Ablation catheter with split tip and current distribution

Abstract

A method of delivering radio-frequency (RF) ablation includes providing a split-tip catheter having a plurality of electrodes and selectively activating one or more of the plurality of electrodes. The method further includes delivering an RF current to activated electrodes and modifying a catheter current delivered to the plurality of electrodes of the split-tip catheter based on a number of activated electrodes.

Description

ABLATION CATHETER WITH SPLIT TIP AND CURRENT DISTRIBUTION TECHNICAL FIELD

[0001] This disclosure is related to medical devices and in particular to catheters utilized to deliver ablation therapy. BACKGROUND

[0002] Radiofrequency (RF) ablation is a procedure in which tissue is ablated using the heat generated from an alternating current signal. Typically, a distal end of a catheter is navigated to a desired location and RF ablation is delivered via an electrode located proximate to the targeted tissue. In particular, the RF ablation results in current – and therefore power - being delivered to the tissue to generate the desired lesions in the tissue.

[0003] The precise amount of power delivered to the tissue is difficult to determine. In most cases a portion of the current-delivering electrode is in contact with the tissue and a portion is in contact with the blood pool located adjacent the tissue. The blood pool presents a lower resistance than the tissue, and therefore it is not uncommon for a large amount of the current delivered to the electrode to be lost to the blood pool. Conversely, if too much of the electrode is placed within the tissue, then 100% of the current is applied to the tissue, which could also lead to adverse events.

[0004] It would be beneficial to develop an RF ablation system that reduces unnecessary current delivered to the blood pool. SUMMARY

[0005] In some aspects, the techniques described herein relate to a method of delivering radio-frequency (RF) ablation, the method including: selectively activating one or more of a plurality of electrodes of a split-tip catheter; delivering an RF current to the activated electrodes; and modifying a catheter current delivered to the plurality of electrodes of the split-tip catheter based on a number of the activated electrodes.

[0006] Modifying the catheter current may include selectively modifying a resistive path provided external to the activated electrodes, wherein the resistive path shunts at least some current from being provided to the plurality of electrodes.

[0007] The resistive path may be modified to increase the current through the resistive path in response to the number of activated electrodes decreasing.

[0008] In addition or alternatively, the resistive path may be modified to decrease the current through the resistive path in response to the number of activated electrodes increasing.

[0009] Modifying the catheter current may include providing instructions to a generator to modify an output power provided by the generator, wherein modifying the output power of the generator modifies the total current delivered to the plurality of electrodes.

[0010] The method may further include detecting tissue contact associated with each of the plurality of electrodes.

[0011] Selectively delivering an RF current to one or more of the plurality of electrodes may be based on the detected tissue contact associated with each of the plurality of electrodes.

[0012] RF current may be selectively delivered to the one or more electrodes determined to be in contact with tissue.

[0013] In some aspects, the techniques described herein relate to a method, wherein RF current may be selectively delivered to electrodes located adjacent to an electrode identified as in contact with tissue.

[0014] The plurality of electrodes may be located at a distal tip of the split-tip catheter. Each electrode may be electrically isolated from adjacent electrodes.

[0015] In some aspects, a catheter ablation system is provided, the system including: a generator configured to generate radio-frequency (RF) ablative energy; an ablation catheter having a plurality of electrodes configured to selectively deliver RF ablative energy provided by the generator; an electrode activation circuit configured to selectively deliver the RF ablative energy from the generator to one or more of the plurality of electrodes; and a current distribution circuit connected between the generator and the plurality ofelectrodes, wherein the current distribution circuit is configured to selectively modify RF ablative energy provided to the plurality of electrodes.

[0016] The ablation catheter may be a split-tip catheter. The RF ablative energy provided by the generator may have an approximately constant power magnitude.

[0017] The current distribution circuit may provide a resistive path having a selectively modifiable resistance connected in parallel with the plurality of electrodes.Modifying the resistance of the resistive path can modify the RF ablative energy delivered to the plurality of electrodes.

[0018] The electrode activation circuit may include a plurality of switches connected between the generator and each of the plurality of electrodes. The plurality of switches may be selectively controlled to selectively deliver the RF ablative energy generated by the generator to one or more of the plurality of electrodes.

[0019] The current distribution circuit may include a plurality of resistors and a plurality of switches. The plurality of switches may be selectively controlled to modify the resistive path provided in parallel with a resistive path presented by the plurality of electrodes.

[0020] A tissue contact detection module may be included. The module may be configured to detect tissue contact associated with each of the plurality of electrodes. The electrode activation circuit may be selectively controlled based on tissue contact determined by the tissue contact detection module.

[0021] The electrode activation circuit may be selectively controlled to activate electrodes determined by the tissue contact detection module to be in contact with adjacent tissue.

[0022] The electrode activation circuit may be selectively controlled to activate electrodes determined by the tissue contact detection module to be located adjacent to an electrode in contact with adjacent tissue.

[0023] In some aspects, the techniques described herein relate to a catheter ablation system including: a generator configured to generate pulse field ablation (PFA) pulses; an ablation catheter having a plurality of electrodes configured to selectively deliver PFA energy provided by the generator; and an electrode activation circuit configured to selectively deliver the PFA energy from the generator to one or more of the plurality of electrodes.

[0024] The system may further include a tissue contact detection module configured to detect tissue contact associated with each of the plurality of electrodes. The electrode activation circuit may be selectively controlled based on tissue contact determined by the tissue contact detection module.

[0025] In some aspects, a system and method for delivering ablation therapy is provided. The ablation catheter may be utilized to deliver the ablation includes a plurality of electrodes selectively activated to deliver ablative current to adjacent tissue. For example, the ablation catheter may be a split-tip catheter that includes a plurality of electrodes located at the tip of the catheter, each electrically isolated from one another. Electrodes may be selectively activated based on, for example, determined contact status of each of the plurality of electrodes with adjacent tissue. It may be desirable to only activate those electrodes determined to be in contact with adjacent tissue. Alternatively, it may be desirable to activate those electrodes located adjacent to the electrode in contact with tissue.

[0026] The ablation catheter may be utilized to deliver RF ablative therapy or pulse field ablation (PFA) therapy.

[0027] In one example, the total current provided to the plurality of electrodes located on the catheter is modified based on the number of activated electrodes. In one example, the total current is decreased in response to a decrease in number of activated electrodes. In one example, the decrease in total current in response to a decreased in activated electrodes ensures that the current density at each electrode remains relatively unchanged. Conversely, the total current provided to the plurality of electrodes is increased in response to an increase in number of activated electrodes. The increase in total current in response to an increase in number of activated electrodes once again ensures that the current density at each electrode remains relatively unchanged. Alternatively, the current density may be selectively modified (up or down) depending on the application. For example, in the current density at each electrode may be decreased as the number of activated electrodes increases. In this case, the total current may remain unchanged or may increase slightly, but is controlled so that the current density at each electrode decreases. This mode may be referred to as a current safety mode because it ensures that even as more electrodes areactivated and the total current increases (at least in some embodiments) the current density at any one of the plurality of electrodes remains below a determined threshold.

[0028] In one example, RF ablative current provided to the plurality of activated electrodes is provided by an RF current generator. The total current provided to the plurality of activated electrodes is modified by either modifying the RF ablative current output by the RF current generator, or selectively creating / modifying a resistive path provided in parallel with the plurality of activated electrodes to draw a portion of the total current through this resistive path. In the latter example, a current distribution circuit is connected between the RF current generator and the plurality of electrodes located on the ablation catheter. The current distribution circuit comprises a plurality of resistors – some in series, some in parallel – with the plurality of electrodes along with a plurality of switches (e.g., power switches, power relays, etc.) selectively turned On / Off to create an external resistive path utilized to draw at least a portion of the total current that would otherwise be supplied to the plurality of activated electrodes. In this way, the current density provided at the plurality of electrodes can be controlled. In one example, this control is utilized to maintain a relatively constant current density at each of the plurality of activated electrodes despite changes in the number of electrodes activated at any given time. In other examples, this control is utilized to selectively modify the current density at each of the plurality of activated electrodes as desired by the particular application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG.1 is a diagrammatic view of an example ablation system.

[0030] FIG.2A is an isometric view of a split-tip ablation catheter.

[0031] FIG.2B is a side view of a split-tip ablation catheter.

[0032] FIG. 3 is a flowchart of a method of selectively controlling current density delivered to one or more electrodes located at a distal tip of the split-tip ablation catheter.

[0033] FIG. 4 is a circuit diagram of a current distribution device utilized to selectively control the current density delivered to the one or more electrodes located at a distal tip of the split-tip ablation catheter.

[0034] FIGS. 5A-5D are circuit diagrams illustrating various switch configurations utilized to maintain an approximately constant current density through the one or more electrodes.

[0035] FIGS. 6A-6D are circuit diagrams illustrating various switch configurations utilized in a current safety mode.

[0036] FIG. 7A is a graph illustrating tissue current as a function of contact status in a constant current density mode.

[0037] FIG.7B is a graph illustrating the delivery of power as a function of contact status in a constant current density mode.

[0038] FIG. 8A is a graph illustrating tissue current as a function of contact status in a current safety mode.

[0039] FIG.8B is a graph illustrating the delivery of power as a function of contact status in a current safety mode. DETAILED DESCRIPTION

[0040] FIG. 1 is a diagrammatic view of an ablation system 100. In one example, the ablation system 100 includes catheter 102, a generator system 130, a controller 132 and a display 142. The catheter 120 is an ablation catheter, and in some cases may be a split-tip ablation catheter. In one example, catheter 102 includes a handle 114, a shaft 116 having a proximal end 118 connected to the handle 114 and a distal end 120 inserted within the body of a patient 108, for example within the heart 121 of the patient 108. The catheter 102 includes a plurality of electrodes (shown in more detail in FIG.2) located at the distal end 120 of the catheter for delivering ablative energy (e.g., radio-frequency (RF) ablation energy, pulse field ablation (PFA) energy) to selected tissue. In one example, ablative energy is supplied to the catheter 102 via electrical cable(s) 144 connected to the connector assembly 112 located on handle 114. One or more conductors extend from the handle 114 through the shaft 116 to the distal end 120 of the catheter 102 to each of the plurality of electrodes located at the distal end of the shaft. As described in more detail with respect to FIGS.2A and 2B, in one example the distal tip of the catheter includes a split tip catheterthat includes a plurality of electrodes configured to deliver ablative energy to adjacent tissue (or blood pool, depending on the location of the catheter relative to tissue).

[0041] In one example, ablative energy provided to the one or more electrodes is provided by generator system 130, which includes an activation / distribution controller 134 and a generator 136. In one example, generator 136 is configured to generate ablative power that is delivered to the one or more electrodes located at the distal end 120 of the catheter 102. In one example, activation / distribution controller 134 is connected between generator 136 and the plurality of electrodes located at the distal end 120 of the catheter 102. As described in more detail with respect to FIG.4, in one example the activation / distribution controller 134 includes a plurality of switches and resistors that are selectively controlled to modify the total power / current delivered to the catheter. In general, utilizing the resistors to modify the total power / current delivered to the catheter is only utilized for delivery of RF ablative energy. In addition, in some examples, the activation / distribution controller 134 includes a second plurality of switches that are utilized to selectively deliver ablative current to the one or more electrodes located at the distal end 120 of the catheter 102. Selectively delivering ablation current / energy to one or more electrodes may be utilized both with RF ablative energy and PFA ablative energy.

[0042] Controller 132 may be configured to receive one or more sensor signals from one or more sensors included as part of the catheter 102 via electrical cable(s) 146 and to provide instructions to the generator system 130 to control the generation and distribution of ablative power to the one or more electrodes. In one example the feedback provided by electrical cables includes one or more of localization, mapping, ablation assessment, contact force, and electrode contact status. Localization feedback refers to the location of one or more sensors (e.g., electrodes, magnetic coils, etc.) located at a distal end 120 of the catheter. Localization feedback is provided to aid in navigating the distal end 120 of the catheter 102 to a desired location with the patient’s body. Mapping feedback refers to the mapping of electrophysiology signals within the patient and can be utilized to guide the delivery of ablation therapy. Ablation assessment feedback may be utilized to assess the efficacy of delivered ablation therapy and may be utilized to determine whether a particularregion of tissue requires further treatment. Contact force sensors may be utilized to detect contact force between the distal tip of the catheter and adjacent tissue. As described in more detail below, contact force feedback may be utilized to detect which of a plurality of electrodes is in contact with tissue and may be utilized to select electrode activation. Electrode contact status may be utilized to determine which of a plurality of electrodes located at a distal end 120 of the catheter 102 are in contact with or in close proximity to tissue. As with contact force feedback, electrode contact status feedback may be utilized to detect which of a plurality of electrodes is in contact with tissue and may be utilized to select electrode activation.

[0043] Controller 132 may include a processor 138 and computer readable medium (CRM) 140 that stores instructions executed by the processor to implement one or more of the functions described above, including localization, mapping, ablation assessment, and electrode contact status based on the received feedback. In addition, controller 132 is configured to display information to a user / technician via display 142 and to receive input from the user / technician 142 (via display 142 and / or via other input devices). Controller 132 may also provide commands / instructions to generator system 130 regarding the delivery of ablative therapy to the one or more electrodes. For example, in one example controller 132 may provide instructions regarding which of the plurality of electrodes should receive ablative current. As described in more detail below, controller 132 may also provide instructions to activation / distribution controller 134 to modify the current delivered to the catheter 102, in general, and to the activated electrodes in particular.

[0044] Power delivered by generator 136 to desired target locations within the patient is based at least in part on the contact status between the one or more electrodes and the adjacent tissue. For RF ablation, electrodes not in contact with the tissue will dissipate power received from the generator 136 within the blood pool. For example, FIG. 2A illustrates an exemplary split-tip catheter 120 that includes a plurality of electrodes 202a, 202b, 202c, and 202d located at the distal tip of the catheter 120 and electrically isolated from one another. As shown in FIGS. 2A and 2B the split-tip catheter 120 includes a plurality of ring electrodes 204a, 204b, and 204c located along shaft 216. In the exampleshown in FIG.2A, electrode 202b is in direct contact with the adjacent tissue, electrodes 202a and 202c are in indirect contact with the adjacent tissue, and electrode 202d is not in contact with the tissue at all. As the contact status between the one or more electrodes changes, the power dissipated within the blood pool versus within the tissue changes. For example, if the one or more electrodes are 100% embedded within the tissue then all of the power provided by the generator will be dissipated within the adjacent tissue. In one example, it may be beneficial to selectively deliver power only to those electrodes determined to be in contact with adjacent tissue to avoid RF energy being unnecessarily dissipated within the blood pool. In one example, the generator 136 is configured to generate an output (i.e., RF ablation energy) that remains approximately constant in the output power delivered. However, the power delivered to tissue depends on the contact status of the electrodes delivering the RF ablation energy and on the number of electrodes delivering RF ablation energy. For example, if none of the electrodes is in contact with adjacent tissue, then the RF ablation energy delivered by generator 136 is dissipated within the blood pool. As contact with tissue increases the percentage of the RF ablation energy dissipated within the blood pool decreases and the percentage of the RF ablation energy dissipated within tissue increases. In one example, controller 132 provides instructions to activation / distribution controller 134 with instructions on which of the plurality of electrodes should receive RF ablation energy from the generator 136. In one example, because the output power delivered by the generator 136 remains approximately constant, modifying the number of electrodes that receive RF ablation energy from the generator 136 changes the output power delivered to each of the selected electrodes. For example, selectively reducing the number of electrodes that receive RF ablation energy from the generator 136 increases the RF ablation energy delivered to the remaining active electrodes.

[0045] If delivering PFA energy, it may still be beneficial to determine which of the plurality of electrodes are in contact with the adjacent tissue and selecting electrodes to receive PFA energy based on contact status between the one or more electrodes and the adjacent tissue.

[0046] FIG. 3 is a flowchart of a method of selectively controlling current density delivered to one or more electrodes located at a distal tip of the split-tip ablation catheter 120. At step 302, a catheter – such as split-tip catheter 120 shown in FIGS.2A and 2B – having a plurality of electrodes is introduced and guided to an ablation site. In the embodiment shown in FIGS.2A and 2B, the plurality of electrodes located at a distal end of the split-tip catheter 120 includes four electrically isolated electrodes 202a, 202b, 202c, and 202d. In other embodiments, fewer or greater numbers of electrodes may be utilized to deliver RF ablation energy.

[0047] At step 304, tissue contact associated with one or more of the plurality of electrodes is identified. A number of known methods may be utilized to assess and identify tissue proximity / contact status between individual electrodes and adjacent tissue. For example, bipolar electrode complex impedance (BECI) measurements taken by the electrodes are utilized to assess and identify tissue contact. In other examples, other means of measuring impedance may be utilized. In other embodiments, voltage measurements taken by the electrodes are utilized to assess and identify tissue contact. In still other embodiments, force sensors may be utilized to detect tissue proximity / contact status of the electrodes with adjacent tissue. In other embodiments, other types of sensors may be utilized to identify tissue proximity / contact status between individual electrodes and adjacent tissue.

[0048] At step 306, RF ablation energy is delivered to one or more of the plurality of electrodes. In one example, RF ablation energy is delivered to those electrodes identified at step 304 as being in contact with adjacent tissue. For example, in the embodiment shown in FIG.2A, in which electrode 202b is in contact (best contact) with the adjacent tissue, only electrode 202b would be selected to deliver RF ablation energy. As a result, all RF ablation energy output by the RF generator 136 would be provided to electrode 202b, with electrodes 202a, 202c, and 202d being turned OFF receiving no RF energy. In other embodiments, RF ablation energy is delivered to select electrodes based on the identification of electrodes in contact with tissue at step 304. For example, in one embodiment, electrodes located on either side of an electrode in contact with tissue are selected to deliver RF ablation energy. In the embodiment shown in FIG.2A, electrodes202a and 202c – located on either side of electrode 202b in contact with tissue – are activated to receive RF ablation energy while electrodes 202b and 202d remain OFF.

[0049] As described in more detail with respect to FIGS.5A-5D and FIGS.6A-6D, in one example an electrode activation circuit 402 comprised of a plurality of switches S8, S9, S10, and S11 is utilized to selectively deliver RF ablation energy to selected electrodes 202a, 202b, 202c, and 202d. For example, RF ablation energy is delivered to electrode 202a by selectively closing or turning ON switch S11, RF ablation energy is delivered to electrode 202b by selectively closing or turning ON switch S10, RF ablation energy is delivered to electrode 202c by selectively closing or turning ON switch S9, and RF ablation energy is delivered to electrode 202d by selectively closing or turning ON switch S8. In one example the switches S8-S11 are implemented utilizing solid-state switches, relays, solid-state relays, etc.

[0050] At step 308, the total current (and therefore the total power) delivered to the electrodes selected at step 306 (i.e., the activated electrodes) is modified. In one example, the total current delivered to the activated electrodes is modified based on the number of activated electrodes. Typically, the output power of the generator 136 remains relatively constant such that a decrease in the total number of electrodes activated to receive power from the generator 136 increases the current density at the activated electrodes. In order to maintain the current density at desired levels (based on the assumption that energy is distributed evenly to each of the plurality of electrodes), in one example the total current provided to the electrodes is modified. In one example, a portion of the RF ablation energy that would typically be provided to the plurality of electrodes is provided to an external resistive path. As described with respect to FIGS.5A-5D and 6A-6D, at least a portion of the output power provided by generator 136 is shunted through a current distribution circuit 400. In one example, the amount of current shunted through the current distribution circuit 400 is related to the number of activated electrodes. In other embodiments, rather than shunt a portion of the current through an external current distribution circuit, the total power provided by generator 136 is modified.

[0051] As described in more detail with respect to FIGS. 5A-5D and 6A-6D, a current distribution circuit 400 is comprised of a plurality of switches and a plurality of resistive elements selectively controlled to provide a resistive path selected to shunt at least a portion of the current away from the plurality of electrodes. In one example, the current distribution circuit 400 includes some resistive elements selectively connected in series with the plurality of electrodes and some resistive elements selectively connected in parallel with the plurality of electrodes.

[0052] In one example, controller 132 selectively controls the electrode activation circuit 402 and current distribution circuit 400 based on feedback received by controller 132 regarding tissue contact status associated with each of the electrodes. In one example, controller 132 provides instructions to activation / distribution controller 134 and / or to generator 136 to selectively activate particular electrodes and / or to control the total current supplied to the catheter 102 and in particular to the activated electrodes associated with catheter 102. In other embodiments, controller 132 may provide information regarding those electrodes in contact with tissue and activation / distribution controller 134 and / or generator 136 may perform functions associated with selectively activating particular electrodes and / or controlling the total current supplied to the catheter 102 and in particular to the activated electrodes associated with the catheter 102.

[0053] FIG. 4 is a circuit diagram of an exemplary embodiment of an activation / distribution controller 134 utilized to selectively control the current density delivered to the one or more electrodes located at a distal tip of the split-tip ablation catheter. In the embodiment shown in FIG.4, current distribution device 134 includes an electrode activation circuit 402 and a current distribution circuit 400. In one example, current distribution circuit 400 includes a plurality of switches S8, S9, S10, and S11, each connected to one of the plurality of electrodes 202a, 202b, 202c, and 202d located at the distal end of the catheter 102 (e.g., switch S8 connected to electrode 202d, switch S9 connected to electrode 202c, etc.). In general, current distribution circuit 400 is selectively controlled to control which electrodes 202a-202d are activated. In one example, current distribution circuit 400 includes a plurality of switches S1, S2, S3, S4, S5, S6, and S7 anda plurality of resistors R1, R2, R3, R4, R5, and R6. In general, current distribution circuit 400 is selectively controlled to control / modify the total current supplied to the catheter electrodes 202a-202d by selectively shunting a portion of the total current through the resistive network. In one example, controller 132 (shown in FIG. 1) controls the opening / closing of switches S1-S11. For example, controller 132 may identify those electrodes 202a-202d in contact with adjacent tissue and selectively controls switches S8- S11 to activate or provide current to select electrodes 202a-202d based on tissue contact status. In addition, controller 132 would control the switches S1-S7 to shunt a portion of the power provided by generator 136 through the current distribution circuit 400. In other embodiments, controller 132 may provide information regarding the electrodes in contact with adjacent tissue and circuit associated with generator 136 may selectively control the opening / closing of switches S1-S11.

[0054] In one example, the power supplied by the generator 136 is approximately constant. The resulting current I1 supplied by generator 136 varies based on a number of factors such as the total impedance presented by the electrodes 202a, 202b, 202c, and 202d and the corresponding return paths through blood / tissue of the patient. However, assuming no current is shunted through the current distribution circuit 400 then all of the current I1sourced by the generator 136 would be provided to the catheter electrodes 202a, 202b, 202c, and 202d, collectively catheter current I3. Assuming all four electrodes 202a, 202b, 202c, and 202d are activated, the current I3would be distributed at least approximately equally through each electrode with differences being based on differences in impedance presented by each electrode path. As one or more of the electrodes are deactivated, leaving a smaller number of activated electrodes, the total current I1provided by the generator 136 remains (approximately) unchanged, and therefore the total catheter current I3 provided to the catheter electrodes remains unchanged. However, the amount of current being provided to the remaining activated electrodes – that is, the current density at a given electrode – increases. In one example, the catheter current I3 provided to the catheter electrodes 202a- 202d is modified by shunting at least a portion of the generator current I1 through the resistive network, wherein the shunted current is designated shunt current I2.The totalcurrent I1 is equal to the sum of the shunted current I2 and the catheter current I3. Increasing the shunted current I2 decreases the catheter current I3 and vice versa. In one example, the goal is to maintain an approximately constant current density at each of the catheter electrodes 202a, 202b, 202c, and 202d despite changes in the number of activated electrodes (referred to herein as a “constant current density mode”) as described in more detail with respect to FIGS.5A-5D. In other embodiments, the goal may be to ensure that the catheter current supplied to the electrodes does not exceed some threshold value (referred to herein as a “current safety mode”) as described in more detail with respect to FIGS.6A-6D.

[0055] In one example, the power supplied by the generator 136 is selectively variable. In embodiments in which the output power of generator 136 is variable, only the electrode activation circuit 402 is required to selectively distribute current to one or more electrodes 202a-202d based on the determined electrode contact status. That is, because the power delivered by generator 136 may be decreased as the number of electrodes activated is decreased, no current needs to be dissipated through current distribution circuit 400. In one example, electrode activation circuit 402 is utilized once again to provide current to selected electrodes 202a-202d based on the electrodes identified to be in contact with the adjacent tissue. In one example, either controller 132 or generator 136 may store (e.g., via a look-up table) output power setpoints corresponding with a number of activated electrodes. For example, controller 132 may determine based on the identified electrodes in contact with adjacent tissue to supply current only to electrodes 202a and 202b. In this embodiment, controller 132 may utilize the look-up table to determine the desired power output of generator 136 when only two electrodes are activated and provide instructions to generator 136 including the desired power output. In one example, controller 132 may also provide instructions to electrode activation circuit 402 to selectively close switches S8 and S9 (to provide current to electrodes 202a and 202b) and to open switches S10 and S22 (to prevent current from being delivered to electrodes 202c and 202d).

[0056] FIGS. 5A-5D are circuit diagrams illustrating various switch configurations utilized to maintain an approximately constant current density through the one or moreelectrodes. FIG.5A illustrates the circuit configuration utilized when only electrode 202d is activated; FIG.5B illustrates the circuit configuration utilized when electrodes 202c and 202d are activated; FIG. 5C illustrates the circuit configuration utilized when electrodes 202b, 202c, and 202d are activated; and FIG. 5D illustrates the circuit configuration utilized when electrodes 202a, 202b, 202c, and 202d are activated. The bold line in each figure illustrates the current paths activated. In this example, the resistors are assigned the following resistive values: R1 - 30Ω R2 – 50Ω R3 – 100Ω R4 – 80Ω R5 – 200Ω R6 – 400Ω

[0057] In FIG.5A switch S8 is closed and switches S9, S10, and S11 are open such that current is provided only to catheter electrode 202d. To prevent the total generator current I1from being provided to electrode 202d (resulting in a relatively high current density), switches S3 and S5 within current distribution circuit 400 are closed such that some current is dissipated by resistor R2 and shunted through resistor R4. In this configuration, the shunt current I2is likely greater than the catheter current I3. For example, in one embodiment the current sourced by generator 136 is equal to approximately 700 milliamps (mA), the total current provided to the catheter I3 is equal to 182 mA and the shunt current I2 is equal to 518 mA.

[0058] In FIG.5B switches S8 and S9 are closed and switches S10 and S11 are open in electrode activation circuit 402 such that current is provided to catheter electrodes 202c and 202d. To prevent the total generator current I1 from being provided to electrodes 202c and 202d (resulting in a relatively high current density), switches S2 and S6 within current distribution circuit 400 are closed such that some current is dissipated by resistor R1 and shunted through resistor R5. In this configuration, the shunt current I2 is decreased as compared to the configuration shown in FIG.5A and the catheter current is increased. Forexample, in one embodiment the current sourced by generator 136 is equal to approximately 700 milliamps (mA), the total current provided to the catheter I3 is equal to 383 mA and the shunt current I2is equal to 317 mA.

[0059] In FIG.5C switches S8, S9, and S10 are closed and switch S11 is open in electrode activation circuit 402 such that current is provided to catheter electrodes 202b, 202c and 202d. To prevent the total generator current I1from being provided to electrodes 202b, 202c and 202d (resulting in a relatively high current density), switches S2 and S7 within current distribution circuit 400 are closed such that some current is dissipated by resistor R1 and shunted through resistor R6. In this configuration, the shunt current I2may be less than the catheter current I3. For example, in one embodiment the current sourced by generator 136 is equal to approximately 700 milliamps (mA), the total current provided to the catheter I3 is equal to 538 mA and the shunt current I2 is equal to 162 mA.

[0060] In FIG.5D switches S8, S9, S10, and S11 are closed in electrode activation circuit 402 such that current is provided to catheter electrodes 202a, 202b, 202c and 202d. In this example, all electrodes are activated, so it is desirable that the total generator current I1 is supplied to the catheter electrodes. In this configuration, switch S1 within current distribution circuit 400 is closed (while all other switches remain opened) such that no current is dissipated by the current distribution circuit 400 (i.e., I2 = 0). In this configuration, the total generator current I1is equal to the total catheter current I3.

[0061] FIGS. 6A-6D are circuit diagrams illustrating various switch configurations utilized when operating in a current safety mode. FIG. 6A illustrates the circuit configuration utilized when only electrode 202d is activated; FIG.6B illustrates the circuit configuration utilized when electrodes 202c and 202d are activated; FIG.6C illustrates the circuit configuration utilized when electrodes 202b, 202c, and 202d are activated; and FIG. 6D illustrates the circuit configuration utilized when electrodes 202a, 202b, 202c, and 202d are activated. In contrast with the embodiment described with respect to FIGS.5A-5D, in the embodiment shown in FIGS.6A-6D as additional electrodes are activated the current density at each electrode is decreased.

[0062] In FIG.6A switch S8 is closed and switches S9, S10, and S11 are open such that current is provided only to catheter electrode 202d. To prevent the total generator current I1from being provided to electrode 202d (resulting in a relatively high current density), switches S3 and S5 within current distribution circuit 400 are closed such that some current is dissipated by resistor R2 and shunted through resistor R4. In this configuration, the shunt current I2is likely greater than the catheter current I3. For example, in one embodiment the current sourced by generator 136 is equal to approximately 700 milliamps (mA), the total current provided to the catheter I3 is equal to 182 mA and the shunt current I2 is equal to 518 mA. In this embodiment, with a single electrode activated, the configuration shown in FIG. 6A (current safety mode) is the same as the configuration shown in FIG. 5A (constant current density mode).

[0063] In FIG.6B switches S8 and S9 are closed and switches S10 and S11 are open in electrode activation circuit 402 such that current is provided to catheter electrodes 202c and 202d. To prevent the total generator current I1 from being provided to electrodes 202c and 202d (resulting in a relatively high current density), switches S3 and S4 within current distribution circuit 400 are closed such that some current is dissipated by resistor R2 and shunted through resistor R3. In this configuration, the shunt current I2is decreased as compared to the configuration shown in FIG.6A and the catheter current I3 is increased. However, the current density at electrodes 202c and 202d is decreased as compared to the current density at electrode 202d in the configuration shown in FIG.6A. For example, in one embodiment the current sourced by generator 136 is equal to approximately 700 milliamps (mA), the total current provided to the catheter I3is equal to 263 mA (approximately 131.5 mA through each electrode) and the shunt current I2is equal to 437 mA. In the configuration shown in FIG.6A, the current through electrode 202d is equal to approximately 182 mA. In this way, as additional electrodes are activated in the current safety mode, the current density at each electrode is decreased.

[0064] In FIG.6C switches S8, S9, and S10 are closed and switch S11 is open in electrode activation circuit 402 such that current is provided to catheter electrodes 202b, 202c and 202d. To prevent the total generator current I1from being provided to electrodes 202b,202c and 202d (resulting in a relatively high current density), switches S3 and S4 within current distribution circuit 400 are closed such that some current is dissipated by resistor R2 and shunted through resistor R3. In this configuration, the current sourced by generator 136 is equal to approximately 700 milliamps (mA), the total current provided to the catheter I3 is equal to 318 (mA approximately 106 mA through each electrode) and the shunt current I2is equal to 382 mA . In this way, as additional electrodes are activated in the current safety mode, the current density at each electrode is decreased as compared with the configuration shown in FIG.6A and 6B.

[0065] In FIG.6D switches S8, S9, S10, and S11 are closed in electrode activation circuit 402 such that current is provided to catheter electrodes 202a, 202b, 202c and 202d. In this example, all electrodes are activated. Switches S3 and S4 within current distribution circuit 400 are closed such that some current is dissipated by resistor R2 and shunted through resistor R3. In this configuration, the current sourced by generator 136 is equal to approximately 700 milliamps (mA), the total current provided to the catheter I3 is equal to 338 mA (approximately 84.5 mA through each electrode) and the shunt current I2 is equal to 362 mA. In this way, as additional electrodes are activated in the current safety mode, the current density at each electrode is decreased as compared with the configuration shown in FIG.6A, 6B, and 6C.

[0066] FIG.7A is a graph illustrating tissue current as a function of contact status while operating in the constant current mode of operation and compares that tissue current for a standard ablation catheter. Line 700 illustrates the tissue current supplied by the split tip catheter while operating in the constant current density mode implemented by activation / distribution controller 134 and line 702 illustrates tissue current supplied by a standard catheter while operating without an activation / distribution controller 134. As shown in FIG. 7A, operation in the constant current density mode acts to mirror tissue current supplied by a standard catheter, and thus line 700 tracks with line 702 very closely. The difference between the operation of the split tip catheter operating in the constant current density mode is in the current that is not delivered to the tissue. In the standard catheter any power that is not delivered to the tissue (as tissue current) is delivered insteadto the blood pool. In some instances, this can result in a large amount of current being provided to the blood pool, particularly when tissue contact percentage is fairly low. In contrast, operation in the constant current density mode by the activation / distribution controller 134 allows at least a portion of the power / current that would otherwise be delivered to the blood pool to be delivered instead to the resistive network. This is illustrated in FIG.7B, which is a graph illustrating the distribution of power between the resistive network (indicated by area 704), the blood pool (indicated by area 706), and the tissue (indicated by area 708). As shown in FIG.7B, to the left of point 710 (contact surface % ranging from 0% to about 24%, presumably within the range that only one of the four electrodes is in contact with the tissue), the constant current density mode operates to shunt most of the current through the resistive network, with a small portion of the total power being supplied to the tissue and a similarly small portion being supplied to the blood pool. In this example, current is supplied to a single electrode on the split-tip catheter and the circuit configuration would be similar to that shown in FIG.5A. Between points 710 and 712 (contact surface % ranging from 24% to about 50%, presumably within the range that two of the four electrodes is in contact with the tissue), the circuit configuration is modified to that shown in FIG. 5B. That is, the electrode activation circuit 402 is controlled to deliver current to two of the four electrodes (e.g., the two electrodes determined to be in contact with the tissue) and the current distribution circuit 400 is configured to limit the total current supplied to the catheter electrodes by shunting a portion of the current through the resistive network. As shown in FIG.7B in the region between points 710 and 712, less power is delivered to the resistive network as additional electrodes are activated and the resistive network is modified. Between points 712 and 714 (contact surface % ranging from 50% to about 74%, presumably within the range that three of the four electrodes is in contact with the tissue), the circuit configuration is modified to that shown in FIG. 5C. That is, the electrode activation circuit 402 is controlled to deliver current to three of the four electrodes (e.g., the three electrodes determined to be in contact with the tissue) and the current distribution circuit 400 is configured to limit the total current supplied to the catheter electrodes by shunting a portion of the current through the resistive network. Asshown in FIG.7B in the region between points 712 and 714, less power is delivered to the resistive network as additional electrodes are activated and the resistive network is modified. Finally, from point 714 to the right-most end of the graph (contact surface % ranging from 74% to 100%, presumably with all four electrodes in contact with the tissue), the circuit configuration is modified to deliver current to all four electrodes and the current distribution circuit 400 is configured such that no current is shunted through the resistive network. As shown in FIG. 7B, no current is dissipated by the resistive network in this region.

[0067] FIG.8A is a graph illustrating tissue current as a function of contact status while operating in the current safety mode of operation and compares that tissue current for a standard ablation catheter. FIG. 8B is a graph illustrating the delivery of power as a function of contact status in the current safety mode of operation. Referring to FIG.8A, line 802 illustrates the tissue current supplied by the split tip catheter while operating in the current safety mode implemented by activation / distribution controller 134 and line 800 illustrates tissue current supplied by a standard catheter while operating without an activation / distribution controller 134. As shown in FIG.8A, operation in the current safety mode prevents the tissue current from exceeding threshold values, and therefore tissue current in the current safety mode remains less than the tissue current associated with the standard catheter. Once again, operation in the current safety mode causes a large portion of the current to be shunted through the resistor network. FIG. 8B illustrates the distribution of power between the resistive network (indicated by area 804), the blood pool (indicated by area 806), and the tissue (indicated by area 808). To the left of point 810 (contact surface % ranging from 0% to about 24%), the current safety mode operates to shunt most of the current through the resistive network, with a small portion of the total power being supplied to the tissue and a similarly small portion being supplied to the blood pool. In this example, current is supplied to a single electrode on the split-tip catheter and the circuit configuration would be similar to that shown in FIG.6A. Between points 810 and 812 (contact surface % ranging from 24% to about 50%), the circuit configuration is modified to that shown in FIG.6B. That is, the electrode activation circuit 402 is controlledto deliver current to two of the four electrodes (e.g., the two electrodes determined to be in contact with the tissue) and the current distribution circuit 400 is configured to limit the total current supplied to the catheter electrodes by shunting a portion of the current through the resistive network. As shown in FIG.8B in the region between points 810 and 812, less power is delivered to the resistive network as additional electrodes are activated and the resistive network is modified. Between points 812 and 814 (contact surface % ranging from 50% to about 74%), the circuit configuration is modified to that shown in FIG.6C. That is, the electrode activation circuit 402 is controlled to deliver current to three of the four electrodes (e.g., the three electrodes determined to be in contact with the tissue) and the current distribution circuit 400 is configured to limit the total current supplied to the catheter electrodes by shunting a portion of the current through the resistive network. As shown in FIG.8B in the region between points 812 and 814, less power is delivered to the resistive network as additional electrodes are activated and the resistive network is modified. From point 814 to the right, the right-most end of the graph (contact surface % ranging from 74% to 100%), the circuit configuration is modified to deliver current to all four electrodes and the current distribution circuit 400 shunts at least some current. In contrast with the constant current density mode shown in FIG.7B, the current safety mode shown in FIG. 8B continually shunts a considerable portion of the generator current through the resistive network in order to maintain the tissue current below a threshold level.

[0068] While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

[0069] Clause 1. A method of delivering radio-frequency (RF) ablation, the method comprising: selectively activating one or more of a plurality of electrodes of a split-tipcatheter; delivering an RF current to the activated electrodes; and modifying a catheter current delivered to the plurality of electrodes of the split-tip catheter based on a number of the activated electrodes.

[0070] Clause 2. The method of clause 1, wherein modifying the catheter current includes selectively modifying a resistive path provided external to the activated electrodes, wherein the resistive path shunts at least some current from being provided to the plurality of electrodes.

[0071] Clause 3. The method of clause 2, wherein the resistive path is modified to increase the current through the resistive path in response to the number of activated electrodes decreasing.

[0072] Clause 4. The method of clauses 2 or 3, wherein the resistive path is modified to decrease the current through the resistive path in response to the number of activated electrodes increasing.

[0073] Clause 5. The method of clauses 1-4, wherein modifying the catheter current includes providing instructions to a generator to modify an output power provided by the generator, wherein modifying the output power of the generator modifies the total current delivered to the plurality of electrodes.

[0074] Clause 6. The method of clauses 1-5, further including detecting tissue contact associated with each of the plurality of electrodes.

[0075] Clause 7. The method of clause 6, wherein selectively delivering an RF current to one or more of the plurality of electrodes is based on the detected tissue contact associated with each of the plurality of electrodes.

[0076] Clause 8. The method of clause 7, where RF current is selectively delivered to the one or more electrodes determined to be in contact with tissue.

[0077] Clause 9. The method of clause 7, wherein RF current is selectively delivered to electrodes located adjacent to an electrode identified as in contact with tissue.

[0078] Clause 10. The method of clauses 1-9, wherein the plurality of electrodes are located at a distal tip of the split-tip catheter, wherein each electrode is electrically isolated from adjacent electrodes.

[0079] Clause 11. A catheter ablation system comprising: a generator configured to generate radio-frequency (RF) ablative energy; an ablation catheter having a plurality of electrodes configured to selectively deliver RF ablative energy provided by the generator; an electrode activation circuit configured to selectively deliver the RF ablative energy from the generator to one or more of the plurality of electrodes; and a current distribution circuit connected between the generator and the plurality of electrodes, wherein the current distribution circuit is configured to selectively modify RF ablative energy provided to the plurality of electrodes.

[0080] Clause 12. The catheter ablation system of clause 11, wherein the RF ablative energy provided by the generator has an approximately constant power magnitude.

[0081] Clause 13. The catheter ablation system of clause 11 or 12, wherein the current distribution circuit provides a resistive path having a selectively modifiable resistance connected in parallel with the plurality of electrodes, wherein modifying the resistance of the resistive path modifies the RF ablative energy delivered to the plurality of electrodes.

[0082] Clause 14. The catheter ablation system of clause 13, wherein the electrode activation circuit includes a plurality of switches connected between the generator and each of the plurality of electrodes, wherein the plurality of switches are selectively controlled to selectively deliver the RF ablative energy generated by the generator to one or more of the plurality of electrodes.

[0083] Clause 15. The catheter ablation system of clause 14, wherein the current distribution circuit includes a plurality of resistors and a plurality of switches, wherein the plurality of switches are selectively controlled to modify the resistive path provided in parallel with a resistive path presented by the plurality of electrodes.

[0084] Clause 16. The catheter ablation system of clauses 11-15, further including: a tissue contact detection module configured to detect tissue contact associated with each of the plurality of electrodes, wherein the electrode activation circuit is selectively controlled based on tissue contact determined by the tissue contact detection module.

[0085] Clause 17. The catheter ablation system of clause 16, wherein the electrode activation circuit is selectively controlled to activate electrodes determined by the tissue contact detection module to be in contact with adjacent tissue.

[0086] Clause 18. The catheter ablation system of clause 16, wherein the electrode activation circuit is selectively controlled to activate electrodes determined by the tissue contact detection module to be located adjacent to an electrode in contact with adjacent tissue.

[0087] Clause 19. The catheter ablation system of clauses 11-18, wherein the ablation catheter is a split-tip ablation catheter.

[0088] Clause 20. A catheter ablation system comprising: a generator configured to generate pulse field ablation (PFA) pulses; an ablation catheter having a plurality of electrodes configured to selectively deliver PFA energy provided by the generator; and an electrode activation circuit configured to selectively deliver the PFA energy from the generator to one or more of the plurality of electrodes.

[0089] Clause 21. The catheter ablation system of clause 20, further including: a tissue contact detection module configured to detect tissue contact associated with each of the plurality of electrodes, wherein the electrode activation circuit is selectively controlled based on tissue contact determined by the tissue contact detection module.

Claims

CLAIMS:

1. A method of delivering radio-frequency (RF) ablation, the method comprising: selectively activating one or more of a plurality of electrodes of a split-tip catheter; delivering an RF current to the activated electrodes; and modifying a catheter current delivered to the plurality of electrodes of the split-tip catheter based on a number of the activated electrodes.

2. The method of claim 1, wherein modifying the catheter current includes selectively modifying a resistive path provided external to the activated electrodes, wherein the resistive path shunts at least some current from being provided to the plurality of electrodes.

3. The method of claim 2, wherein the resistive path is modified to increase the current through the resistive path in response to the number of activated electrodes decreasing.

4. The method of claims 2 or 3, wherein the resistive path is modified to decrease the current through the resistive path in response to the number of activated electrodes increasing.

5. The method of claims 1-4, wherein modifying the catheter current includes providing instructions to a generator to modify an output power provided by the generator, wherein modifying the output power of the generator modifies the total current delivered to the plurality of electrodes.

6. The method of claims 1-5, further including detecting tissue contact associated with each of the plurality of electrodes.

7. The method of claim 6, wherein selectively delivering an RF current to one or more of the plurality of electrodes is based on the detected tissue contact associated with each of the plurality of electrodes.

8. The method of claim 7, where RF current is selectively delivered to the one or more electrodes determined to be in contact with tissue.

9. The method of claim 7, wherein RF current is selectively delivered to electrodes located adjacent to an electrode identified as in contact with tissue.

10. The method of claims 1-9, wherein the plurality of electrodes are located at a distal tip of the split-tip catheter, wherein each electrode is electrically isolated from adjacent electrodes.

11. A catheter ablation system comprising: a generator configured to generate radio-frequency (RF) ablative energy; an ablation catheter having a plurality of electrodes configured to selectively deliver RF ablative energy provided by the generator; an electrode activation circuit configured to selectively deliver the RF ablative energy from the generator to one or more of the plurality of electrodes; and a current distribution circuit connected between the generator and the plurality of electrodes, wherein the current distribution circuit is configured to selectively modify RF ablative energy provided to the plurality of electrodes.

12. The catheter ablation system of claim 11, wherein the RF ablative energy provided by the generator has an approximately constant power magnitude.

13. The catheter ablation system of claim 12, wherein the current distribution circuit provides a resistive path having a selectively modifiable resistance connected in parallel with the plurality of electrodes, wherein modifying the resistance of the resistive path modifies the RF ablative energy delivered to the plurality of electrodes.

14. The catheter ablation system of claim 13, wherein the electrode activation circuit includes a plurality of switches connected between the generator and each of the plurality of electrodes, wherein the plurality of switches are selectively controlled to selectively deliver the RF ablative energy generated by the generator to one or more of the plurality of electrodes.

15. The catheter ablation system of claim 14, wherein the current distribution circuit includes a plurality of resistors and a plurality of switches, wherein the plurality of switches are selectively controlled to modify the resistive path provided in parallel with a resistive path presented by the plurality of electrodes.

16. The catheter ablation system of claim 11, further including: a tissue contact detection module configured to detect tissue contact associated with each of the plurality of electrodes, wherein the electrode activation circuit is selectively controlled based on tissue contact determined by the tissue contact detection module.

17. The catheter ablation system of claim 16, wherein the electrode activation circuit is selectively controlled to activate electrodes determined by the tissue contact detection module to be in contact with adjacent tissue.

18. The catheter ablation system of claim 16, wherein the electrode activation circuit is selectively controlled to activate electrodes determined by the tissue contact detection module to be located adjacent to an electrode in contact with adjacent tissue.

19. The catheter ablation system of claims 11-18, wherein the ablation catheter is a split-tip ablation catheter.

20. A catheter ablation system comprising:a generator configured to generate pulse field ablation (PFA) pulses; an ablation catheter having a plurality of electrodes configured to selectively deliver PFA energy provided by the generator; and an electrode activation circuit configured to selectively deliver the PFA energy from the generator to one or more of the plurality of electrodes.

21. The catheter ablation system of claim 20, further including: a tissue contact detection module configured to detect tissue contact associated with each of the plurality of electrodes, wherein the electrode activation circuit is selectively controlled based on tissue contact determined by the tissue contact detection module.

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