A Rare Case of Dual, Decrementally Conducting, Pathway-to-Pathway-Mediated Tachycardia.

We report a rare case of broad complex atrioventricular reentrant tachycardia (AVRT) in an 18-year-old female, mediated by two distinct decrementally conducting accessory pathways (APs). The reentrant circuit consisted of antegrade conduction via an atrio-fascicular (AF) fiber and retrograde conduction through a concealed posteroseptal AP. Both APs exhibited decremental properties, and the circuit was independent of the atrioventricular (AV) node and His-Purkinje system, representing a classic example of pathway-to-pathway reentry. Sequential ablation of the retrograde and then the antegrade limbs successfully eliminated the arrhythmia. This case highlights the importance of meticulous electrophysiologic study (EPS) in identifying non-AV nodal dependent reentry mechanisms.