Recent studies in patients with long-term heart failure have suggested that intrinsic abnormalities in skeletal muscle can contribute to the development of early lactic acidosis and fatigue during exercise. The present study provides an analysis of substrate and enzyme content, fiber typing, and capillarization in skeletal muscle biopsy samples obtained at rest from the vastus lateralis in 11 patients with long-term heart failure (left ventricular ejection fraction, 21 +/- 8%) and nine normal subjects. Patients demonstrated a reduced peak exercise oxygen consumption (13.0 +/- 3.3 ml/kg/min) when compared with normals (30.2 +/- 8.6 ml/kg/min, p less than 0.001) and had an accelerated rise in blood lactate levels during exercise. In mixed fiber skeletal muscle, total phosphorylase and glycolytic enzyme activities were not different in the two groups, whereas mitochondrial enzymes involved in terminal oxidation were decreased in patients as compared with normal subjects as indicated by reductions in succinate dehydrogenase (51 +/- 15 vs. 81 +/- 17 microM/g protein/min, p less than 0.001) and citrate synthetase (26 +/- 7 vs. 43 +/- 20 microM/g protein/min, p less than 0.05). 3-Hydroxyacyl-CoA-dehydrogenase, an important enzyme mediating beta-oxidation of fatty acids, was also reduced in patients as compared with normals (18 +/- 7 vs. 27 +/- 10 microM/g protein/min, p less than 0.05). There was no difference in high-energy phosphagens or lactate concentration of mixed muscle in the two groups, whereas glycogen content was decreased in patients (262 +/- 29 vs. 298 +/- 35 microM glucosyl units/kg dry wt, p = 0.01). Patients demonstrated a reduced percentage of slow twitch type I fibers (36 +/- 7% vs. 52 +/- 22%, p less than 0.05) and had a higher percentage of type IIb fast twitch fibers (24 +/- 9% vs. 11 +/- 12%, p = 0.02), which were smaller than the type IIb fibers seen in normal subjects (p less than 0.05). In patients, the number of capillaries per fiber was decreased for type I and type IIa fibers (both, p less than 0.03), but the ratio of capillaries to cross-sectional fiber area was not different for the two groups. These data demonstrate major alterations in skeletal muscle histology and biochemistry in patients with long-term heart failure, including fiber atrophy, a decrease in percentage of composition of type I fibers, and an increase in type IIb fibers accompanied by a decrease in oxidative enzyme capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

The results of the present study suggest that in patients with chronic heart failure reduced aerobic activity in skeletal muscle plays an important role in mediating the early onset of anaerobic metabolism during exercise. Our findings are consistent with the concept that reduced aerobic enzyme activity in skeletal muscle is, in part, responsible for determining exercise tolerance and possibly the response to chronic intervention in patients with chronic heart failure.