A simple algorithm for localizing accessory pathways in patients with Wolff-Parkinson-White syndrome using only the R/S ratio

Background: Several algorithms for localizing accessory pathways (APs) are based on the delta wave morphology, R/S ratio, and QRS polarity. However, they are somewhat complicated, and an accurate determination of the delta wave morphology is occasionally difficult. The aims of this study were to develop a simple algorithm for localizing APs using only the R/S ratio, and to test the accuracy of the algorithm prospectively. Methods: We studied 142 patients with a single anterogradely conducting AP on a 12-lead ECG. R/S ratios were analyzed in leads V1, V2, and aVF (R/S-V1, R/S-V2, and R/S-aVF). AP locations were divided into five regions based on fluoroscopic anatomy. Results: A new algorithm was developed by correlating R/S-V1, R/S-V2, and R/S-aVF with successful ablation sites in 88 initial consecutive patients. All 55 patients with left free wall APs showed R/S-V1 ≥0.5, and 47 (98%) of 48 patients with left anterior or lateral APs showed R/S-aVF ≥1. In contrast, all seven patients with left posterolateral or posterior APs showed R/S-aVF <1. All nine patients with right-and-left midseptal or posteroseptal APs showed R/S-V1 <0.5 and R/S-V2 ≥0.5. Of 12 patients with right anterior, lateral or anteroseptal APs, 10 (83%) showed R/S-V1 <0.5, R/S-V2 <0.5 and R/S-aVF ≥1. Finally, nine (75%) of 12 patients with right posterolateral or posterior APs showed R/S-V1 <0.5, R/S-V2 <0.5, and R/S-aVF <1. Then this algorithm was tested prospectively in 54 patients. Overall, the sensitivity was 94%, and the specificity was 98%. Conclusions: This ECG algorithm provides a simple and accurate way to identify the AP localization