Background: Left bundle branch pacing (LBBP) is a physiological pacing that captures the main left bundle or its proximal branch. Electromechanical activation time (EMAT) is an acoustic cardiographic metric that provides a simple method for evaluating left ventricular (LV) synchrony. Prolonged EMAT reflects impaired LV electromechanical coupling.Objective: The purpose of this study was to explore whether EMAT can confirm that LBBP produces more satisfactory LV electromechanical synchronization than conventional right ventricular pacing modalities.Methods: Patients with standard pacing indications and narrow QRS duration were recruited for this study. Unipolar pacing under 3 different modalities-right ventricular apical pacing (RVAP), right ventricular high septal pacing (RVHSP), and LBBP-were successively performed in each patient. Pacing parameters, echocardiographic characteristics, and acoustic cardiographic parameters at different pacing modalities and during normal rhythm were collected.Results: A total of 55 patients were enrolled, and all had successful LBBP. Left ventricular activation time (LVAT) was significantly associated with EMAT, with LVAT vs EMAT correlation coefficient of 0.665 (P <.001). LVAT during LBBP was shorter than that during RVHSP (51.93 +/- 2.732 ms vs 85.59 +/- 2.240 ms; P <.001). EMAT of LBBP was significantly lower than either RVAP or RVHSP (95.44 +/- 1.794 ms vs 143.32 +/- 2.376 ms, and 132.22 +/- 1.872 ms; both P <.001) but was similar to that of intrinsic rhythm (95.37 +/- 2.271 ms; P = .862).Conclusion: We found EMAT significantly prolonged in RVHSP and RVAP but not in the LBBP mode. This finding indicates superior electromechanical synchronization in patients having LBBP. EMAT measurement could be an additional method for identifying the ideal pacing position.