A posteroseptal accessory pathway with conflicting predictors to determine the exact location of successful ablation

Radiofrequency ablation of concealed posteroseptal accessory pathway (AP) and differentiating the right posteroseptal from the left is a challenge for electrophysiologists. Considering different electrophysiological characteristics of posteroseptal AP can help to predict the successful ablation site. We report on a 45-year-old man with simultaneous orthodromic reentrant tachycardia and atrioventricular nodal reentrant tachycardia, both of which were successfully ablated in the right posteroseptal area at the site of the slow pathway. The arrhythmia with both right bundle branch block (RBBB) and left bundle branch block (LBBB) aberrant conduction was observed during our study. The ventriculoatrial (VA) interval increased approximately 25 ms when arrhythmia was conducted with LBBB aberrancy, while it did not change during the RBBB aberrancy. This finding is diagnostic for orthodromic reciprocating tachycardia using a left-sided AP rather than right. However, other parameters, such as delta VA interval and sharp/blunt feature in the proximal coronary sinus electrogram, indicated that the AP is located on the right posteroseptal area.