CARDIAC EFFICIENCY DURING CORONARY-OCCLUSION AND DURING REPERFUSION AFTER EMERGENCY REVASCULARIZATION UNDER CARDIOPROTECTION

Myocardial infarction in consequence of a coronary artery occlusion pr esents a serious problem. It is the aim of any emergency revasculariza tion to minimize the ischemia-induced damage or to salvage reversibly injured myocardium. In experiments on 8 anesthetized pigs, myocardial protection by orthograde perfusion with a high-volume cardioplegic sol ution was studied under controlled conditions. The left anterior desce nding artery (LAD) was occluded for 60 min. Then cardiopulmonary bypas s was instituted and cardioplegia induced by 8 min perfusion of Bretsc hneider HTK solution into the aortic root. After 15 min global ischemi a, the LAD was 'revascularized' and 150 min reperfusion followed. Exce pt for the early relaxation (dP/dt(min)) and mean thickening velocity in the ischemic myocardium, all variables remained essentially unchang ed during LAD occlusion. During the entire reperfusion, heart rate was significantly increased compared to control: 93 +/- 23 vs. 126 +/- 20 /min. Left-ventricular (LV) peak pressure was significantly decreased at the end of the reperfusion, 104 +/- 33 and 77 +/- 22 mmHg, as was d P/dt(max): 2155 +/- 655 vs. 1720 +/- 895 mmHg/s. Cardiac output was in significantly decreased at the end of reperfusion, 2.6 +/- 0.6 vs. 2.4 +/- 0.5 L/min, whereas stroke-work index exhibited a significant dete rioration: 1.2 +/- 0.6 vs. 0.5 +/- 0.3 mmHg . ml/kg. LV dP/dt(min) was significantly impaired after ischemia and at the end of reperfusion, - 1575 +/- 385 vs. - 855 +/- 310 mmHg/s, while LV end-diastolic pressu re exhibited only a moderate increase: 8 +/- 5 vs. 9 +/- 3 mmHg. MVO(2 ), in turn, remained almost constant throughout the protocol for each of two methods by which it was predicted. The results show that global work, MVO(2), and external efficiency were unchanged during early and late occlusion compared to control. During the entire reperfusion the myocardium was stunned, i.e. cardiac work was decreased at maintained MVO(2). Thus, external efficiency was decreased. from these results w e conclude that in reperfused myocardium after cardioplegic arrest, th e oxygen is only inefficiently converted to develop force.