Wearable cardioverter defibrillator (WCD) system computing heart rate from noisy ECG signal
In embodiments, a WCD system includes electrodes with which it senses an ECG signal of the patient. A processor may detect sequential peaks within the ECG signal, measure durations of time intervals between the peaks, including between non-sequential peaks, and identify a representative duration that best meets a plausibility criterion. The plausibility criterion may be that the representative duration is the one that occurs the most often, i.e. is the mode. Then a heart rate can be computed from a duration indicated by the representative duration and, if the heart rate meets a shock condition, the WCD system may deliver a shock to the patient. An advantage can be that the representative duration can be close to a good R-R interval measurement of a patient, notwithstanding noise in the ECG signal that is in the shape of peaks.
1. A method for a wearable cardioverter defibrillator (WCD) system, the WCD system including a support structure configured to be worn by an ambulatory patient, an energy storage module storing an electrical charge, a discharge circuit coupled to the energy storage module, a processor, a memory and electrodes, the method comprising:
sensing, by the electrodes, a first Electrocardiogram (ECG) signal of the patient, and then sensing a second ECG signal after sensing the first ECG signal;
detecting with the processor peaks occurring sequentially within the first ECG signal;
establishing pairs of the detected peaks with the processor, at least one of the pairs being established by peaks not occurring sequentially,
measuring with the processor durations of time intervals defined by the established pairs;
identifying with the processor and from the measured durations, a representative duration that meets a plausibility criterion;
computing a heart rate of the patient with the processor from a duration indicated by the representative duration;
storing in the memory from the processor the computed heart rate;
determining with the processor and from the second ECG signal whether or not a shock criterion is met; and
controlling, with the processor and responsive to the shock criterion being met, the discharge circuit to discharge the stored electrical charge through the patient while the support structure is worn by the patient to deliver a shock to the patient.
2. The method of claim 1 , wherein:
the WCD system further includes a communication module, and
further comprising transmitting wirelessly the stored heart rate.
3. The method of claim 1 , wherein:
the WCD system further includes a screen, and
further comprising displaying the stored heart rate on the screen.
4. The method of claim 1 , further comprising:
establishing all possible pairs of the detected peaks.
5. The method of claim 1 , further comprising:
sensing, by the electrodes, another ECG signal of the patient distinct from the ECG signal and from the second ECG signal;
detecting with the processor other peaks occurring sequentially within the other ECG signal;
establishing with the processor other pairs of the detected other peaks, at least one of the other pairs being established by other peaks not occurring sequentially within the other ECG signal;
measuring with the processor other durations of time intervals defined by the established other pairs; and
identifying with the processor the representative duration from both the measured durations and the measured other durations.
6. The method of claim 1 , wherein:
the plausibility criterion includes that the representative duration is the one that occurs the most often among the measured durations.
7. The method of claim 1 , wherein:
the plausibility criterion includes that a fraction of the identified representative duration occurs less often than an occurrence threshold.
8. The method of claim 1 , wherein:
the plausibility criterion includes that the representative duration has a value of D and occurs M times, and
a duration having a value of D/N, where N takes one of the values of 2, 3, 4 and 5, occurs less often than M/N times.
9. The method of claim 1 , wherein:
the heart rate is computed from the representative duration.
10. The method of claim 1 , further comprising:
discerning clusters of the measured durations, and
in which the representative duration is identified from the cluster that best meets the plausibility criterion.
11. The method of claim 10 , wherein:
the clusters are identified by filtering the measured durations.
12. The method of claim 10 , wherein:
the plausibility criterion includes that the representative duration is the one that occurs the most often among the measured durations.
13. The method of claim 10 , wherein:
the plausibility criterion includes that a fraction of the identified representative duration occurs less often than an occurrence threshold.
14. The method of claim 10 , wherein:
the plausibility criterion includes that the representative duration has a value of D and occurs M times, and
a duration having a value of D/N, where N takes one of the values of 2, 3, 4 and 5, occurs less often than M/N times.
15. The method of claim 1 , wherein:
the shock criterion is bast at least in part on the heart rate of the patient computed from the duration indicated by the representative duration.
16. The method of claim 15 , wherein:
the shock criterion is further based at least in part on a width of one or more QRS complexes corresponding to the detected peaks of the first ECG signal.