Unusual QRS complexes associated with the simultaneous presence of a right-sided accessory pathway, fasciculoventricular pathway, and incomplete right bundle branch block.

ABSTRACT

A 52-year-old man presented with delta waves on a body surface electrocardiogram, which suggested the presence of a right-sided accessory pathway (AP). Patients with right-sided APs generally have an rS pattern in leads V1-2, while he had an rS in lead V1 but an Rs in lead V2, which could not rule out the possibility of the presence of a septal AP or fasciculoventricular pathway (FVP). On the other hand, patients with septal APs or FVPs generally have a QS pattern in lead V1 instead of an rS pattern. An electrophysiological study demonstrated that the simultaneous presence of a right-sided posterolateral AP and FVP with incomplete right bundle branch block (ICRBBB) generated those unusual QRS complexes. The FVP arose distal to the site with ICRBBB, and the ICRBBB delayed the initiation of the FVP conduction. The delayed QS and Rs waves in leads V1-2 generated by the FVP conduction with ICRBBB appeared to produce rS and Rs patterns in leads V1-2, respectively. A radiofrequency application along the posterolateral tricuspid annulus eliminated the right-sided AP conduction. If the localization of APs based on the QRS morphology is difficult, multiple APs or an FVP with a conduction system disturbance should be noted. Learning objective: Patients with right-sided posterolateral accessory pathways (APs) generally have an rS pattern in lead V2, while patients with fasciculoventricular pathways (FVPs) generally have a QS pattern in lead V1. The present case with a suspected right-sided posterolateral AP had unusual QRS complexes, an rS in lead V1, Rs in lead V2, and monophasic R in leads V3-6, which were associated with the simultaneous presence of a right-sided posterolateral AP, FVP, and incomplete right bundle branch block.