Myocardial interstitial fibrosis - histological and immunohistochemical aspects

The process of myocardial fibrosis is based on the remodeling of the extracellular matrix (ECM), which leads to increased myocardium stiffness and, in turn, severe alterations of the cardiac function. This phenomenon is consecutive to various types of cardiac disease, primarily infarction, due to inflammatory reactions involving various types of cellular mechanisms. We aimed in this paper to assess both microscopically and immunohistochemically the main aspects of ischemic myocardium found in areas of fibrosis and compare the findings with normal images from unaffected cardiac tissue of the same type.

Our study included infarction fragments of 2/2/2 cm harvested after autopsy from 26 patients who died during 2014 at the Emergency County Hospital of Craiova, Romania, following the diagnostic of ischemic cardiomyopathy. After usual histological preparations, we performed both classical staining with Hematoxylin-Eosin and trichromic Goldner-Szekely, as well as immunohistochemical assessment using anti-alpha-SMA, anti-desmin, anti-CD34 and anti-CD68 antibodies.

We have evaluated myocardial fibrosis in all areas of the myocardium and noted that it primarily develops around the arterioles and metarterioles. The area of myocardial fibrosis was more extensive, myocardiocytes being surrounded by collagen fibers. Collagen interstitial fibrosis, gave a "brindle" look to the myocardium. Myocardial fibrosis areas did not reveal myofibroblasts. We found lower numbers of blood vessels with an uneven distribution in areas of myocardial fibrosis. In the areas of normal myocardium, the macrophage numbers were two to three times lower than in areas of fibrosis, also displaying larger volume, with intense reaction to CD68.

Myocardial interstitial fibrosis occurs in outbreaks, mainly perivascular, but it affects larger areas of the myocardium interstitial space. We believe that interstitial fibrosis is a progressive process that can become permanent, thus constituting a promising therapeutic target for a large variety of cardiac conditions.