Significance of annulus fibrosus of heart in relation to AV conduction and ventricular activation in cases of Wolff-Parkinson-White syndrome

Abstract

A histological examination of accessory atrioventricular connecting fibres in two heart specimens with a Wolff-Parkinson-White (WPW) syndrome revealed the following findings. Parietal subendocardial accessory fibres, mostly composed of ordinary myocardium, connected the atrial with the ventricular wall. In one specimen afew modifiedfibres werefound between the parietal wall of the right atrium and that of the right ventricle. Septal accessoryfibres were alsofound. A part of these connexions was morphologically ordinary myocardium, but many other fibres were found to be bridges of conduction tissue between parts of the His-Tawara bundle and the basal rim of the ventricular septum. Many holes were observed at different locations of the annulusfibrosus, at its parietal as well as at its septal part. It was noted that each hole was an anatomical pathway for at least one accessory fibre; more ordinary myocardial or modified connexions passed through a big gap. It can be stated that the quantity of the accessory muscular atrioventricular connexions was determined by the degree of discontinuity of the annulus fibrosus. The latter structure appeared to be the most important component of the morphological substrate which was presumably related to the existence and a possible progression of atrioventricular and intraventricular conduction anomalies in cases of WPW syndrome.