Microvascular occlusions promote coronary collateral growth

W. M. Chilian, H. J. Mass, S. E. Williams, S. M. Layne, E. E. Smith and K. W. Scheel Microcirculation Research Institute, Texas A & M University College of Medicine, College Station 77843-1114. The objective of this study was to examine whether myocardial ischemia without alterations in pressure gradients between large epicardial coronary arteries was a sufficient stimulus to produce coronary collateral growth and development. To accomplish this aim, we partially embolized the circumflex coronary perfusion territory with 25-microns diameter microspheres to produce multiple microvascular occlusions, sufficient to abolish or greatly attenuate coronary vasodilator reserve. The embolization procedure was performed in two groups of dogs during aseptic surgery. After the dogs recovered for 1-3 wk (short-term embolization) or 6-8 wk (long-term embolization), indexes of vascular growth were compared with a group of control animals in which all operative procedures were performed, except embolization. Retrograde blood flow, an index of collateral blood flow and coronary vascular resistance, was determined in an isolated beating empty heart preparation during coronary vasodilation with adenosine. Circumflex retrograde blood flow from the left anterior descending artery was increased from 0.09 ml.min-1.g-1 (sham) to 0.21 and 0.17 ml.min-1.g-1 in the short-term and long-term groups, respectively (P less than 0.05). Collateral blood flow from the septal artery was also increased from 0.03 ml.min-1.g-1 (sham) to 0.08 ml.min-1.g-1 (P less than 0.05) in the short-term group. Collateral contribution from the right coronary artery was not significantly altered in either group of embolization animals. The contributions of epicardial and intramyocardial collaterals to the total retrograde flow were also determined and were found to be different among the three experimental groups.