Entrance-Site Ablation in Atrial Tachycardia Involving Epicardial Conduction: A Case Series.

Background: Treatment of atrial tachycardia (AT) involving epicardial conduction remains challenging. While endocardial exit sites can serve as targets for radiofrequency (RF) ablation, this approach is sometimes ineffective and may result in treatment failure. Methods: This retrospective study systematically investigated entrance-site ablation for 10 ATs involving epicardial conduction in nine patients who were unresponsive to initial exit-site ablation. The entrance site-identified using high-resolution endocardial mapping and entrainment as the most downstream site where the postpacing interval closely approximated the AT cycle length (ATCL)-was targeted for RF ablation. Results: The median ATCL was 328 ms (289-356). The missing activation time was 140 ms (93-157), corresponding to 42% (35-47) of the ATCL. Possible epicardial conduction inferred from entrainment findings was attributed to the vein/ligament of Marshall in four ATs, the septopulmonary bundle in four, and combinations involving the Bachmann bundle in two. RF ablation at the entrance site terminated four ATs with a single RF application, while in the remaining six, additional lesions with progressive cycle-length prolongation achieved termination. Noninducibility was confirmed in all patients. Conclusions: Systematic identification and ablation of the entrance site of epicardial conduction using detailed entrainment mapping provide a practical and effective strategy for managing ATs involving epicardial conduction, particularly when conventional exit-site ablation is insufficient.