There are many studies about the association of adipose tissue and LV diastolic dysfunction, including global adiposity , central adiposity , and visceral adiposity . Epicardial fat plays an important role in lipid and energy metabolism, which can also have harmful effects because it can secret many proatherogenic and proinflammatory cytokines . In our study, EFT measured by echocardiography was independently correlated with e’ mean, but not with E/e’ mean, in a high-risk community population with an LVEF ≥ 50%. Subgroup analysis showed no interaction with age, sex, BMI, heart rate, or preexisting conditions such as hypertension, diabetes, or CHD, and no correlation of EFT2 with e’ mean.
Epicardial fat can be assessed by multiple imaging methods, including CT, MRI, and echocardiography. The thickness, area, and volume of epicardial fat can be measured by CT with manual or semi-automated methods. However, the high cost and radiation exposure associated with CT are disadvantageous, especially in large population studies. MRI is considered the golden standard for evaluating heart fat, although its use is also limited because of high cost and high requirement. By contrast, echocardiography is the most convenient method to evaluate epicardial fat, and is particularly suitable for epidemiological studies. The thickness and area of the epicardial fat can be measured with echocardiography , although the image quality has a marked influence on accuracy. Further, there can be differences between different readers. We used echocardiography to evaluated EFT in the present study. Echocardiography is widely used to evaluate epicardial fat . Using ultrasound measurements, a Korean study reported a correlation between EFT and CT measurements of epicardial fat volume . Echocardiographic epicardial fat measurements were also shown to have a strong correlation with MRI measurements . It is important to note that paracardial fat consists of epicardial fat and pericardial fat, which should be distinguished during echocardiography examination. Echocardiographic EFT can be measured from the parasternal long and short axis views. However, EFT measured from the long axis view (but not the short axis view) was reported to be the independent predictor of e’ septal and e’ lateral .
In the present study, EFT was associated with most echocardiographic parameters. For example, EFT was positively correlated with ventricular septum and LV posterior wall thickness, but not with LVMI. One study showed that an increasing epicardial fat was significantly related to an increase in LVM because of high free fatty acids levels, insulin resistance and adrenergic activity, and that increased visceral fat directly affected LV output to perfuse the increased body mass . In that study, the participants were younger (mean age, 46.9 years) and more obese (BMI, 30−30.5 kg/m2) than in our cohort. A further study reported that EFT was correlated with atria enlargement in morbidly obese subjects . By contrast, we found no associated of EFT with LAVI, although our participants were older, with a higher prevalence of hypertension. Thus, LVMI and LAVI may be more significantly correlated with hypertension and age.
There are a few echocardiographic parameters used to evaluate LV diastolic function. Mitral inflow pattern, including E and A wave velocity, E/A, and E wave DT, are affected by many factors. A significant association of e’ with LV relaxation was reported in human subjects . The E/e’ ratio can also be used to evaluate LV filling pressures . Further, e’ is a powerful predictor of cardiac mortality in patients, independent of normal or abnormal LV systolic function [23, 24], while mitral E/e’ is a strong predictor of cardiac death or rehospitalization for CHF as well. In our correlation analysis, EFT was negatively associated with E, E/A, and e’, and positively associated with A, DT, and E/e’. In multivariate regression analysis, EFT was independently associated with e’ mean, but not with E/e’. Interestingly, in Japanese patients with known or suspected CAD, EFT was negatively associated with e’ mean and positively correlated with E/e’ mean . Konishi et al. also reported that epicardial fat volumes measured by CT were significantly and independently associated with E/e’ >10 in suspected CAD patients . Further EFT was significantly associated with LV diastolic dysfunction in subjects with normal coronary artery . Finally, Dabbah et al. reported that E/e’ was not associated with EFT , similar to that in the present study.
In our subgroup analysis, there was no effect of CHD on the relationship between EFT2 and e’ mean. Cavalcante and Konishi reported an independent correlation of epicardial fat and E/e’, although as that study included patients suspected of CAD, some patients may have advanced diastolic dysfunction since ischemia . Hypertension is a risk factor for the occurrence of LV diastolic dysfunction. In patients with newly diagnosed and untreated hypertension, increased EFT was significantly and independently related to the degree of LV diastolic function . In our subgroup analysis, we found no effect of hypertension on the relationship between EFT2 and e’ mean. It was also reported that EFT was more common in women than men > 60 years old, and that EFT was significantly related to LV function in women, but not men . By contrast, we found no interactions of different ages or sex on the correlation of EFT with e’ mean. All of these contrasting findings may be relate to the different imaging methods for evaluating epicardial fat, or to different populations of patients.
There are several limitations to our study. First, epicardial fat was measured by echocardiography rather than MRI or CT. However, EFT measured by echocardiography was shown to correlate with volumetric measurements. Second, because of the cross-sectional nature of our study, a causal relationship between EFT and e’ cannot be determined. Prospective studies examining whether increased EFT is predictive of LV diastolic dysfunction are required. Finally, the majority of patients were > 40 years of age, and thus our findings may not reflect the characteristics of epicardial fat in a younger population.
In summary, EFT measured by echocardiography was independently correlated with the e’ mean, but not with the E/e’ mean, in a high-risk community population with an LVEF ≥ 50%. Subgroup analysis showed no interaction with age, sex, BMI, heart rate, or preexisting conditions such as hypertension, diabetes, or CHD, or of the correlation between EFT and e’ mean.