Epicardial fat: more than just an "epi" phenomenon?

Regional body-fat distribution is one of the key variables that explains the metabolic heterogeneity of obesity and its related cardiovascular risks. According to the ectopy concept, the inability of subcutaneous adipose tissue to store surplus triglycerides may lead to the development of fat in ectopic sites, such as the heart. Epicardial adipose tissue is a metabolically active endocrine organ that produces numerous factors that can modulate cardiac structure and function. The development of in vivo noninvasive imaging has made it possible to quantify its thickness and volume with increasing accuracy. In this review, we discuss the local interaction and cross-talk between epicardial fat and neighboring structures, such as coronary arteries and myocardium, and its relevance to cardiac diseases, such as coronary-artery disease or atrial fibrillation. Beneficial and harmful effects of epicardial adipose tissue are described and analyzed. What leads to an imbalance between protective and deleterious actions has to be further explored. We believe that epicardial fat, which has been neglected for years, plays a key role in cardiovascular disease pathophysiology and represents a "new world" exploration for therapeutic targets, which will be addressed in future clinical and research studies. Elucidating the mechanisms that drive the deposition or mobilization of cardiac adiposity between other ectopic-fat stores needs to be accomplished within the next few years.