CATHETER-INDUCED ATRIOVENTRICULAR NODAL BLOCK DURING RADIOFREQUENCY ABLATION

This study examined the incidence and significance of catheter-induced atrioventricular nodal block (AVNB) during a radiofrequency ablation procedure that uses stiff large-tip steerable ablation catheters. AVNB was noted in 10 (1.6%) of 613 consecutive patients undergoing radiofr equency ablation therapy for atrioventricular nodal (AVN) reentrant ta chycardia (592 patients) or atrioventricular reentry tachycardia incor porating a midseptal accessory pathway (21 patients). Of these 10 pati ents, 9 underwent AVN modification for AVM reentrant tachycardia and 1 for ablation of a midseptal accessory pathway. One patient had two ep isodes of AVNB during two sessions undertaken because of recurrence of tachycardia. No patient had a preexisting conduction defect before th e study. In all 10 patients, AVNB was transient, and it lasted for a m ean of 9.1 +/- 19 minutes. It occurred during positioning of the ablat ion catheter in the junctional area before (8 patients) or after (2 pa tients) the start of radiofrequency current applications. Complete AVN B was noted on six occasions, second-degree AVNB on four occasions, an d first-degree AVNB on one occasion. All blocks were associated with n arrow QRS ventricular beats and with a site of block proximal to the H is bundle. The mean ventricular heart rate during AVNB was 60 +/- 23 b eats/min. Two patients had transient asystole, with one having loss of consciousness. No patient required special treatment for heart block. One-to-one conduction resumed after repositioning of the catheters, a nd the subsequent ablation procedure was successfully completed in 8 o f the 10 patients. During a follow-up of 20 +/- 12 months, none of the patients had severe dizziness or syncope, and none required implantat ion of a permanent pacemaker. In conclusion, transient AVNB due to mec hanical injury occurs during positioning of a stiff large-tip steerabl e ablation catheter in the junctional area. Delivery of radiofrequency current to the site that provokes catheter-induced AVNB should be avo ided.