Thioridazine Hydrochloride (Mellaril): Its Effect on the Electrocardiogram and a Report of Two Fatalities with Electrocardiographic Abnormalities

Abstract

Twenty-eight electrocardiograms are presented which depict a quinidine-like effect of thioridazine on ventricular repolarization, in doses as low as 200 mg. a day. T waves have been found to flatten out and sometimes invert. Occasionally S-T segments have become convex and U waves have appeared.

Case reports are presented of two patients who died while receiving large doses of thioridazine, 1500 and 3600 mg. daily, respectively. Terminal ECG patterns in each instance were those of heart block, alternating with episodes of ventricular tachycardia.

The myocardium of one of the fatal cases revealed edema, increased vascularity, and some increase in connective tissue elements, along with fragmentation of muscle fibers. These changes were most pronounced in the interventricular septum.

It is concluded that, because of the quinidine-like action of thioridazine on ventricular repolarization, caution is indicated when it is administered in large doses.

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