Method for establishing defibrillation threshold for a cardiac defibrillator

• US 5,346,506 A
• Filed: 11/10/1992
• Issued: 09/13/1994
• Est. Priority Date: 11/10/1992
• Status: Expired due to Term

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation), Regents of the University of California (University of California)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Mower, Morton M., Chen, Peng S.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): Getzow, Scott M.
• Application Number:
  US07/974,049
• Time in Patent Office: 672 Days
• Field of Search: 607/5, 607/6, 607/7, 607/8
• US Class Current: 607/7
• CPC Class Codes: A61N 1/385 Devices for inducing an abnormal cardiac function, e.g. fibrillation
• CPC Class Codes: A61N 1/3943 for threshold determination

Abstract

A method of determining a defibrillation threshold for an implantable cardiac defibrillator, based upon determining the 50% probability of reaching the upper limit of vulnerability. The 50% probability of reaching the upper limit of vulnerability at the mid-upslope of the T-wave is found to closely approximate the 50% probability of successful defibrillation used to set the shock energy level of the defibrillator. A delayed up-down algorithm is used to determine the shock strength associated with 50% probability of reaching the upper limit of vulnerability.

Claims

1. A method of determining a defibrillation threshold, said method comprising the steps of;

implanting defibrillation electrodes on or about the heart;

observing the electrical activity of the heart so as to determine the occurrence of ventricular depolarization, such that the periodic occurrence of the mid-upslope of the T-wave (ventricular repolarization) may be determined;

applying an initial electrical test shock to the heart through said defibrillation electrodes with an energy level which is a best a priori estimate of the 50% probability of reaching the upper limit of vulnerability;

sensing for the occurrence of ventricular fibrillation following application of said initial electrical test shock;

applying a subsequent electrical test shock to the heart via said defibrillation electrodes reduced in magnitude by a predetermined amount from initial test shock, if ventricular fibrillation has not occurred as a result of said initial test shock;

again sensing for the occurrence of ventricular fibrillation following application of said subsequent test shock;

repeating the steps of applying subsequent electrical test shocks each reduced in magnitude by said predetermined amount from said prior test shock, and sensing for ventricular fibrillation after each said test shock;

upon sensing ventricular fibrillation following the application of a test shock, the energy level of said test shock which causes ventricular fibrillation being considered a second data point and the energy level of the test shock prior to said test shock which causes ventricular fibrillation being considered a first data point, apply a subsequent test shock increased in magnitude by said predetermined amount from the test shock considered said second data point, said subsequent test shock being considered a third data point;

sense for the occurrence of defibrillation and deliver salvage shock if defibrillation does not occur;

if defibrillation is not sensed following said test shock considered said third data point, apply a test shock increased in magnitude by said predetermined amount from said test shock considered said third data point, said test shock being considered a fourth data point;

again sense for ventricular fibrillation and deliver a salvage shock if defibrillation has not occurred;

if ventricular fibrillation is sensed a fifth data point is predicted to be of increased magnitude by said predetermined amount from said shock considered said fourth data point;

if ventricular fibrillation is not sensed then a fifth data point in predicted to be of decreased magnitude by said predetermined amount from said shock considered said fourth data point;

if defibrillation has occurred following the application of the test shock considered said third data point, apply a test shock decreased in magnitude by said predetermined amount, said test shock being considered a fourth data point;

again sense for ventricular fibrillation and deliver a salvage shock if ventricular fibrillation occurs;

if ventricular fibrillation is sensed said fifth data point is predicted to be of increased magnitude by said predetermined amount from said fourth data point;

if ventricular fibrillation is not sensed then said fifth data point is predicted to be of decreased magnitude by said predetermined amount from said fourth data point; and

,

use the average of said five data points as the shock strength associated with 50% probability of successful defibrillation, for establishing the defibrillation threshold.