Wearable cardioverter defibrillator having reduced noise prompts

1. A wearable cardioverter defibrillator (WCD), 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 render an electrocardiogram (ECG) signal of the patient while the patient is wearing the support structure;

a user interface configured to output an alarm in response to a noise alarm signal; and

a processor configured to:

receive the ECG signal,

determine whether noise is present on the ECG signal,

determine from the ECG signal whether a shock criterion is met,

cause the user interface to generate the noise alarm signal when the noise is present on the ECG signal and the shock criterion is met and not generate the noise alarm signal when noise is present on the ECG signal and the shock criterion is not met,

receive an additional ECG signal for a predetermined time after the shock criterion is met,

determine whether noise is present on the additional ECG signal, and

when the noise is determined to be present on the additional ECG signal, generate the noise alarm signal.

2. The WCD of claim 1 , wherein the predetermined amount of time is between five seconds and fifteen minutes.

3. The WCD of claim 1 , wherein the user interface is further configured to receive an input from a user, and wherein the processor is further configured to control the discharge circuit to discharge a stored charge if the input from the user input is not received within a predetermined amount of time after the noise alarm signal is generated.

4. The WCD of claim 1 , wherein the processor is further configured to detect QRS complexes in the ECG signal and determine noise is present on the ECG signal when an amplitude of an unfiltered baseline shift in the vicinity of a detected QRS complex is larger than a threshold.

5. The WCD of claim 4 , wherein the threshold is between 2-20 mV.

6. The WCD of claim 1 , wherein the processor is further configured to detect QRS complexes in the ECG signal and determine noise is present on the ECG signal when a number of baseline crossings near a detected QRS complex is greater than a threshold.

7. The WCD of claim 1 , wherein the processor is further configured to detect QRS complexes in the ECG signal and determine noise is present on the ECG signal when a pulse width of a detected QRS complex is less than a threshold.

8. The WCD of claim 1 , further comprising a physical sensor configured to output a signal and wherein the processor is further configured to determine noise is present on the ECG signal when the signal from the physical sensor and the ECG signal are correlated.

9. The WCD of claim 1 , further comprising a physical sensor configured to output a signal and wherein the processor is further configured to:

detect a high rate of change on the signal;

detect a QRS complex in the ECG signal;

determine whether the high rate of change is coincident with the QRS complex; and

determine noise is present on the ECG signal when the high rate of change is coincident with the QRS complex.

10. The WCD of claim 1 , wherein the alarm is an audible alarm.

11. The WCD of claim 1 , wherein the processor is further configured to detect QRS complexes in the ECG signal and determine noise is present on the ECG signal when an amplitude of the detected QRS complex is greater than a threshold.

12. The WCD of claim 11 , wherein the threshold is between 2-20 mV.