Method for discriminating between ventricular and supraventricular arrhythmias

1. A method of determining whether to deliver therapy in a cardiac defibrillation system, the system comprising operational circuitry for analyzing cardiac signals coupled to a plurality of electrodes for sensing cardiac signals for analysis by the operational circuitry, the method comprising:

detecting cardiac events and calculating an elevated cardiac rate above a first rate threshold and below a second rate threshold;

when an elevated cardiac rate is present, discriminating supraventricular, monomorphic, and polymorphic rhythms using first and second factors wherein:

the first factor comprises a correlation between detected cardiac events and a template of supraventricular rhythm, the first factor being analyzed relative to a first factor threshold to yield high correlation or low correlation;

the second factor comprises variability in correlation between sensed cardiac complexes and a dynamic template, the second factor being analyzed relative to a second factor threshold to yield high variability or low variability;

when the first factor indicates high correlation and the second factor indicates low variability, the rhythm is found to be supraventricular;

when the first factor indicates low correlation and the second vector indicates low variability, the rhythm is found to be monomorphic; and

when the first factor indicates low correlation and the second factor indicates high variability, the rhythm is found to be polymorphic; and

determining whether to withhold or deliver electrical therapy as follows:

when the rhythm is found to be supraventricular, withholding electrical therapy;

when the rhythm is found to be a monomorphic ventricular rhythm, determining to deliver electrical therapy; and

when the rhythm is found to be a polymorphic ventricular rhythm, determining to deliver electrical therapy.

2. The method of claim 1 further comprising delivering defibrillation therapy in response to determining to deliver electrical therapy for a polymorphic ventricular rhythm.

3. The method of claim 2 wherein the operational circuitry is housed in an implantable canister having a conductive surface or electrode, and the implantable canister is coupled to an implantable lead having a stimulus delivery electrode thereon, and the step of delivering defibrillation therapy is performed using the conductive surface of the implantable canister and the stimulus delivery electrode of the lead.

4. The method of claim 3 wherein the lead is configured for subcutaneous placement, and the step of delivering defibrillation therapy is performed with the stimulus delivery electrode and the implantable canister are disposed subcutaneously.

5. The method of claim 3 wherein the lead is configured for transvenous placement, and the step of delivering defibrillation therapy is performed with the stimulus delivery electrode placed in the heart of a patient.

6. The method of claim 2 wherein the operational circuitry and electrodes are included in an external device directed to therapy for tachyarrhythmias.

7. The method of claim 1 wherein the template of supraventricular rhythm comprises a normal sinus rhythm template.

8. The method of claim 1 wherein the dynamic template comprises a continuously updated template.

9. The method of claim 1 wherein the dynamic template comprises a template representative of a cardiac complex with a rate in the range of 170 to 260 beats per minute.

10. A medical device configured to deliver cardiac electrical therapy to a patient, the 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;

wherein the operational circuitry is configured to perform the following:

detecting cardiac events and calculating an elevated cardiac rate above a first rate threshold and below a second rate threshold;

in response to the elevated cardiac rate, discriminating supraventricular, monomorphic, and polymorphic rhythms using first and second factors wherein:

the first factor comprises a correlation between detected cardiac events and a template of supraventricular rhythm, the first factor being analyzed relative to a first factor threshold to yield high correlation or low correlation;

the second factor comprises variability in correlation between sensed cardiac complexes and a dynamic template, the second factor being analyzed relative to a second factor threshold to yield high variability or low variability;

if the first factor indicates high correlation and the second factor indicates low variability, the rhythm is found to be supraventricular;

if the first factor indicates low correlation and the second vector indicates low variability, the rhythm is found to be monomorphic; and

if the first factor indicates low correlation and the second factor indicates high variability, the rhythm is found to be polymorphic; and

determining whether to withhold or deliver electrical therapy as follows:

if the rhythm is found to be supraventricular, withholding electrical therapy;

if the rhythm is found to be a monomorphic ventricular rhythm, determining to deliver electrical therapy; and

if the rhythm is found to be a polymorphic ventricular rhythm, determining to deliver electrical therapy.

11. The medical device of claim 10 wherein the operational circuitry is further configured to deliver defibrillation therapy in response to determining to deliver electrical therapy for a polymorphic ventricular rhythm.

12. The medical device of claim 11 further comprising:

an implantable canister having a conductive surface or electrode which houses the operational circuitry;

an implantable lead having a stimulus delivery electrode thereon and one or more of the plurality of electrodes, the lead being coupled to the canister, wherein:

the operational circuitry is configured to deliver defibrillation using the conductive surface of the implantable canister and the stimulus delivery electrode of the lead.

13. The medical device of claim 11 wherein the operational circuitry and electrodes are included in an external device directed to therapy for tachyarrhythmias.

14. The medical device of claim 10 wherein the operational circuitry is configured such that the template of supraventricular rhythm comprises a normal sinus rhythm template.

15. The medical device of claim 10 wherein the operational circuitry is configured such that the dynamic template comprises a continuously updated template.

16. The medical device of claim 10 wherein the operational circuitry is configured such that the dynamic template comprises a template representative of a cardiac complex with a rate in the range of 170 to 260 beats per minute.

17. A medical device configured to deliver cardiac electrical therapy to a patient, the 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;

wherein the operational circuitry is configured to perform the following:

detecting cardiac events and calculating an elevated cardiac rate above a first rate threshold and below a second rate threshold;

in response to the elevated cardiac rate, discriminating supraventricular from ventricular rhythms using first, second and third factors wherein:

the first factor comprises a correlation between detected cardiac events and a template of supraventricular rhythm, the first factor being analyzed relative to a first factor threshold to yield high correlation or low correlation;

the second factor comprises variability in correlation between sensed cardiac complexes and a dynamic template, the second factor being analyzed relative to a second factor threshold to yield high variability or low variability; and

the third factor comprises width of a sensed cardiac complexes;

determining whether sensed cardiac complexes cluster into:

a first grouping with a defined combination of high correlation using the first factor, low variability using the second factor, and narrow width using the third factor; or

a second grouping not illustrating the defined combination;

if the sensed cardiac complexes cluster into the first grouping, finding that a supraventricular rhythm is occurring or, if not, finding that a ventricular rhythm is occurring; and

determining whether to withhold or deliver electrical therapy as follows:

if the rhythm is found to be supraventricular, withholding electrical therapy;

if the rhythm is found to be a ventricular rhythm, determining to deliver electrical therapy.

18. The medical device of claim 17 further comprising:

an implantable canister having a conductive surface or electrode which houses the operational circuitry;

an implantable lead having a stimulus delivery electrode thereon and one or more of the plurality of electrodes, the lead being coupled to the canister, wherein:

the operational circuitry is configured to deliver electrical therapy for ventricular rhythms found to be polymorphic by delivering defibrillation therapy using the conductive surface of the implantable canister and the stimulus delivery electrode of the lead.

19. The medical device of claim 17 wherein the operational circuitry and electrodes are included in an external device directed to therapy for tachyarrhythmias.

20. The medical device of claim 17 wherein the operational circuitry is configured such that:

the template of supraventricular rhythm comprises a normal sinus rhythm template; and

the dynamic template comprises a continuously updated template.