Histological Study Of The Pulmonary Vein Antrum In Human

Objective:Although the catheter ablation for atrial fibrillation (Af) has gained a good effect, the mechanism of Af is not clear. At present, the ablated targets in most of the ablation strategies include pulmonary vein antrum. Therefore, the anatomic and electrophysiological features of pulmonary vein antrum have become a focus. In this study, we observed the anatomic and histological features of the left atrium, pulmonary vein and pulmonary vein antrum in order to investigate the mechanism of atrial fibrillation.Methods:The samples of left atrium, pulmonary vein and pulmonary vein antrum were obtained from 10 Chinese died of noncardiac causes. After observing the overall anatomy of the pulmonary veins, the pulmonary veins and the left atrium were peeled off. We took down the pulmonary veins and left atriums and observed the distribution of the muscular fascicle within the pulmonary vein antrum. Three milimeters specimens of the left atrium, the left upper and right upper pulmonary vein antrum, the left upper and right upper pulmonary vein were cut down. The specimens were fixed using 4% formalin more than a week. And then the specimens were dehydrated with ethanol and embedded in paraffin. The specimens were cut serially in longitudinal and transverse direction and were stained with hematoxylin and eosin (HE) . Selected sections were stained with Masson-Trichrome. Also, the specimens of the pulmonary vein antrum were stained with general neural marker protein gene product 9.5 (PGP9.5). The pulmonary vein antrum is defined as the part between the orifice of the pulmonary vein and the left atrium, which seems like a filter. Generally, Its edge is 0. 5～1. 5 cm away from the orifice of each pulmonary vein. The observed data include the thickness of myocardium and the musculardistribution in pulmonary vein, pulmonary vein antrum and left atrium, and the distribution of nerve fibers in the pulmonary vein antrum.Results: (1)The myocardium in the pulmonary vein antrum is thinner than that of the left atrium(2.6±0.4 vs 3.0±0.5,p=0.047). (2) The myocardium becomes thinner from the left atrium to the pulmonary vein. Also its number becomes fewer and fewer. In transverse section, myocardium of the pulmonary vein and antrum distributes more inhomogenously by comparison with the left atrium. (3) In longitudinal section, myocardium of the left atrium arranges transversely in parallel, however, it disorganizes in the pulmonary vein antrum. (4) No special node-like cells were observed, but some puce cells. (5) PGP9.5-immunoreactive nerve fibers are distributed in the pulmonary vein antrum.Conclusions: The myocardium of the pulmonary vein antrum distributes in disorganization which may contributes to the substrate of atrial arrhythmia.The abundant nerves distributing in the pulmonary vein antrum may explain the changes of the electrophysiological properties in atria,such as autorhythmicity,refractory period and conduction velocity, which induce or maintain Af.