[Present concepts of accessory pathways].

The possibility of ablation of arrhythmias has revived interest in accessory atrioventricular pathways. The authors propose a classification based on their electrophysiological properties, the nature of the arrhythmias which they induce, their anatomy and localisation. Classical accessory pathways have a rapid "all or nothing" type of conduction and are responsible for the WPW syndrome. They are called bundles of Kent although Kent's description does not correspond exactly to our present concept of their structures. However, some classical accessory pathways do have unidirectional conduction properties. When only retrograde reciprocating orthodromic tachycardia may occur but not preexcitation is observed in sinus rhythm: they have to be differentiated from reciprocating nodal tachycardias. Atypical accessory pathways show decremential conduction and are composed of specific tissues. When the conclusion is mainly or exclusively anterograde, tachycardias may be observed which were generally attributed to nodoventricular Mahaim fibres. When the conduction is essentially retrograde, they usually give rise to chronic junctional tachycardias.