Strength-Duration Curves for Ventricular Defibrillation in Dogs

The threshold voltage and current necessary for ventricular defibrillation was measured in dogs using capacitor-discharge and half-sinusoidal pulses of current of various durations. From these quantities the electrical strength required for defibrillation was determined and expressed as energy, peak current, and charge per gram of heart. The optimum current duration depends on the criterion selected. It was found that with half-sinusoidal current, less energy, current, and charge were required; this type of waveform approximates that delivered by capacitor-inductor defibrillators. For minimum energy with this waveform, the optimum duration range is 1.25 to 8.3 msec and the energy required is approximately 7 mw-sec per gram of heart. For minimum current, the optimum duration is 8.3 msec; with this duration the peak half-sinusoidal current is about 30 mamp per gram of heart. There is no clearly defined duration for minimum charge for capacitor-discharge or half-sinusoidal current.