Severe primary hypothyroidism manifesting with torsades de pointes

Hypothyroidism can manifest with myriad cardiac abnormalities, often consisting of a combination of morphologic and functional changes. Low voltage, sinus bradycardia, and slowed conduction are usually found on electrocardiography. We describe a patient with severe hypothyroidism who presented with presyncope, prolongation of the QT interval, and polymorphic ventricular tachycardia (torsades de pointes). No other cause for the malignant ventricular ectopy was evident. With levothyroxine therapy, the QT interval normalized and the ventricular tachycardia was abolished. In addition to its commonly known cardiac effects, myxedema can predispose to the potentially life-threatening arrhythmia of torsades de pointes. Conversely, in patients presenting with QT interval prolongation and polymorphic ventricular tachycardia, hypothyroidism should be considered in the differential diagnosis.