Endomyocardium

Endomyocardium is a term used in anatomy and pathology to refer to the inner region of the heart wall where the endocardium and the immediately subjacent myocardial tissue meet. In standard cardiac anatomy, the heart wall comprises the endocardium lining the chambers, the myocardium forming the muscular wall, and the epicardium on the outside. The label endomyocardium is not universally adopted as a distinct histological layer but is used to indicate the inner myocardial region near the endocardium, particularly in discussions of pathology.

Histologically, the endomyocardial region includes the endocardial lining with endothelial cells and the subendocardial connective tissue. It may also contain small intramyocardial vessels and, in the ventricles, Purkinje fibers within the subendocardial area. This region is functionally important for the conduction system and for supplying the inner layers of the myocardium, but it is also prone to injury in certain conditions due to its location.

Clinically, the term appears in references to endomyocardial diseases. Endomyocardial fibrosis, for example, involves thickening of the endocardium and the adjacent subendocardial myocardium, contributing to restrictive cardiomyopathy. Endomyocardial biopsy, a diagnostic procedure, targets the endocardial surface of the right ventricle to obtain tissue for histological analysis and diagnosis of various conditions, including inflammatory or infiltrative diseases.

Developmentally, the endomyocardial region forms as part of heart wall differentiation during ontogeny, integrating endothelial, connective tissue, and myocardial components. Imaging modalities such as echocardiography and cardiac MRI can assess endomyocardial thickness and involvement in disease, while biopsy provides definitive histological information.