Myocardial Energetics and Efficiency

heart is an aerobic organ that relies almost exclusively on the aerobic oxidation of substrates for generation of energy. Consequently, there is close coupling between myocardial oxygen consumption (MV O2 ) and the main determinants of systolic function: heart rate, contractile state, and wall stress. In the case of the heart, the ratio of useful energy produced (ie, stroke work SW) to oxygen consumed is defined as mechanical efficiency, as originally proposed by Bing et al. In pathophysiological disease states, such as heart failure, mechanical efficiency is reduced, and it has been hypothesized that the increased energy expenditure relative to work contributes to progression of the disease. Moreover, therapeutic interventions that enhance mechanical efficiency have proven to be beneficial with respect to outcome. It is therefore desirable to quantify efficiency of the heart to study disease processes and monitor interventions.