Abstract
SUMMARY: Thyroid storm is a life-threatening endocrine emergency characterized by severe thyrotoxicosis and multisystem decompensation. Cardiovascular involvement is common and the leading cause of mortality, most commonly presenting with atrial fibrillation or high-output heart failure. Malignant ventricular arrhythmias, however, are exceedingly rare, reported in 0.07% of hospitalizations for thyroid dysfunction and 13% of patients with thyroid storm admitted to intensive care units. We present a case of a previously healthy young woman with uncontrolled Graves' disease who developed out-of-hospital cardiac arrest due to ventricular fibrillation. Coronary angiography revealed diffuse coronary vasospasm without obstructive coronary artery disease, suggesting myocardial ischemia as the precipitating mechanism. She achieved complete neurological and hemodynamic recovery following resuscitation, initiation of antithyroid therapy, beta-blockade, corticosteroids, and restoration of euthyroidism. This case underscores the potential of thyroid storm to induce life-threatening ventricular arrhythmias through a combination of coronary vasospasm, sympathetic overactivity, and altered myocardial excitability. Recognition of thyrotoxicosis as a potential cause of cardiac arrest is crucial, particularly in patients without structural heart disease, since early diagnosis and timely treatment are key to survival and prevention of recurrence. LEARNING POINTS: Ventricular fibrillation and cardiac arrest, even in patients without structural heart disease, can be a presentation of thyroid storm. Coronary vasospasm represents a potential mechanism linking thyrotoxicosis to malignant ventricular arrhythmias. Prompt recognition and restoration of euthyroidism are essential for reversing hemodynamic instability and preventing recurrence. Nonadherence to antithyroid therapy remains a major preventable trigger of thyroid storm.