Systems and methods for ablating body tissue using predicted maximum tissue temperature

• US 5,735,846 A
• Filed: 05/01/1995
• Issued: 04/07/1998
• Est. Priority Date: 06/27/1994
• Status: Expired due to Term

• Current Assignee: EP Technologies Incorporated (Boston Scientific Corporation)
• Original Assignee: EP Technologies Incorporated (Boston Scientific Corporation)
• Inventors: Panescu, Dorin, Swanson, David K., Fleischman, Sidney D.
• Primary Examiner(s): PEFFLEY, MICHAEL F
• Application Number:
  US08/431,775
• Time in Patent Office: 1,072 Days
• Field of Search: 606/27-31, 606/41, 606/42, 606/45-50, 607/96, 607/98, 607/100-105, 607/115, 607/116, 607/122, 604/21, 604/22
• US Class Current: 606/41
• 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 18/20 using laser
• CPC Class Codes: A61B 2017/00092 using thermocouples
• CPC Class Codes: A61B 2017/00154 pulsed
• CPC Class Codes: A61B 2017/003 Steerable
• CPC Class Codes: A61B 2018/00011 with fluids
• 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 2018/00047 using Peltier effect
• 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 2018/00101 low, i.e. thermally insulating
• CPC Class Codes: A61B 2018/00107 Coatings on the energy applicator
• CPC Class Codes: A61B 2018/0016 Energy applicators arranged in a two- or three dimensional array
• CPC Class Codes: A61B 2018/00351 Heart
• CPC Class Codes: A61B 2018/00577 Ablation
• CPC Class Codes: A61B 2018/00636 Sensing and controlling the application of energy
• CPC Class Codes: A61B 2018/0066 : without feedback, i.e. open loop control
• CPC Class Codes: A61B 2018/0069 : using fuzzy logic
• CPC Class Codes: A61B 2018/00744 : Fluid flow
• CPC Class Codes: A61B 2018/00761 : Duration
• CPC Class Codes: A61B 2018/00791 : Temperature
• CPC Class Codes: A61B 2018/00797 : measured by multiple temperature sensors
• CPC Class Codes: A61B 2018/00803 : with temperature prediction
• CPC Class Codes: A61B 2018/00815 : measured by a thermistor
• CPC Class Codes: A61B 2018/00821 : measured by a thermocouple
• CPC Class Codes: A61B 2018/00886 : Duration
• 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 2018/128 : generating two or more frequencies
• 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

Abstract

Systems and methods ablate body tissue using an electrode for contacting tissue at a tissue-electrode interface to transmit ablation energy at a determinable power level. The systems and methods include an element to remove heat from the electrode at a determinable rate. The systems and methods employ a processing element to derive a prediction of the maximum tissue temperature condition occurring beneath the tissue-electrode interface. The processing element controls the power level of ablation energy transmitted by the electrode, or the rate at which the electrode is cooled, or both, based, at least in part, upon the maximum tissue temperature prediction.

Claims

1. An apparatus for ablating body tissue comprising

a source of ablation energy,

an electrode coupled to the source for contacting tissue at a tissue-electrode interface to transmit ablation energy at a determinable power level to create a maximum tissue temperature condition beneath the tissue-electrode interface,

a heat removal element connected to remove heat from the electrode at a determinable rate,

a temperature sensing element in thermal conductive contact with the electrode to sense temperature of the electrode,

a processing element coupled to the source and the temperature sensing element to sample the power level at which the electrode transmits ablation energy and the temperature of the electrode sensed by the temperature sensing element, to derive therefrom a prediction of the maximum tissue temperature condition without sampling an actual tissue temperature beneath the tissue-electrode interface, and to control the power level of ablation energy transmitted by the electrode based, at least in part, upon the prediction of the maximum tissue temperature.

4. An apparatus according to claim 1 or 2 or 3

wherein the heat removal element includes a source of cooling medium and a conduit coupling the source of cooling medium to the electrode to deliver the cooling medium into thermal conductive contact with the electrode,

wherein the processing element includes a medium temperature sensor coupled to the processing element to sense temperature variations in the cooling medium occurring as a result of thermal conductive contact with the electrode, and

wherein the processing element derives a heat removal rate at which heat is removed from the electrode based upon temperature variations sensed by the medium sensor.

wherein the processing element controls the heat removal rate based, at least in part, upon the prediction of the maximum tissue temperature.

5. An apparatus according to claim 4

wherein the cooling medium has a heat capacity (expressed in J/kg K), and a mass flow rate (expressed in kg/sec) when delivered into thermal conductive contact with the electrode,

wherein the heat removal rate is expressed as Å

, where where;

space="preserve" listing-type="equation">Å

c×

Δ

T×

RATE

is the heat capacity of the cooling medium,

Δ

T is the temperature drop in the cooling medium (expressed in K) sensed by the medium sensor, and

RATE is the mass flow rate of the cooling medium.

6. An apparatus according to claim 1 or 2 or 3

wherein the source generates radio frequency energy for transmission by the electrode.

7. An apparatus according to claim 1 or 2

wherein the processing element includes a neural network predictor to derive the prediction of the maximum tissue temperature condition without sampling an actual tissue temperature at the tissue-electrode interface.

2. An apparatus for ablating body tissue comprising

a source of ablation energy,

an electrode coupled to the source for contacting tissue at a tissue-electrode interface to transmit ablation energy at a determinable power level to create a maximum tissue temperature condition beneath the tissue-electrode interface,

a heat removal element connected to remove heat from the electrode at a determinable rate,

a temperature sensing element in thermal conductive contact with the electrode to sense temperature of the electrode,

a processing element coupled to the source, the temperature sensing element, and the heat removal element to sample the power level at which the electrode transmits ablation energy, the temperature of the electrode sensed by the temperature sensing element, and the rate at which heat is removed from the electrode by the heat removal element, to derive therefrom a prediction of the maximum tissue temperature condition without sampling an actual tissue temperature beneath the tissue-electrode interface, and to control the power level of ablation energy transmitted by the electrode based, at least in part, upon the prediction of the maximum tissue temperature.

3. An apparatus for ablating body tissue comprising

a source of ablation energy,

an electrode coupled to the source for contacting tissue at a tissue-electrode interface to transmit ablation energy at a determinable power level to create a maximum tissue temperature condition beneath the tissue-electrode interface,

a heat removal element connected to remove heat from the electrode at a determinable rate,

a temperature sensing element in thermal conductive contact with the electrode to sense temperature of the electrode, and

a processing element coupled to the source, the heat removal element, and the temperature sensing element for retaining a function that correlates an observed relationship among maximum tissue temperature below the tissue-electrode interface and a set of predetermined operating conditions;

for sampling an actual operating condition from at least one of the source, the heat removal element, and the temperature sensing element, without sampling an actual tissue temperature beneath the tissue-electrode interface;

for comparing the actual operating condition to the function;

for deriving from the comparison a prediction of the maximum tissue temperature; and

for controlling the power level of ablation energy transmitted by the electrode based, at least in part, upon the prediction of the maximum tissue temperature.

8. A method for ablating body tissue comprising the steps of

placing an electrode in contact with body tissue to form a tissue-electrode interface,

supplying ablation energy to the electrode at a determinable power level to create a maximum tissue temperature condition beneath the tissue-electrode interface,

conducting heat from the electrode at a determinable heat conduction rate,

sensing temperature of the electrode,

sensing the power level transmitted by the electrode,

deriving from the sensed temperature of the electrode and sensed power level a prediction of the maximum tissue temperature condition without sensing an actual temperature beneath the tissue-electrode interface, and

controlling the power level based, at least in part, upon the prediction of the maximum tissue temperature.

16. A method according to claim 8 or 9

wherein the step of deriving the predicted maximum tissue temperature uses a neural network predictor.

9. A method for ablating body tissue comprising the steps of

placing an electrode in contact with body tissue to form a tissue-electrode interface,

supplying ablation energy to the electrode at a determinable power level to create a maximum tissue temperature condition beneath the tissue-electrode interface,

conducting heat from the electrode at a determinable heat conduction rate,

sensing temperature of the electrode,

sensing the power level transmitted by the electrode,

sensing the heat conduction rate,

deriving from the sensed temperature of the electrode, sensed power level, and sensed heat conduction rate a prediction of the maximum tissue temperature condition without sensing an actual tissue temperature beneath the tissue-electrode interface, and

controlling the power level based, at least in part, upon the prediction of the maximum tissue temperature.

10. A method for ablating body tissue comprising the steps of

placing an electrode in contact with body tissue to form a tissue-electrode interface,

supplying ablation energy to the electrode at a determinable power level to create a maximum tissue temperature condition beneath the tissue-electrode interface,

conducting heat from the electrode at a determinable heat conduction rate,

sensing temperature of the electrode,

sensing the power level transmitted by the electrode,

comparing the sensed temperature of the electrode and sensed power level to a function that correlates an observed relationship among maximum tissue temperature below the tissue-electrode interface and a set of predetermined operating conditions including temperature of the electrode and power level,

deriving from the comparison a prediction of the maximum tissue temperature condition without sensing an actual tissue temperature beneath the tissue-electrode interface, and

controlling the power level based, at least in part, upon the prediction of the maximum tissue temperature.

11. A method according to claim 8 or 9 or 10

and further including the step of controlling the heat conduction rate based, at least in part, upon the predicated maximum tissue temperature condition.

12. A method according to claim 11

wherein the step of conducting heat removes heat by directing a cooling medium into thermal conductive contact with the electrode.

13. A method according to claim 12

wherein the heat conduction rate is sensed based upon temperature variations in the cooling medium as a result of thermal conductive contact with the electrode.

14. A method according to claim 12

wherein the heat conduction rate is derived from a heat removal rate expressed as Å

, where

space="preserve" listing-type="equation">Å

=c×

Δ

T×

RATE

where;

c is the heat capacity of the cooling medium (in J/kg K),

Δ

T is the temperature drop in the cooling medium due to thermal conductive contact with the electrode (in K), as sensed by the second sensing element, and

RATE is the mass flow rate of the cooling medium when coming into thermal conductive contact with the electrode (in kg/sec).

15. A method according to claim 8 or 9 or 10

wherein radio frequency energy is supplied to the electrode.

17. A method according to claim 10

wherein the step of conducting heat removes heat by directing a cooling medium into thermal conductive contact with the electrode,

and further including the step of sensing the flow rate at which the cooling medium is directed into thermal conductive contact with the electrode,

wherein the set of predetermined operating conditions of the function includes flow rate of the cooling media and the comparison step also compares the sensed flow rate to the function.