Apparatus and method for predicting ablation depth

• US 6,322,558 B1
• Filed: 10/01/1999
• Issued: 11/27/2001
• 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: He, Ding Sheng, Taylor, Junius E.
• Primary Examiner(s): COHEN, LEE S
• Application Number:
  US09/410,407
• Time in Patent Office: 788 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 18/1206 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

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 formation and thereafter decreases in value. A short duration inflection or bump of the curve occurs prior to charring and carbonization of the lesion. A further curve representative of the impedance of the tissue between the electrodes is displayed; it shows a rapid impedance rise upon occurrence of carbonization and charring of the tissue. The impedance rise occurs after the bump of the output current signal occurs. By terminating application of RF power after occurrence of the bump, and before impedance rise charring of the tissue and other negative results will not occur. A physician can use the bump and the impedance rise as limit indicators for determining lesion formation of a predictable depth without incurring unwanted damage.

Claims

1. Apparatus for ablating tissue at an ablation site to form a lesion of predictable depth 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 upon irradiation of the tissue at the ablation site with RF energy, said 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 for regulating the operation of said source of RF energy to control radiation of RF energy at the ablation site upon detection of the inflection in value of said electrical signal.

2. The apparatus as set forth in claim 1 including means for detecting a rise in impedance of the tissue at the ablation site subsequent to occurrence of the inflection value of said electrical signal and reflective of the tissue and defining an end limit for terminating application of RF energy.

3. Apparatus 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 apparatus 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 having a peak value reflective of occurrence of ablation and formation of a lesion in the tissue at the ablation site and having a characteristic inflection in value representative of the occurrence of adequate depth of 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 applying RF energy from said RF generator to said first and second electrodes and for terminating application of RF energy after said output current signal has reached a peak value.

4. Apparatus for ablating tissue at an ablation site, which tissue has an abrupt increase in impedance upon occurrence of charring of the tissue, 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 and for producing an output current signal having a peak value reflective of the occurrence of ablation and having an inflection in value subsequent to a decrease in value after the peak value and reflective of the ablation, said galvanic cell including;

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

(e) a circuit for terminating application of RF energy to the ablation site subsequent to the inflection in value of said output current signal produced by said galvanic cell for controlling the RF energy applied to said probe.

5. 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 having a peak value reflective of the occurrence of ablation of the tissue at the ablation site and an inflection in value after occurrence of the peak value 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) terminating application of RF energy at the ablation site subsequent to the inflection in value of the output current signal generated by said generating step to prevent charring of the tissue at the ablation site.

6. 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 having a peak value reflective of the occurrence of ablation at the ablation site tissue and an inflection in value after occurrence of the peak value 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 electrode; and

(e) terminating application of RF energy at the ablation site subsequent to the inflection of the signal produced by said producing step to avoid charring of the tissue.

7. 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 having a peak value followed by a decrease in value representative of the occurrence of ablation at the ablation site and a subsequent inflection in value representative of a predictable depth of ablation; and

(d) a circuit for terminating the RF energy transmitted to said tip subsequent to the inflection in value of the electrical signal.

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 representative of a predictable depth of ablation of the tissue at the ablation site; and

(e) a circuit responsive to said unique electrical signal for terminating 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 representative of a predictable depth of ablation of the tissue at the ablation site with a galvanic cell formed by the tip, the electrode and the tissue; and

(e) terminating the RF energy transmitted to the tip upon generation of the 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 representative of a predictable depth of ablation of the tissue at the ablation site, said generator comprising said tip, said electrode and the tissue; and

(e) a circuit for terminating the RF energy transmitted to said tip in response to the inflection in value of 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 representative of a predictable depth ablation of the tissue at the ablation site with a generator formed by the tip, the electrode and the tissue; and

(e) terminating the RF energy transmitted to the tip in response to inflection in value of the electrical signal.

12. Apparatus for ablating tissue at an ablation site to form a lesion of predictable depth 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 suitable for electrically contacting an area of tissue of the human being, such that said first electrode, said second electrode and the tissue of the human being are capable of forming a galvanic cell wherein the tissue of the human being can serve as an electrically interconnecting electrolyte for generating an electrical signal upon irradiation of the tissue at the ablation site with RF energy, said 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

(e) a control circuit for regulating the operation of said source of RF energy to control radiation of RF energy at the ablation site upon detection of the inflection in value of said electrical signal.

13. The apparatus as set forth in claim 12 including means for detecting a rise in impedance of the tissue at the ablation site subsequent to occurrence of the inflection value of said electrical signal and reflective of the tissue and defining an end limit for terminating application of RF energy.

14. Apparatus 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 apparatus 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 formed of a material having a second work function different from the first work function which electrode is adapted for electrical contact with the tissue of the living being and is capable of forming a galvanic cell with said first electrode and the tissue of the living being wherein the tissue of the living being can serve as an electrolyte intermediate said first electrode and said second electrode for generating an output current signal having a peak value reflective of occurrence of ablation and formation of a lesion in the tissue at the ablation site and having a characteristic inflection in value representative of the occurrence of adequate depth of ablation of the tissue at the ablation site;

(c) 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

(d) a control circuit for applying RF energy from said RF generator to said first and second electrodes and for terminating application of RF energy after inflection of said output current signal.

15. Apparatus for ablating tissue at an ablation site, which tissue has an abrupt increase in impedance upon occurrence of charring of the tissue, 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 second electrode displaced from said first electrode and adapted for contact with tissue displaced from the ablation site and which in combination with said first electrode and an electrolyte in electrical contact with said first and second electrodes is capable of forming a galvanic cell which can produce an output current signal having a peak value reflective of the occurrence of ablation and having an inflection in value subsequent to a decrease in value after the peak value and reflective of the ablation, and;

(e) a circuit for terminating application of RF energy to the ablation site subsequent to the inflection in value of said output current signal produced by said galvanic cell for controlling the RF energy applied to said probe.

16. 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) means suitable for forming a galvanic cell which galvanic cell uses the tissue as an electrolyte for generating an electrical signal having a peak value followed by a decrease in value representative of the occurrence of ablation at the ablation site and a subsequent inflection in value representative of a predictable depth of ablation; and

(d) a circuit for terminating the RF energy transmitted to said tip subsequent to the inflection in value of the electrical signal.

17. 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 contactable with adjacent tissue;

(d) said tip, said electrode and the tissue being capable of forming a galvanic cell for generating a unique electrical signal having an inflection in value representative of a predictable depth of ablation of the tissue at the ablation site; and

(e) a circuit for terminating the RF energy transmitted to said tip in response to the inflection in value of said unique electrical signal.

18. 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 an area of tissue;

(d) said tip, said electrode and the tissue being capable of forming a generator for generating an electrical signal having an inflection in value representative of a predictable depth of ablation of the tissue at the ablation site; and

(e) a circuit for terminating the RF energy transmitted to said tip in response to the inflection in value of said electrical signal.

19. Method for determining the occurrence of ablation of tissue at an ablation site by determining the temperature of a region of the tissue, said method comprising the steps of:

(a) contacting a first electrode with a first region of tissue;

(b) contacting a second electrode with a second region of tissue to form a galvanic cell from the first electrode, the second electrode and the tissue as an interconnecting electrolyte; and

(c) determining the current in said galvanic cell as representative of the temperature at the ablation site.

20. Method as set forth in claim 19 further comprising the step of calibrating the current in the galvanic cell with the temperature of the first region of tissue.

21. Method for determining the occurrence of ablation of tissue at an ablation site by determining the conductivity of a first region of the tissue which has been subjected to ablation by RF energy, said method comprising the steps of:

(a) contacting a first electrode with the first region;

(b) contacting a second electrode with a second region of tissue to form a galvanic cell comprising the first electrode, the second electrode and the tissue as an interconnecting electrolyte; and

(c) determining the current in said galvanic cell;

whereby, the ability of the ablated region of tissue to conduct a current is representative of the degree of ablation occurred.

22. Method as set forth in claim 21 wherein the first region of tissue is heart tissue.

23. Method as set forth in claim 21 wherein the second electrode is adapted to be contactable with tissue adjacent the ablation site.