RESUMO
BACKGROUND: Ablation of slow-fast atrioventricular nodal reentrant tachycardia (S/F-AVNRT) is occasionally refractory. We hypothesized that the site of ablation for curing S/F-AVNRT can be screened by simple differential atrial entrainment pacing (EP) from the high right atrium (HRA) and proximal coronary sinus (prox-CS). METHODS: We enrolled 43 patients with S/F-AVNRT who underwent successful differential atrial EP followed by successful ablation of slow pathway (SP) using step-wise approach, and compared the atrio-His (A-H) interval at the recording of His bundle immediately after EP from the HRA [A-H(HRA)], with the interval between atrial deflection at the prox-CS and His bundle electrogram after EP at an identical cycle length from the prox-CS [A-H (prox-CS)]. RESULTS: A typical A-H(CS) shorter than A-H(HRA), consistent with typical SP conduction, was observed in 39 patients (91%), and an atypical A-H(HRA) shorter than A-H(CS) was observed in 4 patients (9%). Successful ablation was obtained at the posteroseptum/midseptum in 32/7 patients with typical responses but only at the midseptum in all 4 patients with atypical responses (P = .0027). The atypical responses predicted a necessity for ablation at the midseptum, with positive and negative predictive values of 100% and 82%, respectively. The mechanism of an atypical response remains unclear but may involve an anatomical variation of Koch's triangle and/or the participation of a variant of the SP, including the superior SP, over which retrograde conduction was observed more frequently in patients with atypical responses (P = .0013). CONCLUSIONS: Differential atrial EP predicts the ablation site for successfully curing S/F-AVNRT.