Method to detect noise in a wearable cardioverter defibrillator

A wearable cardioverter defibrillator (WCD) system, comprising:

• a support structure wearable by a patient;
• a processor;
• and
• a discharge circuit configured to discharge stored electrical charge through a body of the patient, the discharge circuit in communication with the processor, wherein the processor is configured to:
• receive signals from at least three sensing electrodes that include a first sensing electrode located at a first location on the patient, a second sensing electrode located on a second location of the patient, and a third sensing electrode located on a third location of the patient, the at least three sensing electrodes configured to monitor electrical activity of a heart of the patient;
• obtain, during the monitoring, a first signal from the first sensing electrode, wherein the first signal is based on a cardiac rhythm measured by the first sensing electrode at the first location during a first time period;
• obtain, during the monitoring, a second signal from the second sensing electrode, wherein the second signal is based on the cardiac rhythm measured by the second sensing electrode at the second location during the first time period;
• obtain, during the monitoring, a third signal from the third sensing electrode, wherein the third signal is based on the cardiac rhythm measured by the third sensing electrode at the third location during the first time period;
• define, during the monitoring, at least three channels between the at least three sensing electrodes;
• calculate, during the monitoring, a morphological similarity value of at least one combination of the at least three channels by comparing the first signal with at least one of the second signal or the third signal;
• and
• determine, during the monitoring, a noise level based, at least in part, on the morphological similarity value calculated for the at least one combination of the at least three channels, wherein the noise level is used, at least in part, in determining that the patient has experienced an event of arrhythmia.