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Right Bundle Branch Block Affecting the Morphology of Septal Right Ventricular Outflow Tract Premature Ventricular Beats

A 49-year-old female with a structurally normal heart underwent elective endocardial ablation for frequent, symptomatic premature ventricular contractions (PVCs) and runs of nonsustained ventricular tachycardia. Her PVCs showed a left bundle branch (LBB) block pattern with an inferior axis and transition at V4-V5, suggesting an origin from the right ventricular outflow tract (RVOT; Fig. 1A). Activation and pace mapping located the origin at the anteroseptal RVOT (Josephson septal site 2/3) where the PVCs were successfully ablated. During mapping, iatrogenic right bundle branch block (RBBB) occurred with catheter manipulation. The PVC morphology showed significant QRS widening and inferior limb lead notching during RBBB (Fig. 1B). Activation and pace mapping after RBBB confirmed the same site of origin. There are limited data on the contribution of the right bundle branch (RBB), and conversely on the effects of RBBB, to depolarization of focal PVCs arising from the RVOT. A not unreasonable hypothesis would be that septal RVOT PVCs would be less affected by RBBB than free-wall RVOT PVCs by virtue of the majority of the depolarization wavefront traveling down the septum and penetrating the LBB. In the absence of data on the influence of RBBB on RVOT arrhythmias, we can potentially draw inferences from studies of the influence of RBBB on antegrade depolarization of the RVOT. Data from the era of 3-D mapping have revealed that the RVOT septum shows considerable delay in depolarization during RBBB. Thus “passive” depolarization from the LBB