Tissue ablation catheter with insulation between inner and outer electrodes - Patents.com

Abstract

A catheter for tissue ablation, in which one or more electrodes are attached to the inner surface of the catheter body facing the lumen and one or more electrodes are attached to the outer surface. The electrodes are offset from the distal end of the catheter. The material between the inner and outer electrodes is an insulator, which may be, for example, a high permittivity dielectric. This catheter configuration generates an electric field that curves around the tip of the catheter. The electric field strength near the catheter tip is relatively symmetric, such that the orientation of the catheter is relatively insensitive to the depth of tissue removal. In embodiments, multiple inner or outer electrodes may be provided, and the voltage configuration between the electrodes may be switched to vary the direction of the electric field over time to improve the consistency of removal.

Description

[Technical field]

[0001] One or more embodiments of the present invention relate to the field of medical catheters used for tissue ablation. More particularly, but not by way of limitation, one or more embodiments of the present invention provide a tissue ablation catheter that includes insulation between an inner electrode and an outer electrode. [Background technology]

[0002] Catheters fitted with electrodes are widely used for tissue ablation to address a variety of medical problems. For example, in cardiac applications, specialized multi-electrode catheters have been invented to perform electroporation of the pulmonary vein ostia in the left atrium. Many of these devices are designed to perform anatomical ablation of the pulmonary veins to treat a common arrhythmia called atrial fibrillation.

[0003] Existing ablation catheters have a variety of electrode configurations, but they all typically have multiple electrodes located on the exterior surface of the catheter and one electrode located at the tip of the catheter. These configurations limit the shape of the electric field generated by the catheter. In particular, the electric field profile is typically elongated because it is generated by dipoles located along the longitudinal axis of the catheter. Such elongated field shapes are not optimal for tissue ablation, as the depth of ablation depends on the orientation of the catheter relative to the tissue to be ablated.

[0004] Due to at least the limitations discussed above, there is a need for a tissue ablation catheter that includes insulation between the inner and outer electrodes. Summary of the Invention

[0005] One or more embodiments described herein relate to tissue ablation catheters that include insulation between an inner electrode and an outer electrode. Embodiments of the invention can generate novel electric field shapes that improve ablation consistency.

[0006] One or more embodiments of the invention may include a catheter comprising a tubular element having a longitudinal axis, a distal end, a lumen, an inner surface surrounding the lumen, and an outer surface. An electrical insulator may be provided between the inner surface and the outer surface. The catheter may have one or more inner electrodes coupled to the inner surface and one or more outer electrodes coupled to the outer surface. The inner and outer electrodes may each be offset from a distal end of the catheter. An electrical insulator may separate the inner electrode from the outer electrode. The distal end of the catheter may be located proximate the tissue to be removed. A controller may set voltages on the inner and outer electrodes to generate an electric field on the outside of the tubular element that induces removal of tissue by electroporation.

[0007] In one or more embodiments of the invention, the shortest path for current to flow from the inner electrode to the outer electrode may be longer than the distance between the inner and outer electrodes.

[0008] In one or more embodiments of the present invention, the electrical insulator may be a dielectric material such as, for example, an aluminum nitride ceramic. In one or more embodiments, the electrical conductivity of the electrical insulator may be less than 0.1 microsiemens / centimeter.

[0009] In one or more embodiments, the distance between the distal end of the catheter tubular element and each of the inner electrodes can be from 0.01 millimeters to 1 meter. In one or more embodiments, the distance between the distal end of the catheter tubular element and each of the outer electrodes can be from 0.01 millimeters to 1 meter.

[0010] In one or more embodiments of the invention, the controller may set the potential difference between the at least one inner electrode and the at least one outer electrode to greater than 5000 volts.

[0011] In one or more embodiments of the invention, the controller may vary the voltage of the inner and outer electrodes within a pulse time that is less than twice the membrane recovery time of the tissue being ablated.

[0012] In one or more embodiments, the controller may vary the voltage of the inner and outer electrodes within a period of 10 milliseconds or less.

[0013] In one or more embodiments, the controller may vary the voltages of the inner and outer electrodes to change the direction of the electric field outside the tubular element over time. For example, the controller may set the electrode voltages at one time to generate a first average electric field vector in an area of ​​tissue to be ablated and set the electrode voltages at another time to generate a second average electric field vector in an area of ​​tissue to be ablated, where the angular difference between the first and second average electric field vectors is at least 1 degree. [Brief description of the drawings]

[0014] The above and other aspects, features and advantages of the present invention will become more apparent from the following more particular description, presented in conjunction with the following drawings. [Figure 1] FIG. 1A shows a typical prior art ablation catheter with electrodes on its outer surface, and FIG. 1B shows a cross-sectional view of the catheter of FIG. 1A. [Diagram 2] (A) shows an exemplary embodiment of the present invention, which is an ablation catheter with an outer electrode and an inner electrode; (B) shows a cross-sectional view of the catheter of FIG. 2(A); and (C) shows an enlarged cross-sectional view of the distal end of the catheter of FIG. 2(A). [Diagram 3] FIG. 2(A) illustrates an exemplary shortest current path between the inner and outer electrodes of the catheter, showing that because the electrodes are separated by insulators, the current path is longer than the straight-line distance between the electrodes. [Figure 4]2(A) shows exemplary electric field vectors in a region near the distal end of the catheter, illustrating how the electric field bends around the insulator at the distal end between the inner and outer electrodes. [Diagram 5] (A) shows an exemplary electric field intensity contour around the distal end of the catheter of FIG. 1(A), and (B) shows an exemplary electric field intensity contour around the distal end of the catheter of FIG. 2(A), showing that the catheter of the present invention has a more symmetric electric field contour than prior art catheters. [Figure 6] The advantage of the symmetrical electric field contour shown in FIG. 5(B) is shown, demonstrating that the depth of tissue ablation is largely independent of the orientation of the catheter relative to the tissue being ablated. [Figure 7] 2(A) shows a variation of the catheter of FIG. 2(A) with multiple inner electrodes and multiple outer electrodes. [Figure 8] FIG. 7 illustrates how by varying the voltage on the electrodes of the catheter, the direction of the electric field acting on the cells of the tissue being ablated can be changed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, a tissue ablation catheter with an insulator between an inner electrode and an outer electrode will be described. In the following exemplary description, numerous specific details are set forth in order to provide a more detailed understanding of the embodiments of the present invention. However, it will be apparent to one skilled in the art that the present invention can be practiced without incorporating all aspects of the specific details described herein. In other instances, certain features, quantities, or measurements well known to those skilled in the art have not been described in detail so as not to obscure the present invention. The reader should note that although examples of the present invention are described herein, the full scope of the claims and any equivalents defines the scope of the present invention.

[0016] Intravascular catheters are used in medicine to deliver high voltage, short duration pulses of electricity, also known as pulsed electric field ablation, electroporation, direct current ablation, or flugulation, to tissue targets within the body for the purpose of soft tissue ablation. Figures 1(A) and 1(B) are schematic diagrams of a typical ablation catheter 100 currently used for these applications. Figure 1(A) shows a side view of the ablation catheter, and Figure 1(B) shows a cross-sectional view along a plane through the longitudinal axis 102 of the catheter. Catheter 100 is a typical bipolar ablation catheter, having a central lumen 103 within a tubular element and two electrodes on the outer surface 121 of the tube, with electrode 111 at or near the tip of the catheter's distal end 101 and electrode 112 located on the tube of the catheter remote from the tip electrode. The electrodes are not attached to the inner surface 122. Applying a voltage difference between the two electrodes forms a dipole. Tissue can be ablated by radio frequency (RF) thermal energy or by electroporation, where an electric field directly causes cell damage. Electric field-mediated cell injury has advantages over thermal ablation, and interest in using this approach in a variety of disease states is growing. Tissue response to electroporation differs from thermal injury in three important ways. First, tissue susceptibility to electric field-mediated injury varies by orders of magnitude, thus benefiting some organs, such as the heart, from selective ablation. Tissue selectivity reduces the risk of unintended damage to collateral structures, such as respiratory nerves, esophagus, and blood vessels, a common concern when performing pulmonary vein isolation. Second, the ablation lesion volume closely follows the electric field contour, so lesion size and shape are more predictable and / or precise than thermal approaches. And third, electroporation is much faster than RF ablation, with each procedure taking microseconds to seconds, thereby reducing risk and resource demands in terms of total procedure time.

[0017] Some ablation catheters have more than two electrodes on the exterior surface 121 of the catheter 100. For example, in cardiac applications, specialized multi-electrode catheters have been devised to electroporate the ostia of the pulmonary veins in the left atrium. Many of these devices are designed to perform anatomic ablation of the pulmonary veins to treat a common arrhythmia called atrial fibrillation.

[0018] 2(A), 2(B), and 2(C) show different views of an exemplary embodiment of the present invention, which is an ablation catheter 200 with novel geometric and electrical characteristics that provide advantages over conventional ablation catheters such as catheter 100. FIG. 2(A) shows a side view of catheter 200, FIG. 2(B) shows a cross-sectional view along a plane through the longitudinal axis 202 of the catheter, and FIG. 2(C) shows an enlarged cross-sectional view of the distal end of catheter 200. Catheter 200 has an outer electrode 211 attached to the outer surface 221 of the tubular catheter body and an inner electrode 212 attached to the inner surface 222 of the tubular catheter body (facing lumen 203). Both electrodes 211, 212 are offset from the distal end 201 of the catheter along the longitudinal axis 202, and there is no electrode at the tip of the catheter. The distance 241 between the outer electrode 211 and the distal end 201 may be at least 0.01 millimeters and at most 1 meter in one or more embodiments of the invention. The distance 242 between the inner electrode 212 and the distal end 201 may be at least 0.01 millimeters and at most 1 meter in one or more embodiments of the invention. The distances 241 and 242 may be equal or unequal. Depending on the application, the distal end of the catheter 200 may be placed at or near the location of the tissue to be removed. The outer electrode 211 may contact the tissue. The inner electrode 212 does not directly contact the tissue to be removed. The electrodes may generate an electric field on the outside of the tubular catheter body to induce ablation of nearby tissue by electroporation. The catheter lumen 203 may carry an irrigation fluid that is infused into the tissue, which may be electrically conductive. An exemplary fluid may be, for example, 9% saline.

[0019] The inner electrode 212 and the inner electrode 211 are separated by a distal portion of the catheter body that may include an electrically insulating material 250. In one or more embodiments, the electrical conductivity of the insulating material 250 may be, for example, less than 0.1 microsiemens per centimeter. In one or more embodiments, the material 250 may be a dielectric and have a high dielectric constant. An exemplary material that may be used in one or more embodiments is, for example, aluminum nitride ceramic (the portion of the catheter body below the electrodes (away from the distal end) may or may not be made of the same material as the portion of the body between the electrodes). All or a portion of the catheter body may be flexible. The tubular catheter body may be of any desired length.

[0020] The electrodes 211 and 212 may be coupled to a controller 230 that sets the voltage of each electrode, as shown in FIG. 2(B) (the wires connecting the controller and the electrodes are shown diagrammatically separate from the catheter body for ease of illustration, but depending on the application, for example, the wires may be integral with or attached to the catheter body). The controller 230 may provide voltage pulses to the electrodes 211 and 212. The pulses may be monophasic pulses, for example, with a duration between 10 ns and 10 ms, a duty cycle of less than 50%, an amplitude between 1 kV and 10 kV, and a pulse repetition between 1 and 10,000 pulses / sec, inclusive. In particular, in one or more embodiments of the present invention, the voltage applied between the at least one inner electrode and the at least one outer electrode may be greater than 5,000 volts. However, any potential pattern may be used with this electrode configuration, including, but not limited to, any combination of multiple duration rectangular pulses, biphasic square or trapezoidal waves, bipolar sine waves, offset sine waves, asymmetric square waves, asymmetric rectangular linear waves, and / or any waveform or pulse pattern.

[0021] One or more embodiments of the present invention may have multiple inner electrodes or multiple outer electrodes. FIG. 7 shows an exemplary embodiment having multiple inner electrodes and multiple outer electrodes. An embodiment may have any number of inner electrodes and any number of outer electrodes. The inner and outer electrodes may be separated by an insulator, such as a high dielectric constant material. The inner and outer electrodes may all be offset from the distal end of the catheter.

[0022] 3 illustrates the effect that the geometry of catheter 200 has on current flow between the electrodes. (For purposes of illustration) when the inner electrode is set at a positive voltage relative to the outer electrode, current 301 flows from the inner electrode 212, along the lumen to the distal end of the catheter tip, then bends down to the outer electrode 211. Thus, the length of the shortest current path 301 between the electrodes is longer than the linear distance 302 between the electrodes. This feature is in contrast to conventional catheter geometries, such as catheter 100 of FIG. 1(A), where the electrodes are not separated by insulation, so the length of the shortest current path between the electrodes is equal to the linear distance between the electrodes.

[0023] Figure 4 shows a similar bending effect on the shape of the electric field that occurs when a voltage difference is applied between the electrodes. The electric field lines 400 bend around the distal end of the catheter. The dielectric of the catheter body amplifies the electric field strength as it bends around the tip.

[0024] 5A and 5B show the potential advantages of the curved field shape shown in FIG. 4 compared to the field shape of a conventional ablation catheter. FIG. 5A shows the field intensity contour 501 for a conventional catheter 100, and FIG. 5B shows the field intensity contour 511 for a catheter 200. The contours 501 and 511 separate the areas within the contour where the field intensity exceeds a threshold value from the areas outside the contour where the field intensity is below this threshold. Since tissue ablation by electroporation is highly correlated with the field intensity, the shape of the field intensity contour determines the area where tissue is ablated. Because the electrodes of the catheter 100 operate in a conventional dipole configuration, the contour 501 is elongated, whereas the contour 511 is relatively symmetric around the tip of the catheter 200 due to the phenomenon of field bending. This symmetric shape results in a consistent ablation depth in the tissue, regardless of the orientation of the catheter relative to the tissue to be ablated. This advantage is shown in FIGS. 6A and 6B. The catheter 200 is placed against tissue 600 with the goal of ablating a portion of the tissue adjacent to the catheter. However, it is not always possible to control the exact orientation of the catheter relative to the tissue. For example, in FIG. 6(A) the longitudinal axis of the catheter 200 is approximately perpendicular to the tissue boundary, whereas in FIG. 6(B) this axis is approximately parallel to the tissue boundary. The electric field intensity contour 511 is substantially symmetric, so that the portion 601 of the tissue that experiences an electric field intensity greater than the threshold when the catheter is perpendicular is approximately the same as the portion 602 of the tissue that experiences this electric field intensity when the catheter is parallel. Thus, regardless of the orientation of the catheter, the depth of the tissue that is ablated is approximately the same. This feature of the catheter 200 represents a substantial advance over conventional catheters, where the electric field intensity contour is highly asymmetric and the depth of ablation can be highly dependent on the orientation of the catheter, which is not always controllable.

[0025] The catheter 200 has a single inner electrode and a single outer electrode. One or more embodiments of the invention may have multiple inner electrodes or multiple outer electrodes (or both). FIG. 7 shows an exemplary catheter 700 with two inner electrodes 212 and 714 and three outer electrodes 211, 712, and 713. All electrodes are offset from the distal end of the catheter, and the inner and outer electrodes are separated by an insulating catheter body. All electrodes are coupled to a controller 230. The controller may set the voltage of any of the electrodes and may vary the voltage of the electrodes over time to change the direction and strength of the electric field vector. By varying the electrode voltage, the target tissue may be exposed to multiple electric field vectors from a single catheter position.

[0026] 8(A), 8(B), and 8(C) show an embodiment in which the electrode voltage is changed to change the direction of the electric field vector over time. The effect of the electric field on tissue ablation depends on both the electric field strength and the orientation of the electric field vector relative to the cell membrane. In general, cells are most stressed where the electric field vector is perpendicular to the cell membrane. However, cell membranes are non-uniformly oriented throughout the tissue, so a single electric field direction does not generate maximum stress for all cells at the same time. By subjecting the tissue to multiple electric field directions over time, ablation of cells in the tissue becomes more uniform, as each cell experiences an electric field vector that is more likely to cause high stress on the cell membrane. FIGS. 8(A)-8(C) show different voltage patterns applied to the electrodes of the catheter 700 at different times, and the resulting average electric field directions 801a-801c near an exemplary cell 800 in the target tissue. The controller can, for example, cycle through these three voltage patterns repeatedly. By varying the voltage, the cells are exposed to different electric field directions at different times. For example, a volume sample within a target tissue may be exposed to two or more average electric field vectors at different times that differ by a calculated vector angle difference between 1° and 90° inclusive. In one or more embodiments, the switching time between different voltage configurations may be less than or equal to twice the membrane recovery time of the target cells or material within the treatment volume. For example, the switching time between configurations may be between 10 nanoseconds and 1 second.

[0027] One or more embodiments of the invention include a tissue ablation catheter with a varying electric field direction, the tissue ablation catheter having a tubular element having a distal end configured to be positioned proximal to the tissue to be removed, a proximal end opposite the distal end, an inner surface surrounding a lumen, an outer surface, and an electrical insulator between the inner and outer surfaces, one or more inner electrodes coupled to the inner surface, each offset in a proximal direction toward the proximal end, away from the distal end, one or more outer electrodes coupled to the outer surface, and a controller coupled to the one or more inner electrodes and the one or more outer electrodes and configured to set a voltage on the one or more inner electrodes and a voltage on the one or more outer electrodes to generate an electric field on the outside of the tubular element that induces ablation of the tissue to be removed by electroporation, and varying the voltage on the one or more inner electrodes and the one or more outer electrodes over time to change the direction of the electric field on the outside of the tubular element over time.

[0028] In one or more embodiments, the controller is further configured to set first voltages of the one or more inner electrodes and the one or more outer electrodes at a first time to generate a first average electric field vector in the area of ​​tissue to be removed, and set second voltages of the one or more inner electrodes and the one or more outer electrodes at a second time to generate a second average electric field vector in a second area of ​​tissue to be removed, where an angular difference between the first and second average electric field vectors is at least 1 degree.

[0029] In one or more embodiments, the shortest path for current to flow from an inner electrode, which is one of the one or more inner electrodes, to an outer electrode, which is one of the one or more outer electrodes, is longer than the distance between the inner electrode and the outer electrode.

[0030] In one or more embodiments, the electrical insulator comprises a dielectric material.

[0031] In one or more embodiments, the dielectric material includes an aluminum nitride ceramic.

[0032] In one or more embodiments, the electrical conductivity of the electrical insulator is less than 0.1 microsiemens / centimeter.

[0033] In one or more embodiments, the controller is further configured to set a potential difference between at least one of the one or more inner electrodes and at least one of the one or more outer electrodes to greater than 5000 volts.

[0034] In one or more embodiments, the controller is further configured to vary the voltage of the one or more inner electrodes and the one or more outer electrodes within a pulse time that is less than twice the membrane recovery time of the tissue being ablated.

[0035] In one or more embodiments, the controller is further configured to vary the voltage of the one or more inner electrodes and the one or more outer electrodes within a period of 10 milliseconds or less.

[0036] In one or more embodiments, each of the one or more inner electrodes is offset in a proximal direction away from the distal end toward the proximal end, with the furthest distal point of the one or more inner electrodes resting within the lumen.

[0037] One or more embodiments include a tubular element having a distal end configured to be positioned proximal to the tissue to be removed, a proximal end opposite the distal end, an inner surface surrounding a lumen, an outer surface, and an electrical insulator between the inner surface and the outer surface, one or more inner electrodes coupled to the inner surface, each offset in a proximal direction toward the proximal end, away from the distal end, one or more outer electrodes coupled to the outer surface, and a controller coupled to the one or more inner electrodes and the one or more outer electrodes and configured to set voltages on the one or more inner electrodes and voltages on the one or more outer electrodes to generate an electric field that induces ablation of the tissue to be removed by electroporation, the electric field comprising a first field line portion connected to one of the one or more inner electrodes, a second field line portion connected to the first field line portion, the second field line portion bending around the distal end of the tubular element, and a third field line portion connected to the second field line portion and connected to one of the one or more outer electrodes. The electric field comprises one or more electric field lines, including a portion of the electric field line.

[0038] In one or more embodiments, the shortest path for current to flow from an inner electrode, which is one of the one or more inner electrodes, to an outer electrode, which is one of the one or more outer electrodes, is longer than the distance between the inner electrode and the outer electrode.

[0039] In one or more embodiments, the electrical insulator comprises a dielectric material.

[0040] In one or more embodiments, the dielectric comprises an aluminum nitride ceramic.

[0041] In one or more embodiments, the electrical conductivity of the electrical insulator is less than 0.1 microsiemens / centimeter.

[0042] In one or more embodiments, the controller is further configured to set a potential difference between at least one of the one or more inner electrodes and at least one of the one or more outer electrodes to greater than 5000 volts.

[0043] In one or more embodiments, the controller is further configured to vary the voltage of the one or more inner electrodes and the one or more outer electrodes within a pulse time that is less than twice the membrane recovery time of the tissue being ablated.

[0044] In one or more embodiments, the controller is further configured to vary the voltage of the one or more inner electrodes and the one or more outer electrodes within a period of 10 milliseconds or less.

[0045] In one or more embodiments, the one or more inner electrodes are offset in a proximal direction from the distal end to the proximal end, with the furthest distal point of the one or more inner electrodes resting within the lumen.

[0046] While the invention disclosed herein has been described in terms of specific embodiments and applications thereof, numerous modifications and variations may be made by those skilled in the art without departing from the scope of the invention as set forth in the claims.

Claims

1. 1. A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode, A tubular element, A distal end. a proximal end opposite the distal end; and A longitudinal axis; an inner surface surrounding the lumen; The exterior and an electrical insulator between the inner surface and the outer surface; one or more inner electrodes coupled to the interior surface, each offset in a proximal direction toward the proximal end, away from the distal end; one or more outer electrodes coupled to the exterior surface, each offset in the proximal direction from the distal end toward the proximal end and separated from the one or more inner electrodes by the electrical insulator; a controller coupled to the one or more inner electrodes and the one or more outer electrodes; the distal end is configured to be positioned adjacent to tissue to be removed; the controller is configured to set a voltage of the one or more inner electrodes and a voltage of the one or more outer electrodes to generate an electric field on the outside of the tubular element that induces ablation of the tissue to be removed by electroporation. A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

2. 2. The tissue ablation catheter according to claim 1, further comprising an insulator between the inner electrode and the outer electrode. a shortest path for a current flowing from an inner electrode, which is one of the one or more inner electrodes, to an outer electrode, which is one of the one or more outer electrodes, is longer than a distance between the inner electrode and the outer electrode; A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

3. 2. The tissue ablation catheter according to claim 1, further comprising an insulator between the inner electrode and the outer electrode. The electrical insulator comprises a dielectric material. A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

4. 4. The tissue ablation catheter according to claim 3, further comprising an insulator between the inner electrode and the outer electrode. The dielectric material comprises an aluminum nitride ceramic. A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

5. 2. The tissue ablation catheter according to claim 1, further comprising an insulator between the inner electrode and the outer electrode. The electrical conductivity of the electrical insulator is less than 0.1 microsiemens / centimeter. A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

6. 2. The tissue ablation catheter according to claim 1, further comprising an insulator between the inner electrode and the outer electrode. the distance between the distal end and each of the one or more inner electrodes is greater than or equal to 0.01 millimeters and less than or equal to 1 meter; A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

7. 6. The tissue ablation catheter according to claim 5, further comprising an insulator between the inner electrode and the outer electrode, the distance between the distal end and each of the one or more outer electrodes is greater than or equal to 0.01 millimeters and less than or equal to 1 meter; A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

8. 2. The tissue ablation catheter according to claim 1, further comprising an insulator between the inner electrode and the outer electrode. The controller is further configured to set a potential difference between at least one of the one or more inner electrodes and at least one of the one or more outer electrodes to greater than 5000 volts. A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

9. 2. The tissue ablation catheter according to claim 1, further comprising an insulator between the inner electrode and the outer electrode. The controller is further configured to vary the voltage of the one or more inner electrodes and the one or more outer electrodes within a pulse time that is less than two times a membrane recovery time of the tissue being ablated. A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

10. 2. The tissue ablation catheter according to claim 1, further comprising an insulator between the inner electrode and the outer electrode. The controller is further configured to vary the voltages of the one or more inner electrodes and the one or more outer electrodes within a period of 10 milliseconds or less. A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

11. 2. The tissue ablation catheter according to claim 1, further comprising an insulator between the inner electrode and the outer electrode. the controller is further configured to vary a voltage on the one or more inner electrodes and the one or more outer electrodes over time to vary a direction of the electric field on the outside of the tubular element over time. A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

12. 10. The tissue ablation catheter according to claim 9, further comprising an insulator between the inner and outer electrodes, The controller further comprises: setting first voltages on the one or more inner electrodes and the one or more outer electrodes at a first time to generate a first average electric field vector in the region of tissue to be ablated; configuring second voltages on the one or more inner electrodes and the one or more outer electrodes at a second time to generate a second average electric field vector in a second region of the tissue to be ablated; an angular difference between the first average electric field vector and the second average electric field vector is at least 1 degree; A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

13. 2. The tissue ablation catheter according to claim 1, further comprising an insulator between the inner electrode and the outer electrode. each of the one or more inner electrodes is offset in the proximal direction toward the proximal end, away from the distal end, and a distal-most point of the one or more inner electrodes is within the lumen; A tissue ablation catheter comprising an insulator between an inner electrode and an outer electrode.

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