The Resynchronization Effect in Left Bundle Branch Pacing Can be Evaluated Non‐Invasively With the Implementation of Lead V8

BACKGROUND: Left bundle branch area pacing (LBBAP) is increasingly being used for cardiac resynchronization therapy (CRT); however an additional left ventricular (LV) lead is required when resynchronization remains incomplete. This study evaluates whether lead V8 can provide a simple, non-invasive marker of persistent posterolateral LV delay during LBBAP. METHODS: Consecutive patients undergoing LOT-CRT implantation were included. Standard 12-lead ECGs were obtained with the V5 electrode repositioned to the V8 location. Local activation time was measured as the steepest negative downslope of the QRS (negative derivative activation time, NDAT) and compared with the LV electrical delay (LVED) determined from the LV lead during LBBAP. RESULTS: Thirty consecutive patients undergoing LOT-CRT implantation were included with a total of 106 ECG recordings with corresponding LVED measurements. The NDAT-V8 demonstrated a strong correlation with the LVED during intrinsic conduction (r = 0.95) and during all LBB pacing subtypes: combined r = 0.922; mean difference 2.5 ± 8 ms; RV septal pacing, r = 0.89; LV septal pacing, r = 0.92; non-selective LBBP, r = 0.91; and selective LBBP, r = 0.81. The correlation of LVED during intrinsic conduction and all LBBAP pacing subtypes was significantly weaker for NDAT-V6 and the RWPT in V6 and V8 (r = 0.681, 0.626, and 0.726, respectively). CONCLUSION: The NDAT-V8 provides a reliable non-invasive surrogate for the LV posterolateral wall delay during LBBAP, outperforming NDAT-V6 and the RWPT in V6 and V8 and establishes the groundwork for future studies evaluating NDAT-V8 as a tool to guide adequate resynchronization during LBBAP.