Systems and methods for sensing sub-surface temperatures in body tissue

• US 6,113,591 A
• Filed: 10/01/1997
• Issued: 09/05/2000
• Est. Priority Date: 06/27/1994
• Status: Expired due to Fees

• Current Assignee: EP Technology (Boston Scientific Corporation)
• Original Assignee: EP Technology (Boston Scientific Corporation)
• Inventors: Panescu, Dorin, Swanson, David K., Fleischman, Sidney D., Bourne, Thomas M., Whayne, James G.
• Primary Examiner(s): Shay, David M.
• Application Number:
  US08/942,251
• Time in Patent Office: 1,070 Days
• Field of Search: 606/31-52
• US Class Current: 606/34
• CPC Class Codes: A61B 18/00 Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body eye surgery A61F9/007; ear surgery A61F11/00
• CPC Class Codes: A61B 18/12 by passing a current through the tissue to be heated, e.g. high-frequency current
• 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 2017/00017 Electrical control of surgical instruments
• CPC Class Codes: A61B 2017/00084 Temperature
• CPC Class Codes: A61B 2017/00243 cardiac
• CPC Class Codes: A61B 2018/00023 closed, i.e. without wound contact by the fluid
• CPC Class Codes: A61B 2018/00029 open
• CPC Class Codes: A61B 2018/00083 low, i.e. electrically insulating
• CPC Class Codes: A61B 2018/00095 high, i.e. heat conducting
• CPC Class Codes: A61B 2018/00351 Heart
• CPC Class Codes: A61B 2018/00577 Ablation
• CPC Class Codes: A61B 2018/00642 with feedback, i.e. closed loop control
• CPC Class Codes: A61B 2018/0066 without feedback, i.e. open loop control
• CPC Class Codes: A61B 2018/00666 using a threshold value
• CPC Class Codes: A61B 2018/00684 using lookup tables
• CPC Class Codes: A61B 2018/0069 using fuzzy logic
• CPC Class Codes: A61B 2018/00791 Temperature
• CPC Class Codes: A61B 2018/00815 measured by a thermistor
• 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 2018/1425 : Needle
• CPC Class Codes: A61B 2018/1435 : Spiral
• CPC Class Codes: A61B 2018/1861 : with an instrument inserted into a body lumen or cavity, e.g. a catheter
• CPC Class Codes: A61M 2230/50 : Temperature
• CPC Class Codes: A61N 1/056 : Transvascular endocardial electrode systems
• CPC Class Codes: A61N 1/403 : for thermotherapy, e.g. hyperthermia

Abstract

Systems and methods supply ablation energy to an electrode in contact with tissue to form a tissue-electrode interface. The system and methods sense, simultaneously with ablation, at least two tissue temperature conditions using at least two tissue temperature sensing elements which are held within a carrier that is substantially isolated from thermal conductive contact with the electrode. The carrier holds the tissue temperature sensing elements in a spaced apart relationship in thermal conductive contact with tissue at different depths beneath the tissue-electrode interface. The systems and methods control the supply of ablation energy to the electrode based, at least in part, upon temperatures sensed by the tissue temperature sensing elements.

Claims

1. An apparatus for ablating body tissue comprising

an ablation electrode having a thermal mass, the ablation electrode having a contact region for contacting tissue at a tissue surface, the ablation electrode adapted to be connected to a source of radio frequency energy to conduct radio frequency energy for transmission by the ablation electrode into the tissue surface contacting the tissue contact region, the ablation electrode including an interior well in the tissue contact region,

a tissue temperature sensing assembly carried within the interior well comprising a cap made of a thermal conductive material having a thermal conductivity that is at least 1.0 W/m K, and an insulating barrier made of thermal insulating material in the interior well to substantially thermally isolate the cap from the thermal mass of the ablation electrode, the cap having a distal end enclosing at least two tissue temperature sensing elements in a spaced apart relationship in thermal conductive contact with the thermal conductive material of the cap, the distal end of the cap projecting outside the interior well and beyond the tissue contact region and into thermal conductive contact with tissue at different distances beneath the tissue surface, the thermal conductive material of the cap reaching thermal equilibrium with tissue temperature conditions without dissipation by the thermal mass of the ablation electrode.

3. An apparatus according to claim 1 or 2 and further including

a generator coupled to the ablation electrode for supplying radio frequency ablation energy, and

a controller coupled to the tissue temperature sensing elements and the generator to control the supply of radio frequency ablation energy based, at least in part, upon tissue temperature conditions sensed by the tissue temperature sensing elements at different distances beneath the tissue surface.

4. An apparatus according to claim 1 or 2

wherein the distal end of the cap comprises a blunt surface that projects outside the interior well and into thermal conductive contact with tissue at different distances beneath the tissue surface.

5. An apparatus according to claim 4

wherein at least one of the tissue temperature sensing elements comprises a thermistor.

6. An apparatus according to claim 4

wherein at least one of the tissue temperature sensing elements comprises a thermocouple.

7. An apparatus according to claim 1 or 2

wherein the distal end of the cap comprises a sharpened point that penetrates tissue outside the interior well and makes thermal conductive contact with tissue at different distances beneath the tissue surface.

8. An apparatus according to claim 7

wherein at least one of the tissue temperature sensing elements comprises a thermistor.

9. An apparatus according to claim 7

wherein at least one of the tissue temperature sensing elements comprises a thermocouple.

10. An apparatus according to claim 1 or 2

and further including a mechanism attached to the cap to selectively move the the cap in the interior well between a first position in which the distal end of the cap and the tissue temperature sensing elements are withdrawn from thermal conductive contact with tissue beneath the the tissue surface and a second position in which the distal end of the cap and the tissue temperature sensing elements are placed into thermal conductive contact with tissue at different distances beneath the tissue surface.

11. A system according to claim 10

wherein the mechanism is configured to rotate the cap in the interior well to thereby move the distal end of the cap beyond the tissue contact region of the ablation electrode.

12. A system according to claim 10

wherein the mechanism is configured to move the distal end of the cap beyond the tissue contact region of the ablation electrode without rotation of the cap in the interior well.

13. An apparatus according to claim 1 or 2

wherein the cap includes spaced regions comprising the thermal conductive material, each spaced region being in thermal conductive contact with one of the tissue temperature sensing elements, the spaced regions being substantially isolated from thermal conductive conduct with each other and with the thermal mass of the ablation electrode.

14. An apparatus according to claim 13

wherein at least one of the regions includes a metallic material.

15. An apparatus according to claim 14

wherein the metallic material is selected from the group consisting of stainless steel, gold, silver alloy, platinum, copper, nickel, titanium, aluminum, and compositions containing stainless steel, gold, silver, platinum, copper, nickel, titanium, and aluminum.

2. An apparatus for ablating body tissue comprising

an ablation electrode having a thermal mass, the ablation element having a contact region for contacting a tissue surface, the ablation electrode being adapted to be connected to a source of radio frequency ablation energy to conduct the radio frequency ablation energy for transmission by the ablation electrode into the tissue surface contacting the tissue contact region, the ablation electrode including an interior well in the tissue contact region,

a tissue temperature sensing assembly carried within the interior well comprising a cap made of a thermal conductive material having a thermal conductivity that is at least 1.0 W/m K, and an insulating barrier made of thermal insulating material in the interior well to substantially thermally isolate the cap from the thermal mass of the ablation electrode, the cap having a distal end enclosing at least two tissue temperature sensing elements in a spaced apart relationship in thermal conductive contact with the thermal conductive material of the cap while being substantially isolated from electrical contact with the cap, the distal end of the cap projecting outside the interior well and beyond the tissue contact region and into thermal conductive contact with tissue at different distances beneath the tissue surface to obtain a profile of tissue temperatures beneath the tissue surface, the thermal conductive material of the cap reaching thermal equilibrium with tissue temperature conditions without dissipation by the thermal mass of the ablation electrode.