CHARACTERIZATION OF JUNCTIONAL RHYTHM AFTER ATRIOVENTRICULAR NODE ABLATION

Background Catheter ablation of the atrioventricular (AV) node with ra diofrequency current (RFC) is associated with the short-term onset of a junctional escape rhythm (JER) in nearly all patients. However, the origin of the JER and short-term thermal effects of RFC on this juncti onal pacemaker activity are ill defined. Methods and Results Short-ter m and noninvasive long-term follow-up studies were performed to examin e the electrophysiological characteristics of the underlying JER in 45 patients who had undergone AV nodal ablation with RFC. Baseline chara cteristics and responses to overdrive ventricular pacing and intraveno us atropine followed by an incremental isoproterenol infusion were det ermined. Short- and long-term responses were compared. HV intervals be fore and after ablation were 49+/-9 and 48+/-9 milliseconds, respectiv ely (P=NS). Follow-up was 11+/-8.3 months. JER cycle length was 1526+/ -298 milliseconds in the short-term setting and was present in 44 pati ents (98%) in the long-term setting, measuring 1426+/-223 milliseconds (P<.005). Junctional recovery times increased exponentially as overdr ive pacing rates increased-there was no difference between short-term and long-term responses. Drug responses within each study were all sig nificant when compared with baseline. However, there was no significan t difference between short- and long-term responses, except at the hig hest dose of isoproterenol. Intravenous atropine (1 mg) caused an 8.6/-9.3% decrease in JER cycle length in the short-term setting compared with a 7.6+/-7.3% decrease in the long-term setting. The decreases in JER cycle length with isoproterenol infusion (short-term versus long- term) were 10.1+/-9.6% versus 9.6+/-7.4% with 1 mu g/min, 15.8+/-11.7% versus 17.4+/-8.5% with 2 mu g/min, 17.9+/-11.2% versus 21.4+/-9.1% w ith 3 mu g/min (all P=NS), and 20.6+/-12.1% versus 24.8+/-9.1% with 4 mu g/min (P<.01). Conclusions Radiofrequency ablation of the AV node i s associated with development of a JER that is stable in the long-term setting. The lack of change in HV interval after ablation locates the junctional pacemaker proximal to the central fibrous body. The patter n of drug responses suggests an origin within the proximal His bundle at its junction with the AV node rather than the AV node itself. The o verall similarity between short- and long-term characteristics of junc tional pacemaker activity mitigates against any reversible thermal eff ects of RFC on this pacemaker focus.