Epicardial fat (E_fat) is an active ectopic fat depot, directly surrounding coronary arteries, and secreting high level of inflammatory adipokines; its development has been associated with coronary atherosclerosis. We investigated the relationship between E_fat and endothelium dependent vasoreactivity of the coronary microcirculation.

Myocardial blood flow (MBF) was determined by measuring coronary sinus flow with velocity-encoded cine magnetic resonance imaging at 3 teslas. We measured MBF at baseline and in response to sympathetic stimulation by cold pressor testing (CPT) in 17 healthy volunteers with normal left ventricular function (age 24±6 years, BMI=21.1±2.6kg/m2). E_fat volume was volumetrically assessed by manual delineation on short-axis views. CPT was applied by immersing one foot in ice water for 4 minutes.

A significant increase in MBF was observed: 1.18±0.58 vs 0.84±0.47mL.min-1.g-1, CPT vs rest, p=0.002. Mean relative MBF increase (ΔMBF) was 50±47%. Mean E_fat volume was 82±31mL and varied from 43 to 131 mL; mean LV mass and Left ventricular ejection fraction were 104±31g and 64±5%, respectively. CPT significantly increased heart rate (HR) by 28±13%, systolic blood pressure (BP) by 17±13%, diastolic BP by 23±19% and rate-pressure product by 52±25%, p<0.01, indicating an increase in myocardial work load. The increase in HR, reflecting sympathetic stimulation, was not influenced by sex, age or E_fat volume. CPT induced a decrease in coronary vascular resistance (150±93 vs 114±44 mmHg.mL-1.min.g) by trend (p=0.08). Interestingly, we found a significant negative correlation between E_fat volume and ΔMBF (r=-0.51, p=0.03), which remained significant after adjusting for age and sex. ΔMBF was not associated with waist circumference, BMI, CRP, lipid or glycemic parameters.

The increase in E_fat is associated with a decrease in endothelium dependent vasoreactivity response, suggesting that E_fat could early influence endothelial function.