Is echocardiographic epicardial adipose tissue thickness measurement a reliable and reproducible method for risk stratification?

To the Editor,

With great interest, we read the article titled “Epicardial adipose tissue thickness is associated with myocardial infarction and impaired coronary perfusion” published by Tanindi et al. (1) in Anatol J Cardiol 2015; 15: 224-31. It is a good paper with well-conducted analysis. Tanındı et al. (1) investigated the association between epicardial adipose tissue thickness (EAT) and acute myocardial infarction (AMI) in their population. The measurement of EAT was performed manually at end-systole on the free wall of the right ventricle perpendicular to the aortic annulus in standard parasternal long-axis view. Tanındı et al. (1) found a positive correlation between EAT and AMI. They highlighted that the echocardiographic measurement of EAT is a useful method for risk stratification and for choosing patients who need more aggressive treatment in terms of risk reduction.

At present, the echocardiographic measurement of EAT, which reflects cardiac and visceral adiposity, has become one of the leading topics in cardiovascular imaging studies. EAT is suggested as a new cardiometabolic risk factor. Correlations between increased EAT and insulin resistance, metabolic syndrome, hypertension as well as cardiovascular diseases have been studied (2-4). The echocardio-graphic measurement of EAT is a widely available, simple, safe, non-invasive, cheap, and rapid method; however, it should be questioned whether EAT is a reliable and reproducible method. If it is not a reliable and reproducible method, then inaccurate measurements may affect our clinical decision and research results. In addition, EAT that was measured from the free wall of the right ventricle by echocardiography does not reflect all subepicardial adipose tissue volume.

Saura et al. (5) investigated the reproducibility of the echocardiographic measurement of EAT and compared the values with those obtained using multi-detector computed tomography (MDCT). Although the contrary was claimed, in a study by Saura et al. (5), they found a poor reproducibility of the echocardiographic measurements of EAT assessed by intraclass correlation coefficient. Moreover, measurements with echocardiography and MDCT showed low concordance. Saura et al. (5) found that echocardiography yielded larger values than those yielded by MDCT. In particular, there was a notable difference of up to 7 mm within two standard derivations of the mean values measured by these two different methods. The results of Saura et al. (5)’s study indicate that EAT measurements by echocardiography may lead to the misclassification of patients. Therefore, clinicians should be careful when this parameter is used as a diagnostic tool for risk stratification.

Furthermore, there are some other controversial issues regarding EAT. There are no normality values of EAT, and the discussion on how to measure EAT by echocardiography is still ongoing. EAT may be deformed through the cardiac cycle, and to ensure the maximal stability of true EAT, it should be measured in end-diastole (5). Further comprehensive studies are required to investigate the reproducibility of EAT and to answer the other questions.