Atypical ventricular tachycardia (torsade de pointes) induced by amiodarone: arrhythmia previously induced by quinidine and disopyramide.

A 44-year-old woman is described in whom amiodarone, disopyramide, and quinidine, administered alone separately, induced atypical ventricular tachycardia (AVT, torsade de pointes). Following a closed mitral valvotomy, she received quinidine, 1.2 g/day, without interruption for 17 years. Because of a recurrence of paroxysmal atrial fibrillation, the dose of the drug was increased to 1.4 g/day; 24 hours later AVT with syncope developed but responded promptly to atropine. Two years later, 24 hours following an increase in the dose of disopyramide from 300 to 600 mg/day, AVT with syncope occurred; isoproterenol abolished the arrhythmia instantly. Amiodarone was the third drug to induce AVT in this patient; she received 200 mg/day six days per week for six months. The dose was subsequently increased to 200 and 400 mg/day on alternate days, six days per week, and two months later AVT occurred. That time the only effective treatment was ventricular pacing.