Noninvasive electrocardiographic imaging assessment of conduction system pacing: A novel algorithm to assess intraventricular synchrony

Background: Left bundle branch area pacing (LBBAP) has become the procedure of choice for various indications including atrioventricular block and considered to be physiologic modality of pacing compared with right ventricular apex pacing. Objective: The purpose of this study was to assess ventricular activation and synchrony in patients with an LBBAP device using electrocardiographic imaging (ECGI). Methods: A total of 25 consecutive patients underwent an LBBAP device implantation were included in the study. Electrocardiography (ECG) and ECGI analyses have been performed the day after implantation. Native and paced QRS, left ventricular activation time, right ventricular activation time, and V1-V6 activation delay were calculated using ECG. Total ventricular activation time, left ventricular activation time, intrinsic left ventricular activation time, right ventricular activation time, intrinsic right ventricular activation time, and intraventricular dyssynchrony were calculated based on ECGI. All patients have been followed up to 12 months. Results: All patients were divided in 2 groups (wide and narrow QRS) based on intrinsic ECG and then based on paced ECG parameters. The study showed that for initially narrow QRS group activation time and synchrony during pacing was comparable to native. In wide QRS group these parameters were significantly improved. For paced rhythm analysis classic ECG LBBAP parameters (paced QRS and left ventricular activation time) were not sufficient to properly evaluate the ventricular activation for paced rhythm. Discordance between classic ECG parameters and ECGI analysis was identified. Two additional 12-lead ECG parameters predicting the ECGI measurements were found. Follow-up did not show any worsening of ejection fraction, paced QRS, or pacing parameters. Conclusion: ECG imaging can bring a significant value into assessing the efficacy of new pacing modalities and provide much more data for precise determination of implantation outcome including detailed activation assessment and comparison with intrinsic conduction. Key ECGI values confirming proper ventricular activation have been defined, and corresponding 12-lead parameters were also identified, which allows to predict ventricular activation by using 12-lead ECG only.