AV NODAL REENTRY .2. AV NODAL, AV JUNCTIONAL, OR ATRIONODAL REENTRY

The classical model of ''atrioventricular (AV) nodal'' reentrant tachy cardia suggests that the reentrant circuit is entirely within the comp act AV node and that AV nodal tissue is present proximal and distal to the circuit. Recent evidence from mapping studies and from examinatio n of the effects of curative procedures, however, suggests that the up per end of the circuit uses perinodal atrial or transitional tissue. M oreover, the anatomical substrate of dual ''AV nodal'' pathways is lik ely to be the multiple connections between compact AV node and atrium rather than discrete intranodal pathways. The antegrade slow pathway a ppears to be situated at the posteroinferior approaches to the AV node in the region between the coronary sinus orifice and the tricuspid an nulus. The retrograde fast pathway appears to be situated in the anter ior atrionodal connections at the apex of Koch's triangle, close to th e His bundle. The lower turnaround point of the circuit is likely to b e within the AV node.