Precise Activation Within the Triangle of Koch: Insights from Ultra‐High‐Resolution Mapping and Cryoablation Terminating AVNRT

Background Although slow pathway (SP) ablation is highly effective for atrioventricular nodal reentrant tachycardia (AVNRT), the detailed activation sequence and the functional significance of electrogram components within the triangle of Koch (ToK) remain unclear. Objective To define the activation pattern within the ToK and clarify the mechanistic significance of sharp and dull potentials using ultra‐high‐resolution mapping and fractionated potential‐guided cryoablation. Methods Thirty‐five patients with slow–fast AVNRT underwent ultra‐high‐resolution mapping during sinus rhythm (SR) and/or AVNRT using the RHYTHMIA‐system with LUMIPOINT tools. Propagation of sharp and dull potentials was analyzed by sliding the local activation window in 5‐ms increments. Cryoablation targeted fractionated potential sites where AVNRT terminated during cryomapping. Results Two distinct electrogram components—sharp and dull potentials—were consistently identified in the mid‐to‐superior ToK. During SR, sharp potentials descended within the ToK, followed by dull potentials ascending toward and merging with His potentials. During AVNRT, ascending dull potentials preceded descending sharp potentials. Dull potentials were visualized with confidence levels ≥ 24% and consistently overlapped with sites causing transient atrioventricular block. Successful ablation sites were located immediately inferior to the dull‐potential region and corresponded to the fractionated potential area during AVNRT. AVNRT terminated during cryomapping in 25 of 30 patients (mean 13 ± 4 s). No recurrences were observed during follow‐up. Conclusion Sharp and dull potentials represent distinct components of atrial activation and nodal–His transitional conduction. Fractionated potential‐guided cryoablation targeting early AVNRT termination enables safe and efficient ablation while avoiding injury to the nodal–His axis.