Prolonged impairment of coronary vasodilation after reversible ischemia: Evidence for microvascular 'stunning'

Reperfusion after brief, reversible myocardial ischemia is associated with prolonged depression of contractile function (myocardial 'stunning'); however, the effect on coronary vascular function has not been defined. Thus, open-chest dogs (n = 14) underwent a 15-minute left anterior descending coronary artery (LAD) occlusion followed by reflow. Four hours after reperfusion, regional myocardial blood flow (microspheres) was significantly (p < 0.01) lower and coronary vascular resistance significantly (p < 0.01) higher in the postischemic as compared with the nonischemic endocardium. Furthermore, during maximal vasodilation elicited by intravenous adenosine (n = 6), myocardial blood flow was lower (p < 0.05) and coronary vascular resistance higher (p < 0.05) in the postischemic as compared with the nonischemic myoardium, both in the endocardial and in the epicardial layers. Similary, during maximal dilation elicited by intravenous papaverine (n = 8), myocardial blood flow was lower (p < 0.05) and vascular resistance higher (p < 0.05) in the postischemic as compared with the nonischemic endocardium; a directionally similar trend was observed in the epicardium. Four hours after reperfusion, all indexes of reactive hyperemia after a 40-second coronary occlusion were significantly lower in the LAD than in the control circumflex coronary artery (n = 8). There was no appreciable correlation between systolic wall thickening in the stunned myocardium and 1) the resting myocardial perfusion, 2) the hyperemia attained during adenosine or papaverine, and 3) the hyperemic response to a 40-second coronary occlusion. In control dogs that did not undergo a 15-minute LAD occlusion (n = 15), there were no differences in myocardial blood flow or vascular resistance between the LAD-dependent and the circumflex-dependent bed, either before or during adenosine (n = 7) or papaverine (n = 8). Furthermore, reactive hyperemia after a 40-second occlusion did not differ between the LAD and the circumflex artery (n = 8). In conclusion, a brief (15 minute), reversible ischemic insult causes a prolonged increase in resting vascular resistance and a prolonged impairment in vasodilator responsiveness, both of which persist for at least 4 hours. The severity of the vascular derangements is not related to the severity of contractile depression, suggesting that they may represent a relatively independent phenomenon. It is proposed that, in addition to myocardial 'stunning', reversible ischemia also causes a microvascular 'stunning'.