Early changes in collateral blood flow during myocardial infarction in conscious dogs

We studied the early changes in collateral blood flow (CBF) after acute coronary artery occlusion and the relation of these changes to subsequent necrosis. We measured CBF with 7-9 μm radioactive microspheres before and at various times after circumflex artery occlusion in 42 conscious dogs that were killed 48 h later. CBF increased from 20 s postocclusion to later measurements (5 min, 15 min, 1 h, or 6 h) and did so in both necrotic and nonnecrotic areas of the occluded bed. However, the increase in CBF over time was not gradual, but appeared to occur between 20 s and 5 min, with no further changes for up to 6 h. There was a gradation of CBF in the occluded bed, from periphery to center and subepicardium to subendocardium. Central and subendocardial regions with CBF < 0.40 ml.min^-1.g^-1 at 5-15 min postocclusion subsequently showed necrosis whereas epicardial and lateral regions with CBF > 0.50 ml/min did not. Thus CBF increases very early throughout the occluded coronary bed, and the level of CBF by 5 min appears to determine whether necrosis ultimately occurs.