Decreased myocardial free fatty acid uptake in patients with idiopathic dilated cardiomyopathy:: Evidence of relationship with insulin resistance and left ventricular dysfunction

Background: Results on myocardial substrate metabolism in the failing heart have been contradictory. Insulin resistance, a common comorbidity in heart failure patients, and medical therapy may modify myocardial metabolism in complex fashions. Therefore, we characterized myocardial oxidative and free fatty acid (FFA) metabolism in patients with idiopathic dilated cardiomyopathy (IDCM) and investigated the contributions of insulin resistance and beta-blocker therapy. Methods and Results: Nineteen patients with IDCM (age 58 +/- 8 years, ejection fraction 33 +/- 8.8%) and 15 healthy controls underwent examination of myocardial blood perfusion, oxidative and FFA metabolism using positron emission tomography and [O-15]H2O, [C-11]acetate and [C-11]palmitate, respectively. Echocardiography was used to assess myocardial function, work, and efficiency of forward work. Insulin resistance was calculated using the homeostasis model assessment index (HOMA index) and the degree of beta-blockade was estimated with a beta-adrenoceptor occupancy test. IDCM patients were characterized by decreased cardiac, efficiency (35 +/- 2 versus 57 +/- 12 mm Hg.L.g(-1), P < .0001) and reduced myocardial FFA uptake (5.5 +/- 2.0 versus 6.4 +/- 1.2 mu mol.100 g(-1). min(-1), P < .05), but the FFA beta-oxidation rate constant was not changed. In the patients, myocardial FFA uptake was inversely associated with left ventricular (LV) ejection fraction (r = -0.63, P < .01), indicating that further depression of LV function induces an opposite switch to greater FFA uptake. The FFA beta-oxidation rate constant correlated positively with the HOMA index (r = 0.53, P < .05). In patients on beta-1 selective beta-blockers, beta-1 adrenoceptor occupancy correlated inversely with LV work, oxidative metabolism, and FFA uptake; similar relationships were not found in patients on nonselective beta-blocker. Conclusions: Myocardial FFA metabolism is reduced in patients with IDCM. However, when LV function is further depressed and insulin resistance manifested, myocardial FFA uptake and oxidation are, in turn, upregulated. These findings may partly explain the discrepancies between previous studies about cardiac metabolism in heart failure.