Orthodromic atrioventricular reentrant tachycardia using a concealed isoproterenol-sensitive accessory pathway

Accessory pathways (APs) represent the substrate for atrioventricular reentrant tachycardia. Catecholamine-sensitivity is an uncommon feature of APs and has been almost exclusively been described in APs with antegrade conduction. We present the rare case of a catecholamine-dependent concealed AP that was only unmasked upon isoproterenol stimulation and successfully ablated. This case highlights the importance of systematic isoproterenol stimulation in patients referred for ablation of supraventricular tachycardia - in particular if the baseline electrophysiology study is negative. Otherwise, ablation targets may be missed. LEARNING OBJECTIVE: The absence of retrograde ventriculo-atrial conduction does not automatically exclude the presence of a concealed accessory pathway. Systematic isoproterenol stimulation should be part of any electrophysiology study for supraventricular tachycardia, to search for catecholamine-sensitive accessory pathways that may be otherwise missed.