A-V dissociation with interference in partial heart block ∗

Abstract

Electrocardiograms are presented illustrating the following: (1) A-V dissociation with interference in the presence of partial block, presumably 3:1 block; and (2) the transition from 2:1 block into A-V dissociation. The duration of the refractory period could be determined with great accuracy. When the refractory period was close to two or three times the atrial period, minimal alterations of the P-P interval affecting only one atrial period or minimal alteration of the refractory period caused the transformation of 2:1 or 3:1 block into A-V dissociation. At the height of the effect of isoproterenol, 3:1 block alternated with complete A-V dissociation. This stage was followed by a period of A-V dissociation with interference in, presumably, 3:1 block. Two hours after administration of the drug measurements had returned to the level present before isoproterenol.