When Rhythm Control Backfires: Flecainide-Precipitated Transient Cardiomyopathy in the Setting of Electrical Cardioversion

Flecainide, a class Ic antiarrhythmic, is a potent sodium channel blocker that slows conduction through the atria, atrioventricular (AV) node, and His-Purkinje system. It is effective for rhythm control in atrial fibrillation (AF) in appropriately selected patients but carries a risk of significant bradyarrhythmia, conduction system suppression, and negative inotropy. Flecainide is generally considered safe in patients without structural heart disease, left ventricular dysfunction, or significant coronary artery disease; however, rare cases of reversible cardiomyopathy have been reported. Current guidelines continue to recommend flecainide for rhythm control in carefully selected patients with AF who do not have structural heart disease, including for cardioversion of recent-onset AF, pretreatment before direct current cardioversion, the “pill-in-the-pocket” approach, and ongoing maintenance of sinus rhythm. This case describes a 73-year-old male with long-standing persistent AF, no structural heart disease, and normal left ventricular systolic function who was started on flecainide following successful AF ablation. Subsequently, he developed recurrent AF and underwent elective cardioversion, which was complicated by profound conduction suppression and likely flecainide-precipitated transient cardiomyopathy in the setting of electrical cardioversion. Prompt recognition and management led to a full recovery, emphasizing the importance of careful patient selection and monitoring when using flecainide, as it may, in rare cases, be associated with or precipitate cardiomyopathy in the peri-cardioversion setting.