Defibrillation waveforms for a wearable cardiac defibrillator

An external defibrillator, comprising:

• two or more electrodes configured to be attached to a patient;
• an energy storage module;
• a discharge circuit, coupled to the energy storage module and at least two of the two or more electrodes, and configured to output energy from the energy storage module to the patient in the form of a shock;
• an impedance measurement module configured to measure a transthoracic impedance (TTI) of the patient using at least some of the two or more electrodes;
• a memory configured with:
• a first threshold,
• a first algorithm to determine a duration of a shock from the external defibrillator, and
• a second algorithm to determine a duration of a shock from the external defibrillator,
• the second algorithm being different from the first algorithm;
• and
• a processor coupled to the memory, the discharge circuit, and the impedance measurement module, the processor configured to:
• determine a shock duration, wherein responsive to a measured TTI being smaller than the first threshold, the processor is configured to determine the shock duration using the first algorithm, and responsive to the measured TTI being larger than the first threshold, the processor is configured to determine the shock duration using the second algorithm, and
• cause the discharge circuit to output energy from the energy storage module to the patient so that the shock delivered to the patient has the determined shock duration.