Effect of Extrasystoles on Idioventricular Rhythm

Abstract

When premature ventricular contractions (PVCs) occur in the idioventricular rhythm of patients with complete heart block (CHB), one of several rhythm alterations may occur: the postextrasystolic or returning cycle (RC) may be prolonged, unaltered, or even shortened without any apparent reason. To elucidate the mechanisms by which these alterations occur, the effect of spontaneous and of electrically induced PVCs was studied in five patients with CHB. Over 500 observations were obtained. PVCs occurring late in the basic cycle, i.e., after the T wave of the last spontaneous idioventricular beat, almost uniformly resulted in lengthening of the first RC. In sharp contrast, PVCs elicited early in the cycle, i.e., during the T wave, were followed by a shortened RC in 95% of instances. The underlying electrophysiologic mechanisms responsible for the relationship of RC length to degree of prematurity of the PVC are discussed.