Case Report: An Unusual Case of Fasciculoventricular Pathway.

A 30-year-old man with an ECG demonstrating ventricular preexcitation with a normal PR interval and a QR pattern in lead V1 was evaluated. Electrophysiology studies showed a normal AH interval and a shortened HV interval at sinus rhythm; while the degree of preexcitation (QRS waveform) and HV interval were not affected by multisite or incremental atrial pacing. These findings implied ventricular preexcitation due to a fasciculoventricular pathway (FVP). Moreover, temporarily blocking FVP conduction mechanically resulted in normal HV interval, absence of delta wave, and an rSR pattern in V1, which indicated incomplete right bundle branch block (IRBBB). These findings suggested the coexistence of FVP and IRBBB, which is very rare.