Terminal end of retro-aortic root branch: An unrecognized origin for “proximal left anterior fascicle” premature ventricular complexes with narrow QRS duration

Background Premature ventricular complexes (PVCs) with narrow QRS duration, inferior frontal plane QRS axis, and right bundle branch block (RBBB) pattern generally originate from the proximal segment of the left anterior fascicle (LAF). Objective The purpose of this study was to investigate the exact origin of this category of PVCs. Methods Twenty-two patients with assumed proximal LAF-PVCs were enrolled in the study. Detailed mapping of fascicular potentials (FPs) was performed during sinus rhythm (SR) and PVCs. Results During SR, a cluster of FPs could be found at the most superior portion of the left ventricle (LV). These FPs represented the terminal end of a discrete branch of the left fascicular system, which we named the “retro-aortic root branch” (RARB). The shortest distance between the proximal LAF and the terminal end of the RARB was 13.5 ± 4.2 mm. The earliest activation site (EAS) of PVCs in all patients were confirmed at the terminal end of the RARB, where the FP-V interval was 35.1 ± 4.3 ms during PVCs. The shortest distance from the right coronary cusp (RCC) to the EAS was 5.3 ± 3.5 mm. PVCs could be eliminated by ablation from the RCC in 45.5% (10/22) cases, in the remaining cases, ablation at the EAS in the LV endocardium successfully abolished PVCs. Conclusion The terminal end of the retro-aortic root branch was the actual origin site for PVCs with inferior frontal plane axis, RBBB pattern and narrow QRS duration. Ablation in the RCC or at the EAS in the LV could both eliminate PVCs safely with high efficacy.