SITE OF ACCESSORY PATHWAY BLOCK AFTER RADIOFREQUENCY CATHETER ABLATION IN PATIENTS WITH THE WOLFF-PARKINSON-WHITE SYNDROME

Site of Accessory Pathway Block. Introduction: Recent studies have dem onstrated that the most common site of accessory pathway conduction bl ock following the introduction of a premature atrial stimulus during a trial pacing is between the accessory pathway potential and the ventri cular electrogram, consistent with block at the ventricular insertion of the accessory pathway. However, no prior study has evaluated the si te of conduction block during radiofrequency catheter ablation procedu res. Therefore, the objective of this study was to determine the site of conduction block after catheter ablation of accessory pathways by a nalyzing and comparing the local electrograms recorded before and afte r radiofrequency energy delivery at successful ablation sites. Methods and Results: The electrograms evaluated in this study mere obtained f rom 85 consecutive patients who underwent successful radiofrequency ca theter ablation of a manifest accessory pathway. The 50 left free-wall accessory pathways were ablated using a ventricular approach and the 35 right free-wail or posteroseptal accessory pathways were ablated us ing an atrial approach. The characteristics of local electrograms reco rded immediately before and immediately after successful ablation of t he accessory pathway were determined in each patient. The site of acce ssory pathway block was determined by comparing the amplitude, timing, and morphology of the local electrograms at successful sites of radio frequency catheter ablation before and after delivery of radiofrequenc y energy. A putative accessory pathway potential was present at the su ccessful target site in 74 of the 85 patients (87%). Conduction block occurred between the atrial electrogram and the accessory pathway pote ntial in 66 patients (78%) and between the accessory pathway potential and the ventricular electrogram in eight patients (9%). The site of b lock could not be determined in 11 patients (13%) in whom an accessory pathway potential was absent. Conduction block occurred most frequent ly 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 conduct ion block. Conclusion: The results of this study demonstrate that cond uction block occurs most frequently between the local atrial electrogr am 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.