Cardiac function and ectopic adiposity in metabolic syndrome : an MRI and 1H-MRS study

Overweight and obesity are major global health concerns affecting around 2 billion people worldwide. Abdominal obesity is particularly hazardous to health associating with metabolic syndrome (MetS), non-alcoholic fatty liver disease (NAFLD), and type 2 diabetes mellitus (T2DM). In MetS, ectopic fat accumulates around the viscera and into organs regularly containing only minor amount of adipose tissue. This cross-sectional study was conceived to discover effects of MetS and ectopic adiposity including myocardial steatosis on cardiac function in non-diabetic men free of known heart diseases. The gold standard non-invasive method for fat quantification, proton magnetic resonance spectroscopy, was used to measure hepatic and myocardial triglyceride (TG) content. Magnetic resonance imaging (MRI) was used to assess cardiac structure and function and to quantify epicardial, pericardial, subcutaneous, and visceral abdominal fat depots. First, we examined the components of cardiac adiposity and their relationship to intra-abdominal ectopic fat deposits and cardiometabolic risk factors. MetS was associated with an increase in all examined ectopic fat depots. Myocardial TG was twofold increased in MetS. However, visceral adipose tissue (VAT) was the best independent predictor of cardiometabolic risk factors. Secondly, we studied left ventricular (LV) diastolic function and its relationship with cardiac fat depots. MetS associated with LV diastolic dysfunction and concentric LV remodeling. However, myocardial TG content was not an independent predictor of LV diastolic dysfunction. Thirdly, we studied the effect of different ectopic fat depots on LV structure and function in subjects with NAFLD and searched the role of hepatic fat content on cardiac steatosis. Epicardial and pericardial adipose tissue as well as myocardial TG content accumulated with increasing amount of both hepatic TG content and VAT. In addition, hepatic steatosis and VAT were associated with LV diastolic dysfunction. Lastly, we studied left atrial (LA) structure and function in MetS and examined the association of different ectopic fat depots and cardiometabolic risk factors with possible LA dysfunction. MetS associated with subclinical LA dysfunction without enlargement of the LA. Moreover, LA dysfunction associated with several contributory factors of MetS including waist circumference, insulin resistance, dyslipidemia, and VAT, which was the best independent predictor of LA dysfunction. Notably, the role of myocardial TG content on LA function remained inconclusive. In conclusion, MetS associates with significant changes in the structure and function of the heart. These changes are subclinical but may be followed by late complications such as heart failure or atrial fibrillation. The value of cardiovascular MRI may be early recognition of those obese subjects at risk for developing cardiovascular disease. Instead of body mass index, VAT is the best predictor of cardiac dysfunction. This study highlights the fundamental role of visceral obesity and hepatic steatosis directing their harmful effects to risk of cardiovascular diseases. The role of myocardial TG on cardiac dysfunction remains indeterminate. Therefore, cardiac energetics and the dynamic role of intramyocytic lipids, which are the primary fuel of the heart, merit further study.