Abstract

Nisoldipine reportedly has little direct myocardial effect. However, because of interactions between the heart and vascular load, the effects on myocardial contractility and left ventricular oxygen consumption (LVO2) have not been established. The authors performed experiments on six isolated, blood-perfused canine left ventricles that were isovolumically contracting and paced at constant rate. Coronary arterial pressure (CAP) and coronary blood flow were measured for evaluation of coronary vascular resistance, and coronary arteriovenous oxygen difference was measured for determination of LVO2. Intracoronary injection of 1 and 10 micrograms of nisoldipine decreased coronary vascular resistance by 16.9 and 36.8% (CAP approximately 40 mm Hg), respectively, and by 21.5 and 47.7% (CAP approximately 80 mm Hg). At both doses, nisoldipine caused no decrease in peak systolic pressure as long as CAP was kept constant at 80 mm Hg. However, when CAP was decreased to 40 mm Hg, peak systolic pressure was significantly decreased even without nisoldipine. This impaired contractile state was associated with a decreased coronary blood flow and a slight decrease in LVO2, whereas 10 micrograms of nisoldipine at CAP approximately 80 mm Hg increased LVO2 significantly. Using the end-systolic pressure-volume relationship as an index of contractility, the authors found nisoldipine not to change the contractile state at CAP approximately 80 mm Hg. They conclude that nisoldipine decreases coronary vascular resistance over a wide range of CAP. It neither depresses the contractile state nor decreases LVO2 in the canine left ventricle. Nisoldipine might effectively counteract anginal attacks by dilating the coronary vessels without depressing myocardial contractility as found in this study on normal ventricle.