Background: Some mutations of cardiac sarcomeric proteins causing hypertrophic cardiomyopathy (beta-myosin heavy chain) are associated with skeletal muscle fiber dysfunction, while subclinical skeletal myopathy can be diagnosed by electromyography (EMG) in a substantial proportion of hypertrophic cardiomyopathy patients.
Methods: In 49 consecutive, unrelated patients with hypertrophic cardiomyopathy, conventional EMG of deltoid, vastus lateralis, tibialis anterior and soleus muscles was performed. No patient had clinically detectable muscle weakness. We compared the clinical and echocardiographic characteristics between patients with normal and patients with myopathic EMG.
Results: Myopathic EMG findings were demonstrated in 13 patients (26.5%), 26 patients (53.1%) had normal findings and 10 patients (20.4%) had indeterminate recordings. There was no significant difference in mean age, maximum wall thickness, left ventricular fraction shortening, NYHA class, the existence of left ventricular outflow tract obstruction, syncope, or the occurrence of nonsustained ventricular tachycardia in the Holter recording among the three groups. Comparison between the myopathic and the normal group revealed that nine patients from the latter (34.6%) had a positive history of sudden death in the family, whereas no patient had such a history in the former group (P=0.015).
Conclusion: The higher prevalence of a family history of sudden death in patients with normal EMG, although not thoroughly explained by our data, may reflect differences in the genetic substrate produced by the higher prevalence of high-risk mutations that are not expressed in skeletal muscle (e.g. troponin T). Further evaluation in genotyped patients is warranted.