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

• US 6,736,810 B2
• Filed: 07/11/2001
• Issued: 05/18/2004
• 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:
  US09/903,296
• Publication Number:
  US 20020151884A1
• Time in Patent Office: 1,042 Days
• Field of Search: 606/41, 606/42, 606/32-34, 606/48-50, 607/101-105
• 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 a target tissue of a body of a patient, comprising:

a surgical instrument including an ablation electrode for delivery of RF current to the tissue and a fluid aperture for delivery of conductive fluid adjacent the ablation electrode;

a return electrode;

an RF current generator coupled to the ablation and return electrodes to deliver RE current between the ablation and return electrodes;

a fluid source coupled to the fluid aperture to deliver the conductive fluid to the fluid aperture at a defined rate;

an impedance measurer coupled to the ablation and return electrodes to measure rate of change of impedance between the ablation and return electrodes during delivery of the RF current; and

a fluid flow controller coupled to the fluid source and adapted to progressively adjust the rate of delivery of the conductive fluid in response to the measured time rate of change of the impedance between the ablation and return electrodes based upon a pre-determined correlation between fluid flow rate and impedance rate of change.

2. The system of claim 1, wherein the flow controller increases fluid flow in response to an excessive rate of increase of the impedance between the ablation and return electrodes.

3. The system of claim 1 or claim 2, wherein the fluid source comprises a pump.

4. The system of claim 1, wherein the conductive fluid is saline.

5. The system of claim 4, wherein the saline is isotonic saline.

6. The system of claim 4, wherein the saline is hypertonic saline.

7. The system of claim 1 or claim 2, wherein the return electrode is a ground pad.

8. The system of claim 1 or claim 2, wherein the return electrode is mounted to the surgical instrument.

9. The system of claim 8, wherein the return electrode serves as a second ablation electrode.

10. The system of claim 9, wherein the surgical instrument further includes a fluid aperture for delivery of the conductive fluid adjacent the return electrode.

11. The system of claim 10, wherein the surgical instrument further includes a fluid lumen in fluid communication with the fluid aperture for delivery of the conductive fluid adjacent the return electrode.

12. The system of claim 1 or claim 2, wherein the surgical instrument further includes a fluid lumen in fluid communication with the fluid aperture for delivery of the conductive fluid adjacent the ablation electrode.

13. The system of claim 1 or claim 2, wherein the impedance measurer includes means for measuring impedances at predefined time intervals.

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

selecting a surgical instrument including an ablation electrode for delivery of RF current to the tissue and a fluid aperture for delivery of conductive fluid adjacent the ablation electrode;

placing the ablation electrode adjacent the target tissue;

delivering RF current between the ablation electrode and a return electrode;

delivering the conductive fluid to the fluid aperture at a defined rate;

measuring rate of change of impedance between the ablation and return electrodes during delivery of the RF current; and

progressively adjusting the rate of delivery of the conductive fluid during delivery of the RF current in response to the measured rate of change of impedance between the ablation and return electrodes based upon a pre-determined correlation between fluid flow rate and impedance rate of change.

15. The method of claim 14, wherein adjusting the rate of delivery of the conductive fluid comprises increasing fluid flow in response to an excessive rate of increase of impedance between the ablation and return electrodes.

16. The method of claim 14 or claim 15, wherein delivering the conductive fluid comprises delivering the conductive fluid using a pump.

17. The method of claim 14 or claim 15, wherein the conductive fluid is saline.

18. The method of claim 17, wherein the saline is isotonic saline.

19. The method of claim 17, wherein the saline is hypertonic saline.

20. The method of claim 14 or claim 15, wherein the return electrode is a ground pad.

21. The method of claim 14 or claim 15, wherein the return electrode is mounted to the surgical instrument.

22. The method of claim 14 or claim 15, further comprising placing the return electrode adjacent the target tissue.

23. The method of claim 22, further comprising delivery of the conductive fluid adjacent the return electrode.

24. The method of claim 14 or claim 15, wherein measuring the rate of change of impedance comprises measuring impedances at predefined time intervals.

25. A system for ablating a target tissue of a body of a patient, comprising:

a surgical instrument including an ablation electrode for delivery of RF current to the tissue and a fluid aperture for delivery of conductive fluid adjacent the ablation electrode;

a return electrode;

an RF current generator coupled to the ablation and return electrodes to deliver RE current between the ablation and return electrodes;

a fluid source coupled to the fluid aperture to deliver the conductive fluid to the fluid aperture at a defined rate;

an impedance measurer coupled to the ablation and return electrodes to measure the impedance between the ablation and return electrodes during delivery of the RE current; and

a fluid flow controller coupled to the fluid source and adapted to adjust the rate of delivery of the conductive fluid during delivery of the RF current, effecting an increase in the rate of delivery of the conductive fluid in response to a determined increase in measured impedance between the ablation and return electrodes above a pre-determined value.

26. The system of claim 25, wherein the fluid source comprises a pump.

27. The system of claim 25, wherein the fluid source comprises a container.

28. The system of claim 25, wherein the conductive fluid is saline.

29. The system of claim 28, wherein the saline is isotonic saline.

30. The system of claim 28, wherein the saline is hypertonic saline.

31. The system of claim 25, wherein the return electrode is a ground pad.

32. The system of claim 25, wherein the return electrode is mounted to the surgical instrument.

33. The system of claim 32, wherein the return electrode serves as a second ablation electrode.

34. The system of claim 33, wherein the surgical instrument further includes a fluid aperture for delivery of the conductive fluid adjacent the return electrode.

35. The system of claim 34, wherein the surgical instrument further includes a fluid lumen in fluid communication with the fluid aperture for delivery of the conductive fluid adjacent the return electrode.

36. The system of claim 25, wherein the surgical instrument further includes a fluid lumen in fluid communication with the fluid aperture for delivery of the conductive fluid adjacent the ablation electrode.

37. The system of claim 25, wherein the impedance measurer includes means for measuring impedances at predefined time intervals.

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

selecting a surgical instrument including an ablation electrode for delivery of RF current to the tissue and a fluid aperture for delivery of conductive fluid adjacent the ablation electrode;

placing the ablation electrode adjacent the target tissue;

delivering RF current between the ablation electrode and a return electrode;

delivering the conductive fluid to the fluid aperture at a defined rate;

measuring impedance between the ablation and return electrodes during delivery of the RF current; and

increasing the rate of delivery of the conductive fluid during delivery of the RF current, in response to a determined increase in the measured impedance between the ablation and return electrodes above a pre-determined value.

39. The method of claim 38, wherein delivering the conductive fluid comprises delivering the conductive fluid using a pump.

40. The method of claim 38, wherein delivering the conductive fluid comprises delivering the conductive fluid from a container.

41. The method of claim 38, wherein the conductive fluid is saline.

42. The method of claim 41, wherein the saline is isotonic saline.

43. The method of claim 41, wherein the saline is hypertonic saline.

44. The method of claim 38, wherein the return electrode is a ground pad.

45. The method of claim 38, wherein the return electrode is mounted to the surgical instrument.

46. The method of claim 38, further comprising placing the return electrode adjacent the target tissue.

47. The method of claim 46, further comprising delivery of the conductive fluid adjacent the return electrode.

48. The method of claim 38, wherein measuring impedance comprises measuring impedances at predefined time intervals.

49. A system for ablating a target tissue of a body of a patient, comprising:

a surgical instrument including an ablation electrode for delivery of RF current to the tissue and a fluid delivery means adapted to interstitially infuse conductive fluid into the target tissue adjacent the ablation electrode;

a return electrode;

an RF current generator coupled to the ablation and return electrodes to deliver RF current between the ablation and return electrodes;

a fluid source coupled to a fluid aperture to deliver the conductive fluid to the fluid aperture at a defined rate;

an impedance measurer coupled to the ablation and return electrodes to measure impedance between the ablation and return electrodes during delivery of the RF current; and

a fluid flow controller coupled to the fluid source adapted to adjust the rate of delivery of the conductive fluid to provide an increased rate of delivery in response to an increased measured impedance between the ablation and return electrodes.

50. The system of claim 49, wherein the fluid source comprises a pump.

51. The system of claim 49, wherein the fluid source comprises a container.

52. The system of claim 49, wherein the conductive fluid is saline.

53. The system of claim 52, wherein the saline is isotonic saline.

54. The system of claim 52, wherein the saline is hypertonic saline.

55. The system of claim 49, wherein the return electrode is a ground pad.

56. The system of claim 49, wherein the return electrode is mounted to the surgical instrument.

57. The system of claim 56, wherein the return electrode serves as a second ablation electrode.

58. The system of claim 57, wherein the surgical instrument further includes a second fluid aperture for delivery of the conductive fluid adjacent the return electrode.

59. The system of claim 58, wherein the surgical instrument further includes a fluid lumen in fluid communication with the second fluid aperture for delivery of the conductive fluid adjacent to the return electrode.

60. The system of claim 49, wherein the surgical instrument further includes a fluid lumen in fluid communication with the fluid aperture for delivery of the conductive fluid adjacent the ablation electrode.

61. The system of claim 49, wherein the impedance measurer includes means for measuring impedances at predefined time intervals.

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

selecting a surgical instrument including an ablation electrode for delivery of RF current to the tissue and a fluid aperture for delivery of conductive fluid adjacent the ablation electrode;

placing the ablation electrode adjacent the target tissue;

delivering RF current between the ablation electrode and a return electrode;

delivering the conductive fluid into the target tissue interstices through the fluid aperture at a defined rate;

measuring impedance between the ablation and return electrodes during delivery of the RF current; and

increasing the rate of delivery of the conductive fluid during delivery of the RF current, in response to an increase in the measured impedance between the ablation and return electrodes.

63. The method of claim 62, wherein delivering the conductive fluid comprises delivering the conductive fluid using a pump.

64. The method of claim 62, wherein delivering the conductive fluid comprises delivering the conductive fluid from a container.

65. The method of claim 62, 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 the return electrode is a ground pad.

69. The method of claim 62, wherein the return electrode is mounted to the surgical instrument.

70. The method of claim 62, further comprising placing the return electrode adjacent the target tissue.

71. The method of claim 70, further comprising delivery of the conductive fluid adjacent the return electrode.

72. The method of claim 62, wherein measuring impedance comprises measuring impedances at predefined time intervals.