Endomyocardial fibrosis and restrictive cardiomyopathy: pathologic and clinical features.

Restrictive cardiomyopathy (RCM) is a primary myocardial disorder characterized by diastolic dysfunction and wide phenotypic heterogeneity. Clinicopathologic features in cats are currently poorly defined. One form of RCM is associated with endomyocardial fibrosis. The hallmark feature of endomyocardial fibrosis RCM is severe endomyocardial scar that may diffusely involve the left ventricle, or appear as a distinct lesion bridging the ventricular septum and left ventricular free wall. In some cases this may reduce left ventricular chamber volume or result in apical or mid chamber stenosis with associated pressure gradients. Left atrial enlargement is generally severe. Ventricular hypertrophy is variable and is often associated with wall or chamber remodeling. Histopathologic features include striking endocardial scar, myocardial interstitial fibrosis, and in some instances, endomyocarditis.