Ultrastructural aspects of endomyocardial biopsy in restrictive cardiomyopathy: evaluation of elastogenesis.

Besides elastic and collagen fibres, numerous smooth muscle (SM) cells were found in the thickened endocardium in 3 cases of restrictive cardiomyopathy and in 1 case of congenital endocardial fibroelastosis. In 3 other cases of congenital endocardial fibroelastosis, fibroblast-like cells were present besides numerous fibres. The former seemed to originate from SM cells. The authors present their opinion that both in congenital and acquired endocardial fibroelastosis, the lesion develops essentially in the same way. The basic phenomenon consists in increased elastoplastic activity of SM cells. In contrast, the aetiology (stimulus) of higher, elastogenous activity of SM cells remains obscure and seems to be different in individual cases.