The efficacy of ablation at the entrance site of the epicardial circuit of atrial tachycardia

Abstract Background Treatment of atrial tachycardia (AT) involving epicardial conduction remains challenging. While the endocardial breakthrough sites can be targets for radiofrequency (RF) ablation, that approach is sometimes ineffective and lead to treatment failure. Purpose This study aimed to retrospectively evaluate the effectiveness of ablation at the entrance site of the epicardial circuit of ATs identified with entrainment. Methods Six cases with atrial tachycardia (ATs) after ablation of atrial fibrillation (AF) were studied, which were diagnosed to involve epicardial conduction based on the endocardial mapping obtained using the Rhythmia system and entrainment findings. These cases were selected because RF ablation at the endocardial breakthrough site was either ineffective or not performed. The entrance site was diagnosed based on detailed entrainment, identifying the dead-on site where post-pacing interval (PPI) was approximately equal to the tachycardia cycle length (TCL), and RF ablation was applied at that site. Results ATs, in which the vein of Marshall (VOM) was conducted in a clockwise direction resulting in the breakthrough in the posterolateral wall of left atrium (LA), were identified in four patients. In the remaining two patients, roof-dependent ATs, which involved septopulmonary bundles resulting in the breakthrough in the lower portion of the posterior wall, were identified. Missing activation time was 114 ± 34ms accounting 36± 8% of the TCL. RF ablation at the endocardial breakthrough site could not terminate ATs in five patients, with the remaining patient abstaining ablation due to broad conduction there. Based on entrainment findings, the entrance sites of the epicardial circuit of ATs were identified at the upper portion of the left atrial appendage ridge in four patients and at the roof in two, respectively. RF ablation there resulted in the termination of ATs in five patients or the conversion into another AT in a patient. No characteristic potentials were observed at the successful ablation sites, with single potential observed in 3 cases and fragmented potential absent in 3 cases (53±24 ms; 0.6±0.4 mV). During a mean follow-up period of 24±9 months, four patients experienced atrial tachyarrhythmia recurrence, requiring repeat sessions in three cases. There was no evidence suggesting the recurrence of same ATs involving epicardial circuit in the two patients in repeat sessions. In a remaining patient, the recurrence of AT involving VOM was successfully treated with ethanol injection into it. Conclusions RF ablation at the entrance site of the epicardial conduction of AT was considered a therapeutic option. However, in cases with such complex ATs, there was a high rate of recurrence of atrial tachyarrhythmias in follow-up. Ethanol injection into the VOM was required to treat them in a case.