CMR assessment of epicardial fat volume in human morbid obesity at 3 T: relationship to cardiac function and morphology

Introduction

Ectopic fat accumulation within and around the myocardium is involved in the pathogenesis of obesity-related cardiomyopathy and cardiovascular disease. Earlier MR studies have been restricted to a mildly obese population due to magnet bore size limitations. For this study, a 70 cm bore 3 tesla MR system offered the possibility to assess left-ventricular (LV) morphology and function along with EFV in patients with severe obesity.

Purpose

To assess epicardial fat volume (EFV) in severely obese patients with CMR at 3 T, and to determine its potential correlations with left-ventricular function and morphology.

Methods

CMR was performed with a Siemens Verio 3 T system in 24 obese patients (15 with morbid obesity and 9 with diabetes, mean BMI = 42.3 ± 5.7 kg/m²) and in 14 healthy controls (mean BMI = 22.4 ± 2.1 kg/m²). The scanner was equipped with a 32-channel phased-array coil. Sixteen short-axis slices covering the heart and its surrounding adipose tissue were obtained within four breathholds using a balanced SSFP cine sequence with 4-fold GRAPPA k-space reduction (FOV = 340 × 340 mm², TE = 1.2 ms, TR = 61 ms, matrix = 134 × 192, slice thickness 6 mm). The absolute volume of epicardial fat was assessed by manual delineation on every slice from base to apex. Parameters of LV function and morphology were obtained using the same short-axis dataset. All patients underwent an intraabdominal CT scan for visceral adipose tissue (VAT) assessment and biological evaluation.

Results

EFV was increased twofold between lean (64 ± 29 mL) and obese non-diabetic (123 ± 44 mL) subjects. Another twofold increase in EFV was observed in obese diabetic patients (240 ± 140 mL) (p < 0.0001). EFV was strongly correlated with age (r = 0.71, p < 0.0001), VAT (r = 0.89, p < 0.0001), BMI (r = 0.68, p < 0.0001), waist circumference (r = 0.73, p < 0.0001), fasting plasma triglycerides (r = 0.62, p = 0.018), and negatively correlated with thigh circumference (r = -0.45, p = 0.03) and superficial subcutaneous abdominal fat (r = -0.44, p = 0.03). Patients with metabolic syndrome (MS) had higher EFV than patients without MS (p < 0.0001). After multivariate adjustment, only VAT remained independently associated with EFV. EFV was negatively correlated with stroke volume (r = -0.46, p = 0.005), cardiac output (r = -0.46, p = 0.005) and LV end diastolic volume (r = -0.46, p = 0.004), Figure 1.

Figure 1

Epicardial fat in a diabetic obese patient on a short-axis view (left), manual segmentation by drawing the key lines dividing epicardial from paracardial fat and myocardium (middle), and an image from a healthy volunteer (right).

Conclusion

CMR at 3 T allowed quantification of epicardial fat volume and LV morphology and function in severely obese subjects. A significant correlation was shown between LV function and EFV.