Transient right bundle branch block during His bundle electrogram in a case with ventricular parasystole.

A case with ventricular parasystole and transient right bundle branch block during His bundle electrogram is reported. Although on surface electrocardiogram no preexisting atrioventricular (A--V) conduction disturbances could be noted, His bundle electrogram showed latent infrahisian conduction changes. This suggests a susceptibility for induced right bundle branch block during right heart catheterization and may take part in the mechanism of the ventricular ectopic activity of the patient.