Epicardial adipose tissue in coronary microvascular dysfunction.

To the Editor:

We read the article by Mahmoud et al. entitled ‘Epicardial adipose tissue differentiates in patients with and without coronary microvascular dysfunction’ with interest. In this article, the authors claimed that epicardial adipose thickness may be useful in coronary microvascular dysfunction diagnosis, and interventions to decrease epicardial adipose tissue thickness may reduce coronary microvascular dysfunction [1].

Epicardial adipose tissue is a metabolically active ectopic fat accumulation regarded as a novel cardiometabolic risk factor [2]. It possesses inflammatory properties modulating local and possibly remote inflammation. Recently, we found that epicardial adipose tissue thickness is associated with the COVID-19 infection severity [3]. Evidence supports the role of inflammation in coronary microvascular dysfunction and inflammation may be the plausible link between coronary microvascular dysfunction and epicardial adiposity [4].

Coronary microvascular dysfunction can be evaluated invasively or non-invasively. However, the definition of coronary microvascular dysfunction in this article by Mahmoud et al. necessitates further clarification. In the absence of significant epicardial coronary artery stenosis, corrected TIMI frame count or TIMI flow may imply a crude status of coronary microcirculation in the advanced stages of microvascular dysfunction. In addition, the coronary slow flow may be also observed when the diffuse coronary vascular spasm or increased basal coronary vascular tone is present [5]. It is also not uncommon during radial access which was not specified in the study. Furthermore, the presence of increased left ventricular end-diastolic pressure or hypertensive heart disease may only refer to the increased likelihood of coronary microvascular dysfunction and these entities are not equivalents of coronary microvascular dysfunction. In this context, authors may clarify the definition of coronary microvascular dysfunction whether having any one of slow flow, elevated left ventricular end-diastolic pressure or hypertensive heart disease is sufficient for the diagnosis of coronary microvascular dysfunction or having all of these entities is requisite. Even though, this constellation needs to be validated with further studies.