ELECTROCARDIOGRAPHIC IDENTIFICATION OF MID-SEPTAL ACCESSORY PATHWAYS IN CLOSE PROXIMITY TO THE ATRIOVENTRICULAR-CONDUCTION SYSTEM

In order to identify ECG characteristics of overt mid-septal accessory pathways (APs) predictive of close proximity to the AV conduction sys tem we analyzed data from patients who underwent successful RF cathete r ablation of a mid-septal AP. Mean patient age was 31 +/- 16 years, a nd 13 were male. The 40 degrees right anterior oblique view was used t o divide the mid-septal area into 3 zones: 1 (anterior portion); 2 (in termediate); and 3 (posterior portion). The 12-lead ECG was analyzed w ith regard to delta wave polarity and R/S transition in the precordial leads. The findings from patients ablated at zone 3 were compared to those at zones 1 and 2. All patients had a positive delta wave in the leads I, II, aVL, and negative delta wave in the leads III and aVR. Th e R/S transition occurred in lead V-2 in 80% of patients. The delta wa ve in lead aVF was the only ECG characteristic that correlated with th e AP ablation zone. Six of 8 patients ablated at zone 3 had a negative delta wave in lead aVF while 6 out of 7 patients ablated at zone 1 or 2 had a positive or isoelectric delta wave in lead aVF (P = 0.03). A positive or isoelectric delta wave in lead aVF identifies mid-septal A P in close proximity to the AV conduction system.