Angiographic evaluation of saphenous vein bypass grafts: artifactual "occlusion" caused by dual sources of flow.

Angiography after coronary bypass surgery has engendered conflicting reports regarding the effect of grafting on proximal lesions. Analysis of a series of postoperative arteriographic injections demonstrates that routine studies may produce artifactual "occlusion" caused by altered or competitive flow relations. High pressure contrast injection can reveal persistent stenotic lumens at sites of apparent complete occlusion. Thus, angiographic technical factors and not surgical sequelae may be responsible for the disparate reports on this subject.