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 wearable cardioverter defibrillator (WCD) system, comprising:
a support structure configured to be worn by a patient;
an energy storage module configured to store an electrical charge;
a discharge circuit coupled to the energy storage module;
a plurality of electrodes configured to be coupled with the patient's body; and
a processor configured to:
sense, with the plurality of electrodes, a first Electrocardiogram (ECG) signal of the patient in a first channel, and a second ECG signal of the patient in a second channel;
identify a first group of peaks in the first ECG signal;
measure intervals between a first number of peaks in the first group of peaks to provide a first set of intervals from the first channel;
identify a second group of peaks in the second ECG signal;
measure intervals between a second number of peaks in the second group of peaks to provide a second set of intervals from the second channel;
combine the first set of intervals from the first channel with the second set of intervals from the second channel to provide a combined group of intervals;
identify a mode interval in the combined group of intervals corresponding to a mode of the combined group of intervals, wherein the mode of the combined group of intervals comprises a most frequently occurring interval;
compute a heart rate value for the patient from the mode interval;
determine, based at least in part on the heart rate value, whether one or more shock criteria are met; and
control, responsive to the one or more shock criteria 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 therapeutic shock to the patient.
2. The WCD system of claim 1 , further comprising:
a communication module configured to wirelessly transmit heart rate to a remote device.
3. The WCD system of claim 1 , further comprising:
a user interface configured to display heart rate.
4. The WCD system of claim 1 , wherein:
the measured intervals in the first group of peaks and the second group of peaks include consecutive intervals and non-consecutive intervals.
5. The WCD system of claim 1 , wherein:
the first number of peaks comprises all of the peaks in the first group of peaks; and
the second number of peaks comprises all of the peaks in the second group of peaks.
6. The WCD system of claim 1 , wherein:
all of the intervals in the first group of peaks are measured; and
all of the intervals in the second group of peaks are measured.
7. The WCD system of claim 1 , wherein the processor is further configured to:
discern clusters of intervals in the combined group of intervals; and
wherein the mode interval is determined from a cluster that corresponds to the mode of the combined group of intervals.
8. The WCD system of claim 7 , wherein:
the clusters are discerned by filtering intervals in the combined group of intervals to identify the mode interval for the cluster.
9. The WCD system of claim 7 , wherein:
the clusters are discerned by running a grouping kernel on the intervals in the combined group of intervals to identify the node interval for the cluster.
10. The WCD system of claim 9 , wherein:
the grouping kernel is implemented as a boxcar Finite Impulse Response (FIR) filter.
11. A method for a cardiac monitoring device, the cardiac monitoring device including a processor, a memory, and electrodes, the method comprising:
sensing, by the electrodes, an Electrocardiogram (ECG) signal of a patient;
detecting, with the processor, peaks occurring within the 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 of the detected peaks;
identifying, with the processor and from the measured durations of time intervals, a mode duration, wherein the mode duration comprises a most common value of the measured durations of time intervals;
computing a heart rate of the patient, with the processor, from the mode duration;
storing, from the processor, the heart rate in the memory;
determining, with the processor and from the heart rate, whether an arrhythmia event is detected; and
generating a notification regarding patient status responsive to the detected arrhythmia event.
12. The method of claim 11 , wherein:
the cardiac monitoring device further includes a communication module; and
the method further comprises wirelessly transmitting the stored heart rate.
13. The method of claim 11 , wherein:
the cardiac monitoring device further includes a screen; and
the method further comprises displaying the stored heart rate on the screen.
14. The method of claim 11 , further comprising:
establishing all possible pairs of the detected peaks.
15. The method of claim 11 , further comprising:
sensing, by the electrodes, another ECG signal of the patient distinct from the ECG signal;
detecting, with the processor, other peaks occurring 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 mode duration from both the measured durations of time intervals and the measured other durations.
16. The method of claim 11 , wherein:
the most common value comprises a mode of the measured durations of time intervals.
17. The method of claim 11 , wherein:
a fraction of the mode duration occurs less often than an occurrence threshold.
18. The method of claim 11 , wherein:
the mode 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.
19. The method of claim 11 , wherein:
the heart rate is computed from a duration having a number of occurrences that is one-half or one-third of a number of occurrence of the mode duration.
20. The method of claim 11 , wherein:
the cardiac monitoring device includes a support structure configured to be worn by the patient, an energy storage module storing an electrical charge, and a discharge circuit coupled to the energy storage module, and
the method further comprising:
responsive to the detected arrhythmia event, controlling, with the processor and responsive to a 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.