Anterograde Slow Pathway Is Not the Same as Retrograde Slow Pathway Conducted in the Reverse Direction in Patients with Uncommon Atrioventricular Nodal Reentrant Tachycardia

Introduction: The aim of this study was to examine the location of anterograde and retrograde slow pathways in 16 patients with uncommon atrioventricular nodal reentrant tachycardia (AVNRT), including the fast-slow form in 10, slow-slow form in 5, and both fast-slow and slow-slow forms in 1. Methods and Results: Patients were divided into two groups according to the approach used for slow pathway ablation in the initial radiofrequency catheter ablation (RFCA): one approach used earliest atrial activation during tachycardia (ES group, n = 9), and the other used a slow potential during sinus rhythm (SP group, n = 7). When the initial RFCA failed to eliminate slow pathway conduction in the ES group, an additional RFCA guided by a slow potential was performed. The ratio of lengths from the His-bundle region to the RFCA site and coronary sinus ostium (Abl/His-CS ratio) and the ratio of amplitudes of atrial and ventricular potentials at the RFCA site (A/V ratio) were compared between the two groups. In the initial RFCA, retrograde slow pathway conduction was eliminated without impairment of anterograde slow pathway conduction in 8 (89%) patients from the ES group, and bidirectional slow pathway conduction was eliminated in 6 (86%) patients from the SP group. Residual anterograde slow pathway conduction that was preserved after the initial RFCA in 8 of 9 patients was eliminated by an additional slow potential-guided RFCA. Both the Abl/His-CS ratio (0.86 ± 0.07 vs 0.73 ± 0.11, P = 0.01) and A/V ratio (0.80 ± 0.31 vs. 0.14 ± 0.01, P < 0.001) were higher in the ES group than the SP group. The ratios for the residual anterograde slow pathway ablation in the ES group were similar to those in the SP group. Conclusion: The results of this study suggest that the retrograde slow pathway runs more on the atrial side of the tricuspid valve annulus at the level of the coronary sinus ostium compared with the anterograde slow pathway, although both pathways run parallel or are fused in portions more proximal to the His bundle. (J Cardiovasc Electrophysiol, Vol. 14, pp. 722-727, July 2003)