[Anti-angina and coronary dilating effect of low-dose nitroglycerin]

Fourteen patients with typical exercise-induced angina and ST-segment depression received 0.025 mg nitroglycerin intravenously or placebo directly before exercise testing in a double-blind cross-over study. The sum of ST-segment depressions during stress and recovery was 12.8 +/- 4.8 mm after placebo and 8.9 +/- 4.6 mm after nitroglycerin (p less than 0.001). The symptom-free exercise time increased from 3.1 +/- 1.4 to 4.3 +/- 1.9 min (p less than 0.1), whereas severity of angina during exercise decreased significantly (p less than 0.05) after nitroglycerin. There was no influence on either heart rate or blood pressure. In a second randomized double-blind study, 40 patients with coronary heart disease received either 0.025 mg nitroglycerin or placebo intravenously. Before and 2 min after injection the aortic and left ventricular pressures were recorded and coronary angiography was performed. Mean heart rate, blood pressure, left ventricular filling pressure and pre- and poststenotic coronary artery diameter, as well as the diameters of representative distal coronary artery segments showed no significant changes. Coronary artery stenosis diameters remained unchanged after placebo, but increased significantly after nitroglycerin from 1.15 +/- 0.68 to 1.32 +/- 0.73 mm (p less than 0.01). It can be hypothesized from these results that dilatation of coronary stenosis plays an important role in the antianginal action of nitroglycerin. Coronary artery stenoses seem to be more sensitive to nitroglycerin than are other vessel segments.