BackgroundThree‐dimensional electro‐anatomical mapping, previously performed in horses with atrial arrhythmias, has demonstrated the medial region of the caudal vena cava (CaVC), 1–8 cm caudal to the fossa ovalis, as an anatomical predilection site for atrial tachycardia associated with areas of slow conduction and conduction block. Slow conduction has also been recorded in the cranial vena cava (CrVC).ObjectivesTo investigate the morphological characteristics of the myocardial sleeves (MS) in the CaVC and CrVC, in order to identify a potential substrate of right sided atrial arrhythmias.Study designCross sectional.MethodsPost‐mortem dissection of 37 hearts from adult warmblood horses without known cardiovascular disease. Macroscopic examination of the myocardial distribution, evaluated the MS area, length, width, and shape in the CaVC and the CrVC. At least 2 samples from each vena cava MS were histologically examined using Masson's trichrome staining.ResultsMyocardial sleeves into the medial CaVC and into the CrVC were observed in all horses and showed variations in distribution, shape, and size between horses. Their mean ± standard deviation length from the limbus into the CaVC reached 5.7 ± 1.0 cm (maximum 8.3 cm), and from the azygos vein into the CrVC 5.3 ± 1.6 cm (maximum 8.6 cm). Myocardium‐free islands were observed in the CaVC and CrVC in 30% and 6% of horses, respectively. Histologically, MS showed a non‐uniform myocardial fibre arrangement, with presence of fibroadipose tissue, features known to result in slow conduction and pro‐arrhythmia.Main limitationsStudy only included horses without history of atrial arrhythmia.ConclusionsMyocardial sleeves are present in both CaVC and CrVC, showing anatomical variations between horses. Tissue characteristics known to favour re‐entry were identified indicating that these venae cavae MS are a potential substrate for atrial tachyarrhythmias and a target for treatment by ablation.

中文翻译：

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马尾部和颅腔静脉中潜在致心律失常基质的形态学证据

背景三维电解剖标测，以前在患有房性心律失常的马身上进行，已经证明尾部腔静脉（CaVC）的内侧区域，距卵圆窝尾部1-8厘米，是与房性心动过速相关的房性心动过速的解剖学好发部位。慢传导区和传导阻滞区。颅腔静脉 (CrVC) 中也记录到慢传导。目的研究 CaVC 和 CrVC 中心肌袖 (MS) 的形态特征，以确定右侧房性心律失常的潜在基础。研究设计横断面。方法对 37 颗没有已知心血管疾病的成年温血马心脏进行尸检。宏观检查心肌分布，评估 CaVC 和 CrVC 的 MS 面积、长度、宽度和形状。使用马森三色染色对来自每个腔静脉 MS 的至少 2 个样本进行组织学检查。结果在所有马中观察到进入内侧 CaVC 和 CrVC 的心肌袖，并且显示出马之间的分布、形状和大小的差异。从角膜缘到 CaVC 的平均±标准差长度达到 5.7 ± 1.0 cm（最大 8.3 cm），从奇静脉到 CrVC 的长度达到 5.3 ± 1.6 cm（最大 8.6 cm）。分别有 30% 和 6% 的马的 CaVC 和 CrVC 中观察到无心肌岛。组织学上，MS 显示心肌纤维排列不均匀，存在纤维脂肪组织，已知会导致传导缓慢和促心律失常。主要局限性研究仅包括没有房性心律失常病史的马。结论 CaVC 和 CrVC 中都存在心肌袖，显示马之间的解剖学差异。已知有利于折返的组织特征被确定，表明这些腔静脉 MS 是房性快速心律失常的潜在基质，也是消融治疗的目标。