Characteristics and radiofrequency ablation in posteroseptal and left free-wall subepicardial accessory pathways

Accessory pathways (APs) that can only be ablated from the coronary sinus are likely to be located subepicardially. The electrocardiographic (ECG) and electrophysiological characteristics as well as the immediate radiofrequency ablation success rate and the recurrence rate were compared in 15 patients (11 posteroseptal and 4 left free-wall) with subepicardial APs and in 31 control patients with posteroseptal (15) and left free-wall (16) APs matched with age, sex, and AP location during the same study period in whom APs were successfully ablated from the endocardial approach. Patients with posteroseptal subepicardial APs had a longer tachycardia cycle length (355 ± 32 vs 286 ± 49 milliseconds, P <. 05), a lower success rate (9 /11 vs 15/15, P =. 09), and a higher recurrence rate (3/9 vs 0/15, P <. 05) as compared with control patients. A negative delta wave with QS or QR pattern in lead II was present in all 4 patients with a manifest posteroseptal subepicardial AP located in the middle cardiac vein as compared with none of the 5 control patients with posteroseptal APs located in the proximal coronary sinus and 1 of the 9 control patients (P <. 01). A positive delta wave in lead I along with an R/S of less than 1 in lead V₁, and a negative delta wave in lead II, was noted in 1 of the 2 patients with left free-wall subepicardial APs and none of the 7 controls (P =. 047). The local activation time is significantly shorter in the 4 patients with left free-wall subepicardial AP than in the 16 control patients (31 ± 9 vs 89 ± milliseconds, P =. 044). Some ECG characteristics are suggestive of APs located in the middle cardiac vein and left free-wall subepicardial site, while a longer local activation time is characteristic of left free-wall APs. The success rate is lower and the recurrence rate higher with radiofrequency ablation in patients with subepicardial AP.