Case Report: Isoproterenol-dependent concealed right anteroseptal accessory pathway

A 34-year-old male with no history of chronic medical illness or regular medication use presented with recurrent palpitations, chest tightness, and presyncope over two weeks. A wearable smart device recorded brief runs of irregular narrow-complex tachycardia, which were initially misdiagnosed as paroxysmal atrial fibrillation. During baseline electrophysiological study (EPS), ventriculoatrial (VA) conduction exhibited Wenckebach periodicity; no accessory pathway (AP) was identified, and no supraventricular tachycardia (SVT) could be induced. Following intravenous isoproterenol (ISO) infusion, retrograde conduction improved, and narrow-complex tachycardia was successfully induced via programmed stimulation [S1S2 coupling intervals of 330/210 milliseconds (ms)] from the coronary sinus. Orthodromic atrioventricular reentrant tachycardia (AVRT) was confirmed. The concealed AP was localized to the right anteroseptal region (specifically, the 12–1 o'clock position on the tricuspid annulus) and was successfully ablated using radiofrequency energy. Post-ablation EPS demonstrated non-inducibility of tachycardia. The patient remained free of arrhythmia recurrence during 18 months of clinical follow-up. This case illustrates a rare isoproterenol-dependent concealed right anteroseptal AP and underscores the diagnostic utility of ISO provocation in patients with narrow-complex tachycardia when arrhythmia is not induced on standard EPS.