New collateral flow increasing early after coronary occlusion prevented myocardial necrosis in dogs

Increases in regional myocardial blood flow (Qm) developing soon after myocardial infarction may minimize myocardial necrosis. To test this hypothesis, Qm in the area surrounding an acutely occluded coronary artery was determined successively over 4 weeks in 11 dogs. Non-radioactive colored microspheres were injected into the left atrium 5s (Qm at this time is referred to as Q1), 3h (Q2), 12h (Q3), and 4 weeks (Q4) after occlusion of the coronary artery. After termination of the experiment, the heart was removed, and Qm and three indices of myocardial necrosis i.e., myocardial creatine kinase activity (CK), infarct size determined by triphenyl tetrazolium chloride stain (TTC), and myocardial fibrosis visualized by Azan-Mallory stain, were determined. Each Qm was expressed as a percentage of normal: Qm (% of normal) = [Q/Qc] ischemic area/[Q′/Qc′]non-ischemic area × 100, where Qc indicates Qm determined before coronary occlusion. In the ischemic area of the left ventricle, Q1, Q2, Q3, and Q4 were 25 ± 3%, 30 ± 3%, 31 ± 3%, and 42 ± 3% of normal, respectively, in the inner layer, and 31 ± 3%, 52 ± 4%, 52 ± 4%, and 77 ± 6% of normal, respectively, in the outer layer. During the 4-week period, the increase of Qm in the outer layer was greater than that in the inner layer. The inner layer showed a small increase of flow from Q3 to Q4 (9 ± 2%), but in the outer layer there were greater flow increases from Q1 to Q2 (21 ± 3%) and from Q3 to Q4 (24 ± 6%). No consistent flow change from Q2 to Q3 was seen in the inner, middle, or outer layers. Q1 showed good correlation with the three indices of myocardial necrosis, indicating that abundant pre-existing collaterals are important in minimizing myocardial necrosis. The Qm increase within 3h after occlusion (Q2 − Q1) also showed a good correlation with the three indices while that after 12h (Q4 − Q3) showed a variable relationship with these indices. Myocardial necrosis was mild provided that Q2 − Q1 was high. This study demonstrated that there is a considerable flow increase until 3 h after coronary occlusion and that this flow increase may contribute to the reduction of myocardial necrosis.