On the interstitial fibrotic changes in acute and convalescent myocarditis obtained by serial endomyocardial biopsy

In order to determine the characteristics of the interstitial fibrotic change of the myocardium in cases with viral or idiopathic myocarditis, right ventricular endomyocardial biopsy findings in 9 cases where serial endomyocardial biopsy had been performed at the acute (5-10 days after the onset of the disease), subacute (11-21 days) and convalescent stages (22-167 days) and in 1 case at the acute stage were analyzed. They were then compared with right ventricular endomyocardial biopsy findings from 58 cases with chronic right ventricular overloading and which were of various kinds of congenital and valvular heart diseases. The following results were obtained: Interstitial fibrosis was seen at the acute stage along with an increase in fibroblasts, macrophages and lymphocytes. An analysis of the interstitial changes revealed that, at the acute stage, thin collagenous fibers were prominent as well as interstitial edema and at the convalescent stage, the edema became less prominent and instead, thick collagenous fibers increased. Comparison with the 58 cases with chronic right ventricular overloading revealed that diffuse and/or subendocardial fibrosis and endocardial thickening were more frequent and statistically more significant in cases with myocarditis.