Method and apparatus for improving the accuracy of atrial fibrillation detection in lossy data systems

• US 20070073177A1
• Filed: 09/29/2005
• Published: 03/29/2007
• Est. Priority Date: 09/29/2005
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Logan, Beth, Goddeau, David, Kontothanassis, Leonidas
• Granted Patent: US 7,734,335 B2
• Time in Patent Office: Days
• US Class Current: 600/518
• CPC Class Codes: A61B 5/0006 ECG or EEG signals
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• 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: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

An apparatus and a method for detecting cardiac atrial fibrillation events in an EKG signal. The method comprises the steps of detecting a portion of an EKG signal comprising cardiac beats; measuring the duration of a gap in the detected portion of the EKG signal; and computing two or more inter-beat intervals. The computed interval is outputted if the gap in the portion of the EKG signal is not more than a fraction alpha of the computed interval. The method further includes the steps of computing the variance of the inter-beat intervals and classifying the portions of the EKG signal as indicative of an atrial fibrillation event. During classification, the inter-beat interval variance of the portion of the EKG signal that exceeds a pre-determined value V is indicative of an atrial fibrillation event. The method further includes discarding portions of the EKG signal classified as indicative of atrial fibrillation if said portions have a duration less than a pre-determined threshold S and annotating the EKG signal. The non-discarded portions of the EKG signals having inter-beat variances that exceed V are annotated as atrial fibrillation events.

Claims

1. A method of detecting the cardiac atrial fibrillation event in an electronic signal indicative of heart beat (EKG signal), comprising:

a) detecting at least one portion of a subject'"'"'s EKG signal comprising cardiac beats;

b) measuring the duration of a gap in the detected portion of the subject'"'"'s EKG signal;

c) computing two or more inter-beat intervals, wherein the computed interval is outputted if the gap in the portion of the EKG signal is not more than a fraction alpha of the computed interval;

d) computing a variance of the inter-beat intervals;

e) classifying the portions of the EKG signal as indicative of an atrial fibrillation event, whereby the inter-beat interval variance of the portion of the EKG signal that exceeds a pre-determined value V is indicative of an atrial fibrillation event;

f) discarding portions of the EKG signal classified as indicative of atrial fibrillation if said portions have a duration less than a pre-determined threshold S, thereby smoothing the output of step (e); and

g) annotating the EKG signal, whereby the non-discarded portions of the EKG signals having inter-beat variances that exceed V are annotated as atrial fibrillation events.

2. The method of claim 1, wherein the EKG signal comprises time-stamped packets.

3. The method of claim 2, wherein the gap in the EKG signal is detected by comparing the time-stamp of each packet to an expected time-stamp.

4. The method of claim 1, wherein the fraction alpha is about one-half.

5. The method of claim 1, wherein the variance of the inter-beat intervals is computed for a pre-determined number of cardiac beats N.

6. The method of claim 5, wherein the variance of the intervals between cardiac beats is computed if no interval is greater than a predetermined time T.

7. The method of claim 6, wherein N=15 and T is not greater than 2.5 sec.

8. The method of claim 1, wherein pre-determined threshold S is a number of cardiac beats M.

9. The method of claim 8, wherein M is about 300.

10. A method of detecting the cardiac atrial fibrillation event in an electronic signal indicative of heart beat (EKG signal) carried in a data stream that comprises time-stamped packets, said method comprising:

a) detecting at least one portion of an EKG signal comprising cardiac beats;

b) comparing the time-stamp of each packet to an expected time-stamp, thereby measuring the duration of a gap in the portion of the EKG signal data stream;

c) computing two or more inter-beat intervals, wherein the computed interval is outputted if the gap in the portion of the EKG signal is not more than a fraction alpha of the computed interval;

d) computing variance of the intervals between cardiac beats for a pre-determined number of cardiac beats N, if no interval is greater than a predetermined time T;

e) classifying the portions of the EKG signal as indicative of an atrial fibrillation event, whereby the inter-beat interval variance of the portion of the EKG signal that exceeds a pre-determined value V is indicative of an atrial fibrillation event;

f) discarding portions of the EKG signal classified as indicative of atrial fibrillation if said portions have a duration less than a pre-determined number of beats M, thereby smoothing the output of step (e); and

g) annotating the EKG signal, whereby the non-discarded portions of the EKG signals having inter-beat variances that exceed V are annotated as atrial fibrillation events.

11. The method of claim 10, wherein alpha is about one-half.

12. The method of claim 11, wherein N is 15 and T is not greater than 2.5 seconds.

13. The method of claim 12, wherein M is 300.

14. An apparatus for detection the cardiac atrial fibrillation event in electronic signal indicative of heart beat (EKG signal), comprising:

a) means for detecting a portion of an EKG signal comprising cardiac beats;

b) means for measuring the duration of a gap in the portion of the EKG signal;

c) means for computing inter-beat intervals, wherein the computed interval is outputted if the gap in the portion of the EKG signal is not more than a fraction alpha of the computed interval;

d) means for computing variance of the inter-beat intervals (inter-beat variance);

e) means for classifying the portions of the EKG signal as indicative of an atrial fibrillation event, whereby the inter-beat variance of the portion of the EKG signal that exceeds a pre-determined value V is indicative of an atrial fibrillation event;

f) means for discarding portions of the EKG signal classified as indicative of atrial fibrillation if said portions have a duration less than a predetermined threshold S, thereby smoothing the output of step (e); and

g) means for annotating the EKG signal, whereby the non-discarded portions of the EKG signals having inter-beat variances that exceed V are annotated as atrial fibrillation events.

15. The apparatus of claim 14, wherein the EKG signal comprises time-stamped packets.

16. The apparatus of claim 15, wherein the means for measuring the duration of a gap in the portion of the EKG signal includes the means for comparing the time-stamp of each packet to an expected time-stamp.

17. The apparatus of claim 14, wherein the means for computing the inter-beat variance computes said variance for a pre-determined number of cardiac beats N.

18. The apparatus of claim 17, wherein the means for computing the inter-beat variance computes said variance if no interval is greater than a predetermined time T.

19. The apparatus of claim 15, wherein alpha is about one-half.

20. The apparatus of claim 19, wherein N=15 and T is not greater than 2.5 seconds.

21. The apparatus of claim 14, wherein pre-determined threshold S is a number of cardiac beats M.

22. The apparatus of claim 21, wherein M is about 300.

23. An apparatus for detection the cardiac atrial fibrillation event in an electronic signal indicative of heart beat (EKG signal) carried in a data stream that comprises time-stamped packets, said method comprising:

a) means for detecting a portion of an EKG signal comprising cardiac beats;

b) means for comparing the time-stamp of each packet to an expected time-stamp, and thereby measuring the duration of a gap in the EKG signal data stream;

c) means for computing inter-beat intervals, wherein the computed interval is outputted if the gap in the portion of the EKG signal is not more than a fraction alpha of the computed interval;

d) means for computing variance of the inter-beat intervals (inter-beat variance) for a pre-determined number of cardiac beats N, said means computing the variance if no interval is greater than a predetermined time T;

e) means for classifying the portions of the EKG signal as indicative of an atrial fibrillation event, whereby the inter-beat variance of the portion of the EKG signal that exceeds a pre-determined value V is indicative of an atrial fibrillation event;

f) means for discarding portions of the EKG signal classified as indicative of atrial fibrillation if said portions have a duration less than a number of beats M, thereby smoothing the output of step (e); and

g) means for annotating the EKG signal, whereby the non-discarded portions of the EKG signals having inter-beat variances that exceed V are annotated as atrial fibrillation events.

24. The apparatus of claim 23, wherein alpha is about one-half.

25. The apparatus of claim 24, wherein N=15 and T is not greater than 2.5 sec.

26. The apparatus of claim 23, wherein M is 300.