Methods and Devices for Accurately Classifying Cardiac Activity

• US 20120197147A1
• Filed: 03/30/2012
• Published: 08/02/2012
• Est. Priority Date: 03/07/2008
• Status: Active Grant

• Current Assignee: Cameron Incorporated (Schlumberger NV)
• Original Assignee: Cameron Incorporated (Schlumberger NV)
• Inventors: Allavatam, Venugopal, Palreddy, Surekha, Sanghera, Rick, Warren, Jay A.
• Granted Patent: US 8,626,280 B2
• Time in Patent Office: Days
• US Class Current: 600/510
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/6847 mounted on an invasive device
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion
• CPC Class Codes: A61N 1/3987 characterised by the timing or triggering of the shock

Abstract

Methods, systems, and devices for signal analysis in an implanted cardiac monitoring and treatment device such as an implantable cardioverter defibrillator. In illustrative 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. New methods for organizing the use of morphology and rate analysis in an overall architecture for rhythm classification and cardiac signal analysis are also discussed.

Claims

1. An implantable cardiac stimulus device (ICSD) comprising a canister housing operational circuitry and a lead electrode assembly including a plurality of electrodes disposed thereon, with the lead electrode assembly configured to couple to the canister to electrically couple the operational circuitry to the electrodes on the lead electrode assembly, the operational circuitry being configured to perform a method of cardiac signal analysis comprising:

the operational circuitry detecting a series of events;

the operational circuitry identifying intervals between consecutive detected events;

the operational circuitry marking individual detected events as either True or False based upon a set of rules directed at identifying overdetections;

the operational circuitry determining whether a pattern of overdetection has been identified and;

a) if so, the operational circuitry discarding detected events marked as False and the operational circuitry combining intervals on either side of discarded events into combined intervals;

or

b) if not, the operational circuitry marking False detected events as suspect;

the operational circuitry performing rate analysis using combined intervals and intervals between consecutive true events, but not using intervals immediately before and after suspect events; and

the operational circuitry using the rate analysis to determine whether a high cardiac rate condition needing therapy is likely occurring.

2. The ICSD of claim 1 wherein the operational circuitry is further configured to also determine whether a malignant cardiac rhythm is occurring and, if so, to deliver electrical therapy in response to the malignant cardiac rhythm.

3. The ICSD of claim 1 wherein the operational circuitry is further configured such that the step of determining whether a pattern of overdetection has been identified includes:

the operational circuitry observing whether a pattern of alternating long-short intervals appear between detected events; and

the operational circuitry observing whether a pattern of alternating True-False markings occurs;

wherein if either the pattern of alternating long-short intervals or the pattern of alternating True-False markings is found, a pattern of overdetection is identified.

4. An implantable cardiac stimulus device (ICSD) comprising a canister housing operational circuitry and a lead electrode assembly including a plurality of electrodes disposed thereon, with the lead electrode assembly configured to couple to the canister to electrically couple the operational circuitry to the electrodes on the lead electrode assembly, the operational circuitry being configured to perform a method of cardiac signal analysis comprising:

the operational circuitry detecting a series of events;

the operational circuitry identifying intervals between consecutive detected events;

the operational circuitry using morphology analysis to identify overdetections from the series of events;

whenever an overdetection is identified, the operational circuitry combining an interval preceding the overdetection and an interval following the overdetection to form a combined interval;

following the morphology analysis to identify overdetections, the operational circuitry certifying combined intervals and intervals that are not adjacent to overdetections;

the operational circuitry estimating a cardiac rate using only certified intervals; and

the operational circuitry using the estimated cardiac rate to make therapy decisions.

5. The ICSD of claim 4 wherein the operational circuitry is further configured to perform a step of waveform appraisal including determining whether individual detected events are noisy, and wherein the step of identifying intervals between detections in the series of events comprises identifying only intervals between detections that neither result from nor are dominated by noise, as determined in the waveform appraisal step.

6. The ICSD of claim 4 wherein the operational circuitry is further configured such that each detected event is affiliated with a sample window composed of a number of signal amplitude samples and the morphology analysis includes Wide Complex Analysis including interval analysis such that an overdetection is identified when first and second detected events are separated by an interval that is shorter than a predetermined Wide Complex threshold interval and at least one of the following conditions is identified:

the first and second detected events are of opposing polarity;

or

a Peak interval for the first and second detected events is less than a predetermined threshold, wherein the Peak interval is defined as the lesser of;

a) an interval between the maximum amplitude sample of the first detected event and the maximum amplitude sample of the second detected event, and

b) an interval between the minimum amplitude sample of the first detected event and the minimum amplitude sample of the second detected event.

such that, if the Wide Complex analysis is satisfied, one of the first and second events is marked as an overdetection.

7. The ICSD of claim 6 wherein, if the Wide Complex analysis is satisfied, then either:

if a morphology template exists for the ICSD, whichever of the first and second detected events shows lesser correlation to the morphology template is marked as the overdetection;

or

if no morphology template exists for the ICSD, the later in time of the first and second detected events is marked as the overdetection.

8. The ICSD of claim 6 wherein the operational circuitry is further configured such that the morphology analysis also includes a template morphology analysis in which:

detected events are compared to a morphology template to generate correlation scores;

a series of correlation scores are characterized as High or Low;

High-Low-High patterns are identified as indicating overdetection; and

if a High-Low-High pattern is identified, the detected event having the Low correlation score is identified as an overdetection.

9. The ICSD of claim 4 wherein the operational circuitry is further configured such that the morphology analysis includes a template morphology analysis in which:

detected events are compared to a morphology template to generate correlation scores;

a series of correlation scores are characterized as High or Low;

High-Low-High patterns are identified as indicating overdetection; and

if a High-Low-High pattern is identified, the detected event having the Low correlation score is identified as an overdetection.

10. An implantable cardiac stimulus device (ICSD) comprising a canister housing operational circuitry and a lead electrode assembly including a plurality of electrodes disposed thereon, with the lead electrode assembly configured to couple to the canister to electrically couple the operational circuitry to the electrodes on the lead electrode assembly, the operational circuitry being configured to perform a method of cardiac signal analysis comprising:

the operational circuitry detecting a series of events;

the operational circuitry comparing the detected events to a morphology template to establish a series of correlation scores indicative of the extent of correlation between the shape of detected events and the morphology template;

the operational circuitry analyzing the series of correlation scores to observe a high-low-high pattern of;

a first-most recent event having a high correlation score;

a second-most recent event having a low correlation score; and

a third-most recent event having a high correlation score;

when the high-low-high pattern is identified, the operational circuitry determining that the second-most recent event is an overdetection;

upon finding an overdetection, the operational circuitry combining an interval preceding the overdetection and an interval following the overdetection into a combined interval;

the operational circuitry using the combined interval in estimating cardiac rate; and

the operational circuitry using the estimated cardiac rate to make a therapy decision.

11. The ICSD of claim 10 wherein operational circuitry is further configured such that the step of analyzing the series of correlation scores to observe the following pattern includes:

the operational circuitry scaling the correlation scores and defining three zones including a Low Zone in which any correlation score is considered low, a high zone in which any correlation score is considered high, and a hysteresis zone between the low zone and the high zone in which any correlation score is considered high or low depending upon whether an immediately previous correlation score was characterized as high or low; and

the high-low-high pattern is only identified if the third-most recent event has a correlation score above the hysteresis zone.

12. An implantable cardiac stimulus device (ICSD) comprising a canister housing operational circuitry and a lead electrode assembly including a plurality of electrodes disposed thereon, with the lead electrode assembly configured to couple to the canister to electrically couple the operational circuitry to the electrodes on the lead electrode assembly, the operational circuitry being configured to perform a method of cardiac signal analysis comprising:

the operational circuitry detecting a series of events having raw intervals therebetween;

the operational circuitry analyzing the series of events and raw intervals between the events to determine whether individual events and intervals can be certified as not indicating noise or overdetection;

the operational circuitry using a set of certified intervals to estimate an average certified interval; and

the operational circuitry using the average certified interval to determine whether a treatable high-rate condition exists;

wherein the step of analyzing the series of events and intervals includes;

the operational circuitry calculating an average raw interval;

the operational circuitry using the average raw interval to define a voidband between a minimum interval shorter than the average raw interval and a maximum interval longer than the average raw interval;

the operational circuitry analyzing a set of N raw intervals to determine whether consecutive raw interval pairs cross the voidband such that both raw intervals in a pair fall outside the voidband on opposite sides of the voidband;

the operational circuitry determining whether at least M consecutive raw interval pairs cross the voidband and, if so, finding that an alternating interval pattern of overdetection exists; and

if an alternating interval pattern of overdetection exists, the operational circuitry identifying at least one of the set of N raw intervals as an overdetection, combining an interval immediately preceding the overdetection with an interval immediately following the overdetection to create a combined interval, and certifying the combined interval for use in estimating an average certified interval.

13. An implantable cardiac stimulus device (ICSD) comprising a canister housing operational circuitry and a lead electrode assembly including a plurality of electrodes disposed thereon, with the lead electrode assembly configured to couple to the canister to electrically couple the operational circuitry to the electrodes on the lead electrode assembly, the operational circuitry being configured to perform a method of cardiac signal analysis comprising:

the operational circuitry receiving signals from the electrodes;

the operational circuitry comparing the received signals to a detection threshold and identifying crossings of the detection threshold by the received signals as raw detected events, the raw detected events being separated by raw intervals;

the operational circuitry performing waveform analysis on a raw detected event to determine whether it results from or is masked by noise and, if so, marking the raw detected event as a suspect event and marking the raw intervals immediately before and after the suspect event as a suspect intervals, otherwise, marking the raw detected event as a WA detected event;

the operational circuitry performing overdetection analysis on WA detected events and intervals between pairs of WA detected events and, if a WA detected event is surrounded by two non-suspect intervals and is marked as an overdetection, combining the two non-suspect intervals into a single combined interval;

the operational circuitry certifying an interval between two detected events for use in rate calculation if;

neither detected event is marked suspect or overdetection, or

the interval is a combined interval; and

the operational circuitry using only certified intervals to calculate a rate of cardiac events for the purpose of identifying treatable cardiac conditions.

14. The ICSD of claim 13 wherein the operational circuitry is further configured to perform the following steps:

the operational circuitry comparing the calculated rate to one or more thresholds to determine that the calculated rate either indicates a need for therapy or does not indicate a need for therapy;

the operational circuitry maintaining an X/Y counter that records how many (X) of a number (Y) of rate calculations indicate a need for therapy;

the operational circuitry comparing the X/Y counter to a threshold to determine whether a cardiac rhythm indicates a need for therapy;

the operational circuitry using at least the comparison of the X/Y counter to a threshold to determine whether therapy should be applied by the ICSD and, if so, delivering electrical therapy using the ICSD.

15. The ICSD of claim 14 wherein the operational circuitry is further configured to maintain a morphology template, to calculate the width of the QRS complex for detected events, and to maintain a dynamic template as an average of a number of previous detected events that are neither suspect nor overdetections, and to define the following three zones for rate analysis:

a non-shockable zone;

a conditional shock zone; and

a shock zone;

wherein the X/Y counter is maintained by adding a shockable notation to the X/Y counter when a rate calculation is in the shock zone, by adding a non-shockable notation to the X/Y counter when a rate calculation is in the non-shockable zone, and when a rate calculation is in the conditional shock zone;

adding a shockable notation to the X/Y counter if a detected event associated with a rate calculation in the conditional shock zone fails to correlate to the morphology template and either;

a) displays a QRS width that is wider than a predetermined threshold;

or

b) fails to correlate to the dynamic template;

else

adding a non-shockable notation to the X/Y counter.

16. A method of operation in an implantable cardiac stimulus device (ICSD) comprising:

receiving signals from implanted electrodes;

comparing the received signals to a detection threshold and identifying crossings of the detection threshold by the received signals as raw detected events, the raw detected events being separated by raw intervals;

performing waveform analysis on a raw detected event to determine whether it results from or is masked by noise and, if so, marking the raw detected event as a suspect event and marking the raw intervals immediately before and after the suspect event as a suspect intervals, otherwise, marking the raw detected event as a WA detected event;

performing overdetection analysis on WA detected events and intervals between pairs of WA detected events and, if a WA detected event is surrounded by two non-suspect intervals and is marked as an overdetection, combining the two non-suspect intervals into a single combined interval;

certifying an interval between two detected events for use in rate calculation if;

neither detected event is marked suspect or as an overdetection, or

the interval is a combined interval;

using only certified intervals to calculate a rate of cardiac events;

comparing the calculated rate to one or more thresholds to determine that the calculated rate either indicates a need for therapy or does not indicate a need for therapy;

maintaining an X/Y counter that records how many (X) of a number (Y) of rate calculations indicate a need for therapy;

comparing the X/Y counter to a threshold to determine whether a cardiac rhythm indicates a need for therapy;

using at least the comparison of the X/Y counter to a threshold to determine whether therapy should be applied by the ICSD and, if so, delivering electrical therapy using the ICSD.

17. The method of claim 16 wherein the ICSD is configured to store a morphology template, to calculate the width of the QRS complex for detected events, and to maintain a dynamic template as an average of a number of previous detected events that are neither suspect nor overdetections, and to define the following three zones for rate analysis:

a non-shockable zone;

a conditional shock zone; and

a shock zone;

wherein the method further comprises maintaining the X/Y counter by;

adding a shockable notation to the X/Y counter when a rate calculation is in the shock zone;

adding a non-shockable notation to the X/Y counter when a rate calculation is in the non-shockable zone; and

when a rate calculation is in the conditional shock zone;

adding a shockable notation to the X/Y counter if a detected event associated with a rate calculation in the conditional shock zone fails to correlate to the morphology template and either;

a) displays a QRS width that is wider than a predetermined threshold;

or

b) fails to correlate to the dynamic template;

else

adding a non-shockable notation to the X/Y counter.