Elastin in Human Atrial Wall During Atrial Fibrillation

Atrial fibrillation (AF) is a common arrhythmia associated with an increased risk of cardiac failure and mortality. It is accompanied by structural and electrical changes of the myocardium, with atrial fibrosis being one of the most important ones. This specific structural remodelling mechanism has been widely studied and was shown to create a substrate promoting AF. Apart from collagen involved in atrial fibrosis, there are a number of other extracellular molecules that could play an important role in AF. The aim of this study was to expand the knowledge about these molecules and evaluate the effect of AF on the expression of elastin.

The myocardial elastin expression (elastin volume fraction, EVF) was studied in atrial biopsies sampled from right auricle, left auricle and left atrium of patients with AF and sinus rhythm (SR) during bypass or mitral valve surgery. The samples were fixed with 4% paraformaldehyde and embedded into paraffin. The general morphology was evaluated after a routine hematoxylin-eosin staining of the sections, and elastin was detected by an immunohistological staining. The morphometrical evaluation, performed using image analysis software, compared the fraction of elastin fibers in the measured myocardial area between AF and SR samples.

Routine histological examination of the sections independent of the experimental group revealed no site specificity of the elastin expression. When comparing AF to SR samples, our results showed a non-significant higher expression of elastin in the myocardium of SR patients. This is in contrast to the higher collagen fraction during AF atrial fibrosis compared to SR, as observed in our previous study. Furthermore, EVF was significantly increased in the samples from the right auricle in comparison to the left auricle or both.

We conclude that even though the expression of collagen and elastin in human myocardium during AF is reverse, it is closely related and deserves further investigation. The increased EVF in the right auricle suggests that elastin is closely related or could even contribute to the myocardial mechanics.

Supported by research projects of the Charles University in Prague (UNCE 204013 and PRVOUK P25/LF1/2), grants from the Ministry of Health (MZO -00023001), and by the EU Operational Program Prague – Competitiveness; project „CEVKOON “ (CZ.2.16/3.1.00/22126).