Spontaneous transformation of a concealed to manifest posteroseptal accessory pathway requiring epicardial ablation.

Concealed accessory pathways (APs) are considered benign as they can only sustain orthodromic atrioventricular re-entrant tachycardia (ORT). We describe a unique case of a concealed posteroseptal AP where longitudinal surveillance following repeated failed ablation attempts due to abnormal coronary sinus (CS) anatomy revealed spontaneous development of manifest pre-excitation. The pathway was ultimately ablated via the percutaneous epicardial approach. The potential for development of Wolff-Parkinson-White (WPW) syndrome in patients with concealed APs has implications for ongoing surveillance in these patients.