Electrophysiologic studies, echocardiograms, cardiac catheterizations and histologic and biochemical analyses of skeletal muscle biopsies were performed in 10 patients (aged 10 to 37 years, mean 21) who had dysrhythmias as the initial manifestation of cardiomyopathy. Presenting symptoms and signs attributable to dysrhythmias included sudden cardiac arrest in 2 patients, syncope in 3, presyncope in 3 and palpitations in 2. There was no clinical evidence of skeletal muscle weakness in any patient. Multicatheter electrophysiologic evaluation established diagnoses of ventricular tachycardia in 6 patients, primary atrial tachycardia in 2 and third degree infra-Hisian heart block in 1 patient. One patient presenting with palpitations had no inducible arrhythmia or conduction disturbance. Echocardiographic, angiographic and hemodynamic studies demonstrated previously unsuspected dilated cardiomyopathy in 7 patients and restrictive cardiomyopathy in 3. Skeletal muscle histologic characteristics were abnormal in all 10 patients; increases in lipid droplets and endomysial fibrosis were the characterstic findings. Serum free carnitine and short- and long-chain acylcarnitine were normal in 9 patients. However, skeletal muscle long-chain acylcarnitine was reduced in 9 patients. These findings support the concept that in certain patients presenting with dysrhythmias, the dysrhythmia may be a manifestation of cardiac and skeletal (that is, generalized) myopathy.
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