Epicardial Adipose Tissue Measured by Multidetector Computed Tomography: Practical Tips and Clinical Implications

Abstract

Epicardial adipose tissue (EAT) is the fat depot surrounding the heart and is confined within the pericardial sac. It accounts for approximately 20% of the total heart weight and covers 80% of the cardiac surface, mostly in the grooved segments along the paths of the coronary arteries. To clearly delineate the asymmetric distribution of EAT and explore its pathophysiological significance, EAT should be measured in three dimensions using multidetector computed tomography (MDCT): regional thickness, cross-sectional areas, and total volume. Details regarding MDCT measurements of EAT are introduced in this chapter. Regardless of differences in ethnicity and body habitus, EAT thickness in the grooved segments is greater than in the non-grooved segments. Among the grooved segments, the right atrio-ventricular groove (where the right coronary artery is located) has the thickest fat, followed by the left atrio-ventricular groove (where the left circumflex artery and great cardiac vein are located). The maximal EAT thickness surrounding the left anterior descending coronary artery, measured in the superior inter-ventricular groove in the basal short-axis plane, is less than that surrounding the right coronary artery or the left circumflex artery. The average volume of EAT is generally between 110 and 125 cm³. Although EAT constitutes only 1% of the total fat mass, several clinical studies have shown that the amount of EAT is associated with obesity, the amount of intra-abdominal visceral fat, cardio-metabolic risk factors, cardiac structural changes, coronary atherosclerosis, and the incidence of coronary heart disease events. However, it is still a matter of debate as to whether these associations with EAT are direct or indirect, and which EAT measurement provides the best correlate. It appears that EAT thickness in the left atrio-ventricular groove provides a more accurate assessment of its metabolic and atherogenic risks and is therefore a better indicator of its metabolic risk and a stronger coronary risk factor than total EAT volume. Future studies are critical to elucidate whether there is indeed regional variation in the molecular characteristics of EAT and whether this variation confers any clinical, prognostic, and therapeutic implications.