Subcutaneous cardiac signal discrimination employing non-electrophysiologic signal

Abstract

A cardiac monitoring and/or stimulation system includes a housing coupled to a plurality of electrodes configured for subcutaneous non-intrathoracic sensing. A signal processor receives a plurality of composite signals associated with a plurality of sources, separates a signal from the plurality of composite signals, and identifies the separated signal as a cardiac signal using information derived from a non-electrophysiologic sensor, such as an accelerometer or acoustic transducer. The signal processor may iteratively correlate separated signals from the plurality of composite signals with a non-electrophysiologic sensor signal until the cardiac signal is identified.

What is claimed is: 
     
         1 . An arrhythmia discrimination method performed by a medical device comprising an implantable housing, a plurality of non-intrathoracic electrodes configured to sense a plurality of electrical signals, a sensor that senses a non-electrophysiologic signal, a signal processor provided in the housing which is coupled to at least the plurality of non-intrathoracic electrodes, and energy delivery circuitry configured to deliver a tachyarrhythmia therapy, the method comprising:
 sensing electrocardiogram signals at a non-intrathoracic location using at least one of the plurality of non-intrathoracic electrodes;   sensing heart sound information using the sensor;   discriminating, using the electrocardiogram signals and the heart sound information, between a normal sinus rhythm and a cardiac arrhythmia by:
 determining that the electrocardiogram indicates a tachyarrhythmia heart rate; 
 analyzing the heart sound information to determine whether heart sounds are modified relative to heart sounds at non-tachyarrhythmia heart rates; and 
 finding a cardiac arrhythmia needing treatment in response to a combination of tachyarrhythmia heart rate and modified heart sounds; and initiating tachyarrhythmia therapy to terminate the cardiac arrhythmia. 
   
     
     
         2 . The method of  claim 1  wherein the sensor is an acoustic transducer. 
     
     
         3 . The method of  claim 1  wherein the sensor is a piezoelectric sensor. 
     
     
         4 . The method of  claim 1  wherein the tachyarrhythmia therapy comprises a pacing therapy. 
     
     
         5 . The method of  claim 1  wherein the tachyarrhythmia therapy comprises a defibrillation therapy. 
     
     
         6 . The method of  claim 1  wherein the step of determining that the electrocardiogram indicates a tachyarrhythmia heart rate comprises calculating a heart rate using the electrocardiogram and comparing the calculated heart rate to a tachyarrhythmia rate threshold. 
     
     
         7 . An implantable medical device comprising:
 an implantable housing;   a plurality of non-intrathoracic electrodes configured to sense a plurality of electrical signals;   a sensor that senses a non-electrophysiologic signal;   a signal processor provided in the housing which is coupled to at least the plurality of non-intrathoracic electrodes; and   energy delivery circuitry configured to deliver a tachyarrhythmia therapy;   wherein the signal processor is configured to perform the following:   sensing electrocardiogram signals at a non-intrathoracic location using at least one of the plurality of non-intrathoracic electrodes;   sensing heart sound information using the sensor;   discriminating, using the electrocardiogram signals and the heart sound information, between a normal sinus rhythm and a cardiac arrhythmia by:
 determining that the electrocardiogram indicates a tachyarrhythmia heart rate; 
 analyzing the heart sound information to determine whether heart sounds are modified relative to heart sounds at non-tachyarrhythmia heart rates; and 
 finding a cardiac arrhythmia needing treatment in response to a combination of tachyarrhythmia heart rate and modified heart sounds; and 
   in response to finding a cardiac arrhythmia needing treatment, issuing an instruction to the energy delivery circuitry to initiate tachyarrhythmia therapy to terminate the cardiac arrhythmia.   
     
     
         8 . The device of  claim 7  wherein the sensor is an acoustic transducer. 
     
     
         9 . The device of  claim 7  wherein the sensor is a piezoelectric sensor. 
     
     
         10 . The device of  claim 7  wherein the tachyarrhythmia therapy comprises a pacing therapy. 
     
     
         11 . The device of  claim 7  wherein the tachyarrhythmia therapy comprises a defibrillation therapy. 
     
     
         12 . The device of  claim 7  wherein the signal processor is configured such that the step of determining that the electrocardiogram indicates a tachyarrhythmia heart rate comprises calculating a heart rate using the electrocardiogram and comparing the calculated heart rate to a tachyarrhythmia rate threshold.