Morphometric analysis of the His bundle (atrioventricular fascicle) in humans and other animal species. Histological and immunohistochemical study

Abstract

His bundle is a part of the specialized electrical conduction system that, in the normal or anormal hearts, provides connection between the atrial and ventricular myocardial compartments. The aim of this study was to perform a morphometric analysis of the characteristics of His bundle and its association with predetermined electrophysiological variables in humans, dogs, horses, and pigs. We used ve hearts of the species studied. Histological sections of 5 µm thickness were obtained and stained with hematoxylineosin and Masson's trichrome. We also used the desmin and PAS method for precise identi cation of cells. His bundle was longer in horses (2.85 x 0.82 mm) and pigs (1.77 x 0.44 mm) than in dogs (1.53 x 0.26 mm) and humans, which was the shortest (1.06 x 0.23 mm). In His bundle cells, the area and diameters were signi cantly larger in pigs and horses than in humans (p < 0.001) and dogs (p < 0.001). We have found two patterns of organization of the components of His bundle: Group I, with large cells and a high amount of collagen bers in ungulates (pigs and horses); group II, with smaller cells and less amount of collagen bers in humans and dogs. Documenting differences in cell size in His bundle allows us to obtain an additional, alternative identi cation criterion to commonly used ones such as anatomical location. Morphological characteristics of His bundle and its cells in the different species studied coincide with rapid or slow transmission of the electrical impulse when compared with the predetermined electrophysiological variables.

Histopathological changes in the electrical conduction of cardiac nodes after acute myocardial infarction in dogs and horses, compared with findings in humans: A histological, morphometrical, and immunohistochemical study

“…Furthermore, in 70% of infarcted dogs (Figures-1a and c), we observed a decrease in the area occupied by cardiomyocytes in the periphery of the node, which comprised adipose tissue in the atrial myocardium. Another important finding was the higher percentage of collagen fibers (fibrosis) inside the SAN (47%) than the percentage of cells inside the node (33%), which was not observed in our control cases (Table -2 and Figure-2a) [35].…”

“…A greater presence of intermediate filaments has been observed in conduction system cells than in cardiomyocytes, mainly due to the presence of desmin, which is distributed throughout the entire cytoplasm of conduction cells, unlike in cardiomyocytes where it only occurs in certain specific points (intercalated and Z disks). This enables accurate identification of conduction system cells in normal hearts [35,51,52]. In this study of dogs and horses that succumbed to SCD, the use of desmin was not effective in identifying the cells of the heart nodes, as this immunohistochemical stain failed to exhibit differences between nodal cells and cardiomyocytes in the heart nodes of dogs or in the SAN of horses.…”