McArdle's Syndrome with Previously Unreported Electrocardiographic and Serum Enzyme Abnormalities

Abstract

A case of muscle phosphorylase deficiency occurring in a 19 year old male is reported. Of interest in this particular case are the abnormalities noted in the electrocardiographic examination and in the elevation of serum creatine phosphokinase, both of which were not previously reported in connection with this metabolic myopathy. The elevation of serum creatine phosphokinase is of interest. This enzyme is present only in striated muscle and in brain. Its marked elevation after exercise evidences interruption of the sarcolemmal membrane. The electrocardiogram of this patient revealed sinus bradycardia, increased QRS voltage, T-wave inversion in the midprecordial leads, and PR interval prolongation. The sinus bradycardia was terminated with atropine and is presumed to be due to increased vagal tone. However, the increased QRS voltage and T-wave inversion is not unlike that seen in other forms of cardiac glycogenosis. The impaired AV nodal condution may be due to impaired glycolytic metabolism within the conductive system. The conductive tissues of the normal heart contain a relative abundance of glycogen which suggests that this system may be highly dependent on glycolytic metabolism. Further evidence in favor of this hypothesis is the finding of decreased succinic dehydrogenase activity, diminished oxygen consumption and resistance to cyanide and anoxia in the conductive tissues of the heart. Therefore it seems possible that myocardial phosphorylase deficiency may be responsible for impairment of AV nodal conduction in this patient.