Facilitation of atrioventricular reentrant tachycardia by iatrogenic right bundle branch block.

The present case report describes the diagnosis of a concealed bypass tract in the right lateral wall revealed by electrophysiologic evaluation performed in a patient with rare palpitations. A iatrogenic right bundle branch block (RBBB) caused the occurrence of an incessant atrioventricular reentrant tachycardia. The disappearance of the RBBB determined a very difficult induction of the tachycardia that, when induced, showed a shorter cycle length and ventriculoatrial interval than those observed during RBBB tachycardia. The presence of a RBBB ipsilateral to the right free wall accessory pathway provided a critical delay within the circuit thus allowing the bypass tract to recover excitability. This relevant delay also allows the sinus beat to initiate and stabilize the tachycardia thus rendering it incessant.