Electrophysiological characteristics of epicardial atrial tachycardias and endocardial breakthrough site targeting for ablation: a single center experience.

BACKGROUND: Despite being increasingly observed in daily practice, epicardial atrial tachycardias (Epi AT) have not been extensively characterized. In the present study, we retrospectively characterize electrophysiological properties, electroanatomic ablation targeting, and outcomes of this ablation strategy. METHODS: Patients who underwent scar-based macro-reentrant left atrial tachycardia mapping and ablation patients with at least one Epi AT, which had a complete endocardial map, were selected for the inclusion. Based on current electroanatomical knowledge, Epi ATs were classified based by utilization of following epicardial structures: Bachmann's bundle, septopulmonary bundle, vein of Marshall. Endocardial breakthrough (EB) sites were analyzed as well as entrainment parameters. EB site was targeted for initial ablation. RESULTS: Among seventy-eight patients undergoing scar-based macro-reentrant left atrial tachycardia ablation, fourteen (17.8%) patients met the inclusion criteria for Epi AT and were included in the study. Sixteen Epi ATs were mapped, four utilizing Bachmann's bundle, five utilizing septopulmonary bundle, and seven utilizing vein of Marshall. Fractionated, low amplitude signals were present at EB sites. Rf terminated the tachycardia in ten patients; activation changed in five patients and in one patient atrial fibrillation ensued. During the follow-up, there were three recurrences. CONCLUSIONS: Epicardial left atrial tachycardias are a distinct type of macro-reentrant tachycardias that can be characterized by activation and entrainment mapping, without need for epicardial access. Endocardial breakthrough site ablation reliably terminates these tachycardias with good long-term success.