Wearable medical device with zoneless arrhythmia detection

A wearable cardioverter defibrillator (WCD) system, comprising:

• a support structure to be worn by a patient;
• an energy storage module to store an electrical charge;
• at least one therapy electrode coupled to the support structure;
• at least one sensor, coupled to the support structure, configured to generate an electrocardiogram (ECG) of the patient when the patient is wearing the support structure;
• and
• a processor, communicatively coupled to the at least one sensor, configured to:
• receive the ECG of the patient from the at least one sensor;
• determine, based on the received ECG, whether a heart rate and/or QRS width of the patient is within a predefined ventricular fibrillation (VF) zone, wherein the predefined VF zone corresponds to one or more ranges of the heart rate and/or the QRS width indicating VF;
• in response to a determination that the heart rate and/or the QRS width of the patient is outside the predefined VF zone, perform a sudden rate change onset (SRCO) detection of the received ECG, wherein to perform the SRCO detection, the processor is configured to:
• detect a first heart parameter value from the received ECG at a first time,
• detect a second heart parameter value from the received ECG at a second time, wherein the first heart parameter value and the second heart parameter value comprise one of a heart rate (HR), R-R interval, average HR, or an average R-R interval,
• determine a difference between the first heart parameter value and the second heart parameter value, and
• detect the SRCO of the received ECG based, at least in part, on comparison of absolute value of the difference between the first heart parameter value and the second heart parameter value with a predetermined threshold;
• responsive to the detected SRCO, perform a process to determine whether the received ECG is indicative of VF;
• and
• cause the energy storage module to discharge at least a portion of the stored electrical charge to the patient using the at least one therapy electrode, at least in part, in response to a determination that VF is indicated.