Epicardial adipose tissue: emerging physiological, pathophysiological and clinical features

Abstract

Epicardial adipose tissue is an unusual visceral fat depot with anatomical and functional contiguity to the myocardium and coronary arteries. Under physiological conditions, epicardial adipose tissue displays biochemical, mechanical and thermogenic cardioprotective properties. Under pathological circumstances, epicardial fat can locally affect the heart and coronary arteries through vasocrine or paracrine secretion of proinflammatory cytokines. What influences this equilibrium remains unclear. Improved local vascularization, weight loss, and targeted pharmaceutical interventions could help to return epicardial fat to its physiological role. This review focuses on the emerging physiological and pathophysiological aspects of the epicardial fat and its numerous and innovative clinical applications. Particular emphasis is placed on the paracrine/endocrine properties of epicardial fat and its role in the development and progression of atherosclerosis.

Epicardial fat, cardiac geometry and cardiac function in patients with non-alcoholic fatty liver disease: Association with the severity of liver disease

“…In the last years growing evidence also suggests that the increase in epicardial fat can be considered a cardiometabolic risk factor [32], being associated with the metabolic syndrome [33], with a diagnosis of NAFLD both by US or MR spectroscopy [14][15][16][17][18], with carotid atherosclerosis [34] and coronary artery disease [35]. Accordingly, we confirmed the association of epicardial fat thickness with older age, visceral obesity, hypertension and statin use, well-known factors associated with an increased cardiovascular risk.…”

“…However, we may put forward a few hypotheses, leaving the demonstration of pathophysiological mechanisms to experimental studies. First, increased epicardial fat is able to act as a paracrince/endocrine organ and to secrete proatherogenic and proinflammatory adipokines, as tumor necrosis factor alfa, interleukin 6, interleukin 1beta and angiotensin [32]. In turn, these chemokines may activate stellate cells, leading to liver fibrogenesis.…”

Thermogenic potential and physiological relevance of human epicardial adipose tissue

“…20 In terms of its distribution, postmortem studies have revealed that epicardial fat can cover up to 80% of the heart surface and contribute up to 20% of total ventricular weight under normal conditions, while being capable of covering the heart completely and even extending up to 2 cm in thickness during obesity in humans. 21,22 Anatomically, epicardial fat is not separated from the underlying myocardium with any fascia-like structure and is also known to share coronary blood supply with the latter, thereby supporting the idea of plausible 'vasocrine' or 'paracrine' cross talk between the two. However, a direct microcirculatory interconnection between the two has not been established so far.…”

“…Considering that fatty acids are the major source of fuel for contracting heart muscle, this proposal is highly plausible and therefore widely accepted. 8,22,27 However, it is important to note that these observations have not been repeated in other animal models or validated for human epicardial fat. Considering that rodents do not necessarily possess epicardial fat under normal conditions and even when observed (that is, due to obesity or aging), such as in the case of guinea pigs, epicardial fat distribution differs from that in humans.…”

“…55 These observations tend to support the 'outside to inside' signaling hypothesis, which suggests that secretory products of dysfunctional epicardial fat or adventitia can lead to the development of intimal atherosclerotic lesions in coronary arteries and other blood vessels. 22 …”