Patterns of myocardial fibrosis in idiopathic cardiomyopathies and chronic Chagasic cardiopathy

Abstract

Objective: To study the fibrillar nature and structural features of the collagenous interstitium of the myocardium in normal and cardiomyopathic human hearts, employing the picrosirius red technique and polarization microscopy.

Design: A survey, case series study.

Setting: Referral autopsy service at a university medical centre (Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto).

Cases and methods: A total of 46 adult hearts obtained at autopsy were used: five control hearts without evidence of cardiac disease, nine hearts with dilated cardiomyopathy, five with hypertrophic cardiomyopathy, four with endomyocardial fibrosis affecting the left ventricle, and 23 with chronic Chagasic cardiopathy. Fragments of myocardial tissue were obtained from the equator of the left ventricular free wall, fixed in formalin, dehydrated, and embedded in paraffin. Sections were stained with a modification of the picrosirius red technique and examined using direct light and polarization microscopy.

Results: The findings in the control myocardium did not differ from those reported in the literature. The myocardium in both dilated and hypertrophic cardiomyopathies showed diffuse fibrosis varying in degree from one case to another, but present in all cases. The basic pattern was characterized by a diffuse increase in both endomysial and perimysial collagen thick fibres, particularly surrounding individual myocytes (endomysial sheath). The microscopic study of the cases of endomyocardial fibrosis showed a thickened fibrotic endocardium consisting predominantly of thick collagen fibres extending as a septum, corresponding to broad perimysial sheaths, into the myocardium. In the superficial muscle fibre bundles usually composed of atrophic fibres, there was an increase in thickness of collagen fibres in both the perimysial and endomysial connective tissue matrix. To a variable degree (but present in all cases) interstitial and diffuse fibrosis could be observed in the chronic myocarditis of Chagas's disease. This was manifested by a diffuse increase in the amount of thick collagen fibres surrounding muscle fibre bundles (perimysial matrix), varying in intensity from one area to another, and around intramural coronary vessels, combined with a less pronounced increase in the endomysial collagen matrix.

Conclusions: These findings extend knowledge of the various expressions of interstitial myocardial fibrosis in the idiopathic cardiomyopathies and chronic Chagasic cardiopathy and perhaps provide insight into pathogenesis. Further research into the patterns and pathogenesis of myocardial fibrosis are needed in order to offer prevention and corrective forms of therapy of the fibrotic process.