Spontaneous pulmonary vein (PV) activity triggers atrial fibrillation (AF) in humans. Although AF frequently occurs in horses, the origin remains unknown. This study investigated the structural and electro-anatomical properties of equine PVs to determine the potential presence of an arrhythmogenic substrate. Endocardial three-dimensional electro-anatomical mapping (EnSite Precision) using high-density (HD) catheters was performed in 13 sedated horses in sinus rhythm. Left atrium (LA) access was obtained retrogradely through the carotid artery. Post-mortem, tissue was harvested from the LA, right atrium (RA), and PVs for histological characterization and quantification of ion channel expression using immunohistochemical analysis. Geometry, activation maps, and voltage maps of the PVs were created and a median of four ostia were identified. Areas of reduced conduction were found at the veno-atrial junction. The mean myocardial sleeve length varied from 28 ± 13 to 49 ± 22 mm. The PV voltage was 1.2 ± 1.4 mV and lower than the LA (3.4 ± 0.9 mV, P < 0.001). The fibrosis percentage was higher in PV myocardium (26.1 ± 6.6 %) than LA (14.5 ± 5.0 %, P = 0.003). L-type calcium channel (Ca1.2) expression was higher in PVs than LA (P = 0.001). T-type calcium channels (Ca3.3), connexin-43, ryanodine receptor-2, and small conductance calcium-activated potassium channel-3 was expressed in PVs. The veno-atrial junction had lower voltages, increased structural heterogeneity and areas of slower conduction. Myocardial sleeves had variable lengths, and a different ion channel expression compared to the atria. Heterogeneous properties of the PVs interacting with the adjacent LA likely provide the milieu for re-entry and AF initiation.

中文翻译：

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马肺静脉的结构和电解剖特征：对心房颤动的影响

自发性肺静脉 (PV) 活动会引发人类心房颤动 (AF)。尽管马匹经常发生房颤，但其起源仍不清楚。本研究调查了马 PV 的结构和电解剖特性，以确定致心律失常底物的潜在存在。使用高密度 (HD) 导管对 13 匹处于窦性心律的镇静马进行心内膜三维电解剖标测 (EnSite Precision)。通过颈动脉逆行进入左心房（LA）。尸检后，从 LA、右心房 (RA) 和 PV 采集组织，使用免疫组织化学分析进行组织学表征和离子通道表达定量。创建了 PV 的几何形状、激活图和电压图，并确定了四个孔口的中位数。在静脉-心房交界处发现传导减少的区域。平均心肌袖长度从 28 ± 13 毫米到 49 ± 22 毫米不等。 PV 电压为 1.2 ± 1.4 mV，低于 LA（3.4 ± 0.9 mV，P < 0.001）。 PV 心肌的纤维化百分比 (26.1 ± 6.6 %) 高于 LA (14.5 ± 5.0 %, P = 0.003)。 PV 中 L 型钙通道 (Ca1.2) 的表达高于 LA (P = 0.001)。 T 型钙通道 (Ca3.3)、连接蛋白 43、兰尼定受体 2 和小电导钙激活钾通道 3 在 PV 中表达。静脉-心房连接处的电压较低，结构异质性增加，传导速度较慢。与心房相比，心肌袖具有不同的长度和不同的离子通道表达。与邻近 LA 相互作用的 PV 的异质特性可能为再入和 AF 启动提供环境。