Electrophysiological studies in left bundle branch block as a result of procainamide therapy

A patient of coronary heart disease with depressed intraventricular conduction who developed left bundle branch block upon administration of procainamide instead of the usual nonspecific widening of qrs is presented. The possible mechanism of genesis of this very rare side effect of procainamide is discussed and the review of the literature revealed this patient to be the first documented, electrophysiologically studied case with this side effect of procainamide.