When Hyperthyroidism Slows the Heart: Graves' Disease Complicated by a High-Grade Atrioventricular Block

This case report describes an uncommon presentation of Graves' disease (GD) with a high-degree atrioventricular block (AVB). We describe a previously healthy teenage male who presented with clinical and biochemical features of GD. Shortly after starting standard therapy, he experienced a syncopal episode and was found to have a tachyarrhythmia with high-degree AVB and intermittent asystole. Cardiopulmonary resuscitation was initiated, followed by temporary pacing and eventual permanent pacemaker (PPM) implantation. Although he later stabilized, adherence to antithyroid medication remained suboptimal.  This case highlights a rare but serious presentation of GD, in which conduction system involvement necessitated both temporary and permanent pacing. Management was further complicated by the use of beta-blockers, the challenge of achieving euthyroid status, and the absence of clear guidelines for pacing in this context. Clinicians should maintain a high index of suspicion for conduction disturbances in hyperthyroid patients presenting with syncope. This case underscores the need for vigilance regarding conduction disturbances in thyrotoxic patients. It highlights the urgent need for multicenter data to guide long-term pacing strategies in this unique overlap of endocrinology and cardiology.