Ectopic adipose tissue in subsistence populations with minimal coronary disease, large left atria, and very low rates of atrial fibrillation

Background: Greater deposits of epicardial adipose tissue are associated with atrial fibrillation and coronary disease, but have not been studied in subsistence populations. Methods: We performed CT imaging to measure coronary artery and thoracic aortic calcium (CAC, TAC), epicardial fat thickness (EFT), liver density, and left atrial (LA) anteroposterior diameter and, using a deep learning-enabled software program, epicardial and thoracic fat volume (EFV, TFV), in two remote Amerindian subsistence populations with minimal coronary artery calcification and virtually no atrial fibrillation. We compared 893 adult Tsimane (mean age 58.3±10.5 y, 51.6% male), 440 Moseten (55.9±10.4 y, 53.6% male) to 955 U.S. (56.8±10.8 y, 51.6% male) subjects. Results: Tsimane and Moseten had 43%-52% lower EFT, EFV, TFV, and 48-92% less CAC and TAC, respectively than the U.S. cohort. Mean liver measurements were 14-22% denser and LA diameters 10-14% larger (≈ 40% larger by volume). For EFV, Tsimane, Moseten, and U.S. cohorts averaged 54.2±25.6, 60.3±35.1, and 106±53.5 cc, respectively (p< 0.05 for all comparisons). EFV remained significantly smaller after adjustment for age, BMI, and other characteristics. For all CT metrics, the more acculturated Moseten measures were intermediate between Tsimane and the U.S. cohort. Conclusions: Tsimane mean EFV was the lowest of any population ever reported in the literature, achieving a new population standard. The low levels of EFV in the Tsimane and Moseten add to the body of evidence linking ectopic fat and atherosclerosis and further confirm (in the negative) the association, and likely causative role, of epicardial fat and atrial fibrillation.