Myocardial fatty acid utilization as a determinant of cardiac efficiency and function

Cardiac efficiency describes the relationship between cardiac work, an index of function, and oxygen consumption, an index of energy substrate metabolism. As the heart obtains upwards of 95% of its ATP requirements from oxidative metabolism the choice of energy substrate strongly impacts cardiac efficiency. The increased utilization of fatty acids relative to glucose as an energy substrate decreases cardiac efficiency. This effect is attributable to differing phosphorous/oxygen ratios of fatty acid and glucose metabolism, increased mitochondrial uncoupling induced by increased rates of fatty acid oxidation, futile cycles engaged by fatty acids and effects of fatty acid use on cardiac ionic homeostasis. Increasing myocardial glucose utilization at the expense of fatty acid utilization can improve cardiac efficiency in various pathophysiologies characterized by an increased reliance on fatty acids as an energy substrate. In this review we present current information regarding the mechanisms contributing to the effects of fatty acids on cardiac efficiency.