Quantitative study of the effect of lidocaine on the threshold for ventricular fibrillation in the dog

Abstract

The effects of lidocaine upon the current required to induce ventricular fibrillation was assessed during normal supraventricular rhythm and after premature ventricular beats. Ventricular fibrillation thresholds were determined by passing a train of 10 to 15 constant current pulses, each 4 msec in duration, at 10 msec intervals through ventricular epicardial electrodes during the vulnerable period. The intensity of the current pulses was varied, and the ventricular fibrillation threshold was defined as the current in milliamperes which caused ventricular fibrillation. Our data show that during administration of lidocaine the ventricular fibrillation threshold after both normal and premature beats increased; that is, fibrillation was more difficult to evoke in the presence of lidocaine. Over a range of 0 to 6¦μ¦g/ml the ventricular fibrillation threshold increased in direct proportion to the increase in blood level of lidocaine. The time courses describing the change in ventricular fibrillation threshold and the blood levels of lidocaine correlated directly with each other. The half-life for the disappearance of lidocaine from the blood was 32 minutes. These studies describe the metabolism of lidocaine in the anesthetized dog and quantify the ability of lidocaine to reduce the vulnerability of the heart to fibrillation.