Wide QRS complex tachycardia with a mysterious mask-Tricuspid isthmus-dependent atrial flutter with preexcitation syndrome and dual atrioventricular nodal pathway conduction.

KEY CLINICAL MESSAGE: Atrial flutter (AFL) and supraventricular tachycardia (SVT) are common arrhythmias in clinic. However, some AFL cases may present additional complexities, such as both accessory pathways (AP) and dual atrioventricular node pathways, putting on a mysterious mask and making it challenging to distinguish on electrocardiograms (ECGs).

ABSTRACT: A 60-year-old male patient had a sudden syncope, and an ECG showed wide QRS complex tachycardia. This diagnostic ambiguity is further compounded by the fact that SVT via AP conduction can exhibit wide QRS complex tachycardia characteristics resembling ventricular tachycardia (VT). Consequently, a definitive diagnosis through electrophysiological (EP) examination becomes imperative, as it dictates subsequent ablation strategies. In this article, we present a rare case involving three distinct arrhythmias including AFL, AP, and dual atrioventricular node pathways, and successfully treated through ablation.