Severe amiodarone-induced thyrotoxicosis with persistent atrial flutter: A case report

Amiodarone-induced thyrotoxicosis (AIT) can complicate the management of atrial tachyarrhythmias, particularly when endocrine and rhythm responses diverge. A man in his early 70s with persistent atrial fibrillation and flutter, prior catheter ablations, and previously recovered tachycardia-induced cardiomyopathy presented with atrial flutter with rapid ventricular response after prolonged amiodarone exposure. Evaluation demonstrated severe thyrotoxicosis and a newly reduced left ventricular ejection fraction. Thyrotoxicosis persisted despite methimazole, prednisone, cholestyramine, and beta-blockade; plasma exchange followed by total thyroidectomy achieved biochemical control. Atrial flutter nevertheless persisted and sinus rhythm was maintained only after amiodarone was reintroduced. Recurrent sinus pauses with syncope subsequently required dual-chamber pacemaker implantation. At follow-up, device interrogation showed no recurrent atrial fibrillation or flutter, and left ventricular ejection fraction had recovered to 50-55%. This case illustrates that definitive treatment of AIT may not by itself resolve a coexisting atrial arrhythmia and that endocrine and rhythm-control strategies may need to proceed independently.