Curriculum in Cardiology
Human epicardial adipose tissue: A review

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We discuss the anatomy, physiology, and pathophysiology of epicardial adipose tissue and its relationship to coronary atherosclerosis. Epicardial fat stores triglyceride to supply free fatty acids for myocardial energy production and produces adipokines. It shares a common embryological origin with mesenteric and omental fat. Like visceral abdominal fat, epicardial fat thickness, measured by echocardiography, is increased in obesity. Epicardial fat could influence coronary atherogenesis and myocardial function because there is no fibrous fascial layer to impede diffusion of free fatty acids and adipokines between it and the underlying vessel wall as well as the myocardium. Segments of coronary arteries lacking epicardial fat or separated from it by a bridge of myocardial tissue are protected against the development of atherosclerosis in those segments. However, when epicardial fat is totally absent in congenital generalized lipodystrophy, coronary atherosclerosis can still occur. Macrophages are more numerous and densely packed in the periadventitial fat of human atherosclerotic coronary arteries with lipid cores than in that of fibrocalcific or nonatherosclerotic coronary arteries. In obese patients with multiple cardiovascular risk factors, epicardial fat around atheromatous coronaries secretes several proinflammatory cytokines and is infiltrated by macrophages, lymphocytes, and basophils. Epicardial adipokine expression in obesity without coronary atherosclerosis has not been determined. In nonobese patients, epicardial fat around atheromatous coronary arteries expresses proinflammatory cytokines but produces either less adiponectin, a vasoprotective adipokine, than fat around nonatheromatous coronaries or a similar amount compared with thoracic subcutaneous fat. Further studies should be done to test the hypothesis that adipokines produced by and released from human epicardial adipose tissue might contribute locally to the pathogenesis of coronary atherosclerosis.

Section snippets

Anatomy and physiology of EAT

The epicardium or visceral layer of the pericardium is a population of mesothelial cells that migrate onto the surface of the heart from the area of the septum transversum (the embryological source of the diaphragm). Epicardial, mesenteric, and omental fat all share the same origin from the splanchnopleuric mesoderm associated with the gut.11 In the normal adult, epicardial fat is concentrated in the atrioventricular (AV) and interventricular (IV) grooves and along the major branches of the

Autopsy

Corradi et al27 dissected epicardial fat from the underlying myocardium in a series of 117 patients and found that it accounted for approximately 15% (mean, 54 ± 23 g [±SD]) of a normal heart weight (365 ± 49 g). They also found a direct correlation between LV and RV mass and corresponding epicardial fat mass. In a later study, the same authors confirmed the direct correlation (r = 0.755, P = .01) between EAT mass and myocardial ventricular mass measured by echocardiography in 60 subjects with

Pathophysiology of adipose tissue and adipokines in obesity

The pathophysiology of adipokine expression and secretion in VAT and SCAT needs to be reviewed to provide a conceptual basis for understanding adipokine pathophysiology. In contrast to the lack of studies comparing EAT in healthy nonobese and obese humans, the expression and secretion of adipokines in VAT and SCAT have been well documented in biopsies taken from lean healthy patients at elective intra-abdominal surgery as compared with biopsies from obese healthy patients undergoing bariatric

Epicardial fat in obesity

In their 1933 report on adiposity of the heart, Smith and Willius58 performed autopsies on 136 obese patients (mean 43% above ideal body weight; range, 13%-103%). They noted that “in most instances, a definite relationship between the excess of epicardial fat and the degree of general obesity occurred.” This observation was based on increased heart weight and not on dissected epicardial fat mass. As epicardial fat increases, it extends over the anterior surface of the heart, more over the RV

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    Disclosure: Harold S. Sacks is a member of the Speakers Bureau and has received honoraria from Takeda Pharmaceuticals and Merck Pharmaceuticals.

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