The usefulness of an endomyocardial biopsy in heart disease of unknown etiology.

Light-, electron microscopic and enzyme histochemical examinations (phosphorylase, LDH, NADH:TR, SDH and 3-HBDH) were performed on endomyocardial biopsies of 26 patients with heart diseases of unknown etiology. On the basis of the clinical findings the patients were grouped into hypertrophic cardiomyopathy patients), dilated-congestive cardiomyopathy (8 patients), latent cardiomyopathy and small vessel disease (11 patients) and myocarditis (4 patients). Morphologic changes which might characterize the pathogenesis, were found in 7 patients: small vessel disease in 3 patients, nonspecific myocarditis in 1, iron storage disease in 1, adriamycin cardiomyopathy in 1 and cardiomyopathy with inclusions typical of Fabry's disease in 1 patient. In the other patients the morphologic changes were not sufficiently characteristic to be indicative of an etiopathogenesis. Several pathologic alterations did, nonetheless, appear to have a certain prognostic value such as endocardial and interstitial fibrosis, myofibrillolysis, myolysis, mitochondrial degeneration and increased lipid content in the muscle fibers. The frequency of these changes was evaluated partly semiquantitatively, partly by means of the point-counting method and graded with 1-3 points. Three patients with congestive cardiomyopathy scored at least 7 points. Two of them died within 8 weeks, 1 patient with adriamycin cardiomyopathy recovered after discontinuation of the therapy but he died 4 years after the biopsy. Six to 50 months after the biopsy (mean 31.5, median 6.5) the score was less than 7 in the other patients and all these patients were still alive. The histochemical changes manifested as an increase and/or a decrease of the enzymatic activities, involving scattered muscle fibers or their segments. A decrease of the activities of all dehydrogenases examined appeared to be prognostically ominous, correlating with a score of 7 or higher. A decrease of SDH activity in 7 cases, in combination with a decrease of the HBDH activity in 4 of them, was indicative of a disturbance in the Krebs cycle and lipid metabolism in the absence of ischemic damage. The alterations in the phosphorylase activity did not, however, appear to have a prognostic significance. Normal activity of the phosphorylase seemed to be prognostically favorable.