The Relationship Between Epicardial Fat and Indices of Obesity and the Metabolic Syndrome: A Systematic Review and Meta-Analysis

Epicardial fat (epicardial adipose tissue, EAT) has been implicated in the pathogenesis of coronary artery disease (CAD). The objective of this study was to examine the relationship between EAT and generalized obesity, central or visceral adipose tissue (VAT), and the components of the metabolic syndrome--systolic blood pressure (SBP), triglycerides (TGs), high-density lipoprotein cholesterol (HDL-C), and fasting blood glucose (FBG)--that are linked to CAD. A systematic review of the literature, following meta-analysis guidelines, was conducted until May, 2013, using the search strategy "Obesity" OR "abdominal obesity" OR "metabolic syndrome" OR "metabolic syndrome X" AND "epicardial fat". Thirty-eight studies fulfilled the criteria. There was a highly significant (P<0.00001) correlation between EAT and body mass index (BMI), waist circumference (WC), or VAT. The correlation between EAT and VAT was significantly (P<0.0001) greater than the correlation between EAT and WC, which in turn was significantly greater than the correlation between EAT and BMI. Overall, EAT was 7.5 ± 0.1 mm in thickness in the metabolic syndrome (n=427) compared to 4.0 ± 0.1 mm in controls (n=301). EAT correlated significantly (P<0.0001) with SBP, TGs, HDL, and FBG, but the strength of the association was less than one-half of the relationship of EAT to indices of obesity. The results of multivariate analysis were less consistent but show a relationship between EAT and metabolic syndrome independent of BMI. In summary, the very strong correlation between EAT and VAT suggests a relationship between these two adipose tissue depots. Measurement of EAT can be useful to indicate VAT. Whereas EAT correlates significantly with each of the components of the metabolic syndrome- SBP, TGs, HDL, or FBG-the magnitude of the relationship is considerably and significantly less than the relationship of EAT to BMI. These data show the strong relationship between EAT and BMI but especially with WC and VAT. They also demonstrate the smaller magnitude of the association of EAT with standard coronary risk factors, related to the metabolic syndrome, and suggest that the unique features of this adipose tissue warrant detailed investigation.