Wearable cardioverter defibrillator (WCD) system reacting to high-amplitude ECG noise
In embodiments a WCD system is worn and/or carried by an ambulatory patient. The WCD system analyzes an ECG signal of the patient, to determine whether or not the patient should be given an electric shock to restart their heart. If so, then the WCD system first gives a preliminary alarm to the patient, asking them to prove they are alive if they are. The WCD system further determines whether the ECG signal contains too much High Amplitude (H-A) noise, which can distort the analysis of the ECG signal. If too much H-A noise is detected for a long time, the WCD system may eventually alert the patient about their activity, so that the ECG noise may be abated. The WCD system may even pause the analysis of the ECG signal, so that there will be no preliminary alarms that could be false until the ECG noise is abated.
1. A wearable cardioverter defibrillator (WCD) system, comprising:
a support structure configured to be worn by an ambulatory patient;
an energy storage module configured to store an electrical charge;
a discharge circuit coupled to the energy storage module;
electrodes configured to sense an Electrocardiogram (ECG) signal of the patient;
a processor configured to:
set a noise-detected flag responsive to the sensed ECG signal meeting a High-Amplitude (H-A) noise criterion, and unset the noise-detected flag responsive to the sensed ECG signal meeting a High-Amplitude (H-A) quiet criterion, wherein the H-A noise criterion is met when a fraction of ECG portions in a group of ECG portions having a potential R peak exceeding a threshold amplitude is greater than a threshold fraction, and the H-A quiet criterion is met when the H-A noise criterion is no longer met;
determine, from the sensed ECG signal, whether a shock criterion is met, and
control, responsive to the shock criterion being met and the noise-detected flag being unset, 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, wherein the discharge circuit is controlled to not discharge when the noise-detected flag is set even when it is determined that the shock criterion is met.
2. The WCD system of claim 1 , in which
the noise-detected flag becomes unset responsive to the noise-detected flag having been set for a tolerance time.
3. The WCD system of claim 2 , in which
the tolerance time is at least 0.5 minutes.
4. The WCD system of claim 1 , in which
it is not determined whether the shock criterion is met when the noise-detected flag is set.
5. The WCD system of claim 1 , further comprising:
a user interface configured to output an alert responsive to the noise-detected flag being set.
6. The WCD system of claim 5 , in which
the alert is output further responsive to the noise-detected flag having been set for a tolerance time.
7. The WCD system of claim 6 , in which
the tolerance time is at least 0.5 minutes.
8. The WCD system of claim 5 , in which
the noise-detected flag becomes unset responsive to outputting the alert.
9. The WCD system of claim 1 , in which
ECG portions of the sensed ECG signal are defined, and
the H-A noise criterion is met responsive to a group of the most recent ECG portions meeting a noise condition.
10. The WCD system of claim 9 , in which
if the H-A noise criterion is not met, it is determined whether a shock criterion is met only from the ECG portions that do not meet the noise condition.
11. The WCD system of claim 9 , in which
ECG portions of the group become marked responsive to meeting a noisiness criterion,
a noise fraction is computed of a number of the marked ECG portions of the group over a total number of the ECG portions of the group, and
the noise condition is met responsive to the noise fraction exceeding a threshold noise fraction.
12. The WCD system of claim 11 , in which
potential R peaks of QRS complexes are identified in a certain ECG portion of the group,
the identified potential R peaks in the certain ECG portion that meet a spuriousness criterion are deemed invalid,
a validity ratio is defined for the certain ECG portion by a number of the potential R peaks in the certain ECG portion that are deemed invalid over a total number of the identified potential R peaks in the certain ECG portion, and
the certain ECG portion meets the noisiness criterion responsive to the validity ratio exceeding a threshold validity ratio.
13. The WCD system of claim 12 , in which
an identified potential R peak in the certain ECG portion meets the spuriousness criterion responsive to having an amplitude larger than a threshold amplitude.
14. The WCD system of claim 13 , in which
the certain ECG portion is filtered, and
an identified potential R peak in the certain filtered ECG portion meets the spuriousness criterion responsive to having an amplitude larger than a threshold amplitude.
15. The WCD system of claim 12 , in which
an ECG segment is defined to have a time duration that includes a certain one of the identified potential R peaks in the certain ECG portion, and
the certain identified potential R peak meets the spuriousness criterion responsive to a starting amplitude at the beginning of the ECG segment differing from an ending amplitude at the end of the ECG segment by more than a threshold baseline shift.
16. The WCD system of claim 9 , in which
potential R peaks of QRS complexes are identified in the sensed ECG signal, and
the ECG portions are defined as the identified potential R peaks.
17. The WCD system of claim 16 , in which
the identified potential R peaks are marked responsive to meeting a spuriousness criterion,
a noise fraction is computed from a number of the identified potential R peaks of the group over a total number of the identified potential R peaks of the group, and
the noise condition is met responsive to the noise fraction exceeding a threshold noise fraction.
18. The WCD system of claim 17 , in which
an identified potential R peak meets the spuriousness criterion responsive to having an amplitude larger than a threshold amplitude.
19. The WCD system of claim 18 , in which
the sensed ECG signal is filtered, an
an identified potential R peak meets the spuriousness criterion responsive to having an amplitude larger than a threshold amplitude.
20. The WCD system of claim 17 , in which
an ECG segment becomes defined to have a time duration that includes a certain one of the identified potential R peaks in the certain ECG portion, and
the certain identified potential R peak meets the spuriousness criterion responsive to a starting amplitude at the beginning of the ECG segment differing from an ending amplitude at the end of the ECG segment by more than a threshold baseline shift.
21. The WCD system of claim 9 , in which
the H-A quiet criterion is met responsive to another group of the most recent ECG portions not meeting the H-A noise condition, at least one ECG portion of the other group occurring after at least one ECG portion of the group.
22. The WCD system of claim 9 , in which
the H-A quiet criterion is met responsive to another group of the most recent ECG portions meeting a quiet condition, at least one ECG portion of the other group occurring after at least one ECG portion of the group.
23. The WCD system of claim 22 , in which
ECG portions of the group become marked responsive to meeting a noisiness criterion,
a quiet fraction is computed of a number of the marked ECG portions of the group over a total number of the ECG portions of the group, and
the quiet condition is met responsive to the quiet fraction being less than a threshold quiet fraction.
24. The WCD system of claim 23 , in which
potential R peaks of QRS complexes are identified in a certain ECG portion of the other group,
the identified potential R peaks in the certain ECG portion that meet a spuriousness criterion are deemed invalid,
a validity ratio is defined for the certain ECG portion by a number of the potential R peaks in the certain ECG portion that are deemed invalid over a total number of the identified potential R peaks in the certain ECG portion, and
the certain ECG portion meets the noisiness criterion responsive to the validity ratio exceeding a threshold validity ratio.
25. The WCD system of claim 24 , in which
an identified potential R peak in the certain ECG portion meets the spuriousness criterion responsive to having an amplitude larger than a threshold amplitude.
26. The WCD system of claim 25 , in which
the certain ECG portion is filtered, and
an identified potential R peak in the certain filtered ECG portion meets the spuriousness criterion responsive to having an amplitude larger than a threshold amplitude.
27. The WCD system of claim 24 , in which
an ECG segment becomes defined to have a time duration that includes a certain one of the identified potential R peaks in the certain ECG portion, and
the certain identified potential R peak meets the spuriousness criterion responsive to a starting amplitude at the beginning of the ECG segment differing from an ending amplitude at the end of the ECG segment by more than a threshold baseline shift.