Ablating Right-Sided Accessory Pathways With Atrial Insertions Far From Tricuspid Annulus. Background: It is difficult to ablate a right-sided accessory pathway (AP) with atrial insertion far from the tricuspid annulus ( TA). We report our initial experience of ablating this rare AP by a 3-dimensional electroanatomical mapping system (CARTO). Methods: From January of 2006 to April of 2008, 18 patients with right-sided APs who failed previous outside ablations were enrolled in this study. Retrograde AP conduction was mapped during pacing at the right ventricular apex by activation-mapping the right atrium (RA) using a 3-dimensional electroanatomical mapping system. AP atrial insertion was defined as the earliest retrograde atrial activations and successful ablation of the APs at this site. Results: Among the 18 patients who had failed previous ablation, 10 patients (7 patients with right manifest APs and 3 patients with right conceal APs) had atrial insertions far from the TA. Of the 10 patients, the atrial insertions were found at the base of the RA appendage in 3 patients, at the high lateral RA in 5 patients, at the low lateral RA in other 2 patients. Ablation at the atrial insertions successfully abolished the AP conduction. The mean distance between the atrial insertion sites and the TA was 20.2 +/- 2.7 mm. No patients reported recovered AP conduction or recurrent tachycardias after 6-month follow-up. Conclusions: The right-sided APs may have atrial insertion far from the TA. These uncommon variation of APs can be reliably identified and ablated using CARTO system. (J Cardiovasc Electrophysiol, Vol. 22, pp. 499-505 May 2011).