A histopathological study on the hypertrophy of the atrioventricular conduction system

A microscopical study of the AV conduction system using a serial sectioning method, was performed on 81 autopsied hearts with blocks anywhere in the hearts without arrhythmia. Pre-blockade hypertrophy in the AV conduction system was seen in 38%, 38%, 50-58% corresponded respectively to 3 degrees AV block, 1-2 degrees AV block and bundle branch block (including left hemiblock). Post-blockade hypertrophy was also observed in 58%, 38% and 42-25% of the above mentioned types of blocks respectively. Hypertrophy anywhere in the AV conduction system was seen in 77%, 42%, 78%, 39%, 30% and 74% of the cases with blocks, sick sinus syndrome, pre-excitation syndrome, other arrhythmias, normal hearts and hypertrophied hearts without arrhythmia, respectively. Hypertrophy of the proximal AV conduction system to the bundle of His was specific for arrhythmia group, whereas hypertrophy of the bundle branches occurred in either hypertrophy without arrhythmia or in bundle branch block. Hypertrophy of the Purkinje cells was remarkable in sudden cardiac death by clinically-proved ventricular fibrillation. Incidence of sclerosis of the AV node artery was high in the arrhythmia group, especially the highest (90%) in the sudden death group.