Electrophysiological mechanisms of conversion of typical to atypical atrioventricular nodal reentrant tachycardia occurring after radiofrequency catheter ablation of the slow pathway

This report presents an adult patient with conversion of typical to atypica l atrioventricular nodal reentrant tachycardia (AVNRT) after slow pathway a blation. Application of radiofrequency energy (3 times) in the posterosepta l region changed the pattern of the atrioventricular (AV) node conduction c urve from discontinuous to continuous, but did not change the continuous re trograde conduction curve. After ablation of the slow pathway, atrial extra stimulation induced atypical AVNRT. During tachycardia, the earliest atrial activation site changed from the His bundle region to the coronary sinus o stium. One additional radiofrequency current applied 5 mm upward from the i nitial ablation site made atypical AVNRT noninducible. These findings sugge st that the mechanism of atypical AVNRT after slow pathway ablation is ante grade fast pathway conduction along with retrograde conduction through anot her slow pathway connected with the ablated antegrade slow pathway at a dis tal site. The loss of concealed conduction over the antegrade slow pathway may play an important role in the initiation of atypical AVNRT after slow p athway ablation.