Atrial fibrillation detection
Atrial fibrillation is detected in an electrical signal representative of a beating heart by measuring atrial activity over a time window of three or more beats, measuring beat interval variation over the time window and combining the measures of atrial activity and beat interval variation to produce an indication of an atrial fibrillation condition in the electrical signal.
1. A computer implemented method comprises:
receiving an electrical signal representative of a beating heart;
measuring by the computer beat interval variation over a time window of three or more beats in the electrical signal;
measuring by the computer atrial activity to produce an atrial activity measure, by:
detecting a TQ interval in the electrical signal, the TQ interval defined by an offset of the T wave in the electrical signal and an onset of a subsequent QRS interval in the electrical signal;
detecting P-waves in the electrical signal within the detected TQ interval of the electrical signal;
classifying the detected P-waves as conducted or non-conducted; and
combining by the computer the atrial activity measure of classified P-waves and beat interval variation measure to produce an indication of an atrial fibrillation condition in the electrical signal.
2. The method of claim 1 wherein the electrical signals are provided from plural electrical channels and the method further comprises:
determining whether one or more P-waves are detected during a TQ interval on a channel from the plural channels with a largest expected P-wave;
combining a number and times of detected P-waves from that channel when plural P-waves are detected; otherwise,
combining a number and times of detected P-waves from an alternate one of the plural channels.
3. The method of claim 1 wherein measuring atrial activity further comprises:
computing a measure of the fraction of beat intervals that have one detected P wave.
4. The method of claim 1 measuring atrial activity further comprises determining if more than one P wave was present in a beat interval.
5. The method of claim 1 wherein detecting P waves further comprises:
provisionally classifying a P wave as conducted or non-conducted, by:
classifying a P-wave closest to the R-wave as conducted if the P-wave is within a time interval of 120 ms<PR<400 ms, otherwise
classifying the P-wave as non-conducted; and
classifying any other P-waves in the same TQ interval as non-conducted.
6. The method of claim 1 wherein measuring atrial activity further comprises:
using information from more than one signal channel representative of a beating heart to detect and classify the P-waves.
7. The method of claim 6 wherein measuring atrial activity further comprises:
measuring the atrial activity for a plurality of channels;
determining a quality indicator for the measured channels; and
selecting one of the measures from the channels based at least in part on the determined quality indicators for the measured channels.
8. The method of claim 1 wherein measuring atrial activity further comprises:
removing part or all of a ventricular waveform from the received ECG signal.
9. The method of claim 8 wherein measuring atrial activity further comprises:
measuring the atrial activity from a portion of the signal from which part or all of the ventricular waveform was removed.
10. The method of claim 1 wherein measuring atrial activity further comprises:
producing a measure that indicates whether continuous cyclic atrial activity exists in the electrical signal.
11. The method of claim 10 wherein measuring atrial activity further comprises:
computing a measure of the frequency of the continuous cyclic atrial activity.
12. The method of claim 10 wherein measuring atrial activity further comprises:
computing a measure of the magnitude of the continuous cyclic atrial activity.
13. The method of claim 1 wherein measuring atrial activity, measures the atrial activity over the time window and further comprises:
producing two or more atrial activity measures in the time window; and
combining the atrial activity measures into a representative atrial activity measure for the time window.
14. The method of claim 1 wherein measuring atrial activity comprises determining a measure for a subwindow of the time window.
15. The method of claim 1 wherein measuring atrial activity comprises combining measures from subwindows of the time window.
16. The method of claim 13 wherein combining the individual atrial activity measures uses a filtering function.
17. The method of claim 13 wherein combining uses a weighted average.
18. The method of claim 1 wherein measuring beat variation activity over the time window comprises:
producing two or more beat variation measures in the time window; and
combining the beat variation measures into a representative beat variation measure for the time window.
19. The method of claim 18 wherein combining the individual beat variation measures uses a filtering function.
20. The method of claim 18 wherein the combining the individual beat variation measures uses a weighted average.
21. The method of claim 1 wherein measuring beat interval variation comprises:
excluding beat intervals that meet one or more rejection criteria.
22. The method of claim 21 wherein the rejection criteria comprise determining that:
the beat interval is longer than a maximum duration, or
the beat interval is bounded by a beat that is not of an atrial origin, or
the beat interval includes a non-conducted P wave.
23. The method of claim 1 wherein combining comprises producing a combined measure C[i] determined by:
C
[
i
]
=
{
R
[
i
]
+
p
(
P
[
i
]
-
0.5
)
if
Q
[
i
]
and
P
[
i
]
>
r
R
[
i
]
otherwise
.
where Q[i] is t determined Boolean quality indicator; R[i] is the RR variability measure for the i th beat interval and P[i] is the P wave measure for the i th beat intervals,p is a P-wave multiplier value and r is a P-wave minimum threshold detection value.
24. The method of claim 1 wherein combining comprises:
coasting a value of the AF indication based on a value of a quality measure.
25. A computer program product residing on a computer readable medium for detecting the presence of atrial fibrillation in an electrical signal, the computer program product comprising instructions for causing a computer to:
receive the electrical signal representative of a beating heart;
measure beat interval variation over a time window of three or more beats in the electrical signal;
measure atrial activity over the time window of three or more beats by instructions to:
detect a T-Q interval in the electrical signal the TQ interval defined by an offset of the T wave in the electrical signal and an onset of a subsequent QRS interval in the electrical signal;
detect P-waves in the electrical signal within the detected TQ interval of the electrical signal;
classify the detected P-wave as conducted or non-conducted; and
combine the measures of atrial activity and beat interval variation to produce an indication of an atrial fibrillation condition in the electrical signal with the indication being negative if one conducted P-wave was detected in the beat interval.
26. The computer program product of claim 25 wherein instructions to classify the detected P-waves provisionally classify the P wave as conducted or non-conducted.
27. The computer program product of claim 26 wherein instructions to detect P-waves further comprises instructions to:
compute a measure of the fraction of beat intervals that have one detected P wave.
28. The computer program product of claim 25 wherein instructions to measure atrial activity comprise instructions to:
use information from more than one signal channel representative of a beating heart to detect and classify P-waves.
29. The computer program product of claim 25 wherein instructions to measure atrial activity comprise instructions to:
filter part or all of a ventricular waveform from the received ECG signal.
30. The computer program product of claim 25 wherein instructions to measure atrial activity comprise instructions to:
produce a measure that indicates whether continuous cyclic atrial activity exists in the electrical signal.
31. The computer program product of claim 25 wherein instructions to measure atrial activity over the time window comprise instructions to:
produce two or more atrial activity measures in the time window; and
combine the atrial activity measures into a representative atrial activity measure for the time window.
32. The computer program product of claim 25 wherein instructions to measure beat variation activity over the time window comprises instructions to:
produce two or more beat Variation measures in the time window; and
combine the beat variation measures into a representative beat variation measure for the time window.
33. The computer program product of claim 25 wherein instructions to measure beat interval variation comprises instructions to:
filter out beat intervals that meet one or more rejection criteria.
34. The computer program product of claim 25 wherein instructions to combine comprises instructions to:
coast a value of the AF indication based on a value of a quality measure.
35. An apparatus comprises:
circuitry to process an electrical signal for forming an indication of atrial fibrillation in the electrical signal, the circuitry comprising circuitry configured to:
receive the electrical signal representative of a beating heart;
measure beat interval variation over a time window of three or more beats in the electrical signal;
detect a T-Q interval in the electrical signal the TQ interval defined by an offset of the T wave in the electrical signal and an onset of a subsequent QRS interval in the electrical signal:
detect P-waves in the electrical signal within the detected TQ interval of the electrical signal;
classify the detected P-wave as conducted or non-conducted; and
combine the measures of atrial activity and beat interval variation to produce an indication of an atrial fibrillation condition in the electrical signal with the indication being negative if one conducted P-wave was detected in the beat interval.
36. The apparatus of claim 35 wherein the circuitry comprises:
a digital processor device; and
a computer readable medium storing a computer program product that comprises instructions that causes the processor to process the electrical signal to detect the presence of atrial fibrillation in the electrical signal.
37. The apparatus of claim 35 wherein the electrical signals are provided from plural electrical channels and further comprising circuitry to
determine whether one or more P-waves are detected during a TQ interval on a channel from the plural channels with a largest expected P-wave;
combine a number and times of detected P-waves from that channel when plural P-waves are detected; otherwise,
combine a number and times of detected P-waves from an alternate one of the plural channels.
38. The apparatus of claim 36 wherein circuitry to detect P-waves further comprises circuitry to:
compute a measure of the fraction of beat intervals that have one detected P wave.
39. The apparatus of claim 35 wherein circuitry to measure atrial activity comprise circuitry to:
determine if more than one P wave was present in a beat interval; and
classify a P-wave closest to the R-wave as conducted if the P-wave is within a time interval of 120 ms<PR<400 ms, otherwise
classify the P-wave as non-conducted: and
classify any other P-waves in the same TQ interval as non-conducted.
40. The apparatus of claim 35 wherein circuitry to measure atrial activity comprise circuitry to:
filter part or all of a ventricular waveform from the received ECG signal.
41. The apparatus of claim 35 wherein circuitry to measure atrial activity comprise circuitry to:
produce a measure that indicates whether continuous cyclic atrial activity exists in the electrical signal.
42. The apparatus of claim 35 wherein circuitry to measure atrial activity over the time window comprise circuitry to:
produce two or more atrial activity measures in the time window; and
combine the atrial activity measures into a representative atrial activity measure for the time window.
43. The apparatus of claim 35 wherein circuitry to measure beat variation activity over the time window comprises circuitry to:
produce two or more beat variation measures in the time window; and
combine the beat variation measures into a representative beat variation measure for the time window.
44. The apparatus of claim 35 wherein circuitry to measure beat interval variation comprises circuitry to:
filter out beat intervals that meet one or more rejection criteria.
45. The apparatus of claim 35 wherein circuitry to combine comprises circuitry to:
coast a value of the AF indication based on a value of a quality measure.