Site of accessory pathway block after radiofrequency catheter ablation in patients with the Wolff-Parkinson-White syndrome.

INTRODUCTION Recent studies have demonstrated that the most common site of accessory pathway conduction block following the introduction of a premature atrial stimulus during atrial pacing is between the accessory pathway potential and the ventricular electrogram, consistent with block at the ventricular insertion of the accessory pathway. However, no prior study has evaluated the site of conduction block during radiofrequency catheter ablation procedures. Therefore, the objective of this study was to determine the site of conduction block after catheter ablation of accessory pathways by analyzing and comparing the local electrograms recorded before and after radiofrequency energy delivery at successful ablation sites. METHODS AND RESULTS The electrograms evaluated in this study were obtained from 85 consecutive patients who underwent successful radiofrequency catheter ablation of a manifest accessory pathway. The 50 left free-wall accessory pathways were ablated using a ventricular approach and the 35 right free-wall or posteroseptal accessory pathways were ablated using an atrial approach. The characteristics of local electrograms recorded immediately before and immediately after successful ablation of the accessory pathway were determined in each patient. The site of accessory pathway block was determined by comparing the amplitude, timing, and morphology of the local electrograms at successful sites of radiofrequency catheter ablation before and after delivery of radiofrequency energy. A putative accessory pathway potential was present at the successful target site in 74 of the 85 patients (87%). Conduction block occurred between the atrial electrogram and the accessory pathway potential in 66 patients (78%) and between the accessory pathway potential and the ventricular electrogram in eight patients (9%). The site of block could not be determined in 11 patients (13%) in whom an accessory pathway potential was absent. Conduction block occurred most frequently between the atrial electrogram and the accessory pathway potential regardless of accessory pathway location. No electrogram parameter or accessory pathway characteristic was predictive of the site of conduction block. CONCLUSION The results of this study demonstrate that conduction block occurs most frequently between the local atrial electrogram and the accessory pathway potential during radiofrequency catheter ablation of accessory pathways. This is true regardless of whether the accessory pathway is ablated from the atrial or ventricular aspect of the mitral or tricuspid annulus.