Remodeling of small intramyocardial coronary arteries distal to total occlusions after myocardial infarction in pigs

Abstract

The present study was designed to investigate whether microvascular remodeling could occur in hibernating myocardium and infarction regions distal to a total occluded coronary artery after acute myocardial infarction. Copper stents were implanted in the left descending coronary arteries of 64 pigs to induce anterior wall myocardial infarction. The pigs were assigned randomly to group A (n=8; killed at 1 week), group B (n=8; killed at 2 weeks), group C (n=16; killed at 4 weeks), group D (n=16; killed at 3 months), and group E (n=16; killed at 6 months). The control group included six pigs that were subjected to the same procedures but without implantation of copper stents. The wall area (WA) and lumen area (LA) of small intramyocardial coronary arteries (SIMCA) distal to occlusions were measured and the ratios of WA/LA and LA/total vessel area (%L) were calculated. The composition of the arterial wall was determined by Masson's trichrome stain, transmission electron microscope. A significant increase in WA/LA and decrease %L in SIMCA were observed in group B (P<0.05), group C (P<0.01), group D (P<0.01), and group E (P<0.01) compared with the control. There was increased area of collagen fiber in the thickened arterial wall in group C (P<0.05), group D (P<0.01), and group E (P<0.01) compared with the control group, group A, and group B. A significantly increased ratio of the synthetic phenotype vascular smooth muscle cells were found in group B (P<0.05), group C (P<0.01), group D (P<0.01), and group E (P<0.01) compared with the control group. Several weeks after occlusion of epicardial coronary, the SIMCAs distal to occlusion developed remodeling, with an increase in wall thickness and a decrease in lumen size. These structural changes may restrict blood flow to ischemic or hibernating myocardium after revascularization.