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.

Acute ST-elevation myocardial infarction (STEMI) is rarely seen in young adults, however, when encountered, the underlying cause is either a genetic condition leading to early-onset coronary artery disease (CAD), an acquired pro-thrombotic condition, or an idiopathic condition like spontaneous coronary artery dissection (SCAD). Our case describes a healthy 23-year-old female who presented with sudden onset severe angina and was found to have a laminated thrombus in the left anterior descending coronary artery (LAD), with no evidence of intraluminal dissection or plaque rupture. Although the underlying etiology of thrombus formation remains unknown, coronavirus disease 2019 (COVID-19) related thrombotic event is the prime suspect. In addition, another culprit that cannot be excluded is phentermine-induced coronary vasospasm, a commercially available medication for weight loss. This report addresses current literature on acute coronary syndromes in young adults and reviews the potential etiologies for coronary artery thrombosis, which led to a near-fatal acute coronary syndrome in our patient.