Quinidine syncope: torsade de pointes with low quinidine plasma concentrations.

In 2 patients without clinically significant ischemic heart diseases, oral quinidine was used to control supraventricular arrhythmias. In both patients, syncopal attacks occurred, caused by a particular type of ventricular tachyarrhythmia called torsades de pointes. Quinidine plasma concentrations were low (2.6 and 1.2 mg/1, respectively); QRS duration was normal, but the Q-T interval was markedly prolonged.