Effects of oral quinidine on left ventricular performance in normal subjects and patients with congestive cardiomyopathy.

To evaluate the effects of oral quinidine therapy on left ventricular performance, 10 normal subjects and 8 patients with cardiomyopathy were studied with echocardiography at rest, after intravenous injection of atropine and during infusion with phenylephrine. The echocardiographic studies were performed during oral quinidine therapy and during placebo administration. In the normal subjects heart rate was significantly faster with quinidine than with placebo (74 +/- 8 (standard deviation) versus 68 +/- 9 beats/min, P less than 0.01), but there was no significant change in blood pressure or left ventricular size and performance. After administration of atropine, heart rate was identical with and without quinidine but the mean normalized velocity of left ventricular dimension shortening was significantly less with quinidine than with placebo (1.28 +/- 0.19 versus 1.44 +/- 0.21, P less than 0.01). During acute pressure loading with phenylephrine there was no difference in left ventricular size or performance during quinidine therapy. In the patients with cardiomyopathy, no significant differences in left ventricular function were detected with this protocol during quinidine therapy. It is concluded that oral quinidine therapy appears to have little adverse effect on left ventricular performance at rest or during acute pressure loading.