The relationship of ectopic lipid accumulation to cardiac and vascular function in obesity and metabolic syndrome

Abstract

Storage of lipid in ectopic depots outside of abdominal visceral and subcutaneous stores, including within the pericardium and liver, has been associated with obesity, insulin resistance, and cardiovascular risk. We sought to determine whether anatomically distinct ectopic depots were physiologically correlated and site-specific effects upon cardiovascular function could be identified. Obese subjects (n = 28) with metabolic syndrome but without known atherosclerotic disease and healthy controls (n = 18) underwent magnetic resonance imaging (MRI) and proton MR spectroscopy (MRS) to quantify pericardial and periaortic lipid volumes, cardiac function, aortic compliance, and intrahepatic lipid content. Fasting plasma lipoproteins, glucose, insulin, and free-fatty acids were measured. Pericardial and intrahepatic (P < 0.01) and periaortic (P < 0.05) lipid volumes were increased in obese subjects vs. controls and were strongly and positively correlated (P <or= 0.01) but independent of BMI (P = NS) among obese subjects. Intrahepatic lipid was associated with insulin resistance (P < 0.01) and triglycerides (P < 0.05), whereas pericardial and periaortic lipid were not (P = NS). Periaortic and pericardial lipid positively correlated to free-fatty acids (P <or= 0.01) and negatively correlated to high-density lipoprotein (HDL) cholesterol (P < 0.05). Pericardial lipid negatively correlated to cardiac output (P = 0.03) and stroke volume (P = 0.01) but not to left ventricular ejection fraction (P = 0.46). None of the ectopic depots correlated to aortic compliance. In conclusion, ectopic storage of lipid in anatomically distinct depots appeared tightly correlated but independent of body size. Site-specific functional abnormalities were observed for pericardial but not periaortic lipid. These findings underscore the utility of MRI to assess individual differences in ectopic lipid that are not predictable from BMI.

Figure 1

Differing pericardial lipid volume among obese subjects. Axial T1-weighted MR images obtained at the level of the heart from two subjects with differing BMI are illustrated. Both show a pronounced subcutaneous adipose layer (arrows). The smaller depots that are the focus of this study (pericardial lipid and periaortic lipid) are identified by their prominent bright signals. In the two examples shown, (a) illustrates a subject with a greater BMI but less pericardial lipid compared to the subject in b, as assessed by the area in this slice as well as the total volume of pericardial lipid. These images suggest that pericardial lipid is not correlated with BMI in obese subjects. MR, magnetic resonance.

Figure 2

Correlation between ecotopic lipid depots. Scatter plots of ectopic lipid volumes are presented showing strong correlations between (a) pericardial vs. periaortic and (b) pericardial vs. intrahepatic lipid depots for obese subjects.

Figure 3

Site-specific effect of pericardial lipid and cardiac function. A scatter plot of pericardial lipid normalized to left ventricular mass (in ml/g) is presented vs. cardiac output for obese subjects. Cardiac output values presented are all within the normal range.