IS VAGAL INNERVATION TO THE ATRIOVENTRICULAR NODE IMPAIRED AFTER RADIOFREQUENCY ABLATION OF THE SLOW ATRIOVENTRICULAR NODAL PATHWAY

To assess the potentially adverse effects of RF catheter ablation (RFC A) of the slow AV nodal pathway on the parasympathetic innervation to the AV node in patients with AV nodal reentrant tachycardia (AVNRT), A V nodal conduction was evaluated following vagal stimulation by means of a phenylephrine bolus injection (200 mu g) before and after RFCA in ten patients (mean age, 37 +/- 14 years). Nine patients with AV reent rant tachycardia (AVRT) due to a left free wall accessory pathway serv ed as a control group (mean age of 37 +/- 12 years). Whereas no prolon gation of the AH interval was observed in the AVNRT group following th e phenylephrine bolus during sinus rhythm, despite a significant slowi ng in sinus rate, phenylephrine administration in AVRT patients was as sociated with both slowing of the sinus rate and prolongation of the A H interval. Following successful RFCA, the same responses were observe d. To delineate the indirect effect of heart rate on AV conduction in response to the phenylephrine bolus, the AH interval was also measured during fixed atrial pacing. A marked prolongation of the AH interval occurred in both groups following phenylephrine administration. This p rolongation was biphasic in 50% of AVNRT patients before ablation, sug gesting a predominant effect of vagal stimulation on the fast AV nodal pathway. RFCA was associated with disappearance of discontinuous AV c onduction in all but one patient with AVNRT. Vagal stimulation caused the same amount of AH interval prolongation as before RFCA in both stu dy groups. In conclusion, patients with AVNRT have a preserved modulat ion of AV nodal conduction in response to vagal stimulation during sin us rhythm. In addition, vagal stimulation seems to exert a predominant effect on the fast AV nodal pathway. RFCA of the slow AV nodal path w ay in patients with AVNRT does not ca use detectable damage to the vag al innervation to the AV node.