Exercise responses after cardiac transplantation in mitochondrial myopathy

Since the first description by Luft et al1 in 1962, mitochondrial myopathy has become an increasingly recognized cause of neuromuscular disease. A wide variety of clinical syndromes has been described in patients with this disorder. 2 Although many appear to be restricted to skeletal muscle, other highly oxidative organs including the central nervous system, kidney, liver and heart have been affected in some patients with multisystem mitochondrial abnormalities. In the heart, cardiac conduction defects have been described in many patients with mitochondrial myopathy, 3,4 whereas cardiomyopathy has been reported infrequently.5–10 In this report we describe the morphologic findings of cardiac and skeletal muscle and the unique cardiorespiratory exercise responses in 2 patients who underwent successful cardiac transplantation for end-stage cardiomyopathy resulting from mitochondrial myopathy.