Protective effect of early and late treatment with nifedipine during myocardial infarction in the conscious dog.

The effect of early and late nifedipine treatment on collateral blood flow and myocardial infarct size was investigated in 24 previously instrumented conscious dogs. Nifedipine was infused intravenously for 5 hr beginning 15 min (n = 9) and 3 hr (n = 6) after permanent occlusion of the midcircumflex coronary artery and compared with early and delayed vehicle treatment (controls; n = 9). Doses of nifedipine (90 to 168 micrograms/hr) were titrated to reduce mean arterial pressure by 5% to 10%. After animals died or were killed 2 to 7 days later, the anatomic risk region, or occluded coronary bed, was defined by postmortem coronary arteriography. The masses of infarct and risk region were measured by planimetry of weighed transverse sections of the left ventricle. Infarct size was smaller (p less than .05) with early and late nifedipine treatment compared with control, both as percent of left ventricle (15.6% and 14.6% vs 21.6%) and as percent of risk region (46.7% and 41.6% vs 65.7%). Collateral blood flow,...