Histological and ultrastructural characteristics of the atrial appendages in atrial fibrillation
Abstract
Introduction. Atrial fibrillation is one of the commonest forms of arrhythmia in clinical practice, posing a risk of thromboembolism affecting vital organs. Removal of the atrial appendages during cardiac surgery prevents thrombus formation and minimizes the risk of complications. The histological and ultrastructural basis of atrial fibrillation has been insufficiently studied. We aimed to compare histological and ultrastructural manifestations of changes in the atrial appendages in atrial fibrillation using surgical specimens from cardiac surgery patients. Materials and methods. We examined the atrial appendages removed from cardiac surgery patients with and without atrial fibrillation (64 and 33 samples, respectively) using histological, immunohistochemical, and transmission electron microscopy techniques. Van Gieson, Mallory, Lie, and Congo red staining combined with polarization microscopy was performed. Immunohistochal analysis included S-100, CD-117, and desmin. Results. We identified acute and chronic changes in the myocardium of the atrial appendages in the setting of increased vascular permeability. Cardiomyocyte damage, manifested as myocytolysis, is characterized by cytoskeletal destruction and disintegration of cardiomyocyte myofibrils. Amyloid deposits in the myocardial stroma were found in 6 out of 64 biopsy specimens with atrial appendage (9%). Immunohistochemically, telocytes were identified in the stroma but were absent in areas of sclerosis and lipomatosis. Conclusion. Histological and ultrastructural changes in the atrial appendages in atrial fibrillation are characterized as acute cardiomyocyte damage against a background of increased vascular permeability and chronic manifestations, including amyloidosis in some cases. These changes provide a morphological basis for disturbances in electrical stability and myocardial contractility and for the development of mural thrombosis. Keywords: heart, atrial fibrillation, heart appendages, histological structure, ultrastructure