Oxygen consumption and coronary reactivity in postischemic myocardium

Coronary vascular responses in regions of reversible postischemic myocardial contractile dysfunction (stunned myocardium) were examined in chronically instrumented, awake dogs. Left anterior descending coronary artery blood flow and oxygen extraction, aortic and left ventricular pressures, and regional myocardial segment shortening were determined. Regional myocardial blood flow was measured with microspheres. Coronary reactive hyperemia and vasodilator reserve, and regional myocardial oxygen consumption were determined. Three sequential 10-minute left anterior descending coronary artery occlusions separated by 30-minute reperfusion periods resulted in progressive dysfunction so that 1 hour after the final coronary artery occlusion, myocardial segment shortening was reduced to 37% of baseline. Despite this decrease in contractile function, left anterior descending artery flow (19.6±2.6 vs. 18.4±3.0 ml/min), myocardial blood flow and the transmural distribution of flow measured with microspheres, and regional myocardial oxygen consumption were unchanged. Although the coronary vasodilator reserve in response to adenosine was unaltered (63±9 vs. 70±15 ml/min), the reactive hyperemia response to a 10-second coronary occlusion was decreased in intensity (debt repayment ratio=474±78% vs. 322±74%; p<0.05) and duration (57±9.1 vs. 35±4.5 seconds; p<0.05), while the peak flow response was unchanged (57±6.8 vs. 60±7.1 ml/min). Thus, in the intact awake animal postischemic myocardial contractile dysfunction was not associated with decreased myocardial oxygen consumption and did not impair the normal relation between coronary blood flow and myocardial oxygen utilization. Although coronary vessels showed a normal ability to vasodilate in response to adenosine, coronary reactive hyperemia was reduced.