A cardiopathological study on the anatomical substrate for fatal arrhythmias in aged companion animals

对11例猫和4例犬的完全性房室传导阻滞（CAVB）采用连续切片法对心脏传导系统进行组织学检查，得到以下结果和结论：在CAVB猫中，基础疾病包括肥厚性心肌病9例，二尖瓣发育不良和慢性间质性肾炎继发的严重心脏肥大各1例。组织学上，在纤维化的中心纤维体的最下部可见软骨或骨化生病变，向下突出至室间隔嵴。病变压迫了His束的穿透部分和/或分支部分，引起不同程度的退行性改变和松解，束纤维明显纤维化。具有软骨或骨形成的中心纤维体的明显纤维化似乎是由于心脏纤维骨架的应力和应变而发生的，也可能是由于室间隔肥大造成的机械因素。在所有4只CAVB犬中，与传导系统异常相关的大体解剖改变包括双房室瓣膜心内膜病和最上层室间隔的心内膜纤维化。组织学上，由于纤维或纤维脂肪替代，在某种程度上，在His束的穿透和/或分支部分观察到中度至重度的传导细胞减少。此外，4例中有3例在两束分支近端共存病变。犬的这种类型阻滞是由于两个房室瓣膜黏液瘤变性的扩展导致中央纤维体的病理过程中传导系统的参与。

The cardiac conduction system was histologically examined in 11 feline cases and 4 canine cases of complete atrioventricular block(CAVB) with the serial sectioning method and the following results and conclusions were obtained. In the cats with CAVB, underlying diseases included 9 cases of hypertrophic cardiomyopathy and each one case of mitral valve dysplasia and severe cardiac hypertrophy secondary to chronic interstitial nephritis. Histologically, a chondroid-or osseous-metaplastic lesion was seen in the lowermost portion of the fibrosed central fibrous body, protruding downward to the interventricular septal crest in each case. The lesion had compressed the penetrating portion and/or branching portion of the bundle of His, causing various degrees of degenerative changes and lysis and marked fibrosis of the bundle fibers. The marked fibrosis of the central fibrous body with cartilage or bone formation seems to occur as a result of stress and strain on the fibrous skeleton of the heart and may be due to mechanical factors created by hypertrophy of the interventricular septum. In all the 4 dogs with CAVB, gross anatomic changes associated with conduction system abnormalities included valvular endocardiosis of both atrioventricuar valves and endocardial fibrosis of the uppermost interventricular septum. Histologically, moderate to severe reduction of the conducting cells due to fibrous or fibro-fatty replacement was observed in some level in the penetrating and/or branching portions of the bundle of His in each case. In addition, 3 cases among the 4 had coexisting lesions at the proximal portions of the both bundle branches. This type of block in dogs was due to involvement of the conduction system in pathologic processes of the central fibrous body resulting from extension of myxomatous degeneration of both atrioventricular valves.