Influence of isoproterenol on the accelerated junctional rhythm observed during radiofrequency catheter ablation of atrioventricular nodal slow pathway conduction

Background Accelerated junctional rhythm (AJR) has been considered as a sen sitive but rather nonspecific marker of successful radiofrequency (RF) abla tion of slow pathway in patients with atrioventricular nodal reentrant tach ycardia (AVNRT). However, AJR also occurs commonly during isoproterenol inf usion. We therefore investigated the effect of isoproterenol on the signifi cance of AJR while attempting slow pathway ablation. Methods Forty patients with AVNRT underwent slow pathway ablation. Sixty-ni ne RF applications accompanied by AJR were observed and were separated into 2 groups: applications performed without (group I, n = 26) and with (group II, n = 43) isoproterenol infusion. The specificity of AJR for successful ablation for each group was calculated. Results The specificity of AJR in groups I and II was 73% (19/26) and 49% ( 21/43), respectively (P < .05). There was no significant difference between the groups in the atrial electrogram width, atrial/ventricular electrogram amplitude ratio, the time from application onset to AJR emergence, or AJR cycle length. The catheter-tip temperature of AJR emergence was significant ly lower (47 degreesC +/- 3 degreesC vs 520 degreesC +/- 30 degreesC, P < . 001) and the ratio of junctional beats to total heart beats during RF appli cation was significantly greater (46% +/- 24% vs 33% +/- 18%, P < .05) in g roup II compared with group I. Conclusions Isoproterenol lowers the threshold of AJR emergence during RF a pplication and thereby lowers the specificity of AJR for successful ablatio n. Complete washout of isoproterenol may therefore improve the specificity of AJR during RF ablation in patients with AVNRT.