Epicardial connection after radiofrequency mitral isthmus ablation

Epicardial Marshall bundle (MB) conduction status after successful mitral isthmus (MI) ablation remains uncertain.

This study investigated the incidence of epicardial MB reconduction and its clinical importance as a critical isthmus for atrial tachycardia (AT).

We enrolled consecutive patients undergoing repeat ablation who had a previously confirmed MI conduction block after radiofrequency ablation. MI conduction status, particularly via the epicardial MB, was assessed using a catheter in the vein of Marshall (VOM). MB reconnection was evaluated during sinus rhythm analyzing activation sequences and differential pacing studies via the VOM catheter. During AT, reconnection was further assessed using 3-dimensional mapping and entrainment pacing studies.

55 patients with successful VOM catheter insertion were evaluated. Recurrent MI conduction was observed in 33 patients (60%). 31 of these (94%) had epicardial MB involvement; 17 had reconnections through the endocardial MI and coronary sinus musculature, whereas 14 had reconnections exclusively through the MB. These exclusive epicardial reconnections served as an isthmus for reentrant AT in 7 of the 14 patients (50%). Among 22 patients with sustained MI block including the MB, 2 demonstrated AT using a blocked MB remnant. 33 MBs, including 9 that functioned as an AT isthmus, were ablated. VOM ethanol infusion alone or with radiofrequency ablation successfully eliminated all target MB conductions.

Epicardial MB conduction frequently reconnects, even after a previous MI block creation, and is strongly associated with AT involving this connection. VOM ethanol infusion may facilitate effective epicardial ablation, thereby contributing to durable transmural MI block.