Effect of intravenous and intracoronary nifedipine on coronary blood flow and myocardial oxygen consumption.

The effect of intravenous and intracoronary nifedipine on coronary sinus blood flow, coronary vascular resistance, and myocardial oxygen consumption was studied in 20 patients with coronary artery disease. An intravenous infusion of 1.0 mg nifedipine resulted in a decrease in mean aortic pressure, an increase in heart rate and coronary blood flow, and no significant change in myocardial, oxygen consumption. In contrast, the intracoronary injection of 0.1 mg nifedipine led to a moderate reduction in mean aortic pressure, no change in heart rate, an increase in coronary blood flow, and a significant reduction in myocardial oxygen consumption. During rapid atrial pacing before and approximately 6 minutes after the intracoronary nifedipine injection, coronary blood flow and myocardial oxygen consumption reached identical levels. Thus, only intracoronary injection of nifedipine increases coronary flow in the presence of reduced myocardial oxygen consumption. After intravenous administration, reflex tachycardia counteracts the direct myocardial effect of nifedipine and the potential oxygen-saving effect of afterload reduction. There is no evidence of a prolonged oxygen-sparing effect after cessation of the immediate effects.