Cardiorespiratory Arrest in the Context of Graves' Disease: A Rare Presentation

Thyroid storm is the most severe and life-threatening expression of thyrotoxicosis, and its diagnosis remains clinical. Although sinus tachycardia and atrial fibrillation dominate its cardiovascular manifestations, malignant ventricular arrhythmias are rare, and cardiorespiratory arrest as the presenting manifestation of Graves' disease has been reported only in a limited number of cases. We report the case of a 44-year-old man with a one-week history of symptoms consistent with hyperthyroidism who suffered a witnessed out-of-hospital cardiorespiratory arrest with ventricular fibrillation as the initial rhythm. Return of spontaneous circulation was achieved after three defibrillations, and urgent coronary angiography showed no obstructive coronary artery disease. Laboratory evaluation revealed severe thyrotoxicosis with positive thyroid-stimulating hormone (TSH)-receptor antibodies, and thyroid ultrasound findings supported the diagnosis of Graves' disease. Thyroid storm was suspected and treated empirically, but the diagnosis could not be confirmed: the Burch-Wartofsky score reached the diagnostic threshold only when post-arrest coma was included, and the Japan Thyroid Association criteria were not met. Cardiac magnetic resonance imaging and an ajmaline provocation test did not identify structural heart disease, myocarditis, or a Brugada pattern. Thyroid hormone excess was therefore considered the most likely precipitant of the arrhythmia, although causality cannot be proven. The patient was maintained on antithyroid therapy, and a subcutaneous implantable cardioverter-defibrillator was implanted for secondary prevention following an individualized risk-benefit assessment. This case highlights the importance of considering thyrotoxicosis in the etiological workup of unexplained cardiac arrest. When a clearly established and reversible cause of the arrhythmia cannot be confirmed, management, including the decision on defibrillator implantation, should be based on an individualized risk-benefit assessment.