Research About Histological Characteristics Of Myocardial Sleeve Of Pig's Pulmonary Veins

Background Atrial fibrillation is the most common type of arrhythmia in adults. It is more common as patients age. Electrophysiological studies have demonstrated that most cases of paroxysmal atrial fibrillation originate from the pulmonary veins. Aborting atrial fibrillation by breaking the connections between the left atrium and the pulmonary veins supports this concepts. Pulmonary veins have sleeves of myocardial cells that extend into the veins from the left atrium. Independent pulsation, pacemaker activity, and morphologic studies in a variety of animals suggests the presence of conducting cells in the pulmonary veins, perhaps within the myocardial sleeves. We investigated this hypothesis with a histological and ultrastructural study of pig pulmonary veins.Objective Through observing the special cells and structure of pulmonary veins by using PGP9.5 and S100 antigen immunohistochemistry and ultrastructural study, to discover the pathogenesis of focal atrial fibrillation originate from pulmonary veins.Methods The pulmonary veins were obtained from 14 healthy pigs, 11 of which were fixed in 10% phosphate buffered formalin solution, embedded in paraffin, serially sectioned (5um) transversely and longitudinally. Alternative sections were stained with hematoxylin and eosin staining, Masson staining and irnrnunohistochemistry by using the polyclonal antibody PGP9.5 and S100 respectively. The other 3 pigs' hearts were cut perpendicular to the long axis and fixed in 10% formaldehyde for histological sections and 3% glutaraldehyde for ultrastructural study under 4 C. The pulmonary vein rings were observed under light microscopy (hematoxylin and eosin staining) to look for pale cells as the location for further analysis by electron microscopy.Results First, the myocardium extended beyond the PV-atrial junction, was localized surrounding the vascular smooth muscle layer forming a myocardial sleeve. The peripheral end of the myocardial sleeves were irregular with the distance from 6 to 18mm. The cardiac fibers bundled and mainly distributed in circular directions. There were different interspaces among the muscular bundles. Observed pale cells different from common myocardial cells were found within the pulmonary veins using hematoxylin and eosin staining. Second, immunohistochemical techniques were adopted, there were single or collecting cells, nerves fibres and ganglia possessed a significantly higher density of the general neuronal marker PGP9.5 than did the adjacent myocardial cells, but S100 positive portion only found in nerves fibres and ganglia. Third, electron microscopy confirmed the presence of P-like cells and transitional cells in the pig's pulmonary veins. Finally, there were abundant nerve fibres and ganglia within the myocardial sleeves of pulmonary veins.Conclusion We found P-like cells in the pig's pulmonary veins by using the methods of hematoxylin and eosin straning, immunohistochemistry and electron microscopy. Ectopic beats from pulmonary veins triggering or driving focal atrial fibrillation may be the results of P-like cells in the myocardial sleeves in the pulmonary veins. The nerve fibres and ganglia perhaps adjust the activities of P-like cells.