Microvascular and collateral adaptation in swine hearts following progressive coronary artery stenosis

We chronically implanted hygroscopic occluders around the left circumflex coronary artery in 49 anesthetized young male domestic pigs and we studied the development of a collateral circulation at 4, 8, 12, and 26 weeks after implantation. At these time intervals groups of animals were again anesthetized, the hearts were explanted and perfused in Langendorff-fashion with leucocyte-filtered pig blood. Maximal coronary vasodilation was induced with adenosine and global (electromagnetic), and regional (tracer microspheres) blood flow was measured at 40, 60, 80, and 100 mm Hg of perfusion pressure. At 4 weeks after occluder implantation maximal left circumflex collateral blood flow was about 20% of normal maximal flow. Collateral flow rose to 60% of maximal normal flow between 4 and 8 weeks and did not improve further with longer time intervals. In contrast to the canine heart numerous small vessels develop in response to ischemia in the pig heart. These vessels develop throughout the entire risk region with a slight preference for the subendocardium. They appear on tomographic angiograms as a dense "blush". The study of the relationship between peripheral coronary pressure vs collateral flow showed a relationship much steeper than that of normal maximal flow vs aortic perfusion pressure which indicates that the minimal resistance of the risk region was decreased as part of the mechanism to ensure adequate blood supply in a situation of progressive coronary narrowing.