Cardiac conduction and rhythm disturbances following suicidal ingestion of mesoridazine.

The phenothiazine derivatives, particularly chlorpromazine and thioridazine, are known to produce significant electrocardiographic abnormalities. Until now, documented life-threatening arrhythmias have not been reported following large doses of mesoridazine, the besylate salt of a metabolite of thioridazine and a relatively recent addition to the phenothiazine group. We describe such a case in which alterations in both impulse conduction (first-degree atrioventricular block, prolonged QRS duration, and right axis deviation) and impulse formation (supraventricular and ventricular tachycardia) were noted following a suicidal ingestion of mesoridazine. The electrophysiologic mechanisms underlying phenothiazine-induced arrhythmogenesis are reviewed.