Electrocardiographic Criteria for Differentiating Endocardial from Epicardial Posterseptal Accessory Pathways to Guide Catheter Ablation

Background: Radiofrequency (RF) catheter ablation is the standard treatment for symptomatic patients with Wolff-Parkinson-White (WPW) syndrome. Successful RF ablation of an accessory pathway (AP) depends on accurate localization of its site. Methods: This retrospective, observational, cross-sectional study included all consecutive patients who underwent successful RF ablation of a single manifest posteroseptal AP at the Cardiac Electrophysiology Laboratory of the Cardiovascular Department, Cairo University Hospitals. Twelve-lead electrocardiograms were collected and analyzed to identify electrocardiographic criteria that differentiate epicardial from endocardial posteroseptal APs to guide mapping and ablation strategies. Results: Seventy-three patients with a posteroseptal AP were included: 47 were ablated from the right posteroseptal endocardium; 6 from the left posteroseptal endocardium; and 20 were ablated epicardially (from the coronary sinus or its branches). Epicardial posteroseptal APs were predicted by a negative delta wave in lead II, a positive delta wave in lead aVR, a positive delta wave in lead V1, and/or QRS complex notching in lead II. Endocardial posteroseptal APs were predicted by a negative delta wave in lead V1 and/or an R/S ratio less than 1 in lead V1. Double QRS transition was not useful for differentiation unless combined with a Q wave or predominantly negative QRS complex in lead V1. Conclusion: Epicardial and endocardial posteroseptal APs can be differentiated based on delta wave polarity in leads II, aVR, and V1; R/S ratio in lead V1; and QRS complex notching in lead II.