Flecainide-Induced Rapid Atrial Flutter: A Diagnostic Trap Hidden behind Misleading VT Scores

Abstract

Background: Flecainide is a class IC antiarrhythmic agent used to treat atrial fibrillation (AF). However, it carries a known risk of proarrhythmia, including the rare but potentially life-threatening induction of 1:1 atrial flutter with rapid ventricular response. Case presentation: We report the case of a 51-year-old man with paroxysmal AF treated with flecainide who presented to the emergency department with palpitations and hemodynamic instability. ECG showed a wide QRS tachycardia at 190 bpm with a right bundle branch block pattern, initially raising concern for ventricular tachycardia. Immediate synchronized cardioversion restored sinus rhythm. Subsequent electrophysiological study revealed typical counterclockwise cavotricuspid isthmus–dependent flutter, which was successfully ablated. Pulmonary vein isolation was also performed to address the AF substrate. Flecainide was discontinued, and the patient remained arrhythmia-free during follow-up. Conclusion: This case highlights the potential for flecainide to unmask or induce atrial flutter with 1:1 atrioventricular conduction, mimicking ventricular tachycardia. Clinicians must maintain a high index of suspicion in patients treated with flecainide presenting with wide complex tachycardia. Early cardioversion, atrioventricular nodal blockade, and consideration of catheter ablation are key components of management.