1008-10 Electrocardiographic Configuration Criteria Distinguishing “Endocardial” from “Epicardial” Accessory Pathways in the Left Posteroseptal Space

Abstract

To assess whether the surface ECG allows distinction of manifest accessory pathways (APs) located at the subendocardial from those at the subepicardial aspect of the left postero-septal (PS) space, 12-lead surface ECGs were compared between 17 pts with an “endocardial” (ENDO) AP and 24 pts with an “epicardial” (EPI) manifest AP. Location of the AP was defined by the site of successful pulse delivery: EPI PS APs were ablated from within the coronary sinus (CS); ENDO PS APs were ablated from the left ventricle. PR interval and QRS duration did not differ between the 2 groups at baseline ECG (ENDO, 102 ± 20 ms and 145 ± 22 ms; EPI. 99 ± 18 ms and 149 ± 27). Delta wave polarity in lead V1 was positive or isoelectric in all patients. A negative delta wave simultaneously recorded in leads II, III and aVF was found in 15/24 EPI APs and in 3/17 ENDO APs (p < 0.001). Among EPI APs, wide and deep Q waves in the inferior leads were found in 3/12 ablated from the middle cardiac vein, and in 0/5 EPI APs ablated from within the CS, representing a highly specific but poorly sensitive marker. Delta wave in ENDO APs was simultaneously positive in leads II, III and aVF in 11/17. QRS patterns associated with endo APs showed typical fragmented rsr1s1 in inferior leads in 12/24 cases. Delta wave and QRS activation allow distinction of ENDO vs EPI APs located in the PS space in the majority of cases.