Contrasting effects of pharmacologic vasodilation on true collateral and overlap perfusion in ischemic myocardium.

The effects of chromonar (3.5 and 7.0 mg/kg i.v.), a selective coronary vasodilator, on true collateral blood flow and overlap flow (noncollateral perfusion due to overlapping end arteries of adjacent coronary vessels) were measured independently in anesthetized dogs following acute coronary occlusion. Collateral flow in the ischemic zone was significantly (P less than 0.05) reduced by chromonar in a dose-related manner while transmural overlap flow was increased. True collateral flow was distributed primarily to the subepicardium and chromonar produced a significant reduction in both subepicardial and subendocardial perfusion. Overlap perfusion was distributed equally across the left ventricular wall and chromonar increased perfusion to both subepicardium and subendocardium. The results indicate that there are two independent sources of perfusion of ischemic myocardium and that pharmacologic vasodilation with chromonar produces opposite effects on each: a steal of true collateral blood flow and an increase in overlap perfusion.