The epicardium is the visceral part of the serous pericardium and forms the outer layer of the cardiac wall.
The epicardium is the visceral part of the serous pericardium, envelopes the heart, contains a variable amount of epicedial fatty tissue adjoining the myocardium at its outer border. Coronary arteries, cardiac veins, lymphatic vessels as well as sympathetic and parasympathetic nerve fibers are embedded into the epicardial fatty tissue, with the most amount within and along the atrioventricular and interventricular grooves and along the free wall of the right ventricle 1,2.
The epicardium forms the epicardial surface of the myocardium in which, myocyte strands diverge in different angles 3. It is separated from the parietal part of the serous pericardium by fluid.
The epicardium consists of a lining of mesothelial cells an immediately adjacent subserosal layer of connective tissue and in some parts a layer of the epicardial fatty tissue of variable thickness. In other parts the mesothelial cells a separated from the myocardium only by a thin layer of connective tissue 1,2.
The epicardium can be visualized with echocardiography, cardiac CT or cardiac MRI. It can be best appreciated in a situation of mild to moderate pericardial effusion, where it is separated from the parietal part of the pericardium by fluid 1.
Echocardiography is considered a first-line imaging modality in the evaluation of pericardial disease 1. Due to the epicardial fatty tissue, the epicardium is hyperechoic relative to the adjacent myocardium.
The epicardial fatty tissue is of low attenuation and can be easily visualized and delineated from the myocardium. Differentiation of the epicardium from the parietal pericardium is possible in the presence of pericardial fluid. CT can potentially be used for quantification of epicardial fatty tissue.
The epicardial fatty tissue is characterized by fat isodensity in all sequences. The epicardial surface can be visualized as a chemical shift phenomenon in some sequences, due to the transition between fatty tissue and cardiac muscle. Differentiation of the epicardium from the parietal pericardium is only possible when fluid is present like in the other imaging modalities 1.
After administration of gadolinium-based contrast agents, epicardium and parietal/fibrous pericardium might be outlined by a variable amount of enhancement subject to the degree of inflammation 1.
The following pathologies and diseases are related to the epicardium:
- 1. Klein AL, Abbara S, Agler DA, Appleton CP, Asher CR, Hoit B, Hung J, Garcia MJ, Kronzon I, Oh JK, Rodriguez ER, Schaff HV, Schoenhagen P, Tan CD, White RD. American Society of Echocardiography clinical recommendations for multimodality cardiovascular imaging of patients with pericardial disease: endorsed by the Society for Cardiovascular Magnetic Resonance and Society of Cardiovascular Computed Tomography. (2013) Journal of the American Society of Echocardiography : official publication of the American Society of Echocardiography. 26 (9): 965-1012.e15. doi:10.1016/j.echo.2013.06.023 - Pubmed
- 2. Rodriguez ER, Tan CD. Structure and Anatomy of the Human Pericardium. (2017) Progress in cardiovascular diseases. 59 (4): 327-340. doi:10.1016/j.pcad.2016.12.010 - Pubmed
- 3. Lunkenheimer PP, Redmann K, Kling N, Jiang X, Rothaus K, Cryer CW, Wübbeling F, Niederer P, Heitz PU, Ho SY, Anderson RH. Three-dimensional architecture of the left ventricular myocardium. (2006) The anatomical record. Part A, Discoveries in molecular, cellular, and evolutionary biology. 288 (6): 565-78. doi:10.1002/ar.a.20326 - Pubmed