A wearable cardioverter defibrillator system includes a support structure that is configured to be worn by a patient. When thus worn, the support structure may attach electrodes at different locations of the patient's body, so as to define different vectors. A measurement circuit may sense ECG signals from the different vectors substantially concurrently. A processor may multiply together these substantially concurrent ECG signals to derive a product waveform. The processor may then detect peaks in the product waveform, measure durations of time intervals between successive peaks, and determine the patient's heart rate from these durations. An advantage can be that the heart rate may be computed notwithstanding noise in the individual ECG signals.
