The endocardium defines the inner soft tissue lining of the heart within the cardiac chambers and constitutes the superficial surface of the cardiac valves. It apparently serves as a regulatory mechanism on myocardial contractility.

Gross anatomy

The endocardium represents the inner layer of the cardiac wall and covers the inner surface of the cardiac chambers and the superficial surface of the cardiac valves. It consists of endothelial cells,  connective tissue, elastic fibres and smooth muscle cells and contains nerve fibres ^1-3.

The adjacent subendocardial connective tissue layer contains the Purkinje fibres transmitting electric signals to the myocardium ^1-3.

Histology

The ventricular endocardium consists of different layers ^1-3:

• endothelium
  • consists of endothelial cells (squamous epithelial cells)
• the subendothelial connective tissue layer
  • contains collagen fibrils and fibroblasts
  • more prominent in the atria, in particular, the left atrium
• elastic tissue layer
  • contains elastic fibres, collagen fibres and smooth muscle cells
  • more prominent in the left atrium and the left ventricular septum
• subendocardial tissue layer
  • connects endocardium to the myocardium
  • contains collagen and elastic fibres, small blood vessels and Purkinje fibres
  • merges with the extracellular matrix of the myocardium

Radiographic features

Due to its thin layer, the normal endocardium is not visualised on imaging. 

However, it might be depicted if thickened or altered in the setting of disease.

Ultrasound

Ultrasound is the first-line modality in the evaluation of valvular heart disease.

Irregularities and in particular vegetations suggest endocardial disease.

MRI

The healthy endocardium will not be visible. However cardiac MRI might aid in the diagnosis of pathologically altered endocardium.

An apical filling defect and/or diffuse late gadolinium enhancement of the endocardium in particular if several chambers are involved will suggest endocardial disease e.g. endomyocardial fibrosis or endocardial fibroelastosis ^5-7.

Related pathology

The following pathologies and diseases are related to the endocardium ^5-7:

• endocarditis
  • infective endocarditis
  • eosinophilic endocarditis
  • Libman-Sacks endocarditis
  • nonbacterial thrombotic endocarditis
• mitral valve prolapse / mitral valve calcification
• endomyocardial fibrosis
• endocardial fibroelastosis
• carcinoid heart disease
• subendocardial fat infiltration