Skeletal muscle energy substrates, metabolic products and enzyme activity in infants with symptomatic ventricular septal defect.

Muscle biopsy studies were performed on 26 infants with symptomatic ventricular septal defect (VSD) (mean age 4.7 months) and 10 healthy infants (mean age 7.8 months). Analyses were made of muscle energy substrates, metabolic products, muscle enzyme activity, fibre types and fibre sizes. Relatively few differences were noted between the groups. The most important difference was a reduced ATP level in the VSD group. Glucose 6-phosphate concentrations were also lower in the VSD group. These differences could indicate a low metabolic activity in skeletal muscle in infants with heart failure. Most muscle enzyme activity was comparable with the exception of lactate dehydrogenase (LD), which was lower in the VSD group. Within the VSD group, no differences were revealed in muscle substrate concentrations for muscle enzyme activity in terms of the degree of heart failure. We conclude that low energy levels are probably explained by undernourishment and/or reduced blood flow to skeletal muscle and that the lack of other discrepancies in muscle metabolism indicates a desirable relatively normal motor activity in these infants with symptomatic VSD.