Abstract 1718: The Increase in Intramyocellular Lipid in Leg Skeletal Muscle is Associated With Lowered Aerobic Exercise Capacity in Patients With Heart Failure
Background: Patients with heart failure (HF) have the lowered aerobic exercise capacity, which largely depends on the abnormal energy metabolism of skeletal muscle. The impairment of fatty acid metabolism, an important energy substrate during exercise, may result in the accumulation of intramyocellular lipid (IMCL) within the skeletal muscle.
Hypothesis: We hypothesized that IMCL content was increased in the skeletal muscle from patients with HF, which was associated with the lowered aerobic exercise capacity.
Methods: The incremental exercise tests with a cycle ergometer were performed in 9 male HF patients with idiopathic dilated cardiomyopathy (left ventricular ejection fraction <40%, NYHA I-III), and 9 age- and sex-matched control subjects. Muscular phosphocreatine (PCr) and inorganic phosphorus during unilateral plantar flexion (0.67Hz for 4 min) with a constant load of 20% one-repetition-maximum was measured by using 31P-magnetic resonance spectroscopy (MRS). Intramyocellular lipid (IMCL) was measured in resting leg muscle by 1H-MRS.
Results: Fasting blood glucose, serum insulin level and HOMA index in HF patients did not differ from those in control subjects. Peak oxygen uptake (peak VO2; 20.4 ± 4.2 vs. 32.9 ± 5.1 mL/kg/min, P < 0.01) and anaerobic threshold (AT; 12.8 ± 2.2 vs. 19.8 ± 3.7 mL/kg/min, P < 0.01) were significantly lower in HF patients compared to control subjects. Maximal PCr loss during exercise was significantly greater in HF patients (50 ± 17 vs. 19 ± 6%, P < 0.01), indicating that ATP production was decreased in the skeletal muscle mitochondria. IMCL content was significantly increased in HF patients (3.2 ± 1.1 vs. 1.5 ± 1.0 mmol/kg wet weight, P < 0.01). There was a significant negative relationship between peak VO2 and maximal PCr loss (r = −0.70, P < 0.05) or peak VO2 and IMCL content (r = −0.68, P < 0.01). There was also a significant correlation between maximal PCr loss and IMCL content (r = 0.71, P < 0.01).
Conclusions: Skeletal muscle energy metabolism was impaired and IMCL content was increased in HF patients, which was associated with the lowered aerobic exercise capacity. There may be an intimate pathophysiological link between IMCL accumulation in the skeletal muscle and the impairment of exercise capacity in HF.