Preservation of Coronary Flow Reserve in Stunned Myocardium

Microvascular obstruction and persistent focal ischemia have been suggested as a possible cause of myocardial dysfunction (stunning) after brief coronary occlusion. Microvascular occlusion should result in a reduction in maximal coronary flow reserve, although resting transmural coronary flow may be maintained by release of local vasodilators, such as adenosine. To test the microvascular occlusion hypothesis, coronary flow reserve was measured in 14 anesthetized dogs, before and after myocardial stunning produced by 10 min of ischemia. Intracoronary adenosine infusion (5,900 microM/min) increased coronary flow to the same degree in normal [195 +/- 20 (SE) ml/min] and stunned (212 +/- 23 ml/min) myocardium. Peak hyperemic flow after 100 s of coronary occlusion was also similar in normal (205 +/- 25 ml/min) and stunned (218 +/- 23 ml/min) myocardium. The adenosine antagonist 8-phenyltheophylline (5 mg/kg) reduced the flow response to exogenous adenosine, but neither resting coronary flow nor peak hyperemic flow in stunned myocardium was altered. In stunned myocardium, myocardial shortening at rest (0.2 +/- 2.0%) increased during reactive hyperemia (to 13.8 +/- 2.5%, P less than 0.01), but shortening promptly returned to basal levels after each hyperemia. These findings indicate that fixed microvascular occlusion is unlikely to be an important factor in the pathogenesis of stunned myocardium and that local adenosine release does not appear to have a compensatory role in coronary vasoregulation in stunned myocardium.