Tissue ablation catheter with insulator between inner and outer electrodes

Abstract

A catheter for tissue ablation having one or more electrodes attached to the inner surface of the lumen-facing surface of the catheter body and one or more electrodes 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 and can be, for example, a dielectric with a high dielectric constant. The catheter configuration creates an electric field that curves around the catheter tip. The field strength near the catheter tip is relatively symmetric; thus, the tissue ablation depth is relatively insensitive to catheter orientation. Embodiments can have multiple inner or outer electrodes and can switch the voltage configuration between the electrodes to change the electric field direction over time, improving ablation consistency.

Description

TECHNICAL FIELD

[0001] One or more embodiments of the present invention relate to the field of medical catheters for tissue ablation. More specifically, but not by way of limitation, one or more embodiments of the present invention implement a tissue ablation catheter having an insulator between an inner electrode and an outer electrode. BACKGROUND

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

[0003] While existing ablation catheters have a wide variety of electrode configurations, they all place electrodes on the outer surface of the catheter, and typically have one electrode at the tip of the catheter. These configurations limit the shape of the electric field produced by these catheters. Specifically, the electric field profile is typically elongated because it is produced by a dipole aligned with the longitudinal axis of the catheter. These elongated field shapes are not optimal for tissue ablation because the depth of ablation depends on the orientation of the catheter relative to the tissue to be ablated.

[0004] For at least the above limitations, there is a need for a tissue ablation catheter having an insulator between an inner electrode and an outer electrode. SUMMARY

[0005] One or more embodiments described in this specification relate to a tissue ablation catheter having an insulator between an inner electrode and an outer electrode. Embodiments of the present invention can produce a new electric field shape that improves ablation consistency.

[0006] One or more embodiments of the present invention can include a catheter having a tubular element with a longitudinal axis, a distal end, a lumen, an outer surface, and an inner surface surrounding the lumen. An electric insulator can be present between the inner surface and the outer surface. The catheter can have one or more inner electrodes coupled to the inner surface and one or more outer electrodes coupled to the outer surface. The inner electrodes and the outer electrodes can each be offset from the distal end of the catheter. The electric insulator can separate the inner electrodes from the outer electrodes. The distal end of the catheter can be placed near tissue to be ablated. A controller can set the voltages of the inner electrodes and the outer electrodes to produce an electric field outside the tubular element that induces ablation of the tissue by electroporation.

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

[0008] In one or more embodiments of the application, the electrical insulator can be a dielectric, such as, for example, aluminum nitride ceramic. In one or more embodiments, the electrical insulator can have an electrical conductivity less than 0.1 microsiemens per 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 greater than or equal to 0.01 millimeters and less than or equal 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 greater than or equal to 0.01 millimeters and less than or equal to 1 meter.

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

[0011] In one or more embodiments of the application, the controller can modify the voltage of the inner electrode and the voltage of the outer electrode within a pulse time that is less than twice the membrane recovery time of the tissue to be ablated.

[0012] In one or more embodiments, the controller can modify the voltage of the inner electrode and the voltage of the outer electrode within a period of time less than or equal to 10 milliseconds.

[0013] In one or more embodiments, the controller can modify the voltage of the inner electrode and the voltage of the outer electrode so as to change the direction of the electric field outside the tubular element over time. For example, the controller can set the electrode voltages at one time to produce a first average electric field vector in the region of tissue to be ablated, and can set the electrode voltages at another time to produce a second average electric field vector in the region of tissue to be ablated, where the angle difference between the first average electric field vector and the second average electric field vector is at least 1 degree. BRIEF DESCRIPTION OF DRAWINGS

[0014] The above and other aspects, features, and advantages of the present application will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings, wherein:

[0015] Figure 1A A typical ablation catheter in the prior art is shown, having electrodes on the outer surface of the catheter. Figure 1B A cross-sectional view of the catheter of Figure 1A is shown.

[0016] Figure 2A An illustrative embodiment of the present application is shown, which is an ablation catheter having outer electrodes and inner electrodes. Figure 2B A cross-sectional view of the catheter of Figure 2A is shown, and Figure 2C A close-up cross-sectional view of the distal end of the catheter of Figure 2A is shown.

[0017] Figure 3 An illustrative shortest current path between the inner electrode and the outer electrode of the catheter of Figure 2A ; this current path is longer than the straight-line distance between the electrodes because the electrodes are separated by the insulator.

[0018] Figure 4 An illustrative electric field vector in the region around the distal end of the catheter of Figure 2A ; the electric field curves around the insulator at the distal end between the inner electrode and the outer electrode.

[0019] FIG. 5A shows an illustrative electric field strength profile around the distal end of the catheter of Figure 1A , and Figure 5B shows this profile around the distal end of the catheter of Figure 2A . The catheter of the present invention has a more symmetrical field profile than catheters in the prior art.

[0020] Figure 6A and Figure 6B show Figure 5B the benefit of the symmetrical field profile shown: the tissue ablation depth is largely independent of the orientation of the catheter relative to the tissue to be ablated.

[0021] Figure 7 shows a variation of the catheter of Figure 2A with multiple inner electrodes and multiple outer electrodes.

[0022] Figure 8A , Figure 8B and Figure 8C show how the direction of the electric field acting on the cells of the tissue to be ablated can be modified by changing the voltage in the electrodes of the catheter of Figure 7 . DETAILED DESCRIPTION

[0023] A tissue ablation catheter with an insulator between the inner electrode and the outer electrode will now be described. In the following exemplary description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. However, it will be apparent to one ordinarily skilled in the art that the present invention can be practiced without incorporating all aspects of the specific details described herein. In other instances, specific features, amounts, or measurements well known to those skilled in the art are not described in detail in order to avoid obscuring aspects of the present invention. It should be noted that, although examples of the present invention are set forth herein, the scope of the claims and any equivalents are intended to define the limits of the invention and the scope of equivalents.

[0024] Intravascular catheters are used in medicine to deliver high-voltage short-duration pulsed electric (also called pulsed field ablation, electroporation, DC ablation, electrocautery) to tissue targets in the body for the purpose of soft tissue ablation.Figure 1A and Figure 1B A schematic view of a typical ablation catheter 100 currently used for these applications is shown. Figure 1A A side view of the ablation catheter is shown, and Figure 1B A cross-sectional view along a plane through the longitudinal axis 102 of the catheter is shown. The catheter 100 is a typical bipolar ablation catheter, with a central lumen 103 inside the tubular element, and two electrodes on the outer surface 121 of the tube: electrode 111 at the tip of the catheter at or near the distal end 101 of the catheter, and electrode 112 positioned below the tube of the catheter, away from the tip electrode. The electrodes are not attached to the inner surface 122. When a voltage difference is applied between the two electrodes, they form a dipole. Tissue can be ablated with radiofrequency (RF) heat energy or by electroporation, in which the electric field directly induces cell damage. Electric field-mediated cell damage has advantages over thermal ablation, and there is growing interest in the technique for use in a range of medical conditions. The tissue response to electroporation differs from thermal damage in three important ways. First, the sensitivity of tissue to electric field-mediated damage differs by orders of magnitude, offering the advantage of selective ablation in some organs such as the heart. Tissue selectivity can reduce the risk of inadvertent damage to collateral structures such as the phrenic nerve, esophagus, and blood vessels - a common problem when performing pulmonary vein isolation. Second, the size and shape of the lesion is more predictable and / or precise than with thermal methods, because the ablation lesion volume closely follows the electric field profile. And third, electroporation is much faster than RF ablation, which ranges from microseconds to seconds for each application, reducing the risks and resource requirements associated with total procedure time.

[0025] Some ablation catheters have more than two electrodes on the outer surface 121 of the catheter 100. For cardiac applications, for example, specialized multi-electrode catheters have been invented to deliver electroporation to the ostia of the pulmonary veins within the left atrium. Most of these devices are designed to perform anatomical ablation of the pulmonary veins to treat a common type of cardiac arrhythmia known as atrial fibrillation.

[0026] Figure 2A , Figure 2B and Figure 2C Different views of an illustrative embodiment of the present invention are shown, an ablation catheter 200 with novel geometry and electrical characteristics that offers advantages compared to conventional ablation catheters such as catheter 100. Figure 2A A side view of the catheter 200 is shown; Figure 2B A cross-sectional view along a plane through the longitudinal axis 202 of the catheter is shown; and Figure 2CA close-up cross-sectional view of the distal end of the catheter 200 is shown. The 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 (facing the lumen 203) of the tubular catheter body. The electrodes 211 and 212 are offset from the distal end 201 of the catheter along the longitudinal axis 202; there are no electrodes at the catheter tip. In one or more embodiments of the invention, the distance 241 between the outer electrode 211 and the distal end 201 can be at least 0.01 millimeters and at most 1 meter. Similarly, in one or more embodiments of the invention, the distance 242 between the inner electrode 212 and the distal end 201 can be at least 0.01 millimeters and at most 1 meter. The distances 241 and 242 can be equal or unequal. In use, the distal end of the catheter 200 can be placed at or near the tissue to be ablated. The outer electrode 211 can be in contact with the tissue. The inner electrode 212 is not in direct contact with the tissue to be ablated. These electrodes can generate an electric field outside the tubular catheter body that induces ablation of nearby tissue via electroporation. The lumen 203 of the catheter can carry an irrigation fluid infused into the tissue; such fluid can be electrically conductive. For example, an illustrative fluid can be 9% saline.

[0027] The inner electrode 212 and the outer electrode 211 are separated by a distal portion of the catheter body, which can contain an electrically insulating material 250. In one or more embodiments, for example, the electrical conductivity of the insulating material 250 can be less than 0.1 microsiemens per centimeter. In one or more embodiments, the material 250 can be a dielectric, and it can have a high dielectric constant. An illustrative material that can be used in one or more embodiments can be, for example, aluminum nitride ceramic. (The portion of the catheter body below the electrodes (away from the distal end) can be made of the same material as the portion of the body between the electrodes.) All or a portion of the catheter body can be flexible. The tubular catheter body can have any desired length.

[0028] The electrodes 211 and 212 can be coupled to a controller 230 that can set the voltage of each electrode, as Figure 2BThe controller 230 can deliver voltage pulses to the electrodes 211 and 212. These pulses can be, for example, monophasic pulses, with a duration between 10 ns to 10 ms, <50% duty cycle, 1 kV-10 kV amplitude, pulse repetition between 1 pulse / second to 10,000 pulses / second, including endpoints. Specifically, in one or more embodiments of the invention, the voltage applied between at least one inner electrode and at least one outer electrode can be greater than 5000 volts. However, any potential pattern can be used with such electrode configurations, including but not limited to multiple duration rectangular pulses, biphasic rectangular or trapezoidal waves, sinusoidal biphasic waves, sinusoidal offset, asymmetric rectangular, asymmetric linear waves, and / or any combination of arbitrary waveforms or pulse patterns.

[0029] One or more embodiments of the invention can have more than one inner electrode or more than one outer electrode. Figure 7 An illustrative embodiment with multiple inner electrodes and multiple outer electrodes is shown. Embodiments can have any number of inner electrodes and any number of outer electrodes. Inner electrodes and outer electrodes can be separated by an insulator such as a material with a high dielectric constant. All inner electrodes and outer electrodes can be offset from the distal end of the catheter.

[0030] Figure 3 The effect of the catheter 200 geometry on current flow between electrodes is shown. When the inner electrode is set to a positive voltage relative to the outer electrode (for illustration), current flows from the inner electrode 212 along the lumen to the distal end of the catheter tip, and curves and flows down to the outer electrode 211. Thus, the length of the shortest current path 301 between electrodes is longer than the straight-line distance 302 between them. This feature is in contrast to the traditional catheter geometry of catheter 100 of Figure 1A where the length of the shortest current path between electrodes is equal to the straight-line distance between them, as the electrodes are not separated by an insulator between them.

[0031] Figure 4 A similar curving effect on the shape of the electric field produced when a voltage difference is applied between electrodes is shown. The electric field lines 400 curve around the distal end of the catheter. The dielectric in the catheter body amplifies the field strength as it curves around the tip.

[0032] FIGS. 5A and Figure 5B demonstrate the potential benefits of the curved electric field line shape shown in Figure 4 FIG. 5A shows the electric field strength profile 501 of the traditional catheter 100, Figure 5BA similar profile 511 of catheter 200 is shown. Profiles 501 and 511 separate regions within the profile where the field strength is above a threshold from regions outside the profile where the field strength is below that threshold. Because tissue ablation via electroporation is highly correlated with electric field strength, the shape of the field strength profile determines the area of ​​tissue to be ablated. Since the electrodes in catheter 100 operate in a conventional dipole configuration, profile 501 is elongated; conversely, profile 511 is relatively symmetrical around the tip of catheter 200 due to field bending. This symmetrical shape provides a consistent tissue ablation depth regardless of the catheter's orientation relative to the tissue to be ablated. Figure 6A and Figure 6B This benefit is illustrated in the diagram. The catheter 200 is placed against the tissue 600 with the aim of ablating a portion of the tissue near the catheter. However, it is not always possible to control the precise orientation of the catheter relative to the tissue. For example, in… Figure 6A In the middle, the longitudinal axis of catheter 200 is roughly perpendicular to the tissue boundary, while... Figure 6B In this configuration, the axis is approximately parallel to the tissue boundary. Because the electric field intensity profile 511 is substantially symmetrical, the portion 601 of tissue experiencing a field intensity greater than a threshold when the catheter is perpendicular is almost equivalent to the portion 602 of tissue experiencing that field intensity when the catheter is parallel. Therefore, regardless of the catheter orientation, the depth of ablated tissue will be approximately the same. This feature of catheter 200 represents a substantial advancement beyond conventional catheters with highly asymmetrical field intensity profiles, for which the ablation depth can be highly dependent on the not necessarily controlled catheter orientation.

[0033] 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). Figure 7 An illustrative catheter 700 is shown, having 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 insulated catheter body. All electrodes are coupled to a controller 230. The controller can set the voltage of any of the electrodes and can change these voltages over time to alter the direction and intensity of the electric field vector. By varying the electrode voltages, target tissue can be exposed to multiple electric field vectors from a single catheter location.

[0034] Figure 8A , Figure 8B and Figure 8CEmbodiments are shown that modify the electrode voltage to change the electric field vector direction over time. The effect of the electric field on tissue ablation depends on the field strength and the orientation of the field vector relative to the cell membrane. Generally, the maximum stress on a cell occurs when the electric field vector is perpendicular to the cell membrane. However, the cell membranes are non-uniformly oriented throughout the tissue, so a single field direction will not simultaneously produce maximum stress on all cells. By having the tissue experience multiple field directions over time, the ablation of cells within the tissue will be more uniform, as each cell will experience a field vector that is more likely to provide a high stress on that cell’s membrane. Figures 8A to 8C Different voltage patterns applied to the electrodes of the catheter 700 at different times are shown, as well as the resulting average field directions 801a-c near an illustrative cell 800 in the target tissue. For example, the controller can repeatedly cycle between these three voltage patterns. The modified voltages expose the cell to different field directions at different times. For example, a volume sample within the target tissue can 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 can be less than or equal to twice the membrane recovery time of a target cell or material within the treatment volume. For example, the switching time between configurations can be between 10 ns and 1 second.

[0035] One or more embodiments of the present invention include a tissue ablation catheter with varying field direction, comprising: a tubular element comprising: a distal end configured to be placed proximal to tissue to be ablated, a proximal end opposite the distal end, an inner surface surrounding a lumen, and an electrical insulator between the inner surface and an outer surface; one or more inner electrodes coupled to the inner surface, each inner electrode offset from the distal end in a proximal direction toward the proximal end; one or more outer electrodes coupled to the outer surface; a controller coupled to the one or more inner electrodes and the one or more outer electrodes and configured to set a voltage of the one or more inner electrodes and a voltage of the one or more outer electrodes to produce an electric field outside the tubular element that induces ablation of the tissue to be ablated by electroporation, and modify the voltage of the one or more inner electrodes and the voltage of the one or more outer electrodes over time so as to change a direction of the electric field outside the tubular element over time.

[0036] In one or more embodiments, the controller is further configured to set a first voltage of the one or more inner electrodes and a first voltage of the one or more outer electrodes at a first time to produce a first average electric field vector in a region of tissue to be ablated; set a second voltage of the one or more inner electrodes and a second voltage of the one or more outer electrodes at a second time to produce a second average electric field vector in a second region of tissue to be ablated; wherein an angular difference between the first average electric field vector and the second average electric field vector is at least 1 degree.

[0037] In one or more embodiments, a shortest path of current flow from an inner electrode of the one or more inner electrodes to an outer electrode of the one or more outer electrodes is longer than a distance between the inner electrode and the outer electrode.

[0038] In one or more embodiments, the electrical insulator comprises a dielectric.

[0039] In one or more embodiments, the dielectric comprises an aluminum nitride ceramic.

[0040] In one or more embodiments, the electrical insulator has an electrical conductivity less than 0.1 microsiemens per centimeter.

[0041] In one or more embodiments, the controller is further configured to set a potential difference between at least one inner electrode of the one or more inner electrodes and at least one outer electrode of the one or more outer electrodes to be greater than 5000 volts.

[0042] In one or more embodiments, the controller is further configured to modify the voltage of the one or more inner electrodes and the voltage of the one or more outer electrodes within a pulse time that is less than twice a membrane recovery time of the tissue to be ablated.

[0043] In one or more embodiments, the controller is further configured to modify the voltage of the one or more inner electrodes and the voltage of the one or more outer electrodes within a period that is less than or equal to 10 milliseconds.

[0044] In one or more embodiments, the one or more inner electrodes each diverge distally in a proximal direction toward a proximal end, wherein a distal-most point of the one or more inner electrodes is recessed within the lumen.

[0045] One or more embodiments include a tubular element, one or more inner electrodes, one or more outer electrodes, a controller, the tubular element comprising: a distal end configured to be placed proximal to tissue to be ablated, a proximal end opposite the distal end, an inner surface surrounding a lumen, and an electrical insulator between the inner surface and an outer surface; one or more inner electrodes coupled to the inner surface, each inner electrode offset from the distal end in a proximal direction toward the proximal end; the one or more outer electrodes coupled to the outer surface; the controller coupled to the one or more inner electrodes and the one or more outer electrodes and 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 that induces ablation of the tissue to be ablated by electroporation, wherein the electric field includes one or more field lines, the one or more field lines including a first field line portion, a second field line portion, and a third field line portion, the first field line portion connected to an inner electrode of the one or more inner electrodes; the second field line portion connected to the first field line portion, wherein the second field line portion curves around the distal end of the tubular element; the third field line portion connected to the second field line portion and to an outer electrode of the one or more outer electrodes.

[0046] In one or more embodiments, a shortest path of current flow from an inner electrode of the one or more inner electrodes to an outer electrode of the one or more outer electrodes is longer than a distance between the inner electrode and the outer electrode.

[0047] In one or more embodiments, the electrical insulator includes a dielectric.

[0048] In one or more embodiments, the dielectric includes aluminum nitride ceramic.

[0049] In one or more embodiments, the electrical insulator has an electrical conductivity less than 0.1 microsiemens per centimeter.

[0050] In one or more embodiments, the controller is further configured to set a potential difference between at least one inner electrode of the one or more inner electrodes and at least one outer electrode of the one or more outer electrodes to be greater than 5000 volts.

[0051] In one or more embodiments, the controller is further configured to modify the voltage of the one or more inner electrodes and the voltage of the one or more outer electrodes within a pulse time less than twice a membrane recovery time of the tissue to be ablated.

[0052] In one or more embodiments, the controller is further configured to modify the voltage of the one or more inner electrodes and the voltage of the one or more outer electrodes within a period less than or equal to 10 milliseconds.

[0053] In one or more embodiments, the one or more inner electrodes each diverge distally in a proximal direction toward the proximal end, with a distal-most point of the one or more inner electrodes recessed within the lumen.

[0054] While the application disclosed herein has been described by way of specific embodiments and applications thereof, numerous modifications and variations are possible without departing from the scope of the application, which is defined in the claims.

Claims

1. A tissue ablation catheter having an insulator between inner electrodes and outer electrodes, the tissue ablation catheter comprising: a tubular element, the tubular element comprising: a distal end; a proximal end opposite the distal end; a longitudinal axis; 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 inner electrode offset from the distal end in a proximal direction toward the proximal end; one or more outer electrodes coupled to the outer surface, each outer electrode offset from the distal end in the proximal direction toward the proximal end, wherein the one or more outer electrodes are separated from the one or more inner electrodes by the electrical insulator; and a controller coupled to the one or more inner electrodes and the one or more outer electrodes; wherein the distal end is configured to be placed proximal to tissue to be ablated; wherein 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 outside the tubular element that induces ablation of the tissue to be ablated by electroporation; and wherein the controller is configured to modify the voltage of the one or more inner electrodes and the voltage of the one or more outer electrodes so as to change a direction of the electric field.

2. The tissue ablation catheter having an insulator between an inner electrode and an outer electrode of claim 1, wherein, A shortest path of current flow from an inner electrode of the one or more inner electrodes to an outer electrode of the one or more outer electrodes is longer than a distance between the inner electrode and the outer electrode.

3. The tissue ablation catheter having an insulator between an inner electrode and an outer electrode of claim 1, wherein, The electrical insulator comprises a dielectric.

4. The tissue ablation catheter having an insulator between an inner electrode and an outer electrode of claim 3, wherein, The dielectric comprises aluminum nitride ceramic.

5. The tissue ablation catheter having an insulator between an inner electrode and an outer electrode of claim 1, wherein, An electrical conductivity of the electrical insulator is less than 0.1 microsiemens per centimeter.

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

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

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

9. The tissue ablation catheter having an insulator between inner electrodes and outer electrodes of claim 1, wherein, the controller is further configured to modify the voltage of the one or more inner electrodes and the voltage of the one or more outer electrodes within a pulse time that is less than twice a membrane recovery time of the tissue to be ablated.

10. The tissue ablation catheter having an insulator between inner electrodes and outer electrodes of claim 1, wherein, the controller is further configured to modify the voltage of the one or more inner electrodes and the voltage of the one or more outer electrodes within a period that is less than or equal to 10 milliseconds.

11. The tissue ablation catheter having an insulator between an inner electrode and an outer electrode of claim 9, wherein, the controller is further configured to setting a first voltage of the one or more inner electrodes and a first voltage of the one or more outer electrodes at a first time to generate a first average electric field vector in a region of the tissue to be ablated; setting a second voltage of the one or more inner electrodes and a second voltage of 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; wherein an angular difference between the first average electric field vector and the second average electric field vector is at least 1 degree.

12. The tissue ablation catheter having an insulator between an inner electrode and an outer electrode of claim 1, wherein, the one or more inner electrodes are each offset away from the distal end in the proximal direction toward the proximal end, wherein a distal-most point of the one or more inner electrodes is recessed within the lumen.

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