Quinidine-induced ventricular flutter and fibrillation without digitalis therapy.

Three cases are described with documented ventricular flutter and fibrillation during quinidine medication without concomitant digitalis therapy. In all three patients the arrhythmia developed while they were receiving moderate doses of quinidine. Although no changes in QRS width were observed after administration of quinidine, there was marked prolongation of the Q-T interval. The mechanism of development of ventricular flutter and fibrillation in patients taking quinidine may be similar to that in patients with the Q-T prolongation syndrome.