Electrosurgical systems and methods for treating tissue

• US 20020026186A1
• Filed: 01/10/2001
• Published: 02/28/2002
• Est. Priority Date: 06/07/1995
• Status: Active Grant

• Current Assignee: ArthroCare Corporation (Smith & Nephew PLC)
• Original Assignee: ArthroCare Corporation (Smith & Nephew PLC)
• Inventors: Woloszko, Jean, Eggers, Philip E., Thapliyal, Hira V.
• Granted Patent: US 6,832,996 B2
• Time in Patent Office: Days
• US Class Current: 606/41
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1402 Probes for open surgery
• CPC Class Codes: A61B 18/148 having a short, rigid shaft for accessing the inner body transcutaneously, e.g. for neurosurgery or arthroscopy
• CPC Class Codes: A61B 18/1482 having a long rigid shaft for accessing the inner body transcutaneously in minimal invasive surgery, e.g. laparoscopy
• CPC Class Codes: A61B 18/1485 having a short rigid shaft for accessing the inner body through natural openings
• CPC Class Codes: A61B 18/149 bow shaped or with rotatable body at cantilever end, e.g. for resectoscopes, or coagulating rollers
• 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 2017/00026 Conductivity or impedance, e.g. of tissue
• CPC Class Codes: A61B 2017/00084 Temperature
• CPC Class Codes: A61B 2017/00101 using an array of thermosensors
• CPC Class Codes: A61B 2017/00247 Making holes in the wall of the heart, e.g. laser Myocardial revascularization
• CPC Class Codes: A61B 2018/00029 open
• CPC Class Codes: A61B 2018/00083 low, i.e. electrically insulating
• CPC Class Codes: A61B 2018/00119 with metal oxide nitride
• CPC Class Codes: A61B 2018/0016 Energy applicators arranged in a two- or three dimensional array
• CPC Class Codes: A61B 2018/00178 Electrical connectors
• CPC Class Codes: A61B 2018/00291 using suction
• CPC Class Codes: A61B 2018/00327 Ear, nose or throat
• CPC Class Codes: A61B 2018/00392 Transmyocardial revascularisation
• CPC Class Codes: A61B 2018/00505 Urinary tract
• CPC Class Codes: A61B 2018/00577 : Ablation
• CPC Class Codes: A61B 2018/00583 : Coblation, i.e. ablation using a cold plasma
• CPC Class Codes: A61B 2018/00601 : Cutting
• 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 2018/0072 : Current
• CPC Class Codes: A61B 2018/00726 : Duty cycle
• CPC Class Codes: A61B 2018/00779 : Power or energy
• CPC Class Codes: A61B 2018/00791 : Temperature
• CPC Class Codes: A61B 2018/00827 : Current
• CPC Class Codes: A61B 2018/00875 : Resistance or impedance
• CPC Class Codes: A61B 2018/00982 : combined with or comprising means for visual or photographic inspections inside the body, e.g. endoscopes
• CPC Class Codes: A61B 2018/1213 : creating an arc
• CPC Class Codes: A61B 2018/124 : switching the output to different electrodes, e.g. sequentially
• CPC Class Codes: A61B 2018/1253 : monopolar
• CPC Class Codes: A61B 2018/126 : bipolar
• CPC Class Codes: A61B 2018/1273 : including multiple generators in one device
• CPC Class Codes: A61B 2018/1407 : Loop
• CPC Class Codes: A61B 2018/1467 : using more than two electrodes on a single probe
• CPC Class Codes: A61B 2018/1472 : for use with liquid electrolyte, e.g. virtual electrodes
• CPC Class Codes: A61B 2018/162 : located on the probe body
• CPC Class Codes: A61B 2018/165 : Multiple indifferent electrodes
• CPC Class Codes: A61B 2218/002 : Irrigation
• CPC Class Codes: A61B 2218/007 : Aspiration

Abstract

Electrosurgical methods and apparatus for removing tissue from a target site of a patient, the apparatus including a probe adapted for coupling to a power supply. The electrosurgical probe includes a shaft having a first electrode type and a second electrode type. The electrosurgical apparatus/probe lacks a dedicated return electrode. Instead, the first electrode type and the second electrode type alternate between serving as active electrode and serving as return electrode. The first electrode type comprises at least one ablation electrode adapted for aggressively removing tissue from a target site. The second electrode type comprises at least one digestion electrode adapted for aggressively digesting resected tissue fragments present in an aspiration stream. The apparatus may shift from a first mode of operation wherein the first electrode type serves as active electrode, to a second mode of operation wherein the second electrode type serves as active electrode, and back to the first mode of operation, without operator input. Such a shift may be determined by the presence or absence of tissue at the first and second electrode types, or by a change in electrical impedance in the milieu of the second electrode type, and such a shift may be dependent on a suitable surface area ratio of the first electrode type to the second electrode type. The probe may include an aspiration device which accommodates an aspiration stream emanating from the target site, and a fluid delivery device for delivering an extraneous electrically conductive fluid to the probe or to the target site.

Claims

1. An electrosurgical apparatus for removing tissue from a target site, comprising:

a probe including a first electrode type and a second electrode type, wherein the first electrode type and the second electrode type alternate between serving as an active electrode and serving as a return electrode, such that when the first electrode type serves as the active electrode the second electrode type serves as the return electrode, and when the second electrode type serves as the active electrode the first electrode type serves as the return electrode.

2. The apparatus of claim 1, wherein the probe consists essentially of an ablation electrode and a digestion electrode.

3. The apparatus of claim 1, wherein the first electrode type and the second electrode type are independently coupled to opposite poles of a power supply for supplying alternating current between the first electrode type and the second electrode type, and at any given time point the power supply alternatively supplies electric power preferentially to the first electrode type or preferentially to the second electrode type.

4. The apparatus of claim 1, wherein the first electrode type comprises an ablation electrode and the second electrode type comprises a digestion electrode, and the electrosurgical apparatus lacks a dedicated return electrode.

5. The apparatus of claim 4, wherein the ablation electrode and the digestion electrode have surface areas Sa and Sd, respectively, and the ratio Sa:

Sd is in the range of from about 3;

1 to about 1;

1.

6. The apparatus of claim 5, wherein the ratio Sa:

Sd is in the range of from about 2.5;

1 to about 1.5;

1.

7. The apparatus of claim 1, wherein the probe includes a shaft having a shaft distal end portion and a shaft proximal end portion, and the first electrode type comprises an ablation electrode disposed on an electrode support located at the shaft distal end portion.

8. The apparatus of claim 7, wherein the probe includes an aspiration device including an aspiration port, and the ablation electrode is located distal to the aspiration port.

9. The apparatus of claim 8, wherein the ablation electrode at least partially surrounds a distal portion of the aspiration port.

10. The apparatus of claim 8, wherein the ablation electrode comprises a substantially semi-circular shaped screen.

11. The apparatus of claim 4, wherein the probe includes a shaft having a shaft distal end portion, and an aspiration device having an aspiration lumen terminating distally at an aspiration port, the aspiration port arranged on the shaft distal end portion, and the digestion electrode arranged within the aspiration lumen.

12. The apparatus of claim 1, wherein the second electrode type comprises a digestion electrode, and the digestion electrode comprises a metal ribbon or a flat wire.

13. The apparatus of claim 4, wherein the probe includes a shaft, the digestion electrode comprises a first end coupled to a digestion electrode lead and a second end terminating within the shaft, wherein the digestion electrode is coupled to a high frequency power supply via the digestion electrode lead, and the second end is electrically insulated.

14. The apparatus of claim 1, wherein the first electrode type and the second electrode type are coupled to opposite poles of a high frequency power supply for supplying electrical power thereto, the probe is capable of resecting tissue fragments and aspirating resected tissue fragments, the second electrode type preferentially receives power from the power supply only when the second electrode type is in the presence of tissue.

15. The apparatus of claim 3, wherein, in the absence of tissue in the vicinity of the second electrode type, the first electrode type and the second electrode type serve as active electrode and return electrode, respectively.

16. The apparatus of claim 3, wherein the first electrode type comprises an ablation electrode capable of removing tissue from the target site by a cool ablation process to generate resected tissue fragments, wherein the tissue at the target site is exposed to a temperature in the range of from about 45°

to about 90°

C., the second electrode type comprises a digestion electrode capable of aggressively ablating the resected tissue fragments, and the digestion electrode preferentially receives electric power only in the presence of at least one of the resected tissue fragments.

17. The apparatus of claim 1, wherein the first electrode type and the second electrode type each comprise a material selected from the group consisting of:

tungsten, stainless steel alloys, platinum or its alloys, titanium or its alloys, molybdenum or its alloys, nickel or its alloys, gold, aluminum, and copper.

18. The apparatus of claim 1, wherein at least one of the first electrode type and the second electrode type consists essentially of platinum.

19. The apparatus of claim 1, wherein the probe includes a shaft, and the shaft is covered with an electrically insulating material or constitutes an electrically insulating material.

20. The apparatus of claim 4, wherein the probe includes a shaft having a shaft distal end portion and an electrode support disposed on the shaft distal end portion, and the ablation electrode is affixed to the electrode support via a plurality of ball wires.

21. The apparatus of claim 4, wherein the ablation electrode is affixed to an electrode support comprising a material selected from the group consisting of a ceramic, a glass, and a silicone.

22. The apparatus of claim 3, wherein the electric power supplied by the power supply comprises a high frequency voltage characterized by a peak-to-peak voltage in the range of from about 10 to 2000 volts, a RMS voltage in the range of from about 5 volts to 1000 volts, and a frequency in the range of from about 5 kHz to 20 MHz.

23. The apparatus of claim 1, further comprising a fluid delivery device having a fluid delivery port in communication with a fluid delivery lumen, the fluid delivery port distal to the first electrode type, and the first electrode type comprises at least one ablation electrode.

25. The electrosurgical system of claim 24, wherein alternating between supplying up to about 100% of the electric power to the ablation electrode and supplying up to about 100% of the electric power to the digestion electrode is determined by the presence or absence of tissue in the vicinity of the ablation electrode and the digestion electrode.

26. The electrosurgical system of claim 24, wherein alternating between supplying up to about 100% of the electric power to the ablation electrode and supplying up to about 100% of the electric power to the digestion electrode is determined by the electrical impedance of the milieu of the digestion electrode.

27. The electrosurgical system of claim 24, wherein alternating between supplying up to about 100% of the electric power to the ablation electrode and supplying up to about 100% of the electric power to the digestion electrode is dependent on the ratio of the surface area of the ablation electrode to the surface area of the digestion electrode and is determined by the electrical impedance of the milieu of the digestion electrode.

28. The electrosurgical system of claim 24, wherein the ratio of the surface area of the ablation electrode to the surface area of the digestion electrode is in the range of from about 3:

1 to about 1;

1.

29. The electrosurgical system of claim 24, wherein the ratio of the surface area of the ablation electrode to the surface area of the digestion electrode is in the range of from about 2.5:

1 to about 1.5;

1.

30. The electrosurgical system of claim 24, wherein the electrosurgical system lacks a dedicated return electrode.

31. The electrosurgical system of claim 24, wherein, in the presence of an electrically conductive fluid, both the ablation electrode and the digestion electrode effectively generate a plasma upon application of a high frequency voltage thereto, and both the ablation electrode and the digestion electrode are capable of aggressively breaking down tissue via a cool ablation process, wherein tissue components undergo molecular dissociation, and the tissue which undergoes molecular dissociation is exposed to a temperature not exceeding 90°

C.

32. The electrosurgical system of claim 31, wherein the high frequency voltage is characterized by a peak-to-peak voltage in the range of from about 10 to 2000 volts, a RMS voltage in the range of from about 5 volts to 1000 volts, and a frequency in the range of from about 5 kHz to 20 MHz.

33. The electrosurgical system of claim 24, further comprising an aspiration device having an aspiration port in communication with an aspiration lumen, the digestion electrode disposed adjacent to the aspiration port or within the aspiration lumen.

34. The electrosurgical system of claim 24, wherein the ablation electrode is disposed terminally on the shaft or laterally on the shaft.

36. The electrosurgical probe of claim 35, wherein the at the least one digestion electrode serves as the return electrode when the at least one ablation electrode serves as the active electrode, and the at least one ablation electrode serves as the return electrode when the at the least one digestion electrode serves as the active electrode.

37. The electrosurgical probe of claim 35, wherein the at least one ablation electrode serves as a primary active electrode, and the at the least one digestion electrode serves as a secondary active electrode.

38. The electrosurgical probe of claim 35, wherein the at least one ablation electrode serves as the active electrode when the at least one ablation electrode is in the presence of tissue while the at least one digestion electrode is not in the presence of tissue.

39. The electrosurgical probe of claim 35, wherein the at the least one digestion electrode serves as the active electrode when the at least one digestion is in the presence of tissue while the at least one ablation electrode is not in the presence of tissue.

40. The electrosurgical probe of claim 35, wherein when both the at least one ablation electrode and the at least one digestion electrode are in the presence of tissue, preferential delivery of electric power from the power supply to either the at least one ablation electrode or to the at least one digestion electrode is dependent on the ratio of the surface area of the at least one ablation electrode to the surface area of the at least one digestion electrode.

41. The electrosurgical probe of claim 40, wherein the ratio of the surface area of the at least one ablation electrode to the surface area of the at least one digestion electrode is in the range of from about 3:

1 to about 1;

1.

42. The electrosurgical probe of claim 35, wherein during a given time period of operation of the probe, the at least one ablation electrode or the at least one digestion electrode preferentially or exclusively receives power from the power supply.

43. The electrosurgical probe of claim 35, wherein the at least one ablation electrode functions as the active electrode when the at least one ablation electrode preferentially or exclusively receives power from the power supply, and the at least one digestion electrode functions as the return electrode when the at least one ablation electrode preferentially or exclusively receives power from the power supply.

44. The electrosurgical probe of claim 35, wherein the at least one digestion electrode functions as the active electrode when the at least one digestion electrode preferentially or exclusively receives power from the power supply, and the at least one ablation electrode functions as the return electrode when the at least one digestion electrode preferentially or exclusively receives power from the power supply.

45. The electrosurgical probe of claim 35, wherein during a first mode of operation of the probe the ablation electrode receives from about 60% to about 100% of the power from the power supply, and during a second mode of operation of the probe the digestion electrode receives from about 60% to about 100% of the power from the power supply.

46. The electrosurgical probe of claim 45, wherein the first mode of operation of the probe is longer than the second mode of operation of the probe, the first mode of operation of the probe precedes the second mode of operation of the probe, and wherein the first mode of operation of the probe and the second mode of operation of the probe are repeated sequentially.

47. The electrosurgical probe of claim 35, wherein the at least one ablation electrode comprises a material selected from the group consisting of tungsten, stainless steel alloys, platinum or its alloys, titanium or its alloys, molybdenum or its alloys, nickel or its alloys, gold, aluminum, and copper.

48. The electrosurgical probe of claim 35, wherein the at least one ablation electrode is mounted laterally on the shaft or mounted terminally on the shaft.

49. The electrosurgical probe of claim 35, wherein the at least one ablation electrode at least partially surrounds an aspiration port.

50. The electrosurgical probe of claim 35, wherein the at least one ablation electrode is disposed substantially distal to an aspiration port.

51. The electrosurgical probe of claim 35, wherein the at least one digestion electrode is disposed proximal to an aspiration port.

52. The electrosurgical probe of claim 35, wherein the at least one digestion electrode comprises a material selected from the group consisting of tungsten, stainless steel alloys, platinum or its alloys, titanium or its alloys, molybdenum or its alloys, nickel or its alloys, gold, aluminum, and copper.

53. The electrosurgical probe of claim 35, wherein the at least one digestion electrode comprises a first end coupled to a digestion electrode lead and a second free end, the digestion electrode lead for delivering electric power from the power supply, and the free end does not contact an electrically conductive material.

54. The electrosurgical probe of claim 35, wherein the at least one digestion electrode comprises a first free end which terminates in an electrically insulating material.

55. The electrosurgical probe of claim 53, wherein the at least one digestion electrode comprises a metal ribbon.

56. The electrosurgical probe of claim 35, wherein the probe further consists essentially of an aspiration device having an aspiration port leading to an aspiration lumen, and the at least one digestion electrode is disposed adjacent to the aspiration port or arranged within the aspiration lumen.

57. The electrosurgical probe of claim 35, wherein the probe lacks a dedicated return electrode.

59. The method of claim 58, wherein said step b) is performed before said step c).

60. The method of claim 58, wherein during said step b) the ablation electrode serves as a first active electrode and the digestion electrode serves as a first return electrode.

61. The method of claim 58, wherein during said step c) the digestion electrode serves as a second active electrode and the ablation electrode serves as a second return electrode.

62. The method of claim 58, further comprising the step of:

d) prior to said steps b) and c), selecting a power level to be supplied from the power supply, wherein said step b) comprises supplying up to about 100% of the selected power level from the power supply to the ablation electrode, and said step c) comprises supplying up to about 100% of the selected power level from the power supply to the digestion electrode.

63. The method of claim 58, further comprising

repeatedly alternating between said step b) and said step c).

64. The method of claim 63, wherein repeatedly alternating between said steps b) and c) is inherent in the electrosurgical system and is dependent on the presence or absence of tissue at the ablation electrode and the digestion electrode.

65. The method of claim 64, wherein repeatedly alternating between said steps b) and c) is dependent on a change in electrical impedance in the vicinity of the ablation electrode or the digestion electrode.

66. The method of claim 58, wherein a switch from said step b) to said step c) is induced by the presence of tissue in an electrically conductive fluid in the vicinity of the digestion electrode.

67. The method of claim 58, wherein a switch from said step c) to said step b) is induced by the absence of tissue in an electrically conductive fluid in the vicinity of the digestion electrode while the ablation electrode is in the presence of tissue.

68. The method of claim 58, wherein the ratio of the surface area of the ablation electrode to the surface area of the digestion electrode is in the range of from about 2.5:

1 to about 1.5;

1.

69. The method of claim 58, wherein said step b) results in generation of a plasma in the vicinity of the ablation electrode and removal of at least a portion of the tissue from the target site in a cool ablation process, wherein the tissue at the target site is exposed to a temperature in the range of from about 45°

C. to about 90°

C.

70. The method of claim 58, wherein said step c) results in generation of a plasma in the vicinity of the digestion electrode and the plasma induces molecular dissociation of tissue components of at least one tissue fragment in the vicinity of the digestion electrode to yield low molecular weight ablation by-products.

71. The method of claim 58, wherein at any given time point said step b) and said step c) are mutually exclusive.

72. The method of claim 58, wherein said step b) defines an ablation mode, and said step c) defines an alternative digestion mode.

73. The method of claim 58, wherein said step a) comprises positioning the ablation electrode adjacent to, or in contact with, cartilage tissue, and said step b) results in removal of at least a portion of the cartilage tissue.

74. The method of claim 58, further comprising the step of delivering an electrically conductive fluid to the ablation electrode or to the tissue at the target site.

75. The method of claim 58, further comprising the step of aspirating resected tissue from the target site in an aspiration stream, wherein the aspiration stream contacts the digestion electrode.

76. The method of claim 58, wherein the electric power supplied to the ablation electrode and to the digestion electrode is characterized by a peak-to-peak voltage in the range of from about 10 to 2000 volts, and a RMS voltage in the range of from about 5 volts to 1000 volts.

24. An electrosurgical system for removing tissue from a target site, comprising:

a probe, and a high frequency power supply coupled to the probe for supplying electric power to the probe, the probe including;

a shaft having a shaft distal end portion and a shaft proximal end portion;

an ablation electrode located at the shaft distal end portion, the ablation electrode independently coupled to a first pole of the high frequency power supply;

an aspiration device including an aspiration port in communication with an aspiration lumen, the aspiration port located at the shaft distal end portion; and

a digestion electrode independently coupled to a second pole of the high frequency power supply, wherein the high frequency power supply alternates between supplying up to about 100% of the electric power to the ablation electrode and supplying up to about 100% of the electric power to the digestion electrode.

35. An electrosurgical probe capable of removing tissue from a target site and adapted for connection to a power supply, the electrosurgical probe comprising:

a shaft having at least one ablation electrode and at least one digestion electrode, the at least one ablation electrode and the at the least one digestion electrode independently coupled to opposite poles of the power supply, wherein the at least one ablation electrode can serve as an active electrode or a return electrode, and the at the least one digestion electrode can serve as the active electrode or the return electrode.

58. A method of treating a tissue to be treated at a target site with an electrosurgical system, the electrosurgical system including a probe having an ablation electrode and a digestion electrode, the ablation electrode and the digestion electrode independently coupled to opposite poles of a power supply, and the method comprising:

a) positioning the ablation electrode in the presence of the tissue to be treated;

b) preferentially supplying electric power from the power supply to the ablation electrode; and

c) alternatively to said step b), preferentially supplying electric power from the power supply to the digestion electrode.

77. A method of removing tissue from a target site with an electrosurgical probe, the method comprising:

a) coupling the electrosurgical probe to a power supply, wherein the electrosurgical probe includes a first electrode type and a second electrode type, and the first electrode type and the second electrode type are independently coupled to opposite poles of the power supply;

b) preferentially supplying power from the power supply to the first electrode type; and

c) in response to a change in electrical impedance experienced by the first electrode type or the second electrode type, preferentially supplying power from the power supply to the second electrode type.

78. The method of claim 77, wherein the first electrode type and the second electrode type alternate between serving as an active electrode and serving as a return electrode.

79. The method of claim 77, wherein the first electrode type comprises at least one ablation electrode, and said step b) results in resection of tissue fragments, and the method further comprises aspirating the resected tissue fragments from the target site in an aspiration stream.

80. The method of claim 79, wherein the second electrode type comprises at least one digestion electrode, the at least one digestion electrode is in contact with the aspiration stream, and the change in electrical impedance results from movement of a resected tissue fragment in the aspiration stream towards the at least one digestion electrode.

81. The method of claim 77, wherein the ratio of the surface area of the first electrode type to the surface area of the second electrode type is in the range of from about 3:

1 to about 1;

1.

82. The method of claim 77, wherein said step b) results in localized generation of a plasma in the vicinity of the first electrode type and removal of tissue from the target site, wherein tissue at the target site is exposed to a temperature in the range of from about 45°

to 90°

C.

83. The method of claim 77, wherein during said step b) the first electrode type receives from about 60% to about 100% of the power from the power supply, and during said step c) the second electrode type receives from about 60% to about 100% of the power from the power supply.

84. An electrosurgical system for treating tissue at a target site, comprising:

an electrosurgical probe including a first electrode type and a second electrode type, wherein both the first electrode type and the second electrode type are adapted for having an electrically-induced tissue-altering effect, and the electrosurgical probe is configured such that the first electrode type can be brought into contact with the tissue at the target site while the second electrode type does not contact the tissue at the target site.

85. The system of claim 84, wherein the second electrode type is remote from the tissue at the target site when the first type of electrode is in contact with the tissue at the target site.

86. The system of claim 84, wherein the first electrode type comprises at least one ablation electrode and the second electrode type comprises at least one digestion electrode.

87. The system of claim 84, further comprising a power supply, the first electrode type and the second electrode type independently coupled to opposite poles of the power supply, and the power supply adapted for independently supplying a high frequency AC voltage to the first electrode type and the second electrode type.

88. The system of claim 87, wherein one of the first electrode type and the second electrode type preferentially receives the power from the power supply.

89. The system of claim 88, wherein the first electrode type or the second electrode type receives up to about 100% of the power from the power supply.

90. The system of claim 87, wherein during a first mode of operation of the electrosurgical system the first electrode type preferentially receives the power from the power supply and during a second mode of operation of the electrosurgical system the second electrode type preferentially receives the power from the power supply.

91. The system of claim 84, wherein during a first mode of operation of the electrosurgical system the first electrode type receives from about 70% to about 100% of the power from the power supply and during a second mode of operation of the electrosurgical system the second electrode type receives from about 70% to about 100% of the power from the power supply.

92. An electrosurgical system, comprising:

a probe including a first electrode type and a second electrode type, wherein both the first electrode type and the second electrode type are adapted for having a tissue-altering effect, and wherein during a first mode of operation of the electrosurgical system the first electrode type functions as an active electrode while the second electrode type functions as a return electrode, and during a second mode of operation of the electrosurgical system the second electrode type functions as the active electrode while the first electrode type functions as the return electrode.

93. The electrosurgical system of claim 92, wherein the first electrode type comprises an ablation electrode adapted for ablation of tissue at a target site and the second electrode type comprises a digestion electrode adapted for digesting tissue fragments, and the probe is configured such that the digestion electrode avoids contact with the tissue at the target site when the ablation electrode is in contact with the tissue at the target site.

94. The electrosurgical system of claim 92, further comprising a power supply for supplying electric power to the probe, the first electrode type and the second electrode type independently coupled to opposite poles of the power supply, wherein during the first mode of operation of the electrosurgical system the first electrode type receives from about 60% to about 100% of the power from the power supply, and during the second mode of operation of the electrosurgical system the second electrode type receives from about 60% to about 100% of the power from the power supply.

95. The electrosurgical system of claim 92, wherein during use of the electrosurgical system, the first electrode type and the second electrode type alternately function as the active electrode.

96. The electrosurgical system of claim 92, wherein, during use of the electrosurgical system, the electrosurgical system alternates between the first mode of operation and the second mode of operation.

97. The electrosurgical system of claim 92, wherein the tissue-altering effect comprises cool ablation of tissue and the tissue which undergoes the tissue-altering effect is exposed to a temperature in the range of from about 45°

C. to about 90°

C.

98. The electrosurgical system of claim 92, wherein the first electrode type is adapted for cool ablation of tissue at a target site.

99. The electrosurgical system of claim 92, wherein the second electrode type is adapted for cool ablation of tissue fragments resected from a target site.