We read the report by Wu et al investigating the impact of location of epicardial adipose tissue (EAT), measured by coronary artery calcium-scoring computed tomography angiography on obstructive coronary stenosis. In a retrospective manner, a total of 208 patients underwent coronary calcium scoring and computed tomography angiography for suspicion of coronary artery disease (CAD; obstructive CAD in 97 and nonobstructive CAD in 111 patients). Left atrioventricular (AV) groove EAT thickness was the only EAT measurement that showed association with increasing number of vessels exhibiting ≥50% stenosis (p <0.001). Also, left AV groove EAT thickness well predicted the obstructive CAD (odds ratio 1.16, 95% confidence interval 1.04 to 1.29, p = 0.006). Left AV groove EAT thickness of >15 mm was the optimal cut-off point to predict obstructive CAD (odds ratio 4.62, 95% confidence interval 1.92 to 11.11, p <0.001). Adding left AV groove EAT thickness to the conventional clinical risk factors and coronary calcium score improved the prediction of obstructive CAD (area under the curve from 0.848 to 0.912, p = 0.002).

Human EAT is a type of visceral adipose tissue functioning as a metabolically active endocrine organ by secreting several hormones inflammatory cytokines and chemokines, and it is proposed to play a differential role in the pathogenesis of coronary atherosclerosis. Additionally, the distribution of EAT is asymmetric and mostly localized in the “pericoronary” AV and interventricular grooves. Although there were several studies showing the association of EAT thickness or volume with the presence or absence of CAD, the EAT volume is paradoxically “not” related to the severity of coronary atherosclerosis or plaque burden, which questions the association between EAT and coronary atherosclerosis. Also, EAT is most commonly measured as total volume rather than region-specific locations in most of the clinical studies which might be of particular clinical value. However, it is still not certain whether the severity of atherosclerosis at each coronary artery is related to the amount of EAT surrounding it. In a study, Wang et al showed that only left AV groove EAT thickness but not total EAT volume was significantly associated with the severity of CAD, even after adjustments for conventional risk factors, body mass index, waist circumference, C-reactive protein, and intra-abdominal visceral fat area. They found that left AV groove EAT thickness of >12.2 mm was the optimal cut-off point to predict the presence of ≥50% coronary stenosis. Among the 3 coronary arteries, left AV groove EAT thickness was most strongly correlated with ≥50% diameter stenosis in the embedded left circumflex artery by multivariate regression model. In another study by Wang et al, EAT thickness in the left AV groove was the only parameter consistently associated with all key components of the metabolic syndrome and inflammatory markers. All those studies have suggested that left AV groove EAT thickness might have both local and systemic effects on atherosclerotic process. In consistent with these studies, Wu et al presented the predictive role of left AV groove EAT thickness on the severity of CAD for overall and each coronary artery. The patients with obstructive CAD in this study showed increased waist circumference, higher rate of diabetes mellitus and hypertension, and lower high-density lipoprotein cholesterol level compared with nonobstructive CAD group, which were key components of the metabolic syndrome. Because of the greater amount of patients with metabolic syndrome in obstructive CAD group, in consistent with the study by Wang et al, left AV groove EAT thickness may play a role in both pathologies (metabolic syndrome and CAD). Also, Wu et al showed that left AV groove EAT thickness have had similar predictive value with coronary calcium score in the prediction of coronary stenosis.

In conclusion, although total EAT volume is associated with the presence of CAD, region-specific locations, particularly left AV groove EAT thickness, have significantly well predicted the severity of coronary stenosis at both overall and each coronary artery. Although it has not been primarily aimed in this study, we proposed that left AV groove EAT thickness with coronary calcium score may serve as a better screening tool before proceeding with computed tomography angiography, which may decrease radiation exposure in those patients. Taken together, these findings indicate that measurement of EAT thickness in the left AV groove and coronary calcium score provide a more accurate assessment of patients’ atherogenic risk and are, therefore, better risk factors than conventional risk factors.