Ventricular Fibrillation: Potential Deadly Consequence of Discontinuation of Methimazole Prior to Radioiodine Ablation

The following case involves a 62-year-old female patient suffering from heart failure with reduced ejection fraction (HFrEF) secondary to non-ischemic cardiomyopathy and Graves disease, who developed ventricular fibrillation (VF) after discontinuation of methimazole in preparation for radioiodine ablation. Electrocardiogram (ECG) showed a severely prolonged QTc in the setting of thyrotoxicosis, which significantly improved with high dose methimazole. VF secondary to thyrotoxicosis has rarely been reported and the literature review shows scarce data on its mechanism. Our case demonstrates not only a possible mechanism for the arrhythmia, but also highlights a potential risk factor for it. The report details how discontinuing antithyroid medication leads to VF in our patient and reviews the current literature on antithyroid withdrawal prior to radioiodine ablation therapy. Caution should be taken when discontinuing antithyroid medications in patients with advanced heart failure as potentially lethal ventricular arrhythmias can ensue.