[Atypical forms of atrioventricular nodal reentrant tachycardia]

The concept of functional dissociation of atrioventricular nodal conduction on an underlying structure with different nodal inputs is well established. In the common form of AVNRT, the circuit comprises the slow pathway for antegrade conduction and the fast pathway for retrograde conduction. However, the tachycardia circuit may be slightly or totally different as it is not based on discrete anatomical pathways but on functional pathways due to non-uniform anisotropy of the perinodal atrial tissue involved in the circuit. First, there are variations of the common form. The fast retrograde pathway may be posterior or left instead of being anteriorly-located. The so-called uncommon forms of AVNRT consist in slow-slow and fast-slow forms. The slow-slow form uses two different slow pathways as antegrade and retrograde limb of the circuit. These pathways may be posterior or left. The fast-slow form appears to be complex and heterogeneous. The retrograde slow pathway may be located posteriorly, anteriorly, in-between or sometimes left-sided. Whatever the circuit, targeting the antegrade or retrograde slow pathway remains the aim of ablation and the only therapeutic issue. However, a 1%-AV block rate has to be kept in mind.