Apparatus and method for determining ablation

• US 5,868,737 A
• Filed: 05/06/1997
• Issued: 02/09/1999
• Est. Priority Date: 06/09/1995
• Status: Expired due to Fees

• Current Assignee: Engineering & Research Associates Inc. (Machine Solutions, Inc.)
• Original Assignee: Engineering & Research Associates Inc. (Machine Solutions, Inc.)
• Inventors: Taylor, Junius E., Acker, Loren C.
• Primary Examiner(s): COHEN, LEE S
• Application Number:
  US08/851,879
• Time in Patent Office: 644 Days
• Field of Search: 606/34, 606/38, 606/40, 606/41, 606/49, 600/374, 607/122, 607/99
• US Class Current: 606/34
• 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 2018/00041 Heating, e.g. defrosting
• CPC Class Codes: A61B 2018/00577 Ablation
• CPC Class Codes: A61B 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00738 Depth, e.g. depth of ablation
• CPC Class Codes: A61B 2018/00791 Temperature
• CPC Class Codes: A61B 2018/00827 Current
• CPC Class Codes: A61B 2018/00839 Bioelectrical parameters, e.g. ECG, EEG
• CPC Class Codes: A61B 2018/00875 Resistance or impedance
• CPC Class Codes: A61B 2018/00892 Voltage
• CPC Class Codes: A61B 2018/124 switching the output to different electrodes, e.g. sequentially
• CPC Class Codes: A61B 2562/043 in a linear array
• CPC Class Codes: A61B 5/287 Holders for multiple electrodes, e.g. electrode catheters for electrophysiological study [EPS]
• CPC Class Codes: A61B 5/6855 with a distal curved tip
• CPC Class Codes: A61N 1/06 for high-frequency therapy
• CPC Class Codes: A61N 1/403 for thermotherapy, e.g. hyperthermia

Abstract

A catheter for use in an electrophysiological procedure to ablate a site includes a metallic tip having a first work function and energized by a source of RF energy. The RF energy return path is through a relatively large plate of a metallic material having a second work function and disposed at a location removed from the ablation site. The difference in work functions of the tip and the plate, operating in the presence of an electrolyte represented by intermediate tissue, produces an exchange of electrical charges through chemical reaction to create a galvanic cell. By loading the galvanic cell with a shunt resistor, it becomes a current source providing a current signal having a peak value representative of occurrence of tissue damage. This representation is used to regulate the RF energy applied to the ablation site.

Claims

1. Apparatus for ablating tissue at an ablation site in the heart of a human being while avoiding the possibility of tip coagulation, tissue sticking or tissue perforation, said apparatus comprising in combination:

(a) a source of RF energy for irradiating the tissue at the ablation site to cause a temperature rise of the tissue at the ablation site;

(b) a catheter having a tip for contactingly engaging the ablation site and for irradiating the tissue with RF energy to heat the tissue at the ablation site, said tip comprising a first electrode of material having a first work function;

(c) transmission means for conveying RF energy from said source to said tip;

(d) a second electrode displaced from said first electrode and of material having a second work function different from the first work function for electrically contacting an area of tissue of the human being;

(e) a galvanic cell formed by said first electrode, said second electrode and the tissue of the human being serving as an electrically interconnecting electrolyte for generating an electrical current having a peak value corresponding with the occurrence of ablation of the tissue at the ablation site; and

(f) a control circuit responsive to said electrical current generated by said galvanic cell for regulating the operation of said source of RF energy to control RF radiation of the ablation site before and after the electrical current has reached a peak value.

2. A catheter assembly for irradiating tissue at an ablation site of a living being to raise the temperature of the ablation site, to sense the occurrence of ablation, and to terminate heating of the ablation site, said catheter assembly comprising in combination:

(a) a catheter having a tip locatable at the ablation site, said tip being formed of a material having a first work function;

(b) an electrode displaced from said tip and adapted to be in electrical contact with the tissue of the living being, said electrode being formed of a material having a second work function different from the first work function;

(c) a galvanic cell formed by said tip, said electrode, and the tissue of the living being serving as an electrolyte intermediate said tip and said electrode for generating a current corresponding to the temperature of the tissue at the ablation site and having a characteristic representative of the occurrence of ablation of the tissue at the ablation site;

(d) an RF generator interconnected with said tip and said electrode for applying RF energy through said tip to the tissue at the ablation site to heat the tissue at the ablation site; and

(e) a control circuit for regulating said RF generator as a function of the characteristic of the current.

3. Apparatus for ablating tissue at an ablation site, said apparatus comprising in combination:

(a) an RF generator for applying RF energy to the ablation site to heat the ablation site tissue;

(b) a probe adapted to be in contact with the ablation site tissue for irradiating the ablation site tissue with RF energy;

(c) a transmission line for conveying RF energy from said RF generator to said probe;

(d) a galvanic cell for sensing ablation at the ablation site tissue and for producing a signal reflective of the ablation sensed, said galvanic cell including;

said probe, an electrode displaced from said probe and displaced from the ablation site, and an electrolyte in electrical contact with said probe and said electrode; and

(e) a control circuit responsive to said signal produced by said galvanic cell for controlling the RF energy applied to said probe.

4. A method for ablating tissue at an ablation site in the heart of a human being, said method comprising the steps of:

(a) generating RF energy from a source of RF energy;

(b) conveying RF energy from the source to a tip in contact with the ablation site;

(c) irradiating the tissue at the ablation site with RF energy from the tip to heat the tissue at the ablation site, the tip comprising a first electrode of material having a first work function;

(d) electrically contacting an area of tissue of the human being with a second electrode displaced from the first electrode and of material having a second work function different from the first work function;

(e) generating an electrical current reflective of the occurrence of ablation of the tissue at the ablation site by a galvanic cell formed by the first electrode, the second electrode and the tissue of the human being serving as an electrically interconnecting electrolyte; and

(f) regulating the operation of the source of RF energy with a control circuit responsive to the electrical current generated by said generating step to control RF irradiation of the ablation site.

5. A method for ablating tissue at an ablation site, said method comprising the steps of:

(a) generating RF energy with an RF generator;

(b) conveying RF energy from the RF generator through a transmission line to a probe;

(c) irradiating the ablation site with RF energy through the probe proximate the ablation site;

(d) producing a signal reflective of the occurrence of ablation at the ablation site tissue with a galvanic cell, the galvanic cell comprising the probe, an electrode displaced from the probe and an electrolyte in electrical contact with the probe and the electrode; and

(e) regulating the output of the RF generator with a control circuit responsive to the signal produced by said producing step.

6. Apparatus for detecting the occurrence of ablation of tissue at an ablation site, said apparatus comprising in combination:

(a) a catheter having a tip for contacting the ablation site to irradiate the ablation site with RF energy to heat the tissue;

(b) a source of RF energy for transmitting RF energy to said tip;

(c) a galvanic cell using the tissue as an electrolyte for generating an electrical signal representative of the occurrence of ablation at the ablation site; and

(d) a control circuit responsive to the electrical signal for controlling the RF energy transmitted to said tip.

7. The apparatus as set forth in claim 6 wherein the electrical signal generated by said galvanic cell depicts a peak value upon occurrence of ablation.