Myocardial ultrastructure in Kearns-Sayre syndrome.

Myocardial ultrastructural changes are described in a twenty-five-year-old female with typical Kearns-Sayre syndrome. The electrocardiogram revealed complete atrioventricular block with an occasional torsades de pointes type of ventricular tachycardia. His bundle recording demonstrated HV block with normal AH interval. An endomyocardial biopsy showed "ragged-red fibers" by the modified Gomori trichrome stain, and on electron microscopy there were increased numbers of morphologically abnormal mitochondria: ie, gian mitochondria, a whorled pattern of the cristae, and electron-dense substances, and paracrystalline inclusions in the mitochondria. The patient has been well since pacemaker implantation, but she may develop a clinically overt cardiomyopathy due to progression of myocardial involvement.