Defibrillation waveforms for a wearable cardiac defibrillator

A method for an external defibrillator comprising two or more electrodes configured to be attached to a patient, an energy storage module, a discharge circuit coupled with 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, wherein the shock has a first phase duration and a second phase duration, an impedance measuring circuit to measure a transthoracic impedance (TTI) of the patient using at least some of the two or more electrodes, a memory to store a first shock algorithm and a second shock algorithm, and a processor coupled with the memory to control the impedance measuring circuit and the discharge circuit, the method comprising:

• measuring the TTI of the patient;
• causing the discharge circuit to apply the shock to the patient using the first algorithm when the TTI is below a predetermined TTI value, wherein the first phase duration is equal to the second phase duration;
• and
• causing the discharge circuit to apply the shock to the patient using the second algorithm when the TTI is below the predetermined TTI value, wherein the first phase duration is not equal to the second phase duration.

A wearable cardioverter defibrillator (WCD), comprising:

• a support structure to be worn by a patient;
• two or more electrocardiogram (ECG) electrodes coupled with the support structure and configured to be attached to the patient;
• an energy storage module;
• a discharge circuit, coupled with the energy storage module and two or more defibrillation electrodes coupled with the support structure and configured to be attached to the patient, wherein the discharge circuit is configured to output energy from the energy storage module to the patient in the form of a shock, and the shock has a first phase duration and a second phase duration;
• an impedance measuring circuit to measure a transthoracic impedance (TTI) of the patient using at least some of the two or more ECG electrodes;
• a memory to store a first shock algorithm and a second shock algorithm;
• a processor, coupled with the memory, to control the impedance measuring circuit and the discharge circuit, wherein the processor is configured to:
• measure the TTl of the patient;
• when the TTl is below a predetermined TTl value, cause the discharge circuit to apply the shock to the patient using the first algorithm, wherein the first phase duration is equal to the second phase duration;
• when the TTI is below the predetermined TTI value, cause the discharge circuit to apply the shock to the patient using the second algorithm, wherein the first phase duration is not equal to the second phase duration.