SAFETY OF SLOW PATHWAY ABLATION IN PATIENTS WITH ATRIOVENTRICULAR NODE REENTRANT TACHYCARDIA AND A LONG FAST PATHWAY EFFECTIVE REFRACTORY PERIOD

Radiofrequency catheter oblation is an accepted primary therapy for at rioventricular (AV) node reentrant tachycardia (AVNRT). There is conce rn that slow pathway ablation in patients with a long anterograde fast pathway effective refractory period (ERP) may potentially impair subs equent node conduction. Eighteen patients (14 women; age 53 +/- 20 yea rs) with symptomatic AVNRT, whose fast pathway ERP at baseline was gre ater than or equal to 500 ms, underwent slow pathway ablation. Their o utcome was compared with 24 consecutive control patients (17 women; ag e 42 +/- 17 years) who underwent ablation for AVNRT whose fast pathway ERP at baseline was <500 ms (controls). Slow pathway ablation was suc cessful in 16 patients (90%). One patient had inadvertent fast pathway ablation. In a second patient the slow pathway could not be ablated b ecause of recurrent transient AV block. Ablation was successful in all patients in the control group. Transient AV block related to current application occurred in 4 patients (22%) versus 1 control (4%) (p = 0. 07). After ablation, the AV node refractory period increased in patien ts (368 +/- 68 to 428 +/- 92 ms, p = 0.02) and in controls (282 +/- 35 to 336 +/- 55 ms, p <0.0001), but the fast pathway ERP shortened in b oth groups (patients: 558 +/- 63 to 428 +/- 92 ms, p = 0.083; controls : 356 +/- 53 to 336 +/- 55 ms, p = 0.05). Furthermore, the slope of th e regression line relating to shortening of the fast pathway ERP to th e baseline ERP was markedly steeper in patients compared with controls (1.9 vs 0.4, p <0.0001). The shortening of the fast pathway ERP was g reater in patients compared with controls (122 +/- 130 vs 21 +/- 50 ms , p = 0.001). During a mean follow-up of 18 +/- 11 months, 1 patient w ith severe coronary artery disease died suddenly 2 years after ablatio n. There was no recurrence of clinical tachycardia, and none of the pa tients developed,symptoms of bradycardia or required permanent pacing. Thus, slow pathway ablation in patients with AVNRT and a long fast pa thway ERP is safe and effective. (C) 1997 by Excerpta Medico Inc.