Characteristics of local electrogram predicting successful transcatheter radiofrequency ablation of left-sided accessory pathways

Objectives. The purpose of this study was to analyze and compare the local electrograms recorded at successful and unsuccessful sites of ablation to identify the criteria that may predict successful sites and minimize unnecessary radiofrequency delivery.Background. Transcatheter ablation of accessory pathways using radiofrequency energy requires extremely precise localization of an accessory pathway.Methods. Local electrograms from 50 consecutive patients with left-sided accessory pathways who underwent transcatheter radiofrequency ablation were analyzed. During catheter ablation, localization of accessory pathways was performed in 39 pathways during pre-excited sinus rhythm and in 14 pathways during orthodromic tachycardia. A total of 429 local electrograms at target sites obtained before delivery of radiofrequency current was analyzed. A prospective study was performed in another 20 patients using the criteria derived from the retrospective study.Results. Accessory pathway conduction block was achieved in 36 (92%) of 39 pathways in which mapping was performed during pre-excited sinus rhythm and in 9 (64%) of 14 pathways in which mapping was performed during orthodromic tachycardia (p < 0.05). When mapping was performed during pre-excited sinus rhythm, a combination of four variables (that is, an accessory pathway potential, stability of local electrograms, atrial activation > 1 mV and ventricular activation preceding the onset of the delta wave) showed a 62% probability of success. In contrast, excluding these variables resulted in a 95% probability of failure (noneffective or transiently effective). The prospective study shows that the use of these criteria can significantly reduce the number of current applications. When mapping was performed during orthodromic tachycardia, recording the earliest atrial activation was the most powerful predictor of success. A stable local electrogram with a small notch on the ventricular potential, presumed to be an accessory pathway potential, may add predictive value.Conclusions. Transcatheter radiofrequency ablation is highly effective in the treatment of patients with left-sided accessory pathways. Specific characteristics of local electrograms can be important predictors of success or failure. Mapping during preexcited rhythm renders ablation more effective than does mapping during orthodromic tachycardia.