ABNORMAL SKELETAL-MUSCLE BIOENERGETICS IN FAMILIAL HYPERTROPHIC CARDIOMYOPATHY

Objective-To determine the skeletal muscle metabolic manifestations of familial hypertrophic cardiomyopathy. Design-A case-control study. Se tting-P-31 magnetic resonance spectroscopy of the calf muscle was perf ormed on volunteers from a centre specialising in familial hypertrophi c cardiomyopathy. Patients-Five patients with abnormal beta myosin hea vy chain protein in cardiac and skeletal muscle and five patients with a troponin T abnormality in cardiac muscle were compared with healthy controls. Results-High energy phosphate metabolism in vivo was examin ed in a non-invasive manner. In resting muscle, the beta myosin heavy chain group had a higher ratio of phosphocreatine to ATP concentration (4.51 (SD 0.17)) than either the troponin T group (3.88 (0.42)) or co ntrols (n = 16; 4.04 (0.40)). Exercise duration was reduced compared t o controls, and during the fourth minute of exercise phosphocreatine d epletion and muscle acidification were greater in both patient groups. After exercise, the recovery of phosphocreatine-an index of oxidative metabolic capacity of the muscle-was slower in the beta myosin heavy chain group (mean halftime 0.65 (0.08) minutes) than in the troponin T group (0.60 (0.17) minutes) or controls (0.48 (0.14) minutes). Conclu sions-Exercise metabolism was abnormal in both groups of subjects, and the affected contractile protein determined the metabolic changes in muscle at rest and during recovery. In patients with abnormal beta myo sin heavy chain protein, there was a decrease in oxidative capacity co nsistent with the reduction in mitochondria reported in muscle biopsy studies of similar patients.