Apparatus and method for controlling ablation depth

• US 6,113,592 A
• Filed: 12/01/1998
• Issued: 09/05/2000
• 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.
• Primary Examiner(s): COHEN, LEE S
• Application Number:
  US09/203,996
• Time in Patent Office: 644 Days
• Field of Search: 606/34, 606/38, 606/40, 606/41, 606/49, 600/374, 607/99, 607/122
• US Class Current: 606/34
• 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 2018/00577 Ablation
• CPC Class Codes: A61B 2018/00738 Depth, e.g. depth of ablation
• 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

Abstract

During an ablation procedure in a chamber of the heart RF energy is used to form a myocardial lesion for treatment of some arrhythmias such as sustained supraventricular tachycardia and accessory pathways. A galvanic cell, formed by a metallic electrode having a first work function at the ablation site, a second metallic electrode having a second work function located remote from the ablation site and the intervening tissue serving as an electrolyte, produces an output current signal reflective of the formation of a lesion at the ablation site and is used to control the RF energy applied. A curve depicting the output current signal has a maximum value at the point a burn or lesion begins and thereafter begins to decrease in value. A short duration inflection or bump of the curve occurs prior to charring and carbonization of the lesion and predicts lesion formation of a sufficient depth. Thereafter, RF energy should no longer be applied to prevent unnecessary damage to the myocardial tissue. The bump in the curve serves as an accurate indicator to a physician of successful formation of the lesion.

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

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

(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 signal having a peak value corresponding with initial occurrence of ablation of the tissue at the ablation site followed by a decreasing value, an inflection in value and a decreasing value; and

(f) a control circuit responsive to said electrical signal 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 said electrical signal has reached a peak value and to terminate radiation of the ablation site upon detection of the inflection in value of said electrical signal.

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 a lesion at the ablation site as a result of ablation, and to terminate heating of the ablation site, said catheter assembly comprising in combination:

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

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

(c) a galvanic cell formed by said first electrode, said second electrode, and the tissue of the living being serving as an electrolyte intermediate said first electrode and said second electrode for generating an output current signal corresponding to the depth of the lesion in the tissue at the ablation site and having a characteristic inflection in value representative of the occurrence of adequate ablation of the tissue at the ablation site;

(d) an RF generator interconnected with said first electrode and said second electrode for applying RF energy through said first electrode 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 said output current signal.

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 having a first electrode 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 an output current signal having an inflection in value after a decrease in value reflective of the ablation sensed, said galvanic cell including;

said first electrode adapted to be located at the ablation site, a second electrode adapted to be displaced from the ablation site, and an electrolyte in electrical contact with said first and second electrodes; and

(e) a control circuit responsive to the inflection in value of said output current 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 first electrode in contact with the ablation site;

(c) irradiating the tissue at the ablation site with RF energy from the first electrode to heat the tissue at the ablation site, the first electrode being comprised 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 output current signal reflective of the occurrence of ablation of the tissue at the ablation site with 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 an inflection in value of the output current signal 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 first electrode of a probe;

(c) irradiating the ablation site with RF energy through the first electrode 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 first electrode, a second electrode displaced from the first electrode and an electrolyte in electrical contact with the first and second electrodes; and

(e) regulating the output of the RF generator with a control circuit responsive to an inflection of 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 an inflection in value of the electrical signal for terminating 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 followed by a decrease in value and the inflection in value.

8. Apparatus for sensing ablation of tissue at an ablation site during a tissue ablation procedure, said apparatus comprising in combination:

(a) a catheter having a tip for irradiating the ablation site with RF energy to perform the ablation procedure;

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

(c) an electrode adapted to be adjacent tissue;

(d) a galvanic cell formed by said tip, said electrode and the tissue for generating a unique electrical signal having an inflection in value responsive to ablation of the tissue at the ablation site; and

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

9. A method for sensing ablation of tissue at an ablation site during a tissue ablation procedure, said method comprising the steps of:

(a) transmitting RF energy to a tip from a source of RF energy;

(b) irradiating the ablation site with RF energy from the tip to perform the ablation procedure;

(c) locating an electrode adjacent tissue;

(d) generating an electrical signal having an inflection in value responsive to ablation of the tissue at the ablation site with a galvanic cell formed by the tip, the electrode and the tissue; and

(e) controlling the RF energy transmitted to the tip with a control circuit responsive to the electrical signal and terminating said step of irradiating upon generation of an inflection in value of the electrical signal.

10. Apparatus for sensing ablation of tissue at an ablation site during a tissue ablation procedure, said apparatus comprising in combination:

(a) a catheter having a tip for irradiating the ablation site with RF energy to perform the ablation procedure;

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

(c) an electrode adapted to be adjacent the tissue;

(d) a generator for generating an electrical signal having an inflection in value responsive to ablation of the tissue at the ablation site, said generator comprising said tip, said electrode and the tissue; and

(e) a control circuit for controlling the RF energy transmitted to said tip as a function of ablation of the tissue and in response to the electrical signal.

11. A method for sensing the occurrence of ablation of tissue at an ablation site during a tissue ablation procedure, said method comprising the steps of:

(a) transmitting RF energy from a source of RF energy to a tip;

(b) irradiating the ablation site with RF energy from the tip to perform the ablation procedure;

(c) locating an electrode adjacent the tissue;

(d) generating an electrical signal having an inflection in value responsive to ablation of the tissue at the ablation site with a generator formed by the tip, the electrode and the tissue; and

(e) controlling the RF energy transmitted to the tip with a control circuit as a function of the ablation of the tissue and responsive to the electrical signal.