Fibrosis and inflammatory cells in human chronic chagasic myocarditis: scanning electron microscopy and...

The present study deals with both pathologic fibrosis and matrix connective tissue in chronic chagasic myocarditis. A total of 12 hearts were obtained at autopsy. Eight cases of chronic chagasic myocarditis were selected. Four cases without evidence of cardiac disease were used as controls. The diagnosis of chronic Chagas' heart disease was based on previously established criteria. A cell-maceration method was utilized to evaluate the spatial organization of the fibrillar collagen accumulation after removal of the myocardial tissue non-fibrous elements. The relationship between inflammatory cells identified by monoclonal antibodies and interstitial fibrosis stained with picrosirius red was assessed. Striking structural alterations of the collagen matrix in the perimysium were detected: increase in number and thickness of tendon-like structures, and markedly thickened and aggregated collagen strands. Besides, a diffuse increase in the thickness of collagen fibers surrounding individual myocytes, consisting of the endomysial matrix, mainly adjacent to the perimysium, could be observed. The dense-weave endomysial meshwork was composed of fine collagen fibrils, and it was continuous with those of adjacent myocytes, obscuring the lateral struts. Sometimes, thicker struts tethering myocytes to myocytes could be seen. These changes were associated with scattered dense scar-like foci, probably reflecting repair fibrosis associated with myocyte necrosis. Furthermore, the present results clearly showed the colocalization of foci of myocyte necrosis and degeneration and associated fibrosed areas and fibroblasts with T lymphocytes and macrophages. The accumulation of interstitial collagen fibers in chronic chagasic myocarditis may be expected to decrease myocardial compliance and disrupt synchronous contraction of the ventricles during systole, contributing to a spectrum of ventricular dysfunction that involve either the diastolic or systolic phase of the cardiac cycle or both. Myocardial fibrosis can be also implicated in the genesis of malignant ventricular tachyarrhythmias, major causes of sudden death among chronic chagasic patients. The increase in myocardial fibrosis could be directly related to an inflammatory reaction mainly composed of T lymphocytes and macrophages.