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Macroscopic deposition of epicardial adipose tissue (EAT) has been strongly associated with numerous indices of obesity and cardiovascular disease risk. In contrast, the morphology of EAT adipocytes has rarely been investigated. We aimed to determine whether obesity-driven adipocyte hypertrophy, which is characteristic of other visceral fat depots, is found within EAT adipocytes. EAT samples were collected from cardiac surgery patients (n = 49), stained with haematoxylin & eosin, and analysed for mean adipocyte size and non-adipocyte area. EAT thickness was measured using echocardiography. A significant positive relationship was found between EAT thickness and body mass index (BMI). When stratified into standardized BMI categories, EAT thickness was 58.7% greater (p = 0.003) in patients from the obese (7.3 ± 1.8 mm) compared to normal (4.6 ± 0.9 mm) category. BMI as a continuous variable significantly correlated with EAT thickness (r = 0.56, p < 0.0001). Conversely, no correlation was observed between adipocyte size and either BMI or EAT thickness. No difference in the non-adipocyte area was found between BMI groups. Our results suggest that the increased macroscopic EAT deposition associated with obesity is not caused by adipocyte hypertrophy. Rather, alternative remodelling via adipocyte proliferation might be responsible for the observed EAT expansion.

Background: Epicardial adipose tissue (EAT) deposition has a strong association with aspects of metabolic dysfunction, including obesity. The size of the EAT adipocytes in relation to obesity, however, has rarely been researched. Therefore, to contextualise EAT within the broader framework of pathophysiological adipocyte size changes in obesity, we aimed to determine whether EAT adipocyte size is associated with body mass index (BMI)., Methods: During routine post-mortem examination, adipose tissue biopsies were obtained from four depots of 43 cases, including EAT, as well as pericardial (PAT), appendix mesenteric (AAT), and clavicular subcutaneous (SAT) adipose tissues. Tissues were fixed, sectioned, and stained using haematoxylin and eosin. The size (measured as area) of each adipocyte imaged from the depots was analysed in relation to BMI., Results: Mean size of EAT adipocytes was significantly smaller than that from SAT and AAT depots, while not differing from PAT adipocytes. BMI positively correlated with the size of adipocytes isolated from SAT (r=0.5893, P<.0001), PAT (r=0.5854, P<.0001), and AAT (r=0.5829, P<.0001) depots, but not from EAT (r=0.1242, P=.4274), even after multivariate adjustment for age and sex., Conclusions: EAT adipocyte size is not associated with increased BMI despite significant associations within adipocytes from other adipose depots., (Copyright © 2019 Elsevier Inc. All rights reserved.)