System and method for multi-channel RF energy delivery with coagulum reduction

• US 20050010206A1
• Filed: 05/14/2004
• Published: 01/13/2005
• Est. Priority Date: 05/12/2000
• Status: Active Grant

• Current Assignee: Sichuan Jinjiang Electronic Science and Technology Company Limited
• Original Assignee: Cardima, Inc.
• Inventors: Chan, Eric K. Y., Nasab, Michael
• Granted Patent: US 7,252,664 B2
• Time in Patent Office: Days
• US Class Current: 606/41
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1492 having a flexible, catheter-like structure, e.g. for heart ablation A61B18/1477 takes precedence
• CPC Class Codes: A61B 2018/0016 Energy applicators arranged in a two- or three dimensional array
• CPC Class Codes: A61B 2018/00357 Endocardium
• CPC Class Codes: A61B 2018/00648 using more than one sensed parameter
• CPC Class Codes: A61B 2018/00678 upper
• CPC Class Codes: A61B 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00791 Temperature
• CPC Class Codes: A61B 2018/00797 measured by multiple temperature sensors
• CPC Class Codes: A61B 2018/00827 Current
• CPC Class Codes: A61B 2018/00875 Resistance or impedance
• CPC Class Codes: A61B 2018/00892 Voltage
• CPC Class Codes: A61B 2018/1253 monopolar
• CPC Class Codes: A61B 2018/1467 using more than two electrodes on a single probe

Abstract

A system and method for efficient delivery of radio frequency (RF) energy includes a backplane. At least a single channel card is removably coupled to the backplane for controlling the amount of RF power delivered through a single channel via an electrical coupling to at least one ablation electrode or a catheter. The at least one channel card provides a gradual increase in RF power calculated in real-time during an initial ramp-up phase, and to limit the delivery of RF power through the electrical coupling based on a received temperature of cardiac tissue in contact with the at least one ablation electrode, thereby reducing the likelihood coagulum formation.

Claims

1. A modular channel card for delivering radio frequency (RF) energy to an ablation device, the card comprising:

a computational module for calculating RF power delivery parameters from at least one received measurement; and

a pulse width monitor (PWM) module coupled to the analog computer module and to a single channel of an external ablation device, the PWM module forming and supplying an RF power output to the device, the magnitude and timing of the power output based at least in part upon a sensed temperature received by the PWM module from the device and the RF power delivery parameters.

2. The modular channel card of claim 1 wherein the computational module is substantially analog.

3. The channel card of claim 1 wherein the at least one sensed measurement comprises voltage and current measurements.

4. The channel card of claim 3 wherein the analog computer module is comprised of at least one analog chip for converting the voltage and current into root mean squared (RMS) values and performing a selected mathematical operation on the RM values.

5. The channel card of claim 1, wherein data computed by the analog computer module is used to determine an index indicative of the likelihood of coagulum.

6. The channel card of claim 1, wherein the ablation device is chosen from a group comprising an ablation catheter and therapeutic probe.

7. A system for efficient delivery of radio frequency (RF) energy to cardiac tissue with an ablation device, the system comprising:

a backplane; and

at least one modular channel card removably coupled to the backplane for controlling the amount of RF power delivered through a single channel via an electrical coupling to at least one ablation electrode on the device.

8. The system of claim 7 further comprising an RF generator coupled to the at least one channel card.

9. The system of claim 7 further comprising at least one temperature sensor each positioned in proximity to the at least one ablation electrode, the at least one temperature sensor effective for measuring the temperature of the cardiac tissue in contact with the at least one ablation electrode.

10. The system of claim 7 wherein the electrical coupling is effective for delivering an electric current from an RF generator through the at least one ablation electrode, arranged in a linear or curvilinear assembly at a distal section of the device to the cardiac tissue and a return path of RF current through a reference electrode.

11. The system of claim 7 wherein the at least one channel card comprises an information processor module and RF output controller module.

12. The system of claim 11, further comprising a current sensor effective for measuring current delivered through said electrical coupling, and a voltage sensor effective for measuring voltage delivered through said electrical coupling, wherein the information processor and RF output controller are capable of calculating RF power and impedance in real-time and terminating delivery of RF energy through the electrical coupling based on changes in measured current and voltage, calculated impedance, and calculated power, and wherein the information processor and RF output controller provide RF energy simultaneously to all or any combination of the multiplicity of electrodes in a user-selectable manner.

13. A system as recited in claim 11, wherein said information processor and RF output controller compares the temperature measured at the series of temperature sensors to a user-selected target temperature for ablation of cardiac tissue, and wherein said information processor and RF output controller limits the delivery of the electrical current through said electrical coupling to maintain the target temperature at the cardiac tissue.

14. The method of claim 13, wherein each temperature sensor of the series of temperature sensors is adjacent to an electrode of the series of electrodes, and wherein the information processor and RF output controller utilizes a combined temperature reading from the temperature sensors on both sides of each electrode of the assembly of electrodes to independently control the delivery of current to each electrode.

15. A system as recited in claim 11, wherein said information processor and RF output controller compute the elapsed time for the temperature measured at said temperature sensor to ramp up to a target temperature, the measured ramp up to the target temperature being representative of the power curve indicating power transferred to cardiac tissue, said information processor and RF output controller calculating the slope of the power curve for an ablation event from the elapsed time and the target temperature for determining the likelihood of coagulum formation.

16. A system as recited in claim 15, wherein said information processor and RF output controller computes an index indicative of the likelihood of coagulum by dividing the slope of the power curve by the square of the electrical current delivered through the ablation electrode.

17. A system as recited in claim 11, wherein the system further comprises a multiplicity of current and voltage sensors and the information processor and RF output controller comprises functionality for terminating delivery of RF energy to the series of ablation electrodes by comparing to maximum set points, real-time measurements of at least one of impedance at the ablation site, differential impedance at the ablation site, and temperature at the ablation site.

18. The system as recited in claim 17, wherein the functionality utilizes analog methods for information processing and pulse width modulation for RF energy control.

19. A system as recited in claim 18, wherein said information processor and RF output controller computes a Coagulum Index associated with capacitive properties of the ablation of cardiac tissue at a selected radio frequency as proportional to the index indicating the likelihood of coagulum formation.

20. A system as recited in claim 19, wherein the Coagulum Index of the ablation device is provided for matching the impedance determined for the ablation of cardiac tissue.

21. A system as recited in claim 11, wherein delivery of electrical current is limited based on temperature measurements using analog methods for information processing and pulse width modulation for RF energy control.

22. The system of claim 7 wherein the backplane conducts RF energy and communications between cards.

23. The system of claim 7 wherein the channel card is substantially analog-based.

24. The system of claim 7 wherein the channel card is substantially non-analog-based.

25. The system of claim 24 wherein the channel card is substantially digital.

26. The system of claim 24 wherein the channel card includes neural networks.

27. A system for efficient delivery of radio frequency (RF) energy to cardiac tissue with an ablation device, said system comprising:

an RF generator,

a backplane;

an electrical coupling effective for delivering an electrical current from the RF generator through a multiplicity of ablation electrodes, arranged in a linear or curvilinear assembly at the distal section of the ablation device, to the cardiac tissue and a return path for the RF current through a reference electrode;

a multiplicity of temperature sensors each positioned in proximity to each of the multiplicity of ablation electrodes, said multiplicity of temperature sensors effective for measuring the temperature of cardiac tissue in contact with the multiplicity of ablation electrodes; and

at least a single channel card, coupled to the backplane, the at least one channel card comprising an information processor and RF output controller effective for controlling the amount of RF power delivered through the electrical coupling.

28. A method for forming a cardiac lesion by delivering radio frequency (RF) energy from an RF generator to an ablation site of cardiac tissue using an ablation device having a plurality of channels associated with a plurality of ablation electrodes, said method comprising:

selecting a temperature set point for the ablation site;

applying the ablation device to the ablation site to establish contact between a selected one of the ablation electrodes and the ablation site,

monitoring for effective contact between the selected one of ablation electrodes and the ablation site by monitoring ablation site temperature, and optionally at least one of impedance at the ablation site, power of the RF generator, and current through the ablation site;

initiating and gradually increasing power of the RF generator for a selected one of the plurality of channels in a ramp-up phase to increase the temperature of tissue at the ablation site, said ramp-up phase terminating when temperature at the ablation site reaches a temperature of about the temperature set point; and

maintaining the temperature at the ablation site at about the temperature set point by regulating the power of the RF generator, said maintaining terminating after forming a cardiac lesion, said initiating and increasing step and said maintaining step being regulated automatically and being terminated prematurely if effective contact is not present, thereby reducing coagulum formation.

29. The method of claim 28, wherein the maximum power of the RF generator is set at or below about 30 watts and temperature is regulated to remain within 5°

C. or less from the temperature set point.

30. The method of claim 28, wherein the Coagulum Index is at or below a value of about 12.

31. The method of claim 28, wherein the Coagulum Index is at or below a value of about 8.

32. The method of claim 28, wherein the effective contact between the ablation electrode and the ablation site is determined by real-time measurement of at least one of impedance at the ablation site, differential impedance at the ablation site, and temperature at the ablation site.

33. The method of claim 28, wherein the ablation electrode is a multiplicity of ablation electrodes and maintaining the temperature is regulated using temperature feedback from a multiplicity of thermocouple sensors positioned between the ablation electrodes of the assembly of ablation electrodes.

34. The method of claim 32, wherein the maintaining the temperature is performed independently for each electrode by comparing the temperature of neighboring thermocouple sensors for each electrode.

35. The method of claim 32, wherein the maintaining the temperature is performed by electronically subtracting the temperature of two or more neighboring thermocouple sensors and using the result to control the pulsewidth duration of the pulsewidth modulator.

36. The method of claim 28, wherein the temperature set point is selectable by a user.

37. The method of claim 28, wherein the configuration of simultaneous RF energy delivery through the multiplicity of linear or curvilinear ablation electrodes is selected by a user.