Postischemic mechanoenergetic inefficiency is related to contractile dysfunction and not altered metabolism

Abstract

Mechanoenergetic inefficiency in postischemic nonnecrotic myocardium may partly be explained by an increased fatty acid (FA) oxidation rate. In the present study, left ventricular (LV) postischemic energy transfer was characterized in 10 intact anesthetized pigs. The LV was stunned by 11 brief left main coronary artery occlusions/reperfusions (20-min accumulated ischemia). Seven pigs served as time controls. The relationship between myocardial oxygen consumption (MV˙o 2) and LV pressure-volume area (PVA) was assessed. [14C]glucose and [3H]oleate markers were used to discriminate between glucose and FA consumption. In stunned hearts, severe postischemic dysfunction was observed, and contractile efficiency was reduced (increased MV˙o 2-PVA slope, P = 0.001). Unloaded (nonmechanical) MV˙o 2 was not affected by ischemia. We observed only a small transient increase in FA preference and conclude that the contribution from increased FA utilization to postischemic mechanoenergetic inefficiency is insignificant. Disrupted postischemic chemical-to-mechanical energy transfer in vivo is, therefore, related to inefficient energy utilization in the contractile apparatus.