Analysis of coronary collateral structure, function, and ischemic border zones in pigs.

The purpose of this study was to compare coronary collateral structure and function in pigs with those in dogs and to analyze the distribution of collateral blood flow across the lateral and transmural border zones in the pig. After acute occlusion of the left anterior descending coronary artery (LAD) in 26 anesthetized open-chest pigs, minimal collateral blood flow was indicated by retrograde flow (0.2 +/- 0.1 ml/min) and microsphere-myocardial blood flow (0.005 +/- 0.001 ml X min-1g-1). Postmortem injection of the distal LAD followed by clearance of the heart demonstrated few tiny collateral structures and negligible collateral filling of other arteries. In contrast to dogs, pigs showed no measurable gradient of collateral blood flow across the transmural border zone, and pigs showed no change in collateral blood flow or its transmural distribution during retrograde drainage of collateral blood flow or elevated left ventricular filling pressures. Pigs showed higher myocardial blood flow in the lateral border than in the center of the ischemic zone. As in the dog, however, this gradient of blood flow across the lateral border zone was accounted for by overlap between occluded LAD branches and unoccluded coronary arterial branches rather than by preferential collateral perfusion of the lateral border of the ischemic zone. We conclude that the pig has a homogeneous distribution of collateral blood flow across the transmural and lateral border zones after acute coronary occlusion but that the minimal collateral circulation limits the usefulness of the pig as a model of ischemic heart disease.