Reasons for prolonged or failed attempts at radiofrequency catheter ablation of accessory pathways

Objectives. The purpose of this study was to categorize the reasons for prolonged or failed procedure in series of patients undergoing catheter ablation of an accessory pathway. Background. Radiofrequency ablation of accessory pathways at times requires lengthy procedure or second ablation session, or both, and no prior studies have systematically investigated the reasons for this. Methods. In consecutive series of 619 patients undergoing catheter ablation of an accessory pathway, the mean ablation time ±SD was 68 ± 64 min. The subjects of this study were 14 patients who had an ablation time >2 SD greater than the mean (>196 min) and 51 patients who required second ablation session for successful outcome. The accessory pathway in the 65 patients in this study was located in the right free wall in 19 patients (29%), septum in 14 (22%) and left free wall in 32 (49%). Results. The primary reasons for lenghty or failed ablation attempt were 1) inability to position the ablation catheter at the effective target site (16 patients, 25%); 2) instability of the ablation catheter or inadequate tissue contact at the target site, or both (15 patients, 23%); 3) mapping error due to an oblique course of the accessory pathway (7 patients, 11%); 4) failure to recognize posteroseptal accessory pathway as being left-sided instead of right-sided (4 patients, 6%); 5) other errors in accessory pathway localization (6 patients, 9%); 6) epicardial location of the accessory pathway (5 patients, 8%); 7) recurrent atrial fibrillation (2 patients, 3%); 8) occurrence of complication (2 patients, 3%); 9) unusual right-sided accessory pathway that inserted in the anterior right ventricle, 2 cm away from the lateral tricaspid annulus (1 patient, 1.5%); and 10) unexplained factors (7 patients, 11%). The most common effective strategies employed to achieve successful outcome in these patients were 1) substitution of more experienced operator; 2) use of ablation catheters of varying configurations; 3) switching from retrograde aortic to transseptal approach; 4) switching from an inferior to superior ven caval approach; 5) use of 60-cm guiding sheath; 6) detailed mapping of the atrial or ventricular insertion of the accessory pathway; and 7) searching within the coronary sinus for presumed accessory pathway potential. Conclusions. lengthy or failed attempt at catheter ablation of an accessory pathway may be due to variety of reasons, the most common of which are problems related to some aspect of catheter manipulation and errors in accessory pathway localization. Knowledge of the most common reasons for lengthy or ineffective procedure may facilitate successful outcome of accessory pathway ablation.