ANALYSIS OF JUNCTIONAL ECTOPY DURING RADIOFREQUENCY ABLATION OF THE SLOW PATHWAY IN PATIENTS WITH ATRIOVENTRICULAR NODAL REENTRANT TACHYCARDIA

Background Junctional ectopy may occur during radiofrequency (RF) cath eter ablation of the slow pathway in patients with atrioventricular no dal reentrant tachycardia (AVNRT). The purpose of the present study wa s to characterize this junctional ectopy quantitatively. Methods and R esults The subjects of this study were 52 consecutive patients with AV NRT who underwent slow pathway ablation and 5 additional patients incl uded retrospectively because they had developed high-degree atrioventr icular (AV) block during the procedure. A combined anatomic and electr ogram mapping approach was used for slow pathway ablation, and AVNRT w as successfully eliminated in all patients. In the group of 52 consecu tive patients, the incidence of junctional ectopy was significantly hi gher during 52 effective applications of RF energy than during 366 ine ffective applications (100% versus 65%, P<.001). Compared with ineffec tive RF energy applications, successful RF energy applications had a s ignificantly longer duration of individual bursts of junctional ectopy (7.1+/-7.1 versus 5.0+/-7.0 seconds [+/-SD], P<.05), a greater total number of junctional beats during the applications (24+/-16 versus 15/-8, P<.01), and a greater total span of time during which junctional ectopy occurred (19+/-15 versus 11+/-12 seconds, P<.01). Four of the 5 2 patients plus an additional 5 patients developed transient AV block lasting 34+/-37 seconds. In 1 of the 9 patients who had transient AV b lock, third-degree AV nodal block requiring a permanent pacemaker recu rred 2 weeks later. In each of the 9 patients who developed AV block, there was ventriculoatrial (VA) block in association with junctional e ctopy,during the RF energy application immediately preceding the AV bl ock. Among 48 patients who did not develop AV block, 17 patients had a t least one episode of VA block during junctional ectopy. The positive predictive value of VA block during junctional ectopy for the develop ment of AV block was 19% in the consecutive series of 52 patients. Amo ng 31 patients who always had 1:1 VA conduction in association with ju nctional ectopy, 12 had poor VA conduction in the baseline state, with a VA block cycle length of at least 500 milliseconds during ventricul ar pacing. Conclusions In patients with AVNRT undergoing slow pathway ablation, junctional ectopy during the application of RF energy is a s ensitive but nonspecific marker of successful ablation. The bursts of junctional ectopy are significantly longer at effective target sites t han at ineffective sites. VA conduction should be expected during the junctional ectopy that accompanies slow pathway ablation, even when th ere is poor VA conduction during baseline ventricular pacing. VA block during junctional ectopy is a harbinger of AV block in patients under going RF ablation of the slow pathway. If energy applications are disc ontinued as soon as VA block occurs, the risk of AV block may be marke dly reduced.