LOCALIZATION OF THE ORIGIN OF THE ATRIOVENTRICULAR JUNCTIONAL RHYTHM INDUCED DURING SELECTIVE ABLATION OF SLOW-PATHWAY CONDUCTION IN PATIENTS WITH ATRIOVENTRICULAR NODE REENTRANT TACHYCARDIA

During radiofrequency catheter ablation of slow atrioventricular node pathway conduction in patients with atrioventricular node reentrant ta chycardia, an atrioventricular junctional rhythm is frequently observe d. The origin and relation to ablation success of this junctional rhyt hm was examined in this study. By using standard intracardiac electrop hysiology techniques, we studied the radiofrequency energy-induced atr ioventricular junctional rhythm in 43 consecutive patients with atriov entricular node reentrant tachycardia undergoing selective ablation of slow-pathway conduction. The frequency of atrioventricular junctional activity was correlated with successful and unsuccessful attempts at ablation of slow-pathway conduction. Also, we compared the sequence of retrograde atrial activation of radiofrequency energy-induced atriove ntricular junctional beats in a subgroup of 22 patients with the retro grade activation sequence observed during pacing from the right ventri cular apex and the site of successful ablation of slow-pathway conduct ion. A total of 201 radiofrequency-energy applications was delivered i n 43 patients with greater than or equal to 5 atrioventricular junctio nal beat(s) induced during 110 (55%) of 201 ablation attempts. Atriove ntricular junctional activity was noted during 98% of successful ablat ions but only 43% of the unsuccessful attempts (sensitivity, 98%; spec ificity, 57%; negative predictive value, 99%). The mean time to appear ance of atrioventricular junctional beats was 8.8 +/- 4.1 sec (mean +/ - SD) after the onset of radiofrequency-energy application. In 22 (100 %) of 22 patients in whom detailed atrial mapping was performed, the r etrograde atrial activation sequence of the radiofrequency-induced atr ioventricular junctional beats was earliest in the anterior atrial sep tum, identical to that seen during pacing from the right ventricular a pex. Earliest retrograde atrial activation was at the posterior septum in all patients during pacing from the successful ablation site, a ma rkedly different activation pattern compared with that seen during eit her radiofrequency ablation or ventricular pacing. Whereas the occurre nce of atrioventricular junctional activity during radiofrequency abla tion does not necessarily herald a successful ablation of slow atriove ntricular node pathway conduction, its absence strongly suggests that the energy is being applied in an unsuccessful fashion. Furthermore, i t appears that radiofrequency energy-induced atrioventricular junction al beats originate not from the endocardium in contact with the ablati ng catheter tip but instead appear to exit remotely from the anterior atrial septal region. This finding supports the existence of specializ ed tissues in the atrioventricular junction that preferentially transm it the effects of radiofrequency energy to an anterior exit site, poss ibly identical to the atrial exit site of the retrograde fast atrioven tricular node conduction pathway.