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 ve ntricular septal defect (VSD) (mean age 4.7 months) and 10 healthy inf ants (mean age 7.8 months). Analyses were made of muscle energy substr ates, metabolic products, muscle enzyme activity, fibre types and fibr e sizes. Relatively few differences were noted between the groups. The most important difference was a reduced ATP level in the VSD group. G lucose 6-phosphate concentrations were also lower in the VSD group. Th ese differences could indicate a low metabolic activity in skeletal mu scle in infants with heart failure. Most muscle enzyme activity was co mparable with the exception of lactate dehydrogenase (LD), which was l ower in the VSD group. Within the VSD group, no differences were revea led in muscle substrate concentrations or muscle enzyme activity in te rms 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 t hese infants with symptomatic VSD.