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

• US 7,734,335 B2
• Filed: 09/29/2005
• Issued: 06/08/2010
• Est. Priority Date: 09/29/2005
• Status: Expired due to Fees

• 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
• Primary Examiner(s): Layno; Carl H.
• Assistant Examiner(s): Heller; Tammie K
• Application Number:
  US11/241,294
• Publication Number:
  US 20070073177A1
• Time in Patent Office: 1,713 Days
• Field of Search: 600/509, 600/515, 600/516, 600/519
• US Class Current: 600/515
• 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 a cardiac atrial fibrillation event in a non-continuous electrocardiogram (EKG) signal, the method comprising:

a) detecting a portion of the EKG signal comprising cardiac beats, wherein the portion includes at least one gap;

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

c) computing a plurality of inter-beat intervals using the cardiac beats, wherein a computed inter-beat interval of the plurality is selected if the measured gap duration in the detected portion of the EKG signal is not more than a fraction alpha of the computed inter-beat interval;

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

e) classifying the portion of the EKG signal as indicative of an atrial fibrillation event if the computed variance of the classified portion of the EKG signal exceeds a pre-determined value V;

f) discarding the portion of the EKG signal classified as indicative of atrial fibrillation if the classified portion has a duration less than a pre-determined threshold S; and

g) annotating the EKG signal, a non-discarded portion of the EKG signal having the computed variance that exceeds the pre-determined value V being annotated as an atrial fibrillation event.

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

3. The method of claim 2, wherein the gap duration in the EKG signal detected portion is measured by comparing a time-stamp of each time-stamped 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 selected 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 selected inter-beat intervals is computed if no selected inter-beat interval is greater than a predetermined time T.

7. The method of claim 6, wherein the pre-determined number of cardiac beats N equals about 15 and the predetermined time T is not greater than 2.5 seconds.

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

9. The method of claim 8, wherein the number of cardiac beats M is about 300.

10. A method of detecting a cardiac atrial fibrillation event in a non-continuous electrocardiogram (EKG) signal carried in a data stream that comprises time-stamped packets, the method comprising:

a) detecting a portion of the data stream carrying the EKG signal comprising cardiac beats, wherein the portion includes at least one gap;

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

c) computing a plurality of inter-beat intervals, wherein a computed inter-beat interval of the plurality is selected if the measured gap duration in the portion of the EKG signal data stream is not more than a fraction alpha of the computed inter-beat interval;

d) computing a variance of the selected inter-beat intervals for a predetermined number of cardiac beats N if no selected inter-beat interval is greater than a predetermined time T;

e) classifying the portion of the EKG signal data stream as indicative of an atrial fibrillation event if the computed variance of the classified portion of the EKG signal data stream exceeds a pre-determined value V;

f) discarding the portion of the EKG signal data stream classified as indicative of atrial fibrillation if the classified portion has a duration less than a pre-determined number of cardiac beats M; and

g) annotating the EKG signal data stream, a non-discarded portion of the EKG signal data stream having the computed variance that exceeds the pre-determined value V being annotated as an atrial fibrillation event.

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

12. The method of claim 11, wherein the predetermined number of cardiac beats N is about 15 and the predetermined time T is not greater than 2.5 seconds.

13. The method of claim 12, wherein the pre-determined number of cardiac beats M is 300.

14. An apparatus that detects a cardiac atrial fibrillation event in a non-continuous electrocardiogram (EKG) signal, the apparatus comprising:

a) means for detecting a portion of the EKG signal comprising cardiac beats, wherein the portion includes at least one gap;

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

c) means for computing inter-beat intervals that selects a computed interval if the measured gap duration in the portion of the EKG signal is not more than a fraction alpha of the computed inter-beat interval;

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

e) means for classifying the portion of the EKG signal as indicative of an atrial fibrillation event if the computed variance of the classified portion of the EKG signal exceeds a pre-determined value V;

f) means for discarding the portion of the EKG signal classified as indicative of atrial fibrillation if the classified portion has a duration less than a pre-determined threshold S; and

g) means for annotating the EKG signal, a non-discarded portion of the EKG signal having the computed variance that exceeds the pre-determined value V being annotated as an atrial fibrillation event.

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 a duration of a gap in the portion of the EKG signal comprises means for comparing a time-stamp of each time-stamped packet to an expected time-stamp.

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

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

19. The apparatus of claim 18, wherein the fraction alpha is about one-half.

20. The apparatus of claim 19, wherein the pre-determined number of cardiac beats N is equal to about 15 and the predetermined time T is not greater than 2.5 seconds.

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

22. The apparatus of claim 21, wherein the number of cardiac beats M is about 300.

23. An apparatus that detects a cardiac atrial fibrillation event in a non-continuous electrocardiogram (EKG) signal carried in a data stream that comprises time-stamped packets, the apparatus comprising:

a) means for detecting a portion of an EKG signal comprising cardiac beats, wherein the portion includes at least one gap;

b) means for comparing a time-stamp of each time-stamped packet to an expected time-stamp to measure a duration of the gap in the portion of the EKG signal;

c) means for computing inter-beat intervals that selects a computed inter-beat interval if the measured gap duration in the portion of the EKG signal is not more than a fraction alpha of the computed inter-beat interval;

d) means for computing a variance of the computed inter-beat intervals selected by the means for computing inter-beat intervals, the variance being computed for a pre-predetermined number of cardiac beats N, wherein the means for computing a variance computes the variance if no selected inter-beat interval is greater than a predetermined time T;

e) means for classifying the portion of the EKG signal as indicative of an atrial fibrillation event if the computed variance of the portion of the EKG signal exceeds a pre-determined value V;

f) means for discarding the portion of the EKG signal classified as indicative of atrial fibrillation if the classified portion has a duration less than a number of cardiac beats M; and

g) means for annotating the EKG signal, a non-discarded portion of the EKG signal having the computed variance that exceeds V being annotated as an atrial fibrillation event.

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

25. The apparatus of claim 24, wherein the pre-determined number of cardiac beats N equals about 15 and the predetermined time T is not greater than 2.5 seconds.

26. The apparatus of claim 23, wherein the number of cardiac beats M is about 300.