Influence of coronary collateral vessels on the results of thallium-201 myocardial stress imaging

Although collateral vessels are commonly seen in patients with coronary disease, their functional significance has been debated. In this study segmental analysis of thallium-201 perfusion scintigrams obtained at rest and after exercise was made in 124 patients with angiographically proved coronary artery disease to determine whether collateral vessels could provide protection front myocardial ischemia during stress. All 15 coronary arteries that were completely occluded and had no collateral vessels showed a corresponding stress perfusion abnormality, but only 65 of 92 occluded arteries with angiographically visualized collateral vessels showed a corresponding stress defect (P < 0.05). In 13 hearts with stenosed arteries (more than 50 percent narrowing) without collateral vessels, the scintigraphic region supplied by the most severely stenosed vessel always became abnormal. When collateral vessels were present only 19 of 29 such regions showed a stress-induced perfusion defect (P < 0.05). The 10 protected scintigraphic areas were supplied in eight cases by collateral vessels originating from nondiseased arteries (nonjeopardized) and in two cases by collateral vessels that originated distal to a significant arterial stenosis (jeopardized). Fourteen of the 19 arteries that failed to show protection were supplied by jeopardized collateral vessels. The results (1) demonstrate that nonjeopardized coronary collateral vessels may account for a normal-appearing thallium-201 scintigram in segments supplied by severely narrowed coronary arteries, and (2) suggest that coronary collateral vessels çan provide, at least relative protection from stress-induced ischemia.