Effects of chronic oral quinidine on left ventricular performance.

We studied the effects of 10 to 14 days of oral quinidine administration (200 mg every 8 hrs) on left ventricular (LV) dP/dt max and shortening fraction (% delta D) in seven preinstrumented conscious dogs in the resting state, during atrial pacing at 120 bpm, and during an acute pressure load produced by intravenous phenylephrine. Dogs were studied before, during, and after oral quinidine administration with control measurements varying by less than 10%. In the resting state, heart rate (85 +/- 6 SEM vs 88 +/- 7 bpm), LV end-diastolic pressure (7.2 +/- 1.4 vs 6.7 +/- 1.1 mm Hg), LV end-diastolic diameter (39.6 +/- 3.2 vs 38.9 +/- 3.1 mm), LV dP/dt (2903 +/- 208 vs 3050 +/- 217 mm Hg/sec) and % delta D (21.6 +/- 2.6 vs 22.1 +/- 2.7) did not differ (p less than 0.05) before or during quinidine, respectively. During atrial pacing LV dP/dt increased similarly during the control and quinidine periods (+13 and +11%), and % delta D decreased equally (-26% and -21%) during phenylephrine infusion off and on quinidine. Thus chronic oral quinidine administration in clinically therapeutic doses (serum quinidine levels 2.3 to 7.5 microgram/ml) produced no depression in LV performance at rest or during an acute pressure load.