Myocardial perfusion reserve and oxidative metabolism contribute to exercise capacity in patients with dilated cardiomyopathy

Background: Exercise intolerance is a hallmark symptom in patients with heart failure; however, myocardial factors contributing to the limited exercise capacity are not fully characterized. Methods: Twenty patients with stable heart failure resulting from idiopathic dilated cardiomyopathy (DCM) and 13 controls were studied. Myocardial perfusion, biventricular oxidative metabolism, and insulin-stimulated glucose uptake were measured using positron emission tomography and [O-15]H2O, [C-11]acetate, and [F-18]FDG. Results: Hyperemic perfusion and perfusion reserve were significantly lower in the DCM patients compared with the healthy subjects. There was no difference in left ventricular oxidative metabolism between the 2 groups; however, the patients had a 19% higher right ventricular oxidative metabolism (P = .005). Consequently, the ratio of right to left ventricular oxidative metabolism was also higher (31%) in the patients. There was a strong inverse association between decreased exercise capacity and the ratio of right to left ventricular oxidative metabolism (r = -.68, P < .01) and a positive association with myocardial perfusion reserve (r = .62, P < .01) in the patient group. These 2 parameters along with resting left ventricular work explained 57% of the variability in peak exercise capacity. Conclusions: Impaired perfusion reserve and an exaggerated imbalance in right to left ventricular oxidative metabolism appear to significantly contribute to the impaired exercise capacity in these DCM patients.