Method for discriminating between ventricular and supraventricular arrhythmias

1. A wearable medical device configured to deliver cardiac electrical therapy to a patient when needed, the wearable medical device comprising:

a plurality of electrodes for capturing cardiac signal data;

operational circuitry for receiving the captured cardiac signal data and analyzing the captured cardiac signal data to determine whether a treatable cardiac arrhythmia is occurring;

wherein the operational circuitry is configured to perform the following:

detecting a cardiac event by observation of electrical signals captured using at least some of the electrodes;

calculating a cardiac event rate relative to the detected cardiac event;

determining the cardiac event rate falls within an enhanced analysis zone;

analyzing morphology correlation of the cardiac event relative to a first template; and

determining that the cardiac event has high morphology correlation relative to the first template and is therefore not treatable on the basis of rate and morphology correlation combined;

wherein the operational circuitry is configured such that the first template is a dynamic template which represents an immediately preceding detected cardiac event.

2. The wearable medical device of claim 1 wherein the operational circuitry is further configured to perform the following:

after finding that the cardiac event is not treatable on the basis of rate and morphology correlation combined, analyzing whether the cardiac event illustrates a QRS width that is greater than a predetermined threshold; and one of:

determining that the cardiac event is narrower than the predetermined threshold and, in view thereof, determining that the cardiac event does not indicate cardiac stimulus; or

determining that the cardiac event is wider than the predetermined threshold and determining that the cardiac event indicates a cardiac condition that requires treatment despite its correlation to the first template.

3. The wearable medical device of claim 1 wherein the operational circuitry is configured to acquire the first template from cardiac signal data occurring after a triggering event, wherein the triggering event is the occurrence of a detected rate in a predetermined range.

4. A wearable medical device configured to deliver cardiac electrical therapy to a patient when needed, the wearable medical device comprising:

a plurality of electrodes for capturing cardiac signal data;

operational circuitry for receiving the captured cardiac signal data and analyzing the captured cardiac signal data to determine whether a treatable cardiac arrhythmia is occurring;

wherein the operational circuitry is configured to perform the following:

detecting a cardiac event by observation of electrical signals captured using at least some of the electrodes;

calculating a cardiac event rate relative to the detected cardiac event;

determining the cardiac event rate falls within an enhanced analysis zone;

analyzing morphology correlation of the cardiac event relative to a first template; and

determining that the cardiac event has high morphology correlation relative to the first template and is therefore not treatable on the basis of rate and morphology correlation combined;

wherein the operational circuitry is further configured to perform the following:

after finding that the cardiac event is not treatable on the basis of rate and morphology correlation combined, analyzing whether the cardiac event illustrates a QRS width that is greater than a predetermined threshold; and one of:

determining that the cardiac event is narrower than the predetermined threshold and, in view thereof, determining that the cardiac event does not indicate cardiac stimulus; or

determining that the cardiac event is wider than the predetermined threshold and determining that the cardiac event indicates a cardiac condition that requires treatment despite its correlation to the first template;

wherein the operational circuitry is configured to determine whether the cardiac event is wider or narrower than the predetermined threshold by:

identifying a peak height of the detected cardiac event;

setting a width threshold at half the detected cardiac event peak height;

determining how many samples of a digital representation of the cardiac event lie above the width threshold, out of a total number of samples; and

if more than a selected percentage of the samples lie above the width threshold, finding the detected event to be wider than the predetermined threshold; else, finding the detected event to be narrower than the predetermined threshold.

5. The wearable medical device of claim 4 wherein the operational circuitry is configured such that the first template is a dynamic template which represents an immediately preceding detected cardiac event.

6. The wearable medical device of claim 4 wherein the operational circuitry is configured to acquire the first template from cardiac signal data occurring after a triggering event, wherein the triggering event is the occurrence of a detected rate in a predetermined range.

7. The wearable medical device of claim 4 wherein the operational circuitry is configured such that the template is a stored template representative of normal sinus rhythm.

8. A method of operation in a wearable medical device configured to deliver cardiac electrical therapy to a patient when needed, the wearable medical device comprising:

a plurality of electrodes for capturing cardiac signal data; and

operational circuitry for receiving the captured cardiac signal data and analyzing the captured cardiac signal data to determine whether a treatable cardiac arrhythmia is occurring;

the method comprising:

the operational circuitry detecting a cardiac event by observation of electrical signals captured using at least some of the electrodes;

the operational circuitry calculating a cardiac event rate relative to the detected cardiac event;

the operational circuitry determining the cardiac event rate falls within an enhanced analysis zone;

the operational circuitry analyzing morphology correlation of the cardiac event relative to a first template; and

the operational circuitry determining that the cardiac event has high morphology correlation relative to the first template and is therefore not treatable on the basis of rate and morphology correlation combine;

wherein the operational circuitry is configured such that the first template is a dynamic template which represents an immediately preceding detected cardiac event.

9. The method of claim 8 , further comprising:

after finding that the cardiac event is not treatable on the basis of rate and morphology correlation combined, the operational circuitry analyzing whether the cardiac event illustrates a QRS width that is greater than a predetermined threshold; and one of:

the operational circuitry determining that the cardiac event is narrower than the predetermined threshold and, in view thereof, determining that the cardiac event does not indicate cardiac stimulus; or

the operational circuitry determining that the cardiac event is wider than the predetermined threshold and determining that the cardiac event indicates a cardiac condition that requires treatment despite its correlation to the first template; and

if the operational circuitry determines that the cardiac event indicates a cardiac condition that requires treatment, delivering therapy to the patient.

10. The method of claim 9 wherein the operational circuitry is configured to acquire the first template from cardiac signal data occurring after a triggering event, wherein the triggering event is the occurrence of a detected rate in a predetermined range.

11. The method of claim 9 further comprising the operational circuitry determining whether the cardiac event is wider or narrower than the predetermined threshold by:

the operational circuitry identifying a peak height of the detected cardiac event;

the operational circuitry setting a width threshold at half the detected cardiac event peak height;

the operational circuitry determining how many samples of a digital representation of the cardiac event lie above the width threshold, out of a total number of samples; and

the operational circuitry if more than a selected percentage of the samples lie above the width threshold, finding the detected event to be wider than the predetermined threshold; else, finding the detected event to be narrower than the predetermined threshold.

12. The method of claim 8 wherein the operational circuitry is configured to acquire the first template from cardiac signal data occurring after a triggering event, wherein the triggering event is the occurrence of a detected rate in a predetermined range.