PRESENT CONCEPTS OF ACCESSORY PATHWAYS

The possibility of ablation of arrhythmias has revived interest in acc essory atrioventricular pathways. The authors propose a classification based on their electrophysiological properties, the nature of the arr hythmias 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 K ent although Kent's description does not correspond exactly to our pre sent concept of their structures. However, some classical accessory pa thways do have unidirectional conduction properties. When only retrogr ade reciprocating orthodromic tachycardia may occur but not preexcitat ion is observed in sinus rhythm : they have to be differentiated from reciprocating nodal tachycardias. Atypical accessory pathways show dec remential conduction and are composed of specific tissues. When the co nclusion is mainly or exclusively anterograde, tachycardias may be obs erved which were generally attributed to nodoventricular Mahaim fibres . When the conduction is essentially retrograde, they usually give ris e to chronic junctional tachycardias.