The mechanism of extertional fatigue in heart failure.

The mechanism of exertional fatigue in heart failure appears to be considerably more complex than was originally thought. Although it still seems likely that muscle underperfusion is the major culprit, the possibility that skeletal muscle changes contribute to the fatigue suggests that several new therapeutic modalities may improve exercise capacity in heart failure. If muscle atrophy due to de-conditioning or malnutrition is found to contribute to fatigue, exercise capacity in heart failure could be improved, at least in part, by exercise training or nutritional supplementation. Alternatively, agents such as anabolic steroids or growth hormone could be used to stimulate muscle hypertrophy and, thereby, help to improve the fatigue. Heart failure is a common disorder, affecting over three million Americans and many more people throughout the world. One of the most disabling problems experienced by these patients is exertional fatigue. Patients report that they are easily fatigued during normal daily activity. During maximal exercise testing, patients usually terminate exercise early due to fatigue of the legs associated with an early increase in the concentration of lactate in the blood. Traditionally, such exertional fatigue has been attributed to skeletal muscle underperfusion. Over the past five years, however, there has been increasing evidence that heart failure is associated with intrinsic skeletal muscle changes which may also contribute to the exertional fatigue. Nuclear magnetic resonance studies using 31P have demonstrated abnormal skeletal muscle metabolic responses to exercise that do not appear to be due to muscle under-perfusion. Skeletal muscle biopsy studies have demonstrated a variety of changes in patients. Anthropometric studies suggest that a generalized loss of muscle mass may occur in heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)