Discrimination between His-bundle and the right bundle branch during electrophysiologic studies.

Background: The purpose of this study was to identify the His-bundle (HB) versus right bundle branch (RBB) during electrophysiologic studies, using the V3 phenomenon, and to compare the timing of HB versus RBB potentials of sinus cycles (His-ventricular [H-V] interval).
Methods: The study enrolled 16 patients without structural heart disease, who underwent electrophysiologic studies during which the H-V interval was within normal limits and the V3 phenomenon was induced during recordings of the HB and the RBB potentials by a multi-electrode catheter. The recording site of the earliest HB potential just before the V3 phenomenon was defined as the branching portion of His bundle (HBBP), the site immediately proximal to the HBBP as the HB, and the site immediately distal to the HBBP as the RBB.
Results: The HBBP was identified in all patients. In all cases but one patient, the H-V interval measured at the HB adjacent to the HBBP was > or =35 ms. However, in 12 patients, the H-V interval measured at the RBB adjacent to the HBBP was also > or =35 ms.
Conclusions: The electrophysiologic identification of HB versus RBB by simultaneous recordings of HB and RBB potentials during induction of the V3 phenomenon was feasible. When the discrimination between HB and RBB was based on the measurement of the H-V interval, the proximal portion of the RBB was frequently misidentified as the HB.