The Wolff-Parkinson-White syndrome and its anatomical substrates.

The anatomical substrates that underlie the clinical syndromes of preexcitation are still incompletely understood. Regarding the Wolff-Parkinson-White syndrome, there is increasing evidence that early ventricular activation is caused by accessory atrioventricular connections. These are muscular connections existing outside the specialized conduction tissue axis, which are almost always composed of working myocardial fibers. Left-sided accessory atrioventricular connections have been identified with most frequency. They occur in the presence of a well-developed fibrous annulus, thus contradicting the hypothesis that faulty development of the annulus is a necessary accompaniment. For right-sided and septal connections, this developmental concept may still hold, since there is marked variability in the formation of the right-sided annulus fibrosus. Even within these settings, however, the topography of accessory atrioventricular connections may vary considerably. Usually the accessory connection will pass on the epicardial aspect of the annulus fibrosus, particularly when left-sided. The connections are closely related to the fibrous annulus, but in other instances they may be in a superficial location. Multiple connections can occur in one heart. These anatomical features are of paramount significance for successful surgical ablation of accessory atrioventricular connections.