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

本文用连续切片法对11例猫和4例犬完全性房室传导阻滞（CAVB）的心脏传导系统进行了组织学检查。在CAVB猫中，基础疾病包括9例肥厚性心肌病和各1例二尖瓣发育不良和继发于慢性间质性肾炎的严重心脏肥大。在组织学上，在纤维化的中央纤维体的最下部可见软骨样或骨化生病变，在每种情况下向下突出到室间隔嵴。病变压迫了希氏束的穿透部分和/或分支部分，引起不同程度的退行性变化和纤维溶解，并使束纤维明显纤维化。具有软骨或骨形成的中央纤维体的显著纤维化似乎是由于心脏纤维骨架上的应力和应变而发生的，并且可能是由于室间隔肥大产生的机械因素。在所有4只CAVB犬中，与传导系统异常相关的大体解剖学改变包括两个房室瓣的瓣膜性心内膜病和最上部室间隔的内膜纤维化。组织学上，在每种情况下，在希氏束的穿透和/或分支部分，都观察到由于纤维或纤维脂肪替代而导致的传导细胞中度至重度减少。4例中3例同时存在双束支近端病变。犬的这种类型的阻滞是由于传导系统参与了由两个房室瓣粘液瘤变性扩展引起的中央纤维体的病理过程。

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.