Cardiac Efficiency During Coronary Occlusion and During Reperfusion After Emergency Revascularization Under Cardioprotection

Abstract

Myocardial infarction in consequence of a coronary artery occlusion presents a serious problem. It is the aim of any emergency revascularization 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 solution was studied under controlled conditions. The left anterior descending artery (LAD) was occluded for 60 min. Then cardiopulmonary bypass was instituted and cardioplegia induced by 8 min perfusion of Bretschneider HTK solution into the aortic root. After 15 min global ischemia, the LAD was 'revascularized' and 150 min reperfusion followed. Except for the early relaxation (dP/dt_min) and mean thickening velocity in the ischemic myocardium, all variables remained essentially unchanged 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±22mmHg, as was dP/dt_max: 2155 ± 655 vs. 1720 ± 895 mmHg/s. Cardiac output was insignificantly decreased at the end of reperfusion, 2.6 ±0.6 vs. 2.4 + 0.5 L/min, whereas stroke-work index exhibited a significant deterioration: 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 pressure exhibited only a moderate increase: 8 ± 5 vs. 9 ± 3 mmHg. MVO₂, in turn, remained almost constant throughout the protocol for each of two methods by which it was predicted. The results show that global work, MVO₂, 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 MVO₂. Thus, external efficiency was decreased. From these results we conclude that in reperfused myocardium after cardioplegic arrest, the oxygen is only inefficiently converted to develop force.

Key words

Cardioprotection - Cardioplegia - Ischemic arrest - Pig