[Sudden cardiac death due to conduction disorder. III. Is the so-called idiopathic AV block caused by a congenital abnormality?].

The aim of this third part is to discuss the nature and origin of the destructive lesion of the conduction system. A total of 53 hearts of patients dying from av-block was available for this study, and in morbid anatomy the commonest pattern of lesions responsible for av-block is destruction of the branching bundle and the origin of both bundle branches. The pathological processes found in the heart and conduction system are as follows: ischemic heart disease (49%), surgical lesions (15%), calcificatory destruction (6%), inflammatory destruction (6%), various distinct causes (11%), and primary av-block (13%). Main interest is focused on the group with primary heart block. Morphologically our series shows little fibrosis but an unexplained loss of conduction fibers and strikingly atrophic elements (filiform fibers). At attempt is made to explain the loss of conduction fibers as a consequence of the natural developing process which separates the atria from the ventricles, a separation essential for electrical stability of the heart. It is accepted that the accessory muscle bundles which characterize the Wolff-Parkinson-White syndrome are a failure in reduction of the muscle fibers running from the atria to the ventricles at an early embryological stage. If this same process runs to excess, the result must be an av-block. We consider a part of the so-called primary av-block to be a consequence of this process.