Coronary collaterals in the canine heart: development and functional significance

Abstract

The development and functional significance of coronary collaterals was studied using the tracer microspheres technique in 18 mongrel dogs with complete chronic occlusion of the left circumflex coronary artery. In a first group of eight dogs resistance of the preexisting collaterals was determined during short acute occlusion of the left circumflex coronary artery (LC). The mean value was 8.49 resistance units (R.U.). Six weeks after the implantation of an Ameroid constrictor on the LC, collateral resistance decreased significantly (p < 0.05) to 0.51 R.U. Only two dogs of this group developed a transmural infarction and one a subendocardial infarction after chronic LC occlusion. Aortocoronary bypass grafting restored regional coronary reserve completely in dogs without infarction and partially in dogs with infarction. In the second group of 10 animals no myocardial infarction was found six weeks after Ameroid constrictor implantation. In this group a stress test was performed by infusion of norepinephrine intravenously. In the areas perfused by normal coronary arteries, there was a significant relation between myocardial blood flow (MBF) and pressure-rate product (PRP). The collateralized subendocardium, however, failed to raise its blood flow with increasing PRP. After bypass to the occluded LC, the normal MPF-PRP relation was restored. These observations indicate that a significant collateral circulation develops after chronic coronary obstruction and protects the myocardium against infarction in most cases. The functional capacity of these collaterals, however, is limited and becomes inadequate under stress conditions.