Season and clinical factors influence epicardial adipose tissue attenuation measurement on computed tomography and may hamper its utilization as a risk marker

Background and aims: A small difference in epicardial adipose tissue (EAT) attenuation measured on computed tomography (CT) imaging has been reported between patients who suffered coronary events and event-free patients. EAT consists of beige adipose tissue functionally similar to brown adipose tissue and its attenuation may be affected by seasonal temperature variations and clinical factors. Methods: We retrospectively measured EAT attenuation on cardiac CT in 597 patients submitted to cardiac CT imaging for coronary artery calcium scoring. All scans were performed on the same CT scanner during the summer (June, July, August) or winter (December, January, February) months. EAT attenuation in Hounsfield units (HU) was assessed near the proximal right coronary artery in an area free of artifacts. For comparison, subcutaneous adipose tissue (SCAT) attenuation was measure along the midaxillary line. Results: The clinical and demographic characteristics of patients scanned during the summer (N = 253) and the winter (N = 344) months were similar. One third of patients were women, one quarter used statins and anti hypertensive drugs and 30% were obese. The EAT attenuation was significantly lower during the summer than the winter months (-98.17 +/- 6.94 HUs vs-95.64 +/- 7.99 HUs; p<0.001). Sex, white race, body mass index, diabetes status, treatment with statins and anti-hypertensive agents significantly modulated the seasonal variation in EAT attenuation. SCAT attenuation was not affected by season or other factors. Conclusions: The measurement of EAT attenuation is complex and is affected by season, demographic and clinical factors. These factors may hinder the utilization of EAT attenuation as a biomarker of cardiovascular risk.