A novel ECG marker for predicting left-bundle-branch area pacing success in left-bundle-branch block: Notch/slur-to-QRS-end duration

Background and Aims Left bundle branch area pacing (LBBAP) is a promising therapy for patients with left bundle branch block (LBBB), but intraoperative ECG markers to guide site selection are lacking. This study aimed to evaluate whether the notch/slur-to-QRS-end duration (notch/slur-QRSd) during right ventricular septal pacing (RVSP) can predict successful LBBAP. Methods Consecutive LBBB patients who underwent successful LBBAP were included. Clinical, echocardiographic, and ECG data from all attempted pacing sites were collected and analyzed. Results A total of 98 patients with 252 pacing sites (120 successful, 132 failed) were analyzed. Notch/slur-QRSd in leads V1, V5/V6, I/aVL was independently associated with successful LBBAP (all P < 0.001). Among 118 sites with a V1 "w" pattern, lead V1 notch/slur-QRSd had the highest predictive value (AUC=0.790; cut-off=95ms). In sites without a V1 "w" pattern (n=134), leads V5/V6 notch/slur-QRSd was most predictive (AUC=0.733; cut-off=94ms). Leads V5/V6 and I/aVL showed good agreement with V1 (intraclass correlation coefficient=0.84-0.86) and similar cut-offs (94–96ms). A sequential lead-based imputation approach (V1→V5/V6→I/aVL) using a 95 ms threshold achieved an overall AUC of 0.761 in the total cohort (n=252). Sites with notch/slur-QRSd ≤95ms had a 4.4-fold higher success rate than those >95ms (67.7% vs. 15.5%). Subgroup analyses showed consistent results across LVEDD, LVEF, LA diameter, and intrinsic QRSd. Conclusion Notch/slur-QRSd during RVSP is a simple and reliable ECG marker for predicting LBBAP success at the site level in patients with LBBB. A stepwise lead-based strategy (V1→V5/V6→I/aVL) using a notch/slur-QRSd cut-off of approximately 95ms may facilitate intraoperative site selection.