Arterio-venous difference in lactate levels in myocardial ischemia and reperfusion

The effects of 30-, 60-, and 90-min occlusion of the left anterior descending coronary artery and 60-min reperfusion were studied on the left ventricular dP/dt, myocardial ultrastructure, and tissue as well as blood lactate levels in dogs. The dP/dt was depressed by the occlusion, and reperfusion instituted after 30 min resulted in full recovery whereas that after 90 min had an adverse effect. Varying degrees of ultrastructural damage were noted after 60 and 90 min of occlusion and this was further exaggerated by reperfusion. Coronary occlusion markedly increased lactate content of ischemic myocardium, and the same returned to normal upon reperfusion. Myocardial ischemia for 30 or 60 min did not affect net arterial lactate extraction by the heart, but ischemia for 90 min reversed net lactate extraction to net lactate production by the heart. Reperfusion after 30 min of occlusion significantly increased lactate extraction, but reperfusion after 60 and 90 min of ischemia significantly decreased net lactate extraction and increased net production, respectively. The results indicate that estimation of net lactate exchange across the heart can be of value in assessing the viability of myocardium following coronary bypass surgery.