Apparatus and method for creating, maintaining, and controlling a virtual electrode used for the ablation of tissue

• US 6,849,073 B2
• Filed: 04/24/2002
• Issued: 02/01/2005
• Est. Priority Date: 07/07/1998
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Goetz, Steven M., Christopherson, Mark A., Hoey, Michael F.
• Primary Examiner(s): PEFFLEY, MICHAEL F
• Application Number:
  US10/131,960
• Publication Number:
  US 20030073989A1
• Time in Patent Office: 1,014 Days
• Field of Search: 606/41, 606/42, 606/45, 606/46, 606 48- 52, 606/34, 607101-105
• US Class Current: 606/34
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1233 with circuits for assuring patient safety
• CPC Class Codes: A61B 18/14 Probes or electrodes therefor
• CPC Class Codes: A61B 18/1402 Probes for open surgery
• CPC Class Codes: A61B 18/18 by applying electromagnetic radiation, e.g. microwaves radiation therapy A61N5/00
• CPC Class Codes: A61B 18/1815 using microwaves
• CPC Class Codes: A61B 2018/00029 open
• CPC Class Codes: A61B 2018/00196 reciprocating lengthwise
• CPC Class Codes: A61B 2018/00666 using a threshold value
• CPC Class Codes: A61B 2018/00678 upper
• CPC Class Codes: A61B 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00708 switching the power on or off
• CPC Class Codes: A61B 2018/00779 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 2018/00821 measured by a thermocouple
• CPC Class Codes: A61B 2018/00875 Resistance or impedance
• CPC Class Codes: A61B 2018/1213 creating an arc
• CPC Class Codes: A61B 2018/1253 monopolar
• CPC Class Codes: A61B 2018/1417 Ball
• CPC Class Codes: A61B 2018/1472 : for use with liquid electrolyte, e.g. virtual electrodes
• CPC Class Codes: A61B 2018/1475 : Electrodes retractable in or deployable from a housing
• CPC Class Codes: A61B 2218/002 : Irrigation
• CPC Class Codes: A61B 2218/007 : Aspiration

Abstract

The present invention provides an apparatus and a method for producing a virtual electrode within or upon a tissue to be treated with radio frequency alternating electric current, such tissues including but not limited to liver, lung, cardiac, prostate, breast, and vascular tissues and neoplasms. An apparatus in accord with the present invention includes a supply of a conductive or electrolytic fluid to be provided to the patient, an alternating current generator, and a processor for creating, maintaining, and controlling the ablation process by the interstitial or surficial delivery of the fluid to a tissue and the delivery of electric power to the tissue via the virtual electrode. A method in accord with the present invention includes delivering a conductive fluid to a predetermined tissue ablation site for a predetermined time period, applying a predetermined power level of radio frequency current to the tissue, monitoring at least one of several parameters, and adjusting either the applied power and/or the fluid flow in response to the measured parameters.

Claims

1. A system for ablating tissue of a patient, the system comprising:

an electrode;

a generator for supplying RF energy to the electrode;

a return electrode, the return electrode returning RF energy back from the electrode to the generator;

means for measuring a change in impedance to the passage of the RF energy over a predetermined period of time; and

means for increasing the power level of RF energy supplied to the electrode by a predetermined amount in response to the measured change in impedance being below a predetermined value.

2. The system of claim 1 further comprising a source of conductive fluid, the source supplying the conductive fluid to the electrode.

3. The system of claim 2 wherein the source of conductive fluid comprises a pump.

4. The system of claim 2 wherein the source of conductive fluid comprises a container.

5. The system of claim 4 wherein the container is a bag.

6. The system of claim 4 wherein the container is a syringe.

7. The system of claim 2 wherein the conductive fluid is saline.

8. The system of claim 7 wherein the saline is isotonic saline.

9. The system of claim 7 wherein the saline is hypertonic saline.

10. The system of claim 1 wherein the return electrode is a ground pad.

11. The system of claim 1 wherein a surgical instrument comprises the electrode and the return electrode.

12. The system of claim 11 wherein the surgical instrument further includes at least one fluid aperture for delivery of a conductive fluid to the electrode.

13. The system of claim 12 wherein the surgical instrument further includes a fluid lumen in fluid communication with the at least one fluid aperture for delivery of the conductive fluid to the electrode.

14. The system of claim 12 wherein the surgical instrument further includes at least one fluid aperture for delivery of a conductive fluid to the return electrode.

15. The system of claim 11 wherein the surgical instrument comprises a forceps.

16. The system of claim 1 wherein a surgical instrument comprises the electrode.

17. The system of claim 16 wherein the surgical instrument comprises a needle.

18. The system of claim 16 wherein the surgical instrument comprises a forceps.

19. The system of claim 16 wherein the surgical instrument comprises a catheter.

20. The system of claim 16 wherein the surgical instrument comprises a blade.

21. The system of claim 16 wherein the surgical instrument comprises a rollerball.

22. The system of claim 1 further comprising:

means for reducing the power level of RF energy supplied to the electrode by a predetermined amount in response to the measured change of impedance being above a predetermined value.

23. The system of claim 22 further comprising:

means for determining the time elapsed since the power level of RF energy supplied to the electrode was last increased by a predetermined amount or reduced by a predetermined amount.

24. The system of claim 23 further comprising:

means for inhibiting an increase in the power level of RF energy for a predetermined period following a prior increase or decrease in power level.

25. The system of claim 23 further comprising:

means for inhibiting a reduction in the power level of RF energy for a predetermined period following a prior increase or decrease in power level.

26. The system of claim 1 further comprising:

means for comparing the increased power level with a predetermined maximum power level.

27. The system of claim 26 wherein the maximum power level is supplied as an input by the operator of the system.

28. The system of claim 26 wherein the maximum power level is provided from a memory of the system.

29. The system of claim 26 wherein the predetermined amount of increase is about twenty percent of the predetermined maximum power level.

30. The system of claim 1 further comprising:

means for comparing a measured impedance level with a predetermined maximum impedance level.

31. The system of claim 30 wherein the maximum impedance level is supplied as an input by the operator of the system.

32. The system of claim 30 wherein the maximum impedance level is provided from a memory of the system.

33. The system of claim 30 wherein the means for increasing the power level is activated if the measured impedance level is less than the maximum impedance level.

34. A method for ablating tissue of a patient, comprising:

providing an electrode, a generator for supplying RF energy to the electrode and a return electrode returning RF energy back from the electrode to the generator;

applying the electrode to a selected tissue to be ablated;

ablating the selected tissue by supplying RF energy to the electrode at a power level;

measuring at least one change in impedance to the passage of the RF energy over a predetermined period of time; and

increasing the power level of the RF energy supplied to the electrode by a predetermined amount in response to a measured change in impedance being below a predetermined value.

35. The method of claim 34 further comprising:

supplying conductive fluid to the electrode while ablating the selected tissue.

36. The method of claim 34 further comprising:

reducing the power level of the RF energy supplied to the electrode by a predetermined amount in response to a measured change in impedance being above a predetermined value.

37. The method of claim 36 further comprising:

determining the time elapsed since the power level of RF energy supplied to the electrode was last increased by a predetermined amount or reduced by a predetermined amount.

38. The method of claim 37 further comprising:

inhibiting an increase in the power level of RF energy for a predetermined period following a prior increase or decrease in power level.

39. The method of claim 37 further comprising:

inhibiting a reduction in the power level of RF energy for a predetermined period following a prior increase or decrease in power level.

40. The method of claim 34 further comprising:

comparing the increased power level with a predetermined maximum power level.

41. The method of claim 40 wherein the maximum power level is supplied as an input by the operator of the system.

42. The method of claim 40 wherein the maximum power level is provided from a memory of the system.

43. The method of claim 40 wherein the predetermined amount of increase in power is about twenty percent of the predetermined maximum power level.

44. The method of claim 34 further comprising:

comparing a measured impedance level with a predetermined maximum impedance level.

45. The method of claim 44 wherein the maximum impedance level is supplied as an input by the operator of the system.

46. The method of claim 44 wherein the maximum impedance level is provided from a memory of the system.

47. The method of claim 44 wherein the power level is increased if the measured impedance level is less than the maximum impedance level.

48. A method of ablating a target tissue of a body of a patient, the method comprising:

providing an electrode;

placing the electrode adjacent the tissue;

delivering an RF current power to the tissue through the electrode;

measuring a first impedance of the tissue;

measuring a second impedance of the tissue following a first predetermined time interval;

determining a first impedance rate of change of the tissue during the first predetermined time interval, the first impedance rate of change being the difference between the first impedance measurement and the second impedance measurement divided by the first predetermined time interval;

measuring a third impedance of the tissue following a second predetermined time interval;

determining a second impedance rate of change of the tissue during the second predetermined time interval, the second impedance rate of change being the difference between the second impedance measurement and the third impedance measurement divided by the second predetermined time interval;

determining an average impedance rate of change of the tissue, the average rate of change being the average of the first impedance rate of change and the second impedance rate of change; and

adjusting the delivery of RF current power to the tissue in response to the determined average impedance rate of change.

49. The method of claim 48 further comprising:

measuring a fourth impedance of the tissue following a third predetermined time interval;

determining a third impedance rate of change of the tissue during the third predetermined time interval, the third impedance rate of change being the difference between the third impedance measurement and the fourth impedance measurement divided by the third predetermined time interval;

determining a second average impedance rate of change of the tissue, the second average rate of change being the average of the first impedance rate of change, the second impedance rate of change and the third impedance rate of change; and

adjusting the delivery of RF current power to the tissue in response to the determined second average impedance rate of change.

50. The method of claim 48 further comprising the delivery of a conductive fluid to the electrode.

51. The method of claim 50 wherein the conductive fluid is saline.

52. The method of claim 51 wherein the saline is isotonic saline.

53. The method of claim 51 wherein the saline is hypertonic saline.

54. The method of claim 48 wherein a surgical instrument comprises the electrode.

55. The method of claim 54 wherein the surgical instrument is a bipolar surgical instrument.

56. The method of claim 54 wherein the surgical instrument is a monopolar surgical instrument.

57. The method of claim 54 wherein the surgical instrument comprises a needle.

58. The method of claim 54 wherein the surgical instrument comprises a forceps.

59. A The method of claim 54 wherein the surgical instrument comprises a catheter.

60. The method of claim 54 wherein the surgical instrument comprises a blade.

61. The method of claim 54 wherein the surgical instrument comprises a rollerball.

62. A method of ablating a target tissue of a body of a patient, the method comprising:

providing an electrode;

placing the electrode adjacent the tissue;

delivering an RF current power to the tissue through the electrode;

measuring a first impedance of the tissue;

measuring a second impedance of the tissue following a first predetermined time interval;

determining a first impedance rate of change of the tissue during the first predetermined time interval, the first impedance rate of change being the difference between the first impedance measurement and the second impedance measurement divided by the first predetermined time interval;

measuring a third impedance of the tissue;

measuring a fourth impedance of the tissue following a second predetermined time interval;

determining a second impedance rate of change of the tissue during the second predetermined time interval, the second impedance rate of change being the difference between the third impedance measurement and the fourth impedance measurement divided by the second predetermined time interval;

determining an average impedance rate of change of the tissue, the average rate of change being the average of the first impedance rate of change and the second impedance rate of change; and

adjusting the delivery of RF current power to the tissue in response to the determined average impedance rate of change.

63. The method of claim 62 further comprising:

measuring a fifth impedance of the tissue;

measuring a sixth impedance of the tissue following a third predetermined time interval;

determining a third impedance rate of change of the tissue during the third predetermined time interval, the third impedance rate of change being the difference between the fifth impedance measurement and the sixth impedance measurement divided by the third predetermined time interval;

determining a second average impedance rate of change of the tissue, the second average rate of change being the average of the first impedance rate of change, the second impedance rate of change and the third impedance rate of change; and

adjusting the delivery of RF current power to the tissue in response to the determined second average impedance rate of change.

64. The method of claim 62 further comprising the delivery of a conductive fluid to the electrode.

65. The method of claim 64 wherein the conductive fluid is saline.

66. The method of claim 65 wherein the saline is isotonic saline.

67. The method of claim 65 wherein the saline is hypertonic saline.

68. The method of claim 62 wherein a surgical instrument comprises the electrode.

69. The method of claim 68 wherein the surgical instrument includes the return electrode.

70. The method of claim 68 wherein the surgical instrument comprises a needle.

71. The method of claim 68 wherein the surgical instrument comprises a forceps.

72. The method of claim 68 wherein the surgical instrument comprises a catheter.

73. The method of claim 68 wherein the surgical instrument comprises a blade.

74. The method of claim 68 wherein the surgical instrument comprises a rollerball.