Ultrastructural findings in endomyocardial biopsy of patients with Kearns-Sayre syndrome.

Kearns-Sayre syndrome is clinically defined by progressive external ophthalmoplegia, atypical retinitis pigmentosa and the potential occurrence of complete atrioventricular (AV) block. Right septal endomyocardial biopsy specimens from nine patients (four men and five women with a mean [+/- SD] [corrected] age of 36.3 +/- 14.4 years) with chronic progressive external ophthalmoplegia and mitochondrial skeletal myopathy were studied. Three patients had atypical retinal pigmentation. An atrioventricular or intraventricular conduction defect was observed in five patients. A pacemaker was prophylactically implanted in one patient because of abnormal conduction distal to the His bundle. Ultrastructural investigations revealed mitochondriosis in many heart muscle cells and an increased variability of mitochondrial form and size in all patients. In seven patients, 0.4 to 2.1% of all examined myocytes contained exclusively abnormal mitochondria. Three main types were observed: huge, mainly round mitochondria with concentric cristae; large, round or oval mitochondria with transverse or curved cristae; and small, vacuolated mitochondria. The volume density of myofibrils was reduced (41.9 +/- 11.1 compared with the normal value of 56.5 +/- 2.5 volume density [in percent], p less than 0.01) in these myocytes. Increasing numbers of vacuolated mitochondria correlated significantly with a reduction of myofibrils (r = -0.64, p less than 0.01). The data suggest that the ventricular myocardium of most patients with complete and even incomplete Kearns-Sayre syndrome is affected by disseminated mitochondrial cytopathy.