ECG-based evaluation of ventricular synchrony in left bundle branch area pacing through characterization of the activation sequence.

Left bundle branch area pacing (LBBAP) overcomes ventricular dyssynchrony induced by conventional right ventricular pacing (RVP). Despite QRS duration (QRSd) being the standard ECG marker for biventricular synchrony, it lacks insights into the ventricular activation sequence. Our aim is to assess biventricular synchrony by characterizing the ventricular activation sequence and introducing robust markers using the 12-lead ECG. A prospective single-center study was conducted, involving patients with pacemaker indication due to bradycardia. Patients were divided into LBBAP and RVP, and classified by baseline-QRS morphology. To assess biventricular synchrony, low frequency-based QRS analysis was performed to compute the ventricular activation sequence and precordial activation delay (pAD). Additional QRS markers including QRSd, QRS60, and QRS area (QRSa) were calculated. A total of 176 patients (107 LBBAP, 69 RVP) were included. The paced ventricular activation sequence indicated a more physiological pattern after LBBAP than RVP, with lower pAD values in narrow QRS, RBBB, and LBBB subgroups [ - 10( - 20,14) vs. 26(5, 39) ms;  - 18( - 30,  - 8) vs. 34(26, 55) ms; 10( - 14, 25) vs. 32(12, 48) ms] (p < 0.01). In all subgroups, QRS60 showed lower values after LBBAP than RVP [52(41, 62) vs.73(65, 80) ms; 60(55, 66) vs. 77(67, 83) ms; 59(53, 64) vs. 77(74, 82) ms] (p < 0.01) and QRSa were also lower [53(38, 66) vs. 121(92, 143) μVs; 60(50, 89) vs. 124(97, 159) μVs; 62(52, 80) vs. 133(99, 148) μVs] (p < 0.01). pAD provides valuable insights into ventricular activation beyond paced-QRSd. Together with QRS60 and QRSa, pAD could be a promising tool to assess biventricular synchrony.