Power factor controller for medical device

Abstract

A method for controlling a power factor of a medical system including an RF generator connected to provide an RF output to an high frequency (HF) ablation catheter. A phase angle of the RF output provided to the HF ablation catheter is monitored. The phase angle of the RF output includes a phase difference between an output current and an output voltage. The phase angle is compared to a threshold. A capacitance of a capacitor bank connected in-series with the HF ablation catheter is selectively adjusted when the phase angle exceeds the threshold.

Description

Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1 POWER FACTOR CONTROLLER FOR MEDICAL DEVICE TECHNICAL FIELD

[0001] The subject matter disclosed herein relates to ablation catheters and, in particular, to high-frequency (HF) ablation catheters used for radiofrequency (RF) ablation or electrocautery procedures. BACKGROUND

[0002] High-frequency (HF) ablation catheters used in radiofrequency (RF) ablation or electrocautery include highly inductive components, including for example, catheters, electrodes, and wiring. The highly inductive components of the HF surgical circuitry reduce the power factor, i.e., the ratio of real power to apparent power, of the load. To compensate for the reduced power factor, HF ablation catheters may increase the output voltage to deliver the equivalent real power for RF ablation. However, increasing the output voltage may alter characteristics of the RF output signal, thereby causing interference with other medical systems (e.g., mapping systems, EKGs, CQMs, etc.). Further, the output voltage cannot be increased indefinitely, as for instance, hardware of the HF ablation catheter and / or regulatory standards may impose limits on output voltage. Therefore, there is a need for improved power factor correction of HF ablation catheters and systems. SUMMARY

[0003] According to a first aspect, a method for controlling a power factor of a medical system including an RF generator connected to provide an RF output to an high- frequency (HF) ablation catheter (which may be an ablative ablation catheter). A phase angle of the RF output provided to the HF ablation catheter is monitored. The phase angle (or phase difference) of the RF output includes a phase difference between an output current and an output voltage. The phase angle is compared to a threshold. A capacitanceClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 of a capacitor bank connected in-series with the HF ablation catheter is selectively adjusted when the phase angle exceeds the threshold.

[0004] The selective adjustment of the capacitance of the capacitor bank connected in- series with the HF ablation catheter may be advantageous, as selective connection / disconnection of capacitors change the overall reactance of the system, and thereby, selectively controls the phase angle and power factor. The RF controller may include a voltage sensing transformer to measure a voltage phase and a current sensing transformer to measure a current phase, and a control unit to compare the voltage phase and current phase

[0005] The method may further comprise the capacitor bank having a plurality of capacitors selectively connected in-parallel with each other. The plurality of capacitors is selectively connected in-parallel with each other, and the total capacitance of the capacitor bank is in-series with the RF load.

[0006] The method may further comprise adjusting the capacitance of the capacitor bank via selectively actuating a relay (or switch) to electrically couple or decouple a capacitor of the capacitor bank in-parallel with each other. The relays may be controlled or in communication with a control unit configured to measure and / or actively adjust capacitive reactance XC to reduce overall reactance X, where overall reactance X is a difference between capacitive reactance XCand inductive reactance XL.

[0007] The capacitor bank may be disposed on a return side of the RF generator. The method may further comprise coupling the capacitor bank on a return side (or low side) of the RF generator. This may be advantageous, as for instance, the high side (catheter side) of the circuit provides a path for both stimulation of cardiac tissue and pacing of cardiac tissue, and coupling the capacitor bank on the high side may block the DC pacing signal.

[0008] The method may further comprise coupling the capacitor in-series with a neutral electrode of the HF ablation catheter. Coupling the capacitor in-series with the neutral electrode may be advantageous, as for instance, the patient resistance Rbody may vary throughout an ablation procedure, and if the capacitor bank was coupled in-parallel withClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 the neutral electrode, the capacitive adjustment Cadjust required to cancel or balance the inductive reactance XL of the circuit changes as the patient resistance Rbody and / or patient impedance Zbodychanges. Coupling the capacitor bank in-series with the RF load of the circuit can simplify the processing required to cancel or balance the inductive reactance XL and the capacitive reactance XC, as the inductive reactance XL and the capacitive reactance XCare independent of the patient resistance Rbodyin the in-series configuration.

[0009] The method may further comprise generating a fixed frequency signal between 250kHz and 750kHz with the RF generator. The RF generator within the RF controller may operate a fixed frequency output or signal because the fixed frequency can be filtered, or removed from, other signals of the medical system. For instance, the fixed frequency output can be filtered, or removed from, an impedance field-based positioning system and / or a magnetic field-based positioning system, and thus, the medical positioning system can operate continuously and concurrently with the RF generator. The RF generator may operate in a monopolar mode. For instance, the RF generator 212 may be configured to output a fixed frequency between 250kHz and 750kHz, 300kHz and 600kHz, or between 450kHz and 500kHz. The RF generator may be configured to output a monopolar radio frequency.

[0010] The method may further comprise adjusting the capacitance of the capacitor bank to reduce an overall reactance of the medical system. Reducing an overall reactive of the medical system can thereby increase the power factor of the medical system. The capacitor bank can be configured to provide an active adjustment (i.e., a dynamic or real- time adjustment) of capacitive reactance XCto match, or substantially balance, the inductive reactance XLof the circuit, such that the overall reactance X (X = XL– XC) is reduced. All conductors, cables, devices, systems, etc., of the circuit outside of the RF generator may be treated as an RF load. The circuit may be configured to counteract or balance the variable series inductive reactance with a selectable series capacitive reactance.

[0011] The method may further comprise determining a magnitude of the capacitance adjustment based on a magnitude of the phase angle of the RF output. For instance, if theClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 measured phase angle exceeds the threshold by a large margin (i.e., the phase angle has a large magnitude), a correspondingly large adjustment in capacitive reactance XC may be made by the processor / controller. The processor / controller may determine an appropriate correction to the capacitive reactance XC based on the magnitude of the phase angle to minimize overall reactance X, and selectively actuate one or more of the plurality of capacitors to achieve the desired correction to the capacitive reactance XC.

[0012] The method may be a computer-implemented method, optionally performed by an RF controller. The method may be performed on a cadaver.

[0013] According to a second aspect, a radio-frequency (RF) surgical system is provided. A radio-frequency generator is configured to provide an RF output to a high-frequency (HF) ablation catheter. A capacitor bank is coupled in-series between the ablation catheter and the RF generator. The capacitor bank includes a plurality of capacitors selectively coupled in-parallel with each other. A control unit is coupled to the RF generator to monitor a phase angle of the RF output and to selectively modify a capacitance of the capacitor bank based on the monitored phase angle.

[0014] The selective adjustment of the capacitance of the capacitor bank connected in- series with the HF ablation catheter may be advantageous, as selective connection / disconnection of capacitors change the overall reactance of the system, and thereby, selectively controls the phase angle and power factor.

[0015] The RF surgical system may further include a current sense transformer and a voltage sense transformer in communication with the control unit. The current sense transformer and the voltage sense transformer may sense an output current and an output voltage (i.e., the current and voltage waveforms) of the RF output.

[0016] The control unit may be configured to adjust the capacitance via actuating one or more relays to electrically couple / decouple one or more of the plurality of capacitors in- parallel with each other. The relays may be controlled or in communication with a control unit configured to measure and / or actively adjust capacitive reactance XC to reduce overall reactance X, where overall reactance X is a difference between capacitive reactance XCand inductive reactance XL.Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1

[0017] The capacitor bank may be disposed on a return side of the RF generator. Coupling the capacitor bank on a return side (or low side) of the RF generator may be advantageous, as for instance, the high side (catheter side) of the circuit provides a path for both stimulation of cardiac tissue and pacing of cardiac tissue, and coupling the capacitor bank on the high side may block the DC pacing signal.

[0018] The RF surgical system may further include a safety capacitor. The safety capacitor may be in-series with the capacitor bank. A neutral electrode on the HF ablation catheter may be in-series with the capacitor bank. The safety capacitor may be configured to block low-frequency currents for safety and has a fixed capacitance that cannot consistently offset the varying inductive reactance of the systems, conductors, cables, and devices of the circuit.

[0019] The control unit may be configured to determine an overall reactance of the RF surgical system based on the monitored phase angle and selectively couples one or more of the plurality of capacitors in-parallel with each other to reduce the overall reactance of the RF surgical system. For instance, the controller / processor may determine a magnitude of the phase angle. The magnitude of the phase angle is indicative of overall reactance X and of the power factor of the system / circuit, and thus, the controller / processor may determine the overall reactance and / or the power factor based on the measured phase angle and provide a corresponding correction. The capacitor bank may be configured to provide an active adjustment (i.e., a dynamic or real-time adjustment) of capacitive reactance XC to match, or substantially balance, the inductive reactance XL of the circuit, such that the overall reactance X (X = XL– XC) is reduced. All conductors, cables, devices, systems, etc., of the circuit outside of the RF generator may be treated as an RF load, and the circuit is configured to counteract or balance the variable series inductive reactance with a selectable series capacitive reactance.

[0020] The RF output of the RF generator may be a fixed frequency signal between 250kHz and 750kHz. A medical positioning system may be configured to operate concurrently with generation of the RF output. The RF generator within the RF controller may operate a fixed frequency output or signal because the fixed frequency can beClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 filtered, or removed from, other signals of the medical system. For instance, the fixed frequency output can be filtered, or removed from, an impedance field-based positioning system and / or a magnetic field-based positioning system, and thus, the medical positioning system can operate continuously and concurrently with the RF generator. The RF generator may operate in a monopolar mode.

[0021] According to a third aspect, a device is provided for controlling a power factor for a fixed frequency radio-frequency (RF) surgical system including an RF generator configured to generate a fixed frequency output. A current sense transformer is configured to sense an output current (i.e., the current waveform) of the fixed frequency output. A voltage sense transformer is configured to sense an output voltage of (i.e., the voltage waveform) of the fixed frequency output. A capacitor bank includes a plurality of capacitors selectively coupled in-parallel with each other via a relay. A control unit is in communication with the current sense transformer, the voltage sense transformer, and the capacitor bank. The control unit is configured to measure a phase angle between the output current and the output voltage and selectively actuate the relay of one of more of the plurality of capacitors to control a capacitance of the fixed frequency RF surgical system. The selective adjustment of the capacitance of the capacitor bank connected in- series with the HF ablation catheter may be advantageous, as selective connection / disconnection of capacitors change the overall reactance of the system, and thereby, selectively controls the phase angle and power factor.

[0022] The capacitor bank may be coupled in-series with the RF generator. Coupling the capacitor in-series with the RF generator may be advantageous, as for instance, the patient resistance Rbodymay vary throughout an ablation procedure, and if the capacitor bank was coupled in-parallel with the neutral electrode, the capacitive adjustment Cadjust required to cancel or balance the inductive reactance XL of the circuit changes as the patient resistance Rbodyand / or patient impedance Zbodychanges. Coupling the capacitor bank in-series with the RF load of the circuit simplifies the processing required to cancel or balance the inductive reactance XL and the capacitive reactance XC, as the inductiveClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 reactance XL and the capacitive reactance XC are independent of the patient resistance Rbody in the in-series configuration.

[0023] The control unit may be configured to modify the capacitance of the fixed frequency RF surgical system to reduce an overall reactance of the fixed frequency RF surgical system. The capacitor bank may be configured to provide an active adjustment (i.e., a dynamic or real-time adjustment) of capacitive reactance XCto match, or substantially balance, the inductive reactance XLof the circuit, such that the overall reactance X (X = XL – XC) is reduced. All conductors, cables, devices, systems, etc., of the circuit outside of the RF generator may be treated as an RF load, and the circuit is configured to counteract or balance the variable series inductive reactance with a selectable series capacitive reactance.

[0024] The plurality of capacitors may be coupled in-parallel with each other. The capacitor bank may be couplable in-series with the RF generator. The plurality of capacitors may be selectively connected in-parallel with each other, and the total capacitance of the capacitor bank may be in-series with the RF load.

[0025] The capacitor bank may be disposed on a return side of the RF generator. Coupling the capacitor bank on a return side (or low side) of the RF generator may be advantageous, as for instance, the high side (catheter side) of the circuit provides a path for both stimulation of cardiac tissue and pacing of cardiac tissue, and coupling the capacitor bank on the high side may block the DC pacing signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG.1 is a diagrammatic view of a medical system including a high-frequency (HF) ablation catheter, according to some embodiments.

[0027] FIG.1B is a diagrammatic view of a distal end of an HF ablation catheter, according to some embodiments.

[0028] FIG.2 is a schematic diagram of a circuit for controlling a power factor of an HF ablation catheter, according to some embodiments.Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1

[0029] FIG.3 is a flow chart of a method for controlling a power factor of an HF ablation catheter, according to some embodiments. DETAILED DESCRIPTION

[0030] The present disclosure describes a high-frequency (HF) ablation catheter including a control unit to continuously measure the phase angle (or phase difference) between output voltage and output current, and actively adjust the capacitive reactance within the HF ablation catheter to match the inductive reactance of the full system and load to maintain a fixed output frequency. If the measured phase angle exceeds a threshold, the control unit will communicate with a capacitor bank and selectively connect or disconnect capacitor(s) in-series with the HF ablation catheter neutral electrode. The selective connection / disconnection of capacitors changes the overall reactance of the system, and thereby, selectively controls the phase angle. Prior to HF power delivery, the control unit will adjust the capacitive-reactance in-line with the HF ablation catheter to bring the phase angle near 0 degrees which thereby brings the power factor near 1.

[0031] FIG.1A is a diagrammatic view of a medical system 100 including a high- frequency (HF) ablation catheter 120. The HF ablation catheter 120 includes a handle 118, a shaft 122 having a proximal end 124 and a distal end 126, and a conductive cable 116 coupled with an RF controller 142. The features of the HF ablation catheter 120 (e.g., the cables, conductors, medical devices / sensors) affect the inductive reactance of the medical system 100. The HF ablation catheter 120 can include an elongated medical device such as, for example, a catheter or a sheath. For purposes of illustration and clarity, the description below will be limited to an embodiment wherein the HF ablation catheter 120 comprises a catheter (e.g., catheter 120). It will be appreciated, however, that the present disclosure is not meant to be limited to such an embodiment, but rather in other example embodiments, the medical device may comprise other medical devices, such as, for example and without limitation, sheaths, guidewires and the like. In theClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 example illustrated in FIG.1A, the medical system 100 includes an x-ray source 172 and a patient examination table 168.

[0032] The RF controller 142 is configured to monitor a phase angle of an RF output. The phase angle includes a phase difference between an output current and an output voltage. For instance, the RF controller 142 may include a voltage sensing transformer to measure a voltage phase and a current sensing transformer to measure a current phase, and a control unit to compare the voltage phase and current phase.

[0033] A radio-frequency (RF) generator (shown in FIG.2) is configured to generate a high-frequency (HF) electrical output and provide the HF electrical output to an ablation tip and / or electrodes disposed on the HF ablation catheter 120. The RF generator may operate at a fixed frequency (e.g., at 485kHz). The RF generator may operate in a monopolar mode. The RF controller 142 may communicate with the RF generator to control the generation of the HF electrical output.

[0034] The RF controller 142 may further communicate with a capacitor bank (shown in FIG.2), having two or more capacitors electrically couplable in-parallel with each other, and in-series with a neutral electrode. The RF controller 142 selectively actuates an array of relays (or switches) to couple / decouple capacitors from the capacitor bank, thereby controlling a capacitive reactance of the circuit providing HF electrical output to the HF ablation catheter 120.

[0035] The medical system 100 may include a medical positioning system 140 including an impedance field-based positioning system 136 and a magnetic field-based positioning system 138. The impedance based positioning system 136 may include a plurality of surface patch electrodes 134 adhered to the skin of the patient 160, a switch 148 and alternating current (AC) source 146 connected through switch 148 to the plurality of surface patch electrodes 134. The impedance field-based positioning system 136 may track a position and / or orientation of the HF ablation catheter 120 in a first three- dimensional coordinate system. The magnetic field based positioning system 138 may include a magnetic field generator 130 positioned adjacent to the patient and configured to generate a magnetic field in an area surrounding the patient (in particular, in an areaClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 designated the magnetic motion box) to track a position and / or an orientation of the HF ablation catheter 120 in a second coordinate system. An electronic control unit (ECU) 144 may be connected to the medical positioning system 140 and can be configured to receive impedance based positioning estimates and magnetic based positioning estimates associated with the one or more sensors located at the distal end 126 of the HF ablation catheter 120. The RF generator within the RF controller 142 may operate a fixed frequency output because the fixed frequency can be filtered, or removed from, other signals of the medical system. For instance, the fixed frequency output can be filtered, or removed from, the impedance field-based positioning system 136 and the magnetic field- based positioning system 138. Thus, the medical positioning system 140 can operate continuously and concurrently with the RF generator.

[0036] In some examples, the RF controller 142 is directly coupled with the HF ablation catheter 120, i.e., to the conductive cable 116. In some examples, the RF controller 142 can be coupled with the HF ablation catheter 120 through the medical positioning system 140, the ECU 144, and / or a central control unit of the medical system. The coupling between the HF ablation catheter 120 and the RF controller 142 may affect the overall inductance (or RF load) on the RF controller 142, according to some embodiments.

[0037] FIG.1B is a diagrammatic view of a distal end 126 of HF ablation catheter 120 positioned in a patient's body 160, and more particularly, in a patient's heart. The HF ablation catheter 120 may include one or more sensors, including for example, electrodes 150, 152, 154 and / or magnetic sensor 156, mounted in or on the shaft 122 of the HF ablation catheter 120 and an ablation tip 170. As used herein, “electrode 150” or “electrode 150” may refer to one or more electrodes as appropriate and as generally depicted. The electrodes 150 are disposed at the distal end 126 of the shaft 122. Monitoring by the one or more electrodes 150 are communicated via the shaft 122 to the handle 118 and are received by the medical positioning system 140. Signals received from the one or more electrodes (e.g., electrodes 152, 154) are utilized by the impedance based-positioning system 136 to determine the position of the electrodes within the patient. Likewise, signals received from the magnetic sensor 156 are utilized by theClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 magnetic based-positioning system 138 to determine the position of the magnetic sensor 156 within the patient. The HF ablation catheter 120 may further include other conventional components such as, for example and without limitation, a temperature sensor, additional sensors or electrodes, ablation elements (e.g., the ablation tip electrode 170 for delivering RF ablative energy, high intensity focused ultrasound ablation elements, etc.), and corresponding conductors or leads.

[0038] The shaft 122 can be an elongated, tubular, flexible member for movement within the body 160. The shaft 122 supports, for example and without limitation, sensors and / or electrodes mounted thereon, such as, for example, the electrodes 150, associated conductors, and possibly additional electronics used for signal processing and conditioning. The shaft 122 may also permit transport, delivery, and / or removal of fluids (including irrigation fluids, cryogenic ablation fluids, and bodily fluids), medicines, and / or surgical tools or instruments. The shaft 122 may be made from conventional materials such as polyurethane, and define one or more lumens configured to house and / or transport electrical conductors, fluids, or surgical tools. The shaft 122 may be introduced into a blood vessel or other structure within the body 160 through a conventional introducer. The shaft 122 may then be steered or guided through the body 160 to a desired location, such as the heart, using means well known in the art.

[0039] The electrodes 150 mounted in or on the shaft 122 of the HF ablation catheter 120 may be provided for a variety of diagnostic and therapeutic purposes including, for example and without limitation, electrophysiological studies, pacing, cardiac mapping, and ablation. The ECU 144 provides a means for controlling the operation of various components of the system 100, including the HF ablation catheter 120, an electric signal generator 146, and a switch 148 of the impedance-field-based positioning system 136, and magnetic generator 130 of the magnetic-field-based positioning system 138, according to some embodiments. The RF controller 142 may be incorporated as part of the ECU 144, alternatively, the RF controller 142 is a separate circuit / controller from the ECU 144.Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1

[0040] FIG.2 is a schematic diagram of a circuit 200 that includes the HF ablation catheter 220 as well as the plurality of inductive / reactive components that contribute to the overall reactance of the system. FIG.2 also illustrates the RF controller 142 and associated components utilized to control a power factor of an HF ablation catheter 220. The circuit 200 includes a current sense transformer 202, a voltage sense transformer 204, the RF controller 142 (in this example, implemented with a microcontroller (MCU) 206 with one or more GPIO ports), a de-multiplexer (DEMUX) 208, a capacitor bank 210, an RF generator 212, a safety capacitor 214, an HF ablation catheter 220, and an auxiliary system 222.The RF controller 142 described above may include, and / or be in communication with, any elements of the circuit 200.

[0041] The RF generator 212 is a fixed-frequency signal generator, according to some embodiments. For instance, the RF generator 212 may be configured to output a fixed frequency between 250kHz and 750kHz, 300kHz and 600kHz, or between 450kHz and 500kHz. The RF generator 212 may be configured to output a monopolar radio frequency. The safety capacitor 214 is configured to block low-frequency currents for safety. The safety capacitor 214 has a fixed capacitance that cannot consistently offset the varying inductive reactance of the systems, conductors, cables, and devices of the circuit 200.

[0042] The current sense transformer 202 and the voltage sense transformer 204 are configured to measure signals representative of current (I) and voltage (V), respectively, of the RF output provided by RF generator 212 to the HF ablation catheter 220. The current sense transformer 202 and the voltage sense transformer 204 are in communication with the RF controller 142 (e.g., the MCU 206). In one example, the MCU 206 of the RF controller 142 may include an analog-to-digital converter (ADC) to convert the measured current (I) and voltage (V) waveforms from analog signals to digital signals that can be processed by MCU 206 to calculate the phase angle, and optionally, the magnitude of the RF output. In some examples, the auxiliary system 222 may include an auxiliary controller / control unit configured to measure magnitude and the phase angle (θ) of the output current and the output voltage from the RF generator 212.Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1 The MCU 206 and / or the auxiliary system 222 calculate a phase angle of RF output—i.e., a difference between the phase of the output current and the phase of the output voltage. The phase angle is indicative of inductive reactance XLof the circuit 200. In general, RF ablation circuits will have a positive phase angle θ, indicating an inductive reactance XL is greater than a capacitive reactance XC.

[0043] The cables, conductors, components, and systems connected to the RF generator 212 act as a load, and thereby increase the inductive reactance XLof the circuit 200. For example, the cables running to and from the auxiliary system 222 each include a parasitic inductance Lcableand a resistance Rcable. Likewise, the HF ablation catheter 220 includes a catheter inductance Lcatheter, a catheter resistance Rcatheter, an RF return cable inductance LRFReturn, and an RF return cable resistance RRFReturn. Upon contact with target tissue, the patient’s body provides an impedance Zbody to the circuit 200. The inductive reactance XL (and / or the overall reactance X) of the circuit 200 may fluctuate based on which components and systems are coupled to the catheter. For instance, different ablation tips / coils may each have their own unique inductive reactance XL. Similarly, auxiliary systems such as mapping systems, positioning systems, tracking systems, force sensors, etc., coupled with the circuit may affect inductive reactance XLand / or overall reactance X of the circuit 200. Thus, the inductive reactance XL of the circuit 200 may outweigh the capacitive reactance XCof the circuit 200, thereby resulting in a phase angle. In addition, the inductive reactance XLmay vary within a particular procedure as the position of the cable changes, as the HF ablation catheter 220 contacts different tissue, or as different systems are coupled to the HF ablation catheter 220.

[0044] A phase angle (i.e., a difference or offset in the voltage wave versus the current wave) of the circuit 200 reduces a power factor of the load. A reduced power factor results in decreased real power (W) provided to the ablation site. The HF ablation catheter 220 and / or the circuit 200 have limited output voltages, and thus, increasing an output voltage to compensate for the reduced power factor may be insufficient to deliver the equivalent real power (W) for ablation.Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1

[0045] The capacitor bank 210 is configured to provide an active adjustment (i.e., a dynamic or real-time adjustment) of capacitive reactance XC to match, or substantially balance, the inductive reactance XLof the circuit 200, such that the overall reactance X (X = XL – XC) is reduced. All conductors, cables, devices, systems, etc., of the circuit 200 outside of the RF generator 212 may be treated as an RF load, and the circuit 200 is configured to counteract or balance the variable series inductive reactance with a selectable series capacitive reactance. The capacitor bank 210 thereby corrects a power factor of the circuit 200, as the real power (W) of the circuit 200 is approximately equal to the apparent power (VA). The circuit 200 does not need to increase output voltage to compensate for a reduced power factor, but instead, the circuit 200 can correct a power factor, and thereby maintain constant output voltage and constant RF frequency throughout an ablation procedure.

[0046] The capacitor bank 210 includes a plurality of capacitors 218 and a plurality of relays 216. The capacitor bank 210 is connected in-series with the neutral electrode (or return) of the HF ablation catheter 220. The plurality of capacitors 218 are connected in- parallel with one another. The plurality of relays 216 is coupled to the DEMUX 208 in communication with the MCU 206 of the RF controller 142. The MCU 206 is configured to actuate (open and close) the plurality of relays 216 (or switches) to selectively couple and / or decouple each of the plurality of capacitors 218 to the HF ablation catheter 220. The plurality of relays 216 are coupled in-parallel with each other. Each of the plurality of relays 216 include one terminal coupled with the low side of the RF generator 212, and the other terminal coupled with one of the capacitors 218. The capacitor bank 210 can default to close all of the plurality of relays 216. Each of the plurality of capacitors 218 may be of the same capacitance. Alternatively, the plurality of capacitors 218 have different capacitances—and the MCU 206 is configured to select which of the plurality of capacitors 218 to couple / decouple with the circuit 200 to minimize the phase angle.

[0047] In FIG.3, the capacitor bank 210 is disposed on a return side (low side) of the RF generator 212. Locating the capacitor bank 210 on the return side of the circuit 200—as opposed to the high side (catheter side) —allows the RF generator 212 to provide a DCClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 pacing signal to the HF ablation catheter 220. The high side of the circuit 200 provides a path for both stimulation of cardiac tissue and pacing of cardiac tissue. Locating the capacitor bank 210 on the high side of the circuit 200 may block the DC pacing signal.

[0048] Each of the plurality of capacitors 218 are couplable in-series with the RF load of the circuit 200. The plurality of capacitors 218 are coupled in-parallel with one another, and the total capacitance of the capacitor bank 210 is in-series with the RF load. The plurality of capacitors 218 are coupled in-series with the RF load of the circuit 200 because the patient resistance Rbody varies throughout the ablation procedure, e.g., generally between 50 ohms and 300 ohms depending upon the tissue in contact with the HF ablation catheter 220. If, for instance, the capacitor bank 210 was coupled in-parallel with the RF load of the circuit 200, the capacitive adjustment Cadjust required to cancel or balance the inductive reactance XL of the circuit 200 changes as the patient resistance Rbodyand / or patient impedance Zbodychanges. Coupling the capacitor bank 210 in-series with the RF load of the circuit 200 simplifies the processing required to cancel or balance the inductive reactance XL and the capacitive reactance XC, as the inductive reactance XL and the capacitive reactance XCare independent of the patient resistance Rbodyin the in- series configuration.

[0049] FIG.3 is flow chart of a method 300 for controlling a power factor of an HF ablation catheter. The method 300 can be used with any of the systems or devices described above in FIGS.1A-2. At step 310, the method 300 includes measuring a phase angle of an output of the HF surgical system. The HF surgical system may include the medical system 100 and / or the circuit 200 described above. The phase angle includes a phase difference between an output current and an output voltage, i.e. a difference in phase between an output current waveform and an output voltage waveform. The output current waveform and the output voltage waveform are sensed by the current sense transformer 202 and the voltage sense transformer 204, respectively, and communicated to a controller / processor (e.g., the MCU 206 of the RF controller 142). The representative signals are processed by the controller / processor, which may include an ADC and control unit, to measure the magnitude and the phase angle between the current and voltageClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 waveforms from the RF generator. The controller / processor calculates a phase angle and / or an impedance Z of the circuit based on the magnitude and the phase of the current and voltage waveforms, according to some embodiments.

[0050] At step 320, the method 300 includes comparing the measured phase angle to a threshold. The controller / processor (e.g., the MCU 206 of the RF controller 142) compares the measured phase angle to a threshold, according to some embodiments. The threshold is a predetermined, a preprogrammed, and / or a pre-calibrated threshold stored in the MCU 206 and / or the auxiliary system 222. For instance, the threshold may be preprogrammed at 45°, such that a measured phase angle exceeding the threshold of 45° triggers a correction. The threshold may be preprogrammed at a range between 20°- 30°, at a range between 15°- 20°, at a range between 10° - 15°, or at a range between 1° - 10°. Preferably, the threshold may be preprogrammed at 30°, at 20°, at 10°, or at 5°. In general, a smaller threshold will enable the RF circuit to be tuned more accurately, maximizing the power factor (i.e., power factor approaching 1). However, the smaller threshold will require more active tuning (i.e., actuation of the relays / switches to modify the in-series capacitance of the RF load). The threshold may be predetermined or calibrated based on the particular devices / systems connected to the RF circuit. For example, a particular ablation tip or system may require a high power factor for accurate ablation delivery, and thus, the predetermined or pre-calibrated threshold may be lowered. The threshold may be generated based on real-time measurements, including for example, the measured phase angle, the total RF load, the total impedance Z, and / or other variables.

[0051] At the step 320, the controller / processor (e.g., the MCU 206 of the RF controller 142) determines a magnitude of the phase angle. The magnitude of the phase angle is indicative of overall reactance X and of the power factor of the system / circuit, and thus, the controller / processor may determine the overall reactance and / or the power factor based on the measured phase angle.

[0052] If, for example, the measured phase angle is less than a threshold (indicating the overall reactance X is at an acceptable level and the power factor is at an acceptableClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 level), the method 300 returns to step 310. Thus, the method 300 may include continuously monitoring phase angle (and thereby the overall reactance and power factor) of the RF ablation circuit and comparing the measured phase angle to a threshold. If, for example, the measured phase angle is greater than a threshold (indicating the overall reactance X is above an acceptable level and the power factor is below an acceptable level), the method 300 proceeds to step 330.

[0053] At step 330, the method 300 includes adjusting a capacitive reactance XCof the high frequency ablation catheter. The capacitive reactance XC is actively adjusted via selectively coupling or decoupling one or more capacitors in-series with a neutral electrode of the HF ablation catheter. For instance, if the MCU 206 of the RF controller 142 determines the measured phase angle is greater than a threshold (e.g., at the step 320), the MCU 206 sends a signal to one or more of the plurality of relays 216 to actuate a switch to couple or decouple one or more of the plurality of capacitors 218 in-series with the RF load. Coupling and / or decoupling one or more of the plurality of capacitors 218 with the HF ablation catheter neutral electrode changes the capacitive reactance XC of the circuit 200. The capacitive reactance XCof the circuit 200 can be selectively adjusted via the MCU 206 actuating the plurality of relays 216, such that the capacitive reactance XC is approximately equal to the inductive reactance, bringing the overall reactance X to approximately 0.

[0054] In some embodiments, the adjustment to the capacitive reactance XCis based on the magnitude of the phase angle. For instance, if the measured phase angle exceeds the threshold by a large margin (i.e., the phase angle has a large magnitude), a correspondingly large adjustment in capacitive reactance XCmay be made by the processor / controller. In other words, the processor / controller may determine a appropriate correction to the capacitive reactance XC based on the magnitude of the phase angle to minimize overall reactance X, and selectively actuate one or more of the plurality of capacitors 218 to achieve the desired correction to the capacitive reactance XC. The processor / controller may be configured to make stepped adjustments to theClient Docket No.15864WOO1 B&A Docket No.1604.119PCT1 capacitive reactance XC, e.g., by actuating a single capacitor at a time and repeating steps 310, 320 to determine whether the phase angle is at an acceptable level.

[0055] After performing a first capacitive reactance adjustment, the method 300 may return to step 310 to measure the phase angle. The method 300 may repeat through a plurality of cycles to repeatedly measure phase angle of the RF output and / or adjust a capacitive reactance XCof the RF ablation circuit if the power factor (or overall reactance) exceeds a threshold. The method 300 is configured for continuous monitoring and power factor correction.

[0056] While the invention has been described with reference to example methods, systems and devices, 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 methods, systems and devices disclosed, but that the invention will include all methods, systems and devices falling within the scope of the appended claims.

[0057] Clause 1. A method (300) for controlling a power factor of a medical system (100) including a radio-frequency (RF) generator (212) connected to provide an RF output to a high-frequency (HF) ablation catheter (120), the method comprising: monitoring (310) a phase angle of the RF output provided to the HF ablation catheter, the phase angle of the RF output including a phase difference between an output current and an output voltage; comparing (320) the phase angle to a threshold; and selectively adjusting (330) a capacitance of a capacitor bank (210) connected in-series with the HF ablation catheter when the phase angle exceeds the threshold.

[0058] Clause 2. The method of clause 1, wherein the capacitor bank includes a plurality of capacitors (218) selectively connected in-parallel with each other.

[0059] Clause 3. The method of clause 2, wherein adjusting the capacitance of the capacitor bank includes: selectively actuating a relay (216) to electrically couple or decouple a capacitor of the capacitor bank in-parallel with each other.Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1

[0060] Clause 4. The method of clauses 1, 2, or 3, wherein the capacitor bank is disposed on a return side of the RF generator.

[0061] Clause 5. The method of clauses 1, 2, or 3, wherein the capacitor is coupled in- series with a neutral electrode of the HF ablation catheter.

[0062] Clause 6. The method of any preceding clause, wherein the RF output of the RF generator is a fixed frequency signal between 250kHz and 750kHz.

[0063] Clause 7. The method of any preceding clause, wherein the capacitance of the capacitor bank is adjusted to reduce an overall reactance of the medical system to thereby increase the power factor of the medical system.

[0064] Clause 8. The method of any preceding clause, wherein a magnitude of the capacitance adjustment is based on a magnitude of the phase angle of the RF output.

[0065] Clause 9. A radio-frequency (RF) circuit (200) for a medical system (100), comprising: an RF generator (212) configured to provide an RF output to an HF ablation catheter (120); a capacitor bank (210) coupled in-series between the ablation catheter and the RF generator, the capacitor bank including a plurality of capacitors (218) selectively coupled in-parallel with each other; and an RF controller (142) coupled to the RF generator to monitor a phase angle of the RF output and to selectively modify a capacitance of the capacitor bank based on the monitored phase angle.

[0066] Clause 10. The RF surgical system of clause 9, further comprising a current sense transformer (202) and a voltage sense transformer (204) in communication with the RF controller , wherein the current sense transformer and the voltage sense transformer sense an output current and an output voltage of the RF output.

[0067] Clause 11. The RF surgical system of clauses 9 or 10, wherein the RF controller adjusts the capacitance via actuating one or more relays (216) to electrically couple / decouple one or more of the plurality of capacitors in-parallel with each other.

[0068] Clause 12. The RF surgical system of clauses 9, 10, or 11, wherein the capacitor bank is disposed on a return side of the RF generator.Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1

[0069] Clause 13. The RF surgical system of clauses 9, 10, 11, or 12, further comprising: a safety capacitor (214) in-series with the capacitor bank; and a neutral electrode on the ablation catheter in-series with the capacitor bank.

[0070] Clause 14. The RF surgical system of clauses 9, 10, 11, 12, or 13, wherein the RF controller is configured to determine an overall reactance of the RF surgical system based on the monitored phase angle and selectively couples one or more of the plurality of capacitors in-parallel with each other to reduce the overall reactance of the RF surgical system.

[0071] Clause 15. The RF surgical system of clauses 9, 10, 11, 12, 13, or 14 wherein the RF output of the RF generator is a fixed frequency signal between 250kHz and 750kHz, wherein a medical positioning system (140) is configured to operate concurrently with generation of the RF output.

[0072] Clause 16. A device (200) for controlling a power factor for a medical system (100) including a radio-frequency (RF) generator (212) configured to generate a fixed frequency output, the device comprising: a current sense transformer (202) configured to sense an output current of the fixed frequency output; a voltage sense transformer (204) configured to sense an output voltage of the fixed frequency output; a capacitor bank (210) including a plurality of capacitors (218) selectively coupled in-parallel with each other via a relay (216); and an RF controller in communication with the current sense transformer, the voltage sense transformer, and the capacitor bank, wherein the RF controller is configured to measure a phase angle between the output current and the output voltage and selectively actuate the relay of one of more of the plurality of capacitors to control a capacitance of the medical system.

[0073] Clause 17. The device of clause 16, wherein the capacitor bank is coupled in- series with the RF generator.

[0074] Clause 18. The device of clauses 16 or 17, wherein the RF controller modifies the capacitance of the fixed frequency RF surgical system to reduce an overall reactance of the fixed frequency RF surgical system.Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1

[0075] Clause 19. The device of clauses 16, 17, or 18, wherein the plurality of capacitors are coupled in-parallel with each other and wherein the capacitor bank is couplable in- series with the RF generator.

[0076] Clause 20. The device of clauses 16, 17, 18, or 19, wherein the capacitor bank is disposed on a return side of the RF generator.

Claims

Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1 WHAT IS CLAIMED IS:

1. A method (300) for controlling a power factor of a medical system (100) including a radio-frequency (RF) generator (212) connected to provide an RF output to a high-frequency (HF) ablation catheter (120), the method comprising: monitoring (310) a phase angle of the RF output provided to the HF ablation catheter (120), the phase angle of the RF output including a phase difference between an output current and an output voltage; comparing (320) the phase angle to a threshold; and selectively adjusting (330) a capacitance of a capacitor bank (210) connected in-series with the HF ablation catheter (120) when the phase angle exceeds the threshold.

2. The method of claim 1, wherein the capacitor bank (210) includes a plurality of capacitors (218) selectively connected in-parallel with each other.

3. The method of claim 2, wherein adjusting the capacitance of the capacitor bank (210) includes: selectively actuating a relay (216) to electrically couple or decouple a capacitor (218) of the capacitor bank (210) in-parallel with each other.

4. The method of claims 1, 2, or 3, wherein the capacitor bank (210) is disposed on a return side of the RF generator (212).

5. The method of claims 1, 2, or 3, wherein the capacitor (218) is coupled in-series with a neutral electrode of the HF ablation catheter (120).Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1 6. The method of any preceding claim, wherein the RF output of the RF generator (212) is a fixed frequency signal between 250kHz and 750kHz.

7. The method of any preceding claim, wherein the capacitance of the capacitor bank (210) is adjusted to reduce an overall reactance of the medical system (100) to thereby increase the power factor of the medical system (100).

8. The method of any preceding claim, wherein a magnitude of the capacitance adjustment is based on a magnitude of the phase angle of the RF output.

9. A radio-frequency (RF) circuit (200) for a medical system (100), comprising: an RF generator (212) configured to provide an RF output to an high- frequency (HF) ablation catheter (120); a capacitor bank (210) coupled in-series between the HF ablation catheter and the RF generator (212), the capacitor bank (210) including a plurality of capacitors (218) selectively coupled in-parallel with each other; and an RF controller (142) coupled to the RF generator (212) to monitor a phase angle of the RF output and to selectively modify a capacitance of the capacitor bank (210) based on the monitored phase angle.

10. The RF circuit (200) of claim 9, further comprising a current sense transformer (202) and a voltage sense transformer (204) in communication with the RF controller (142), wherein the current sense transformer (202) and the voltage sense transformer (204) sense an output current and an output voltage of the RF output.

11. The RF circuit (200) of claims 9 or 10, wherein the RF controller (142) adjusts the capacitance via actuating one or more relays (216) to electrically couple / decouple one or more of the plurality of capacitors (218) in-parallel with each other.Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1 12. The RF circuit of claims 9, 10, or 11, wherein the capacitor bank (210) is disposed on a return side of the RF generator (212).

13. The RF circuit of claims 9, 10, 11, or 12, further comprising: a safety capacitor (214) in-series with the capacitor bank (210); and a neutral electrode on the ablation catheter in-series with the capacitor bank (210).

14. The RF circuit of claims 9, 10, 11, 12, or 13, wherein the RF controller (142) is configured to determine an overall reactance of the RF circuit (200) based on the monitored phase angle and selectively couples one or more of the plurality of capacitors (218) in-parallel with each other to reduce the overall reactance of the RF surgical system.

15. The RF circuit of claims 9, 10, 11, 12, 13, or 14 wherein the RF output of the RF generator (212) is a fixed frequency signal between 250kHz and 750kHz, wherein a medical positioning system (140) is configured to operate concurrently with generation of the RF output.

16. A device (200) for controlling a power factor for a medical system (100) including a radio-frequency (RF) generator (212) configured to generate a fixed frequency output, the device comprising: a current sense transformer (202) configured to sense an output current of the fixed frequency output; a voltage sense transformer (204) configured to sense an output voltage of the fixed frequency output;Client Docket No.15864WOO1 B&A Docket No.1604.119PCT1 a capacitor bank (210) including a plurality of capacitors (218) selectively coupled in-parallel with each other via a plurality of relays (216); and an RF controller (142) in communication with the current sense transformer (202), the voltage sense transformer (204), and the capacitor bank (210), wherein the RF controller (142) is configured to measure a phase angle between the output current and the output voltage and selectively actuate one or more of the plurality of relays (216) associated with one of more of the plurality of capacitors (218) to control a capacitance of the medical system.

17. The device of claim 16, wherein the capacitor bank (210) is coupled in-series with the RF generator (212).

18. The device of claims 16 or 17, wherein the RF controller (142) modifies the capacitance of the fixed frequency RF surgical system to reduce an overall reactance of the fixed frequency RF surgical system.

19. The device of claims 16, 17, or 18, wherein the plurality of capacitors (218) are coupled in-parallel with each other and wherein the capacitor bank (210) is couplable in-series with the RF generator (212).

20. The device of claims 16, 17, 18, or 19, wherein the capacitor bank (210) is disposed on a return side of the RF generator (212).

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