Methods and devices for accurately classifying cardiac activity
Methods, systems, and devices for signal analysis in an implanted cardiac monitoring and treatment device such as an implantable cardioverter defibrillator. In some examples, captured data including detected events is analyzed to identify likely overdetection of cardiac events. In some illustrative examples, when overdetection is identified, data may be modified to correct for overdetection, to reduce the impact of overdetection, or to ignore overdetected data. Several examples emphasize the use of morphology analysis using correlation to static templates and/or inter-event correlation analysis.
1. An implantable medical device (IMD) comprising a plurality of electrodes coupled to operational circuitry configured to perform cardiac signal analysis, the IMD including a canister having the operational circuitry and at least one electrode associated therewith, the operational circuitry being configured to:
detect at least first, second and third detected events by comparison of a cardiac signal from the plurality of electrodes to a threshold defined by a detection profile and declaring a detected event having a signal waveform when the threshold is crossed, wherein the first detected event occurs later in time than the second detected event, and the second detected event occurs later in time than the third detected event;
compare the first detected event to the second detected event to yield a first comparison score;
compare the first detected event to the third detected event to yield a second comparison score; and
analyze at least the first and second comparison scores to determine if one of the first, second and third detected events is likely due to overdetection.
2. The IMD of claim 1 wherein the operational circuitry is further configured to:
detect a fourth detected event by comparison of a cardiac signal from the plurality of electrodes to a threshold defined by a detection profile and declaring a detected event having a signal waveform when the threshold is crossed, wherein the third detected event occurs later in time than the fourth detected event; and
compare the first detected event to the fourth detected event to yield a third comparison score;
wherein the operational circuitry is configured such that when it analyzes the first and second comparison scores to determine if one of the first, second and third detected events is likely due to overdetection, the operational circuitry also analyzes the third comparison score.
3. The IMD of claim 1 wherein the operational circuitry is configured to analyze at least the first and second comparison scores to determine if one of the first, second and third detected events is likely due to overdetection by use of at least a first rule set configured to identify double detection including both R-wave and T-wave detection.
4. The IMD of claim 1 wherein the operational circuitry is configured to analyze at least the first and second comparison scores to determine if one of the first, second and third detected events is likely due to overdetection by use of at least a first rule set configured to identify triple detection of a cardiac cycle.
5. The IMD of claim 1 wherein the operational circuitry is configured to further determine, in response to determining that one of the first, second and third detected events is likely due to overdetection, whether the overdetection was of a T- wave.
6. The IMD of claim 1 wherein the operational circuitry is configured to calculate a cardiac rate for a patient using detected events, wherein when the operational circuitry identifies a detected event likely due to overdetection, the operational circuitry removes the detected event that is likely due to overdetection from the calculation of cardiac rate.
7. The IMD of claim 6 , further comprising a capacitive system to store therapy energy, a charger to charge the capacitive system, and delivery circuitry for delivering therapy energy, wherein the operational circuitry is configured determine whether to deliver therapy by an arrhythmia analysis that includes comparing the calculated cardiac event rate to one or more arrhythmia rate thresholds and, in response to a determination to deliver therapy, the operational circuitry is configured to activate the charger to charge the capacitive system to a therapeutic level and operate the delivery circuitry to delivery therapy to the patient.
8. A method of operation in an implantable medical device (IMD) comprising a plurality of electrodes coupled to operational circuitry configured to perform cardiac signal analysis, the IMD including a canister having the operational circuitry and at least one electrode associated therewith, the method comprising:
the operational circuitry detecting detect at least first, second and third detected events by comparing a cardiac signal received by the plurality of electrodes to a threshold defined by a detection profile and declaring a detected event having a signal waveform when the threshold is crossed, wherein the first detected event occurs later in time than the second detected event, and the second detected event occurs later in time than the third detected event;
the operational circuitry comparing the first detected event to the second detected event to yield a first comparison score;
the operational circuitry comparing the first detected event to the third detected event to yield a second comparison score; and
the operational circuitry analyzing at least the first and second comparison scores to determine if one of the first, second and third detected events is likely due to overdetection.
9. The method of claim 8 , further comprising:
the operational circuitry detecting a fourth detected event by comparison of a cardiac signal from the plurality of electrodes to a threshold defined by a detection profile and declaring a detected event having a signal waveform when the threshold is crossed, wherein the third detected event occurs later in time than the fourth detected event; and
the operational circuitry comparing the first detected event to the fourth detected event to yield a third comparison score;
wherein the step of analyzing at least the first and second comparison scores to determine if one of the first, second and third detected events is likely due to overdetection, also includes analyzing the third comparison score.
10. The method of claim 8 wherein the step of analyzing at least the first and second comparison scores to determine if one of the first, second and third detected events is likely due to overdetection includes using at least a first rule set configured to identify double detection including both R-wave and T-wave detection.
11. The method of claim 8 further comprising determining in response to determining that one of the first, second and third detected events is likely due to overdetection, whether the overdetection was of a T-wave.
12. The method of claim 8 further comprising the operational circuitry calculating a cardiac rate for a patient using detected events, wherein when the operational circuitry identifies a detected event likely due to overdetection, the operational circuitry removes the detected event that is likely due to overdetection from the calculation of cardiac rate.
13. The method of claim 12 wherein the IMD further includes comprising a capacitive system to store therapy energy, a charger to charge the capacitive system, and delivery circuitry for delivering therapy energy, the method further comprising:
the operational circuitry determining that therapy is needed using an arrhythmia analysis that includes comparing the calculated cardiac event rate to one or more arrhythmia rate thresholds; and
the operational circuitry activating the charger to charge the capacitive system to a therapeutic level and operating the delivery circuitry to delivery therapy to the patient.