Mechanoenergetic inefficiency in the septic left ventricle is due to enhanced oxygen requirements for excitation-contraction coupling

Objective: Myocardial oxygen consumption (MVO2) in the septic myocardium is increased despite reduced left ventricular mechanical work. We investigated the mechanism behind this energetic inefficiency in the septic myocardium. Methods: To clarify whether energy consumption in basal metabolism or excitation-contraction (EC) coupling is elevated in the septic myocardium, we separated MVO2 used for these two processes. We assessed hemodynamics, left ventricular pressure-volume area, left ventricular MVO2, myocardial substrate metabolism and the inflammatory response in eight control pigs and in eight septic pigs receiving E. coli endotoxin. Using cardiopulmonary bypass (CPB), unloaded MVO2 was assessed before and after arrest of electromechanical activity using KCl infusions. Results: Unloaded MVO2 was significantly higher in the septic group compared to the control group (65.7 +/- 12.9 vs. 43.3 +/- 15.1 J(.)min(-1.)100 g LV-1, p < 0.005), but basal MVO2 after 5 min KCl arrest was equal in the two groups. No difference in mechanical energy consumption or substrate metabolism was observed between groups. Conclusion: Basal MVO2 in the septic myocardium is not elevated, but an increased MVO2 for EC coupling is responsible for the energetic inefficiency. (C) 2004 European Society of Cardiology. Published by Elsevier B.V All rights reserved.