Spatial Clustering and High-Frequency Characteristics of Residual Conduction in the Left Atrial Posterior Wall.

INTRODUCTION: Left atrial posterior wall (LAPW) isolation is frequently limited by residual conduction (RC) despite apparently complete endocardial linear lesions. Such conduction may involve interbundle connections between the septo-atrial and septo-pulmonary bundles or deeper conduction pathways. However, the spatial distribution and electrophysiological characteristics of these functionally defined RCs remain incompletely understood in clinical settings. METHODS: Twenty-two patients undergoing LAPW isolation were prospectively studied. Among 22 patients, 11 required additional ablation after a confirmed roof and bottom line block, in whom residual electrograms were mapped using peak frequency (PF) analysis with the EnSite system. The LAPW was divided into nine predefined anatomical segments, and segments requiring ablation to achieve complete isolation were defined as RC-positive. RESULTS: RC-positive segments predominantly clustered in the mid-central region (82%), whereas other regions were less frequently involved. PF was significantly higher in RC-positive than in RC-negative segments (460 [380-520] vs. 300 [250-400] Hz; p < 0.001), and a PF cutoff of 365 Hz demonstrated moderate discriminatory performance (area under the curve, 0.796). RC-positive segments exhibited greater electrogram fractionation during both atrial fibrillation and atrial pacing, consistent with increased local conduction complexity. Targeted ablation at these sites resulted in complete LAPW isolation in all cases without complications. CONCLUSION: Functionally defined RC within the LAPW exhibits a nonuniform spatial distribution with mid-central clustering and distinct electrophysiological characteristics. PF-based mapping may facilitate targeted identification of these regions and provide functional insights into potential non-endocardial conduction pathways in incomplete LAPW isolation.