The effects of afterload reduction on myocardial carbon 11-labeled acetate kinetics and noninvasively estimated mechanical efficiency in patients with dilated cardiomyopathy

With echocardiography and dynamic carbon 11-labeled acetate (C-11 acetate) positron emission tomographic imaging, C-11 acetate kinetics and a parameter that estimates mechanical ventricular efficiency (the work metabolic index) were defined in eight patients with dilated cardiomyopathy. The effect of afterload reduction with nitroprusside on these parameters was evaluated in six of these patients. Nitroprusside increased stroke work index but decreased the C-11 clearance rate. The work metabolic index determined noninvasively increased and correlated well with an invasive approach. The work metabolic index was inversely correlated with systemic vascular resistance. Nitroprusside shifted this relationship upward and to the left. This method of estimating efficiency is feasible and may represent a unique noninvasive approach for the evaluation of cardiac performance and responses to therapy.