METHOD AND APPARATUS FOR MORPHOLOGY-BASED ARRHYTHMIA CLASSIFICATION USING CARDIAC AND OTHER PHYSIOLOGICAL SIGNALS

• US 20090292332A1
• Filed: 08/06/2009
• Published: 11/26/2009
• Est. Priority Date: 12/22/2005
• Status: Active Grant

• Current Assignee: Dan Li, Jaeho Kim, Kent Lee, Shelley Cazares
• Original Assignee: Dan Li, Jaeho Kim, Kent Lee, Shelley Cazares
• Inventors: Kim, Jaeho, Li, Dan, Lee, Kent, Cazares, Shelley
• Granted Patent: US 7,912,545 B2
• Time in Patent Office: Days
• US Class Current: 607/5
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/36542 controlled by body motion, e.g. acceleration
• CPC Class Codes: A61N 1/36564 controlled by blood pressure
• CPC Class Codes: A61N 1/36571 controlled by blood flow rate, e.g. blood velocity or cardiac output
• CPC Class Codes: A61N 1/36578 controlled by mechanical motion of the heart wall, e.g. measured by an accelerometer or microphone
• CPC Class Codes: A61N 1/36585 controlled by two or more physical parameters
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting
• CPC Class Codes: A61N 1/39622 Pacing therapy
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

A tachyarrhythmia detection and classification system classifies tachyarrhythmias based on an analysis of morphological features of a cardiac signal enhanced by using one or more physiological parameters indicative of hemodynamic stability and/or activity level. The tachyarrhythmia detection and classification system computes a measure of similarity between an arrhythmic waveform of the cardiac signal a template waveform for that cardiac signal, such as a correlation coefficient representative of the correlation between morphological features of the arrhythmic waveform and morphological features of the template waveform. A detected tachyarrhythmia episode is classified by comparing the measure of similarity to a threshold that is dynamically adjusted using the one or more physiological parameters.

Claims

1. A tachyarrhythmia detection and classification system, comprising:

a cardiac sensing circuit configured to sense at least one cardiac signal;

a rate detector configured to detect a heart rate from the at least one cardiac signal;

a tachyarrhythmia detector configured to detect a tachyarrhythmia episode using the heart rate;

a physiological sensor configured to sense a physiological signal; and

a morphology-based tachyarrhythmia classification module including;

a feature extractor configured to extract arrhythmic morphological features of an arrhythmic heart beat of the detected tachyarrhythmia episode from the at least one cardiac signal;

a similarity analyzer configured to compute a measure of similarity between the arrhythmic morphological features and stored template morphological features of a template heart beat of a known type cardiac rhythm;

a classifier configured to classify the arrhythmic heart beat using the measure of similarity and a dynamically adjustable beat classification threshold (T); and

a threshold generator configured to adjust the beat classification threshold (T) using an arrhythmic heart rate and an estimated normal heart rate range, the arrhythmic heart rate being the heart rate detected from the at least one cardiac signal during the detected tachyarrhythmia episode, the estimated normal heart rate range being a normal heart rate range estimated using at least the physiological signal.

2. The system of claim 1, wherein the threshold generator comprises a normal heart rate estimator configured to produce the estimated normal heart rate range using the physiological signal, a normal heart rate associated with a known type cardiac rhythm, and demographic information.

3. The system of claim 2, wherein the physiological sensor comprises an activity sensor to sense an activity signal, and the normal heart rate estimator is configured to produce the estimated normal heart rate range using the activity signal, the normal heart rate, and the demographic information.

4. The system of claim 2, wherein the physiological sensor comprises an impedance sensor to sense an impedance signal indicative of respiratory activities, and the normal heart rate estimator is configured to produce the estimated normal heart rate range using the impedance signal, the normal heart rate, and the demographic information.

5. The system of claim 2, wherein the physiological sensor comprises a hemodynamic sensor to sense a hemodynamic signal having a known approximate relationship with the heart rate, and the normal heart rate estimator is configured to produce the estimated normal heart rate range using the hemodynamic signal, the normal heart rate, and the demographic information.

6. The system of claim 2, wherein the threshold generator comprises a comparator configured to compare the arrhythmic heart rate to the estimated normal heart rate range, and wherein the threshold generator is configured to set the beat classification threshold (T) to a first value in response to the arrhythmic heart rate falling within the estimated normal heart range and a second value in response to the arrhythmic heart rate falling out of the estimated normal heart range.

7. The system of claim 1, wherein the similarity analyzer comprises a correlation analyzer configured to compute a correlation coefficient between the arrhythmic morphological features and the template morphological features for each arrhythmic heart beat of a plurality of arrhythmic heart beats of the detected tachyarrhythmia episode, and the classifier comprises:

a beat classifier including a beat comparator having a first input to receive the correlation coefficient for each of the plurality of arrhythmic heart beats, a second input to receive the beat classification threshold (T), and an output to indicate a classification for the each of the plurality of arrhythmic heart beats as one of a first type tachyarrhythmic heart beat and a second type tachyarrhythmic heart beat;

a beat counter configured to count a number of the arrhythmic heart beats classified as the first type tachyarrhythmic heart beat; and

an episode classifier including an episode comparator having a first input to receive the number of the arrhythmic heart beats classified as the first type tachyarrhythmic heart beat, a second input to receive an episode classification threshold, and an output to indicate a classification of the detected tachyarrhythmia episode as one of a first type tachyarrhythmia and a second type tachyarrhythmia.

8. The system of claim 7, wherein the threshold generator comprises a mapping module to map the physiological signal to values of the beat classification threshold (T).

9. The system of claim 8, wherein the mapping module comprises a look-up table.

10. The system of claim 1, comprising an implantable cardioverter/defibrillator (ICD) including the cardiac sensing circuit, the rate detector, the tachyarrhythmia detector, and the morphology-based tachyarrhythmia classification module.

11. A method for detecting and classifying tachyarrhythmias, the method comprising:

sensing at least one cardiac signal;

detecting a heart rate from the at least one cardiac signal;

detecting a tachyarrhythmia episode from the heart rate;

extracting arrhythmic morphological features of an arrhythmic heart beat of the detected tachyarrhythmia episode from the at least one cardiac signal;

computing a measure of similarity between the arrhythmic morphological features and stored template morphological features of a template heart beat;

classifying the arrhythmic beat using the measure of similarity and a dynamically adjustable beat classification threshold (T);

sensing a physiological signal; and

adjusting the beat classification threshold (T) using an arrhythmic heart rate and an estimated normal heart rate range, the arrhythmic heart rate being the heart rate detected from the at least one cardiac signal during the detected tachyarrhythmia episode, the estimated normal heart rate range being a normal heart rate range estimated using at least the physiological signal.

12. The method of claim 11, wherein adjusting the beat classification threshold (T) comprises producing the estimated normal heart rate range using the physiological signal, a normal heart rate associated with a known type cardiac rhythm, and demographic information.

13. The method of claim 12, wherein sensing the physiological signal comprises sensing an activity signal, and producing the estimated normal heart rate range comprises producing the estimated normal heart rate range using the activity signal, the normal heart rate, and the demographic information.

14. The method of claim 12, wherein sensing the physiological signal comprises sensing an impedance signal indicative of respiratory activities, and producing the estimated normal heart rate range comprises producing the estimated normal heart rate range using the impedance signal, the normal heart rate, and the demographic information.

15. The method of claim 12, wherein sensing the physiological signal comprises sensing a hemodynamic signal having a known approximate relationship with the heart rate, and producing the estimated normal heart rate range comprises producing the estimated normal heart rate range using the hemodynamic signal, the normal heart rate, and the demographic information.

16. The method of claim 12, wherein adjusting the beat classification threshold (T) comprises setting the beat classification threshold (T) to a first predetermined value in response to the arrhythmic heart rate falling within the estimated normal heart rate range and a second value in response to the arrhythmic heart rate falling out of the estimated normal heart rate range.

17. The method of claim 16, comprising producing the normal heart rate associated with the known type cardiac rhythm by detecting the heart rate from the at least one cardiac signal during normal sinus rhythm (NSR).

18. The method of claim 11, wherein the measure of similarity comprises a correlation coefficient, and wherein classifying the detected tachyarrhythmia episode comprises:

comparing the correlation coefficient for each arrhythmic heart beat of a plurality of arrhythmic heart beats to the beat classification threshold (T);

indicating a classification for the each arrhythmic heart beat as one of a first type tachyarrhythmic heart beat and a second type tachyarrhythmic heart beat;

counting a number of the arrhythmic heart beats classified as the first type tachyarrhythmic heart beat;

comparing the number of the arrhythmic heart beats classified as the first type tachyarrhythmic heart beat to an episode classification threshold; and

indicating a classification of the detected tachyarrhythmia episode as a first type tachyarrhythmia in response to the number of the arrhythmic heart beats classified as the first type tachyarrhythmic heart beat being equal to or greater than the episode classification threshold and as a second type tachyarrhythmic heart beat in response to the number of the arrhythmic heart beats classified as the first type tachyarrhythmic heart beat being below the episode classification threshold.

19. The method of claim 18, wherein classifying the detected tachyarrhythmia episode comprises classifying the detected tachyarrhythmia episode as one of supraventricular tachyarrhythmia (SVT) and ventricular tachyarrhythmia (VT).

20. A tachyarrhythmia detection and classification system, comprising:

means for sensing at least one cardiac signal;

means for detecting a heart rate from the at least one cardiac signal;

means for detecting a tachyarrhythmia episode from the heart rate;

means for extracting arrhythmic morphological features of an arrhythmic heart beat of the detected tachyarrhythmia episode from the at least one cardiac signal;

means for computing a measure of similarity between the arrhythmic morphological features and stored template morphological features of a template heart beat;

means for classifying the arrhythmic beat using the measure of similarity and a dynamically adjustable beat classification threshold (T);

means for sensing a physiological signal; and

means for adjusting the beat classification threshold (T) using an arrhythmic heart rate and an estimated normal heart rate range, the arrhythmic heart rate being the heart rate detected from the at least one cardiac signal during the detected tachyarrhythmia episode, the estimated normal heart rate range being a normal heart rate range estimated using at least the physiological signal.