Intraprocedural predictors of successful ablation of slow pathway for atrioventricular nodal reentrant tachycardia.

Atrioventricular nodal reentrant tachycardia (AVNRT) is one of the most common causes of paroxysmal supraventricular tachycardia. For many years, the pharmacological approach was the only therapeutic modality available for managing this arrhythmia. More recently transcatheter radiofrequency (RF) ablation has become a safe and effective alternative to medical therapy. During the last 2 years, 20 patients with AVNRT were evaluated in our department. The diagnosis was made using the classical electrophysiological protocols with three multipolar catheters placed in AV node-His region, coronary sinus and a mapping/ablation catheter. In all cases, a discontinuous AV conduction curve during programmed atrial stimulation with progressively increasing prematurity was demonstrated associated with AV nodal echo beats and induction of the arrhythmia. Typical AVNRT was present in 19 patients. One patient with typical AVNRT also had inducible unusual (slow-slow) AVNRT. An additional patient had unusual slow-slow variant of AVNRT. The arrhythmia was treated in all cases by RFA of the slow AV node pathway, guided by anatomic and electrophysiologic criteria. RF ablation was successful in all patients. Two patients had clinical recurrence of arrhythmia; all have undergone successful reablation. No patient had significant complications of the procedure. As intraprocedural predictors for successful RF ablation were considered the slow pathway potentials with evidence of the junctional accelerated rhythm during RF current delivery and modification of AV node physiology with noninducibility of arrhythmia after RF ablation. The persistence of slow pathway with or without single AV node echo beat during a limited numbers of atrial extrastimuli was accepted as a successful procedure. In all cases, the AV node physiology was tested also after autonomic modulation of AV node. In both cases with clinical recurrence, the intraprocedural RF ablation results were misevaluated probably because of the autonomic modulation of fast pathway electrophysiology masking the persistence of slows pathway conduction. In conclusion invasive electrophysiological evaluation and RF ablation not only eliminate AVNRT, but also provide a unique opportunity to gain insights into the complexity of AV node physiology. This complexity makes more difficult the evaluation of the success of slow pathway ablation for AVNRT and a careful examination of multiple criteria is necessary for a good procedural result.