Cardiac monitoring
View Patent ↗Systems and techniques for monitoring cardiac activity. In one aspect, a method includes collecting information describing the variability in heart rate over a series of beats, designating variability at a lower end of physiological values as being largely irrelevant to atrial fibrillation, designating variability in a midrange of physiological values as being indicative of atrial fibrillation, designating variability in an upper range of physiological values as being negatively indicative of atrial fibrillation, and determining a relevance of the variability described in the collection to atrial fibrillation.
1. A device, comprising:
a beat detector to identify a beat-to-beat timing of cardiac activity;
a ventricular beat detector to identify ventricular beats in the cardiac activity;
variability determination logic to determine a variability in the beat-to-beat timing of a collection of beats;
relevance determination logic to identify a relevance of the variability in the beat-to-beat timing to at least one of atrial fibrillation and atrial flutter; and
an event generator to generate an event when the variability in the beat-to-beat timing is identified as relevant to the at least one of atrial fibrillation and atrial flutter in light of the variability in the beat-to-beat timing caused by ventricular beats identified by the ventricular beat detector.
2. The device of claim 1 , wherein the relevance determination logic is to accommodate variability in the beat-to-beat timing caused by ventricular beats by weighting ventricular beats as being negatively indicative of the one of atrial fibrillation and atrial flutter.
3. The device of claim 1 , wherein the variability determination logic is to compare times between R-waves in three successive QRS complexes to determine the variability in the beat-to-beat timing.
4. The device of claim 1 , wherein:
the variability determination logic is to represent the variability in the beat-to-beat timing as a factor that is lowest when a first time between beats is close to a second time between beats; and
the first time immediately proceeds the second time.
5. The device of claim 4 , wherein the variability determination logic is to represent the variability in the beat-to-beat timing as a factor that increases non-linearly when the absolute difference between the first time the second time grows.
6. The device of claim 4 , wherein the variability determination logic is to represent the variability in the beat-to-beat timing as a factor that increases more rapidly when the first time grows less than the second time than when the first time grows greater than the second time.
7. The device of claim 1 , wherein the event generator is to generate an event by performing operations comprising:
collecting data associated with the collection of beats; and
transmitting the data associated with the collection of beats to a remote receiver.
8. The device of claim 1 , wherein the relevance determination logic comprises weighting logic to:
weight variability at a lower end of physiological values as being substantially irrelevant to the one of atrial fibrillation and atrial flutter;
weight variability in a midrange of physiological values as being positively indicative of the one of atrial fibrillation and atrial flutter; and
weight variability in an upper range of physiological values as being negatively indicative of the one of atrial fibrillation and atrial flutter.
9. The device of claim 8 , wherein the weighting logic is also to weight a beat identified as a ventricular beat as being negatively indicative of the one of atrial fibrillation and atrial flutter.
10. The device of claim 1 , wherein the relevance determination logic comprises logic to identify the relevance of the variability using a non-linear function of a beat-to-beat interval.
11. The device of claim 1 , wherein the beat detector comprises a QRS detector.
12. The device of claim 1 , further comprising a sensor that includes two or more body surface electrodes subject to one or more potential differences related to cardiac activity.
13. A method comprising:
receiving information describing a timing of heart beats of an individual;
determining a first time between a first heart beat and a second heart beat of the individual, wherein the second heart beat follows immediately after the first heart beat;
determining a second time between the second heart beat and a third heart beat of the individual, wherein the third heart beat follows immediately after the second heart beat;
determining a factor reflecting the difference between the first time and the second time, wherein
the factor is lowest when the first time is close to the second time, and
the factor increases non-linearly when the absolute difference between the first time the second time grows; and
identifying at least one of an atrial fibrillation event and an atrial flutter event of the individual based on the factor.
14. The method of claim 13 , wherein the factor increases more rapidly when the first time grows less than the second time than when the first time grows greater than the second time.
15. The method of claim 13 , wherein:
the method further comprises weighting the factor to reflect a relevance of the factor to one of atrial fibrillation and atrial flutter; and
the identifying of the at least one of the atrial fibrillation event and the atrial flutter event is based on the weighted factor.
16. The method of claim 15 , wherein weighting the factor comprises:
weighting the factor at a lower end of physiological values as being substantially irrelevant to the one of atrial fibrillation and atrial flutter;
weighting the factor in a midrange of physiological values as being positively indicative of the one of atrial fibrillation and atrial flutter; and
weighting the factor in an upper range of physiological values as being negatively indicative of the one of atrial fibrillation and atrial flutter.
17. The method of claim 13 , wherein:
the method further comprise repeating the determining of the first time, the determining of the second time, and the determining of the factor for additional heart beats to generate additional factors; and
the identifying of the at least one of the atrial fibrillation event and the atrial flutter event is based on the additional factors.
18. The method of claim 17 , wherein identifying the at least one of the atrial fibrillation event and the atrial flutter event of the individual based on the additional factors comprises identifying the at least one of the atrial fibrillation event and the atrial flutter event of the individual based on between 19 and 199 additional factors.
19. The method of claim 13 , wherein determining the factor comprises determining DRR(n) as given by
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20. An article comprising one or more machine-readable media storing instructions operable to cause one or more machines to perform operations, the operations comprising:
determining a beat-to-beat variability in cardiac electrical activity;
determining a relevance of the variability over a collection of beats to one of atrial fibrillation and atrial flutter using a non-linear function of a beat-to-beat interval; and
identifying one of an atrial fibrillation event and an atrial flutter event based on the determined relevance, the event being a period in time when the information content of the cardiac electrical activity is of increased relevance to the one of atrial fibrillation and atrial flutter.
21. The article of claim 20 , wherein determining the relevance comprises:
weighting variability at a lower end of physiological values as being substantially irrelevant to the one of atrial fibrillation and atrial flutter;
weighting variability in a midrange of physiological values as being positively indicative of the one of atrial fibrillation and atrial flutter;
weighting variability in an upper range of physiological values as being negatively indicative of the one of atrial fibrillation and atrial flutter; and
determining a relevance of the weighted variability to the one of atrial fibrillation and atrial flutter.
22. The article of claim 20 , determining the relevance comprises:
identifying a beat of the collection as a ventricular beat, and
weighting the beat as being negatively indicative of the one of atrial fibrillation and atrial flutter.
23. The article of claim 20 , wherein:
determining the beat-to-beat variability comprises determining a factor reflecting the difference between a first time between a first heart beat and a second heart beat and a second time between a second heart beat and a third heart beat;
the second heart beat follows immediately after the first heart beat; and
the third heart beat follows immediately after the second heart beat.
24. The article of claim 23 , wherein:
the factor is lowest when the first time is close to the second time; and
the factor increases non-linearly when the absolute difference between the first time the second time grows.
25. The article of claim 24 , wherein the factor increases more rapidly when the first time grows less than the second time than when the first time grows greater than the second time.