The epicardium is the outermost layer of the heart wall, serving as a protective covering. It is also the visceral layer of the serous pericardium, the inner part of the double-layered sac surrounding the heart. This thin membrane helps maintain heart health and function.
Anatomy and Role
The epicardium directly adheres to the heart’s muscular wall, the myocardium. It consists of a single layer of mesothelial cells on its outer surface and an underlying layer of loose connective tissue. This connective tissue contains fat, elastic fibers, blood vessels, and nerves that supply the heart muscle.
Its primary function is to provide a smooth, slippery outer surface, reducing friction as the heart beats within the pericardial sac. The epicardial mesothelial cells produce pericardial fluid, which lubricates the space between the epicardium and the parietal pericardium. This fluid allows for the heart’s effortless movement and expansion during each cardiac cycle. The epicardium also houses the major coronary arteries and veins, which supply and remove blood from the heart muscle. These vessels are embedded within the subepicardial layer, a connective tissue region beneath the mesothelial surface.
Epicardial Fat
Epicardial adipose tissue (EAT) is fat located directly on the heart’s surface, beneath the epicardium and near the myocardium and coronary arteries. This position allows EAT to interact directly with the heart muscle and blood vessels through local signaling. While primarily white adipose tissue, EAT can also exhibit characteristics of brown or beige fat, contributing to its thermogenic properties.
Under normal conditions, EAT serves several beneficial roles. It functions as an energy reservoir, providing free fatty acids to the myocardium, especially during high metabolic demand. EAT also offers mechanical protection, cushioning the heart and coronary arteries, and contributes to thermoregulation. However, under pathological circumstances, such as obesity or metabolic syndrome, EAT can become dysfunctional, secreting pro-inflammatory molecules that contribute to cardiovascular diseases, including coronary artery disease.
Conditions Involving the Epicardium
The epicardium can be affected by various medical conditions, impacting heart function. One is epicarditis, inflammation of the epicardium, which often occurs as part of broader pericardial inflammation known as pericarditis. Symptoms of pericarditis include chest pain (worsening with deep breathing or lying flat), fever, and shortness of breath.
Another condition is pericardial effusion, the abnormal accumulation of fluid within the pericardial sac, the space between the epicardium and the outer pericardial layer. While a small amount of fluid is normal, excessive buildup can pressure the heart, hindering its ability to fill and pump blood effectively. Symptoms may include shortness of breath, chest pressure or pain, and a fast heartbeat. Causes range from infections (viral or bacterial) to autoimmune disorders, cancer, or injury. In severe cases, a significant pericardial effusion can lead to cardiac tamponade, a life-threatening condition where the heart is compressed, requiring immediate medical intervention.