Method of using endocardial impedance for assessing tissue heating during ablation

• US 5,562,721 A
• Filed: 05/10/1995
• Issued: 10/08/1996
• Est. Priority Date: 01/28/1994
• Status: Expired due to Term

• Current Assignee: Catholic University of America (Catholic University), Philadelphia Heart Institute, University of Pennsylvania
• Original Assignee: Catholic University of America (Catholic University), Philadelphia Heart Institute, University of Pennsylvania
• Inventors: Chang, Isaac, Marchlinski, Francis E., Gottlieb, Charles D., Schwartzman, David S, Mirotznik, Mark S., Foster, Kenneth R.
• Primary Examiner(s): Sykes, Angela D.
• Assistant Examiner(s): HUANG, STEPHEN D
• Application Number:
  US08/438,326
• Time in Patent Office: 517 Days
• Field of Search: 128/654, 128/672, 128/695 R, 128/734, 128/693, 607/41, 607/99
• US Class Current: 607/99
• CPC Class Codes: A61B 18/1402 Probes for open surgery
• 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 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00875 Resistance or impedance
• CPC Class Codes: A61B 2018/126 bipolar
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 2090/065 for measuring contact or contact pressure
• CPC Class Codes: A61N 1/025 Digital circuitry features of electrotherapy devices, e.g. memory, clocks, processors
• CPC Class Codes: A61N 1/05 for implantation or insertion into the body, e.g. heart electrode A61N1/06 takes precedence
• CPC Class Codes: A61N 1/056 Transvascular endocardial electrode systems
• CPC Class Codes: A61N 1/40 Applying electric fields by inductive or capacitive coupling microwave apparatus A61N5/00; Applying radio-frequency signals

Abstract

A method of locating infarcted myocardial tissue in a beating heart includes the step of inserting an impedance measuring tip of a catheter into the chamber of the beating heart, particularly the left or right ventricle, and measuring the impedance of the endocardium at various locations within the chamber of the beating heart. The values measured are compared to impedance values with a predetermined range of values to identify an infarcted area of myocardium and distinguish such area from normal myocardium. The measurements are also compared to a range of values for an infarction border zone. In accordance with the invention, the infarction border zone may be located. The infarction border zone is a significant source of arrhythmia, and particularly of ventricular tachycardia. Further, in accordance with the methods of the present invention, the risk of arrhythmia in a beating heart may be substantially reduced or eliminated by ablating endocardium within the infarction border zone utilizing the same catheter tip. Impedance measurements may also be utilized to assess the adequacy of the electrode-tissue contact, particularly in a fluid filled body organ or cavity. Further, the effectiveness of the ablation of the tissue may be determined by determining the degree of heating of the tissue by measuring the change in impedance in the area of ablation.

Claims

1. A method for assessing effectiveness of tissue ablution, comprising the steps of:

measuring impedance of tissue at an ablation area at normal body temperature to establish a baseline impedance value;

monitoring impedance of the tissue in an area being ablated immediately after application of ablation energy;

comparing the base line impedance value to the monitored tissue impedance to determine an absolute impedance measurement; and

correlating an amount of tissue heating to the absolute impedance measurement, a substantially linear decrease in impedance corresponding to rising tissue temperature and effective tissue ablation.

2. A method in accordance with claim 1, wherein the previously recited impedance measuring steps are carried out utilizing an electrode mounted on a tip of a catheter.

3. A method in accordance with claim 2, wherein said method is utilized within a beating heart to determine adequacy of endocardial tissue ablation in a beating heart.

4. A method for assessing effectiveness of tissue ablation, comprising the steps

inserting into a beating heart a catheter having an electrode with a design which comes directly into contact with endocardium in such a manner as to minimize contact of a measuring electrode with blood in the beating heart;

measuring impedance of endocardium at an ablation area at normal body temperature to establish a baseline impedance value;

monitoring impedance of the endocardium in an area being ablated immediately after application of ablation energy;

comparing the baseline impedance value to the monitored endocardium impedance to determine an absolute impedance measurement; and

correlating an amount of endocardium heating to the absolute impedance measurement, a substantially linear decrease in impedance corresponding to rising tissue temperature and effective tissue ablation.

5. A method for assessing effectiveness of tissue ablation in accordance with claim 4 wherein said catheter electrode is placed in it entirety directly in contact with the endocardium during said impedance measuring steps.

6. A method for assessing effectiveness of tissue ablation in accordance with claim 4 wherein said steps of measuring impedance are performed using a sharp tipped catheter electrode to achieve exclusive tissue contact by piercing endocardium.