Targeted posterior box isolation guided by functional and substrate mapping improves short-term arrhythmia outcomes

Background Durable posterior wall isolation (PWI) remains challenging in atrial fibrillation (AF) ablation despite its mechanistic rationale. Randomized trials have not shown incremental benefit when empirical posterior wall ablation is added to pulmonary vein isolation (PVI), suggesting that indiscriminate posterior wall homogenization may fail to eliminate critical residual conduction pathways. Purpose To evaluate the feasibility and clinical impact of a mechanistically guided posterior box isolation (POBI) strategy integrating functional lesion assessment and threshold-adjusted substrate mapping after PVI. Methods This single-center retrospective study included 55 consecutive patients undergoing AF ablation. After PVI, patients received either a hybrid pace-capture– and voltage-guided POBI strategy (hybrid group, n=31) or a conventional activation-guided approach (n=24). The hybrid strategy was introduced in October 2021 and applied consecutively thereafter. Roof and floor lines were created to encircle the posterior wall. Lesion integrity was assessed using high-output pacing (10 V/1 ms), and sites with persistent capture underwent targeted reinforcement. Posterior wall bipolar voltage mapping with dynamically adjusted thresholds identified high-voltage islands (≥0.5 mV), which were selectively ablated (Figure). POBI was confirmed by absence of capture during high-output pacing, bipolar voltage <0.1 mV within the box, and no early activation on activation mapping. Results Baseline characteristics were comparable. Complete POBI was achieved in all hybrid patients and 91.7% of conventional patients. In the hybrid group, 38.7% achieved isolation with roof and floor lines alone, whereas 61.3% required limited additional focal ablation (2.9±3.2 lesions). During a mean follow-up of 8.4 months, arrhythmia-free survival was higher in the hybrid group than in the conventional group (87.1% vs. 50.0%, log-rank p=0.022). Propensity score–adjusted and sensitivity analyses showed consistent directional associations. Conclusion A mechanistically guided POBI strategy integrating pace-capture testing and threshold-adjusted voltage mapping enabled targeted posterior wall modification with limited additional lesions and was associated with improved short-term arrhythmia outcomes compared with a conventional activation-guided approach. Prospective validation is warranted. Figure legends (A) Local activation time mapping during coronary sinus pacing demonstrates propagation across the roof line into the posterior wall despite apparently continuous linear lesions. (B) Conventional bipolar voltage mapping shows a broad preserved voltage area (≥0.5 mV) within the posterior box. (C) Threshold-adjusted bipolar voltage mapping reveals discrete high-voltage islands. (D) Targeted focal ablation at high-voltage islands completes POBI, confirmed by absence of local electrograms (<0.1 mV) and non-capture during high-output pacing (10 V/1 ms).