Myocardial salvage by intravenous nitroglycerin in conscious dogs: loss of beneficial effect with marked nitroglycerin-induced hypotension.

We studied the effect of nitroglycerin-induced decreases in mean arterial pressure (MAP) on myocardial salvage. Two hours after occlusion of the left anterior descending coronary artery, 65 conscious dogs were randomly allocated to receive 4 hr intravenous infusions of saline (group 1, 19 dogs), or nitroglycerin in doses to decrease MAP by 10% (group 2, 18 dogs), 25% (group 3, 14 dogs), and 50% (group 4, 14 dogs), respectively. At 7 days, 41 dogs were killed for measurement of infarct size; 24 dogs, given 7 to 10 micron radioactive microspheres for flow calculations, were killed 6 hr after occlusion. Boundaries of the occluded bed were defined by postmortem coronary arteriography. Infarct and occluded bed masses were measured by planimetry of weighed transverse sections of the left ventricle. Compared with saline infusions in group 1, nitroglycerin infusions produced sustained reductions (p less than .001) in mean left atrial pressure and MAP in all dogs, but heart rate was unchanged. The decreases in MAP...