Defibrillation without A-V Block Using Capacitor Discharge with Added Inductance

Abstract

Two hundred and seventy-two defibrillations of the ventricles of 17 dogs by capacitor discharge applied directly to the heart were accompanied by A-V block lasting up to 78 seconds. A range of 150 to 475 volts was employed using a 40 microfarad condenser. The duration of the block was proportional to the energy employed for defibrillation. With the minimum energy of 1.8 watt-sec that produced 100% defibrillation in all trials, A-V block was present in 14 of the 17 animals (average duration of A-V block varying from 3 to 18 seconds). That the A-V block is not vagal in origin was demonstrated by atropinization and vagotomy of the animals. Prolongation of the period of fibrillation up to 15 seconds was found not to be a factor in determining the duration of A-V block. Defibrillation with the same energy levels but with the inclusion of an 0.29 henry inductance abolished the A-V block in 115 defibrillations in the same 17 animals. The current waveform measured without inductance was of the capacitor discharge type (unidirectional and exponentially decaying); with the inductance in the circuit the current waveform was a highly damped sinusoidal alternating current consisting of slightly more than two full cycles of about 40 Hz.