Deleterious effects of vasodilating agents. Induction of subendocardial ischemia in dogs with proximal stenosis of coronary artery.

This study was designed to determine how distal vasodilatory stimuli can alter coronary hemodynamics and the appearance of myocardial ischemia in the presence of severe coronary stenosis. In anesthetized open chest dogs, left circumflex coronary artery (LCx) flow, distal LCx perfusion pressure (DCPP), heart rate, and aortic pressure were monitored and regional myocardial ischemia was estimated from ST segment deviation in the epicardial and intramyocardial electrograms obtained from the electrodes located in the area supplied by LCx. In the presence of severe LCx constriction, intracoronary administration of adenosine (0.01 mg/Kg/min) and dipyridamole (0.05 mg/Kg) failed to augment LCx flow and induced further reduction in DCPP without changing systemic hemodynamics. In parallel with these hemodynamic changes, significant ST elevation was observed in the inner layer of the area supplied by the LCx. These results show that subepicardial vasodilation following vasodilatory stimuli can induce transmural flow redistribution and lead to subendocardial ischemia in the presence of severe coronary stenosis.