Atrioventricular Nodal Reentrant Tachycardia Ablation With irrigATEd catheteR And Three-dimensional elecTroAnatomiC Mapping (WATER ATTAC)

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common supraventricular tachycardia in clinical practice, more common in women than in men. It can occur at all ages, but it is more likely to begin in young adults, with average age of onset around 32 years. Due to its sudden onset and cessation it is classified in the group of paroxysmal supraventricular tachycardias (PSVT), accounting for almost two thirds of the total.

AVNRT is a regular supraventricular tachycardia resulting from formation of reentry circuit confined to atrioventricular node and perinodal atrial tissue. About 80-90% of patients with AVNRT have the common form of arrhythmia, also called "typical" or "slow-fast" type.

Slow-fast AVNRT usually begins when premature atrial complex (PAC) arrives at AV node when fast pathway is in its refractory period. Therefore, antegrade conduction along fast pathway is blocked. If premature beat arrives in specific time window, slow pathway, with shorter refractory period, is available for conduction to ventricle. Premature beat leads through slow way, and, through final common way, to His bundle. As a result, PR interval of premature beat will be longer than normal beats conducted through fast track. If fast pathway has recovered its excitability by the time impulse of the slow pathway reaches distal junction of the two paths, impulse can lead retrograde through fast pathway. Circuit can then become repetitive with antegrade conduction along slow pathway and retrograde conduction along fast pathway with consequent triggering of sustained tachycardia. This proposed mechanism explains series of clinical observations of AVNRTs: single PAC can initiate arrhythmia and in the same way penetration in reentry circuit by PAC can abruptly interrupt arrhythmia.

Up to 20% of patients with AVNRT have uncommon forms of arrhythmia, referred to as "atypical" AVNRT. There are cases in which antegrade conduction can occur along fast pathway with retrograde conduction along slow pathway (fast-slow type).

Some patients, on the other hand, have more slow pathways, in which both antegrade and retrograde pathways of circuit use slow AV nodal pathways (slow-slow type).