Left and right atrial structural remodeling in hearts of patients with sinus rhythm and atrial fibrillation

Atrial fibrillation (AF) is one of the most common arrhythmias in the clinical practice and it is associated with an increase in mortality risk that is strongly related with old age. Its pathogenesis is still not sufficiently explored. One of the generally recognized factors contributing to the initiation and maintenance of atrial fibrillation is structural remodeling of the myocardium. Structural remodeling is reflected by changes that affect both atrial cardiomyocytes as well as endomysium.

Aim:

In this work we focused on morphological characterization of endomysium from both the left and the right atrium in patients undergoing open heart surgery with atrial fibrillation or in sinus rhythm. We also compared extracellular matrix composition, VEG F immunoreactivity, and microvascular density and microvessel pericyte coverage index between patient groups and also based on localization.

Methods:

We studied functional morphology of atrial biopsies performed at 46 patients (19 patients with AF, and 27 with sinus rhythm (SR)) undergoing bypass or mitral valve surgery. The atrial samples were fixed with 4 % paraformaldehyde and embedded into paraffin. Sections from atrium were histologically examined using routine hematoxylin-eosin staining. Immunohistochemistry was used to visualize collagen I, collagen III , elastin, desmin, smooth muscle actin and VEG F in the atrial samples. To detect capillaries UEA -lectin was used.

Results:

We found variable amount of endomysial collagen I and III in myocardial samples from both groups of patients, which was similar when comparing SR and AF group and when comparing left and right atrium as well. The amount of elastin in the atria was similar in AF and SR groups but there was more than twofold amount of elastin in the right atrium compared to the left. Variable amount of VEG F was localized mainly in the mesothelium, blood vessels and adipocytes, but also in the cardiomyocytes. The expression of VEG F, microvascular density and microvessel pericyte coverage index was similar when AF and SR group was compared and also did not differ between left and right atrium.

Conclusion:

Our results document that in patients undergoing open heart surgery variable level of ECM proteins can be found but the amount of collagen I, colagen III and elastin do not differ when the patient group is divided based on the presence of atrial fibrillation or sinus rhythm. Elastin volume fraction is higher in the right atrium compared to the left possibly reflecting different biomechanics or embryonic origin. VEG F is present in myocardia of patients but its amount is not dependent on the heart rhythm. Most of atrial capillaries are associated with pericytes but similar to microvascular density we did not observe changes during atrial fibrillation or when left and right atrium was compared.

This work was supported by the Research Program of Charles University – PRVOUK -P25/LF1/2.