Effects of nitroglycerin on the major determinants of myocardial oxygen consumption. An angiographic and hemodynamic assessment.

A direct and quantitative study of the effects of sublingually administered nitroglycerin on the major determinants of myocardial oxygen consumption was carried out in 10 patients, 7 with coronary artery disease. Left ventricular wall tension, estimates of the contractile state and heart rate were studied directly using simultaneous pressure measurements and angiographically obtained volume determinations. The peak systolic left ventricular wall tension decreased 15 percent after administration of nitroglycerin, suggesting a diminished myocardial oxygen requirement. Increased myocardial oxygen requirements were suggested by the occurrence of both positive chronotropic and inotropic effects. Heart rate increased 15 percent. The mean circumferential fiber shortening velocity increased 26 percent and the ejection fraction 30 percent; these findings, in association with a 23 percent reduction in left ventricular end-diastolic volume, were considered consistent with an increase in the contractile state. The mechanism of action of nitroglycerin seems to relate best to the decrease in systolic wall tension. The end-diastolic tension decreased 57 percent, suggesting the possibility that diastolic coronary blood flow may be augmented by diminished extravascular resistance to flow.