then cause the electrodes to erode proximate the initial arcing region. This is more clearly shown in FIGS. 24A and 24B, which illustrate an enlarged detailed view of the electrode erosion process of the electrode of the electrode assembly 200 of FIG. 17. As shown in FIG. 24A, the distal end 223 of the conductive sheath 222 begins to erode in the arcing region where the distal end 223 of the conductive sheath 222 is closest to the distal end 221 of the flat coil 220. In one or more instances, erosion will begin on the conductive sheath 222 before beginning on the flat coil 220. For example, as shown in FIG. 24A, the distal edge 223 of the conductive sheath 222 has begun to erode, but the distal end 221 of the flat coil 220 has not begun to erode. However, as shown in Figure 24A, the distal end 221 of the flat coil 220 has begun to erode. Thus, the erosion of the distal end 223 of the conductive sheath 222 may be greater relative to the erosion of the distal end 221 of the flat coil 220 (as visible in Figure 24B) because erosion began on the conductive sheath 222 before it began on the flat coil 220.

[0132] In one or more examples, the insulating sheath 240 will also erode based on the application of a voltage to the electrode assembly 200. As shown in FIG. 24A, the distal edge 241 of the insulating sheath 240 begins after the erosion of the distal end 223 of the conductive sheath 222. However, it is envisioned that the insulating sheath 240 may begin to erode before the conductive sheath 222 begins to erode. As the conductive sheath 222 and the insulating sheath 240 erode, the erosion can expose the outer surface 227 of the flat coil 220, as shown in FIG. 24A as part of the distal end 221. In one or more examples, the erosion of the insulating sheath 240 can allow erosion of the flat coil 220 to begin. The exposure of the outer surface 227 of the flat coil 220 can allow the arcing region to shift, and rather than traveling between the distal end 221 of the flat coil, the arcing region may travel between the outer surface 227 of the flat coil 220 and the distal end 223 of the conductive sheath 222. However, in one or more examples, rather than shifting, the arcing region may expand. That is, the arcing region may travel between the entire exposed area of ​​the flat coil (including both the distal end 221 and the exposed outer surface 227) and the distal end 223 of the conductive sheath 222.

[0133] As the erosion begins to wear away the distal end 221 of the flat coil 220, the arcing region can progress to follow the coil of the flat coil 220. That is, in one or more examples, the arcing region can follow the end of the flat coil 220 as the coil erodes. As seen in FIG. 24B, the progressive erosion of the flat coil 220 can lead to an area of ​​the exposed outer surface 227 being completely eroded and thus no longer existing; of course, as the degradation continues, additional areas of the exposed outer surface 227 can be periodically exposed and then eroded. Thus, the inclusion of the flat coil 220 as one of the electrodes of the electrode assembly 200 can allow the erosion of the electrode to progress in a semi-controlled and predictable manner that follows the flat coil 220. This erosion progression is illustrated in Figures 25A and 25B, where Figure 25A illustrates the electrode assembly 200 after initial erosion has begun and Figure 25B illustrates the electrode assembly after extensive erosion has occurred. Additionally, erosion controlled by the presence of the material of the flat coil 220 can provide a relatively more even or uniform erosion pattern progressing around the circumference of the conductive sheath 222.

[0134] As shown in Figure 25A, erosion of the conductive sheath 222 and insulating sheath 240 has begun in the initial arcing region near the end of the flat coil 220, but erosion of the flat coil 220 has not yet begun. In contrast, Figure 25B depicts extensive erosion illustrated by the deformed shapes of both the conductive sheath 222 at the distal end 223 and the insulating sheath 240 at the distal end 241. In contrast to Figure 25A, the flat coil 220 shown in Figure 25B has been eroded to remove an entire turn of the flat coil 220 (the end is no longer visible as it has eroded along the coil turns).

[0135] As discussed above, in the circuit, current can generally flow from a positively charged source to a negatively charged source. Additionally, the positive and negative terminals of a voltage source can be connected to the flat coil 220 and the conductive sheath 222 via wires 230 and 232. In one or more examples, when the flat coil 220 is connected to the negative terminal and the conductive sheath 222 is connected to the positive terminal, erosion can begin on the conductive sheath 222 first. Alternatively, in examples where the flat coil 220 is connected to the positive terminal and the conductive sheath 222 is connected to the negative terminal, erosion can begin on the flat coil 222 first. Thus, reversing the polarity of the electrode assembly (e.g., by swapping the electrodes connected to the positive or negative terminal, also referred to as "polarity switching") can cause current to flow in the opposite direction across the arc discharge region. Altering the direction of current flow can affect which electrode of the electrode assembly 200 experiences the most erosion.

[0136] In one or more examples, the difference in surface area between the electrodes can affect the maximum lifespan of the device. A first electrode with a larger surface area relative to a second electrode may be able to withstand more erosion than a smaller second electrode. As is evident in FIG. 17, the conductive sheath 222 has a greater surface area than the flat coil 220. Thus, in one or more examples, designing the electrode assembly 200 such that erosion occurs primarily on the conductive sheath 222 may enable the electrode assembly 200 to perform longer treatments than if erosion occurred primarily on the flat coil 220.

[0137] In one or more examples, the usable life of an electrode assembly, such as the electrode assembly 200, can be extended by switching the polarity of the electrodes one or more times during a treatment procedure. For example, U.S. Patent No. 10,226,265 describes switching the polarity of a voltage pulse applied across an electrode pair to switch the direction of current flow during a procedure. As previously described, an electrode connected to the positive terminal of a voltage source may generally experience increased erosion compared to an electrode connected to the negative terminal or ground. Thus, switching the polarity of an electrode assembly during a procedure can allow a user to control the relative erosion at the surface of each electrode of an electrode pair. Over the course of a treatment procedure, polarity switching can be used to more evenly distribute erosion across both electrodes of an electrode pair, increasing the usable life of the electrode assembly.

[0138] In one or more examples, the electrode assembly 200 can be used in a catheter that implements the polarity switching technique described above. Polarity switching can be performed using a controller, e.g., a polarity switching circuit and / or a multiplexing device, in electrical communication with an external voltage source and the electrode assembly. As discussed above, the external voltage source connected to the electrode assembly 200 can be configured to selectively deliver a series of high voltage pulses across the wires 230 and 232 to cause current to flow in a particular direction across the electrodes (i.e., from the positive electrode to the negative electrode). Thus, in one or more examples, the controller can be configured to control the direction of current flow across the electrodes (e.g., the conductive sheath 222 and the flat coil 220) of the electrode assembly 200 by altering the polarity of the electrodes. In one or more examples, the controller can be configured to switch polarity after a defined duration or after a certain number of pulses. For example, the polarity of the electrode assembly can be switched after a defined number of minutes, after a defined number of seconds, after every voltage pulse, after a defined number of pulses, etc.

[0139] In one or more examples, the controller may be configured to alter the polarity based on readings from a sensor in electrical communication with the controller. For example, the sensor may be configured to measure operational parameters such as current flow, voltage pulse width, the time between the voltage pulse and the onset of shock waves or cavitation bubbles, the temperature of one or more of the electrodes, and other such measurable parameters and characteristics of the functional catheter. The controller may be configured to alter the polarity based on a given parameter exceeding a predetermined threshold. In one or more examples, the sensor may measure the current flow across the electrode, and the controller may automatically switch the polarity of the electrode assembly when the current falls below a predefined threshold (e.g., a threshold indicating that the current flow is decreasing due to electrode erosion). In one or more examples, the sensor may measure the temperature in proximity to the electrode, and the controller may automatically suspend or terminate the current flow to the electrode assembly when the current exceeds a predefined threshold (e.g., a threshold indicating that the temperature of the electrode is above a target operational status). The controller may also be configured to terminate the delivery of the voltage pulse when the measured parameter exceeds or is below a termination threshold. In one or more examples, the termination threshold may indicate an error mode or an undesirable operating condition.

[0140] In one or more examples, the electrode assembly 200 can be used with a catheter to treat an occlusion (e.g., a lesion) in a body lumen, such as a calcified lesion in a vessel associated with arterial disease. As described above, the electrode assembly 200 can be configured to generate one or more shock waves and / or cavitation bubbles in response to application of a voltage across the electrodes (e.g., the conductive sheath 222 and the flat coil 220) of the electrode assembly 200. Once placed in the catheter, the shock waves and / or cavitation bubbles generated by the electrode assembly 200 can be directed toward the occlusion in the treatment area and can begin to break up the occlusion as described above.

[0141] FIG. 26 illustrates a perspective view of a distal end of an exemplary catheter 201, according to one or more embodiments. The catheter 201 can include an annular catheter body, such as an elongated tube 260. The elongated tube 260 can be formed from a rigid or semi-rigid material, such as a molded polymeric material. As shown in FIG. 26, the catheter 201 includes an electrode assembly 200 mounted at the distal end of the catheter 201 within the elongated tube 260. In one or more examples, the electrode assembly 200 can be as described above and can include a conductive sheath mounted within the elongated tube 260, an insulating sheath mounted circumferentially within the conductive sheath, and a flat coil disposed on an inner surface of the insulating sheath. (Alternative implementations of the electrode assembly can have other structures as described herein, for example, using a cylindrical inner electrode instead of a flat coil electrode as shown.) Thus, in one or more examples, the catheter 201 can be configured to deliver one or more shock waves and / or cavitation bubbles to a treatment site when a voltage pulse is applied across the flat coil and conductive sheath of the electrode assembly 100 to generate an arcing region as described above.

[0142] 26, the catheter 201 also includes a number of suction ports 266, as well as a fluid lumen 252, a suction lumen 254, and optionally a guidewire lumen 256. The guidewire lumen 256 can be sized to receive a guidewire that can be used to position the catheter 201 within a body cavity or lumen. To position the catheter 201, a guidewire can be inserted through the guidewire lumen 256 and used to position the elongated tube 260 of the catheter 201 proximate to a treatment site. In one or more examples, the catheter 201 can be configured without a guidewire lumen 256 (e.g., for rapid exchange implementations of the catheter assembly).

[0143] The lumen of catheter 201 is shown more clearly in FIG. 27A, which illustrates a left side cross-sectional view of the distal end of an exemplary catheter such as catheter 201 cut across the cutting plane shown in FIG. 27B, and FIG. 27B illustrates a front view of the distal end of the catheter.

[0144] In one or more examples, the fluid lumen 252 can be configured to flow fluid along the length of the catheter body and through a fluid outlet port 262 at the distal end of the catheter 201. The suction lumen 254 can be configured to receive debris from the treatment site through a fluid inlet port 264 at the distal end of the catheter 201 and / or through a suction port 266 shown in FIG. 26. In one or more examples, the catheter 201 can provide an inward suction that causes fluid to be drawn into the suction lumen 254 and further enables the catheter 201 to circulate fluid through the treatment site by supplying fluid via the fluid lumen 252 and removing fluid via the suction lumen 254. For example, as shown in FIG. 27A, the arrows illustrate fluid flow exiting the catheter 201 through fluid outlet port 262 (arrow F1), then entering the catheter at one or more of fluid inlet port 264 (arrow F2) and suction port 266 (arrow F3), and finally returning to the proximal end of the catheter 201.

[0145] As shown in FIG. 27A, the electrode assembly 200 is mounted within a fluid lumen 252 of the catheter 201. In one or more examples, the fluid conveyed through the fluid lumen 252 can be a conductive fluid. Thus, in one or more examples, the conductive fluid flowing through the fluid lumen 252 flows through the electrode assembly before exiting the catheter 201. The conductive fluid can provide a path for electrical current to flow between the flat coil 220 and the conductive sheath 222, thereby enabling the generation of shock waves and / or cavitation bubbles during treatment. In one or more examples, the generated shock waves and / or cavitation bubbles can flow out of the fluid exit port 262 of the catheter 201 toward the treatment site.

[0146] 28A and 28B illustrate perspective views of exemplary electrode assemblies 400 and 450 having an inner coiled electrode 420 with a curved distal tip 421. Similar to the embodiment shown in FIGS. 25A and 25B, the inner coil electrode 420 (shown here as a flat coil) is positioned within a cylindrical outer electrode 422 (alternatively referred to as a conductive sheath) with an insulating layer 440 between the cylindrical outer electrode 422 and the inner coil electrode 420. A first insulated wire 430 is electrically connected to the inner coil electrode 420 and a second insulated wire 432 is electrically connected to the cylindrical outer electrode 422. In contrast to the embodiment shown in FIGS. 25A and 25B, the curved distal tip 421 is bent to be initially centered within the circumference of the concentric cylindrical outer electrode 422 and insulating layer 440. Since bubble erosion occurs where the spark travels across the electrode, in the embodiment of FIGS. 25A and 25B, the erosion will begin at the edge of the outer electrode where the distal end and edge of the flat coil are located. Thus, with the distal end of the coil located at the edge of the cylinder, the erosion will begin at an off-center location. In FIGS. 28A and 28B, the curved distal tip 421 of the inner coiled electrode 420 moves the initial spark gap location to the center of the cylindrical electrode assembly, which can further help lead to a relatively even erosion of the cylindrical outer electrode 422. Additionally, initiating the spark and generated shock waves relative to the center of the electrode assembly 400 can align and center the cavitation bubbles formed by the electrode assembly. Having the centered location of bubble formation aligned with the centerline or longitudinal axis of the entire catheter can provide additional precision in delivering shockwave therapy.

[0147] The difference between the electrode assembly 400 of FIG. 28A and the electrode assembly 450 of FIG. 28B is the difference in how the internal coil electrode 420 is positioned. In FIG. 28A with the electrode assembly 400, the internal coil electrode 420 is flush (or nearly flush) with the distal edge of the cylindrical outer electrode 422. In FIG. 28B with the electrode assembly 450, the internal coil electrode 420 is recessed a distance within the insulating layer 440 away from the distal edge of the cylindrical outer electrode 422. The depth to which the internal coil electrode 420 is recessed can be equal to the width of one, two, three, or more than two turns of the internal coil electrode 420. In the embodiment of FIG. 28B, the recessed location of the spark gap and subsequent shock wave can lead to bubble formation that is at least partially within the barrel of the lumen of the electrode assembly 450 as defined by the insulating layer 440 and the cylindrical outer electrode 422. Thus, the expansion of the cavitation bubbles formed within the lumen is primarily directed out the distal end of the electrode assembly 450, imparting a directional nature to the bubbles and corresponding shock wave therapy.

[0148] Although the erosion of the inner coil electrode 420 will eventually progress toward the cylindrical wall, the centrally located location of the initial spark and bubble formation may have a continuing effect throughout the entire cycle of shockwave generation and treatment. In other words, due to physical factors such as residual potential, fluid dynamics following prior bubble formation, even though the curved distal tip 421 will be completely eroded and the eroded distal end of the inner coil electrode 420 will line up with the inner wall of the insulating layer 440, subsequent bubbles may also form in a centrally located location aligned with the centerline of the entire catheter.

[0149] FIG. 29 illustrates a perspective view of an exemplary electrode assembly 500 having an external coiled electrode 522 and a solid-tube internal electrode 520 with an insulating layer 540 therebetween. In this embodiment, a first insulated wire 530 is electrically connected to the external coiled electrode 522 and a second insulated wire 532 is electrically connected to the solid-tube internal electrode 520. When implementing polarity switching as described herein, it may be advantageous for the longest life of the entire device for the solid cylindrical element to be the electrode that is primarily connected to the positive terminal of the voltage source. As shown here, when the cylindrical conductive element of the solid-tube internal electrode 520 is paired with the flat coil of the external coiled electrode 522 as a complementary electrode, the ratio of the frequency with which the solid-tube internal electrode 520 receives current that serves as the positive terminal can lead to the solid cylindrical element becoming hotter than the external coiled electrode 522. Thus, the wire that connects to the positive terminal of the voltage source (in this implementation, the second insulated wire 532) is moved into electrical communication with the solid-tube inner electrode 520, thereby localizing and controlling the heat of the device. The erosion of the outer coiled electrode 522 and the solid-tube inner electrode 520 and the corresponding shock waves and bubble formation can reflect embodiments described herein, such as in FIG.

[0150] FIG. 30 illustrates a perspective view of an exemplary electrode assembly 600 having an outer clockwise coiled electrode 622 and an inner counterclockwise coiled electrode 620. In this embodiment, an insulating layer 640 is positioned between the two coiled electrodes, with a first insulated wire 630 connected to the inner counterclockwise coiled electrode 620 and a second insulated wire 632 connected to the outer clockwise coiled electrode 622. The use of two oppositely twisted coils further serves to maintain consistency in the spark location and location of shock wave formation. In this implementation, the current travels across the distance between the inner coil distal tip 621 and the outer coil distal tip 623, and erosion will occur primarily at these locations. As each of the outer clockwise coiled electrode 622 and the inner counterclockwise coiled electrode 620 is degraded, the respective outer coil distal tip 623 and inner coil distal tip 621 will erode and move around the circumference of the insulating layer 640 between them. The distance between the outer coil distal tip 623 and the inner coil distal tip 621 will vary as the erosion of each element progresses, but the distance will not exceed the diameter of the insulating layer 640. Thus, on average, as the erosion progresses, the spark gap distance between the inner coil distal tip 621 and the outer coil distal tip 623 will be maintained within a desired range. Furthermore, since each electrode is a coil whose respective distal tip is degraded, this implementation can avoid the risk of a permanent erosion bias developing on one side or the other of the electrode. It will be readily appreciated that in an alternative implementation, the outer coil electrodes may be wound in a counterclockwise direction and the inner coil electrodes may be wound in a clockwise direction.

[0151] 31A illustrates a perspective view of an exemplary electrode assembly 700 having an outer electrode 722 arranged in a pattern with erosion control gaps 729 around the surface of the outer electrode 722. In this implementation, the inner electrode is a flat coil 720 with a curved distal tip 721 that is initially bent to be centered, and an insulating layer 740 is layered between the flat coil 720 and the outer electrode 722. A first insulated wire 730 is electrically connected to the outer electrode 722 and a second insulated wire is electrically connected to the flat coil 720. Cylindrical electrodes manufactured as rolled hypotubes, as described in FIG. 2, often have currents that tend to arc where sharp edges or corners exist, and thus erosion will tend to track along the seams of the rolled hypotube material. Taking advantage of the tendency of electrical current to arc toward a sharp edge, the implementation of the electrode assembly 700 as shown in FIG. 31A uses an erosion control gap 729 to draw the arc of electrical current around the entire circumference of the outer electrode distal edge 723 as the outer electrode 722 erodes. Specifically, as the erosion of the outer electrode 722 progresses from the distal end to the proximal end of the electrode assembly 700, the forward-most erosion control gap 729 in the outer electrode 722 will become exposed as a point for electrical current to arc toward and generate a spark, corresponding to the outer electrode distal edge 723 eroding back in a proximal direction along the length of the electrode assembly 700. Thus, the location of erosion of the outer electrode 722 can be limited to the distal-most exposed sharp edge of the erosion control gap 729.

[0152] As erosion of the outer electrode distal edge 723 continues and as the forward most erosion control gap 729 is degraded, a different (relatively closer) erosion control gap 729 will become exposed and present a shorter distance for spark gap and current arcing. Thus, the location of sparking and erosion will tend toward the sharp edge of the subsequently exposed erosion control gap 729. As the material surrounding the erosion control gap 729 is subsequently degraded, the shortest distance for current arcing may return to an earlier erosion control gap 729 or a different, further back erosion control gap 729 in the outer electrode. By directing the location of the spark gap to different areas of the outer electrode distal edge 723 through the use of erosion control gap 729 configuration, the overall degradation pattern of the outer electrode 722 may be maintained as relatively uniform, thereby avoiding directional bias or other physical failure risks resulting from uneven erosion of the outer electrode 722.

[0153] Although the erosion control gaps 729 are each illustrated as having an oblong shape, in other aspects the erosion control gaps 729 can have a circular shape, a rectangular shape, a triangular shape, a diamond shape, a curved arc, other geometric shapes, or combinations thereof. In some aspects the erosion control gaps 729 pass through the full thickness of the outer electrode 722. In other aspects the erosion control gaps 729 pass only partway through the thickness of the outer electrode 722. The pattern of erosion control gaps 729 can be angled relative to one another in alternating rows as shown in FIG. 31A. In alternative embodiments, the erosion control gaps 729 can be patterned at angles parallel to one another, arranged in a Gruyere pattern, patterned as rotationally offset rings as viewed along the length of the outer electrode 722, or otherwise arranged in a regular pattern. The erosion control gaps 729 can be formed in the outer electrode 722 by a laser cutting process or the like as known in the art. It should be readily understood that any of the internally located electrodes described herein may be used in combination with the outer electrode 722.

[0154] 31B-31E illustrate an example progression of electrode degradation for an outer electrode 722 having erosion control gaps 729 in a cutout pattern as shown in FIG. 31A. The progression of erosion region 713 degrades the outer electrode 722 and is shown in FIG. 31B as consuming most of the forward-most erosion control gap 729 and reaching the subsequent erosion control gap 729' along the length of the outer electrode 722. In FIG. 31C, the erosion region 713 spreads relatively laterally (to the right in the illustration) around the circumference of the outer electrode near the next subsequent erosion control gap 729'. In FIG. 31D, the erosion region 713 continues to spread relatively laterally (to the left in the illustration) around the circumference of the outer electrode near the next subsequent erosion control gap 729'' while continuing to erode around the erosion control gap 729' in a similar manner. Finally, in FIGURE 31D, the erosion control region 713 continues to degrade the outer electrode 722 in a generally uniform manner, eroding electrode material relatively equally around the erosion control gaps 729' and 729''. Thus, the erosion control gaps 729 in the outer electrode 722 prevent the development of uneven and irregularly shaped electrode edges over the normal course of degradation due to sparking and cavitation bubble formation.

[0155] In the various externally located electrode alternative embodiments described above, seamless hypotubes can be used to minimize current arcing that can result in uneven erosion of the respective electrodes. Additionally, it should be understood that in the embodiments described above, the metals or alloys used for the various cylindrical or coiled electrodes located within the internal or external locations can be made from erosion resistant materials such as stainless steel, platinum, palladium, iridium, molybdenum, tungsten, copper, or combinations thereof.

[0156] (Experimental Example)

[0157] 32A-32H are paired sets of images or graphs capturing the operation of an electrode assembly as described herein with particular reference to FIG. 17. Specifically, each of FIGS. 32A-32H shows a captured image from a high-speed video showing an exemplary electrode assembly generating forward-directed vapor bubbles. Paired with each image is a graph displaying the average pressure measurements (in MPa) over time (μsec) for such a forward-directed vapor bubble generating electrode assembly. The pressure measurements were made with a hydrophone located approximately 10 mm from the emitter location. As described above, the pressure close to the emitter (approximately 1 mm) is approximately an order of magnitude greater than the pressure measured at a hydrophone 10 mm away from the end of the emitter. The black dots shown in each graph correspond to the time of measurement and image capture in the associated image.

[0158] FIG. 32A shows an initial spark at the distal end of the electrode assembly, at its onset (near zero microseconds) the measured pressure is about 0.25 MPa. FIG. 32B shows the moment immediately following the spark of FIG. 32A, where the pressure drops to just below about 0.0 MPa. FIG. 32C shows the formation of the initial bubble more than 100 μsec after the spark occurs, where the measured pressure remains near about 0.0 MPa. FIG. 32D shows the beginning of bubble destruction and collapse at about 300 μsec, where the measured pressure peaks at just above about 0.8 MPa. FIG. 32E shows the continuation of bubble collapse at about 325 μsec, where the measured pressure drops to about −0.1 MPa. FIG. 32F shows the dissipation of the initial bubble at about 440 μsec, where the measured pressure is again about 0.0 MPa. Figure 32G shows the formation of a secondary bubble driven by the hydrodynamic forces of expansion and collapse of the initial bubble occurring at approximately 480 μs, at which point the measured pressure is at a secondary peak of approximately 0.3 MPa. Figure 32H shows the dissipation of the secondary bubble at approximately 550 μs after the spark, at which point the measured pressure is again approximately 0.0 MPa.

[0159] As can be seen from Figures 32A-32H, the exemplary electrode assembly as described herein is fully capable of generating shock waves and cavitation bubbles with forward directionality. After a voltage pulse is applied, a positive pressure spike is generated (e.g., as in Figure 32D), followed by a negative pressure spike (e.g., as in Figure 32E). Furthermore, the strength and pressure generated by these shock waves and bubbles is sufficient to implement IVL therapy and may have further applications in ablation in vivo processes. The observed results of the exemplary electrode assembly are in line with the conventional understanding of IVL, where both initial and secondary bubbles are generated at their respective pressures. In forward firing directionality applications, both initial and secondary bubbles can be optimized to produce peak pressures that are both functional for delivering therapy to tissue or other in vivo structures.

[0160] Although the electrode assemblies and catheter devices described herein are primarily discussed in the context of coronary indications, such as lesions in blood vessels, the electrode assemblies and catheters herein can be used for a variety of indications. For example, similar designs can be used to treat soft tissues, such as cancers and tumors (i.e., non-thermal ablation methods), blood clots, uterine fibroids, cysts, organs, scar and fibrous tissue removal, or other tissue destruction and removal. The electrode assembly and catheter designs can also be used for neurostimulation therapy, targeted drug delivery, treatment of tumors in body lumens (e.g., tumors in blood vessels, esophagus, intestine, stomach, or vagina), wound treatment, non-surgical removal and destruction of tissue, or as a substitute for thermal therapy or cauterization for venous insufficiency and tubal ligation (i.e., for permanent female contraception). In addition, the electrode assemblies and catheters described herein can also be used for tissue engineering methods, such as mechanical tissue decellularization to generate bioactive scaffolds where new cells (e.g., exogenous or endogenous cells) can replace old cells, introducing porosity to the site and improving cell retention, cell infiltration / migration, and diffusion of nutrients and signaling molecules, promoting angiogenesis, cell proliferation, and tissue regeneration, as well as cell replacement therapy. Such tissue engineering methods can be useful for treating ischemic heart disease, fibrotic liver, fibrotic intestine, and traumatic spinal cord injury (SCI). For example, with respect to the treatment of spinal cord injury, the devices and assemblies described herein can facilitate the removal of scarred spinal cord tissue that acts as a barrier for neuronal reconnection, prior to injection of lentivirus-loaded anti-inflammatory hydrogel to genetically engineer spinal cord neurons to regenerate.

[0161] It should be noted that the elements and features of the exemplary catheters illustrated throughout this specification and drawings may be rearranged, recombined, and modified without departing from the present invention. For example, while this specification and drawings describe and illustrate several exemplary electrode assemblies, the present disclosure is intended to include catheters having a variety of electrode configurations. Additionally, the number, placement, and spacing of electrode pairs and assemblies may be modified without departing from the subject invention.

[0162] It should be understood that the foregoing is merely illustrative of the principles of the present invention, and that various modifications, alterations, and combinations may be made by those skilled in the art without departing from the scope and spirit of the present invention. Any of the various catheter variations disclosed herein may include features described with any other catheter or combination of catheters herein. Furthermore, any of the methods may be used with any of the catheters disclosed. Thus, it is not intended that the present invention be limited, except as by the appended claims.

Claims

1. 1. A catheter for treating an obstruction in a body lumen, the catheter comprising: A long thin tube, a cylindrical inner conductive sheath mounted within the elongate tube, the inner conductive sheath having a distal end; a cylindrical outer conductive sheath mounted circumferentially around the inner conductive sheath within the elongate tube, the outer conductive sheath having a distal end proximate the distal end of the inner conductive sheath; an insulating sheath mounted within the elongated tube between the outer conductive sheath and the inner conductive sheath; Equipped with A catheter in which, when a voltage pulse is applied across the inner and outer conductive sheaths within the conductive fluid, current flows across an arc discharge region between the inner and outer conductive sheaths, generating cavitation bubbles and / or shock waves outside the catheter to treat the occlusion.

2. The catheter of claim 1 , wherein the elongated tube includes a fluid lumen for flowing a conductive fluid along the catheter and through a fluid outlet port at the distal end of the catheter.

3. 3. The catheter of claim 2, wherein the outer conductive sheath, the insulating sheath, and the inner conductive sheath are mounted within the fluid lumen such that fluid flowing through the fluid lumen flows through the inner conductive sheath.

4. The catheter of claim 1 , wherein the elongated tube includes a suction lumen for removing debris from the body lumen.

5. The catheter of claim 1 , wherein the elongate tube includes a guidewire lumen sized to receive a guidewire.

6. The catheter of claim 1 , wherein the arcing region is located where the distal end of the outer conductive sheath is closest to the distal end of the inner conductive sheath.

7. A catheter as described in claim 6, wherein the distal end of the inner conductive sheath is configured to erode in proximity to the arc discharge region, and the erosion of the inner conductive sheath causes current to flow across a secondary arc discharge region between the distal end of the inner conductive sheath and the distal end of the outer conductive sheath.

8. A catheter as described in claim 6, wherein the distal end of the outer conductive sheath is configured to erode in proximity to the arc discharge region, and the erosion of the outer conductive sheath causes current to flow across a secondary arc discharge region between the distal end of the outer conductive sheath and the distal end of the inner conductive sheath.

9. The catheter of claim 1 , wherein the voltage pulse is applied to generate a positive pressure spike followed by a negative pressure spike.

10. 1. A catheter for treating an obstruction in a body lumen, the catheter comprising: A long thin tube, a cylindrical conductive sheath mounted within the elongated tube, the conductive sheath having a distal end; an insulating sheath circumferentially mounted within the conductive sheath, the insulating sheath having a distal end proximal to the distal end of the conductive sheath; a flat coil disposed on an inner surface of the insulating sheath, the flat coil having a distal end proximal to the distal end of the conductive sheath and the distal end of the insulating sheath; Equipped with When a voltage pulse is applied across the flat coil and the conductive sheath, current flows across an arc discharge region between the flat coil and the conductive sheath, generating cavitation bubbles and / or shock waves.

11. The catheter of claim 10 , wherein the flat coil has a rectangular cross section with a planar inner surface opposite the inner surface of the insulating sheath.

12. 11. The catheter of claim 10, wherein the elongated tube includes a fluid lumen for flowing a conductive fluid along the catheter and through a fluid outlet port at the distal end of the catheter, and the conductive sheath, the insulating sheath, and the flat coil are mounted within the fluid lumen such that fluid flowing through the fluid lumen flows through the flat coil.

13. 11. The catheter of claim 10, wherein the arcing region is located where the distal end of the conductive sheath is closest to the distal end of the flat coil.

14. 14. The catheter of claim 13, wherein generating cavitation bubbles and / or shock waves causes the insulating sheath to erode adjacent the arcing region, the erosion of the insulating sheath exposing an outer surface of the flat coil and causing current to flow across a secondary arcing region between the outer surface of the flat coil and the distal end of the conductive sheath.

15. 15. The catheter of claim 14, wherein generating cavitation bubbles and / or shock waves causes the distal end of the conductive sheath to erode proximate the arc discharge region, the erosion of the conductive sheath beginning before the erosion of the insulating sheath begins.

16. The catheter of claim 10, wherein the elongated tube comprises an aspiration lumen for removing debris from the body lumen.

17. The catheter of claim 10 , wherein the elongate tube includes a guidewire lumen sized to receive a guidewire.

18. The catheter of claim 10 , wherein the distal end of the flat coil is bent to be initially centered within the circumference of the cylindrical conductive sheath.

19. 11. The catheter of claim 10, comprising an adhesive disposed on an inner surface of the insulating sheath in areas between the coils of the flat coil, the adhesive filling the areas between the coils and securing the flat coil to the insulating sheath.

20. The catheter of claim 10, wherein the voltage pulse is applied to generate a positive pressure spike followed by a negative pressure spike.

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