Pseudo normalization of H-V interval due to intra-His block in a patient with fasciculoventricular accessory pathway.

A 57-year-old male suffering from cardiogenic syncope was found to have preexcited QRS on surface ECG at admission. A dual-chamber ICD was implanted after discovering intermittent high degree A-V block and ventricular tachycardia during hospitalization. An EP study was performed 2 days later. Fasciculoventricular accessory pathway was diagnosed based on the fixed H-V interval with different A-H interval when atrial activation conducted to ventricle. However, the H-V interval was normal, which can be explained by intra-His block based on the findings of two split His potentials, the second of which was closely followed by local ventricular electrogram. The conduction delay in His bundle led to pseudo normalization of H-V interval.