Predictors of successful radiofrequency ablation of extranodal slow pathways

Catheter positioning for radiofrequency ablation of extranodal slow pathways is often guided by local electrogram recordings. To determine the predictors of successful ablation sites, we reviewed data from 32 successful and 104 unsuccessful sites. Univariate predictors of a successful site included the occurrence of junctional rhythm during ablation (P < 0.001), shorter time to onset of junctional rhythm (P = 0.05), the presence of a discrete slow pathway potential (P < 0.001), a smaller ratio of the amplitude of the atrial:ventricular electrogram (P = 0.04), later timing (P = 0.001) and longer duration (P < 0.001) of the atrial slow pathway electrogram, and the duration of (P < 0.001), and maximal voltage used during ablation (P < 0.001). By multivariate analysis junctional rhythm (P < 0.001), a discrete slow pathway potential (P = 0.003), a longer duration of the atrial slow pathway electrogram (P = 0.01) and the duration of ablation (P = 0.02) were predictors of success. Because ablations at unsuccessful sites were often aborted at 10-30 seconds, a separate analysis was performed using only the 41 unsuccessful sites where the duration of ablation was > or = 30 seconds. The results were nearly identical. Thus, the occurrence of junctional rhythm during ablation and the morphology and duration of the atrial slow pathway electrogram may serve as guides for slow pathway ablation site selection.