Optimal parameters of electrical impulses for defibrillation by condenser discharges.

• Determination of the defibrillation threshold of the heart is important not only for developing the technique of defibrillation per se but also for improving the design of instruments used for that purpose. Previous workhas shown the necessity of selecting, for the discharge circuit, parameters that will keep voltage as low as possible, but many questions concerning the optimal parameters for d-c condenser discharges still remain unanswered. Gurvic has described a major portion of existing information on this subject, and Mackay and Leeds have studied optimal parameters for condenser discharges up to 15 microfarads (/AF). However, none of the work reported thus far has utilized a wide enough range of capacitances; the actual voltage at the electrodes was not measured; and inductive effects in the discharge circuit were not taken into account. The present paper reports results based on more than 1000 measurements of defibrillation threshold, together with statistical evaluation of effects obtained by means of three different types of condenser discharge. In all experiments we measured the voltage at the condenser, the voltage at the electrodes, and the current and duration of the discharge impulse. In order to exclude the influence of ischemia" and other technical artefacts, the experiments were done under standard conditions and for this reason the results are valid only for the given technique. Defibrillation thresholds were determined for three types of discharge: 1) pure condenser discharge, as used most frequently in the literature but with very variable results; 2) condenser discharge through an