Electrocardiographic Imaging: A New Tool to Ensure Cardiac Resynchronization During Left Bundle Branch Pacing Implant

Left bundle branch pacing (LBBP) has emerged as an alternative to biventricular pacing for cardiac resynchronization therapy (CRT). The objective is to pursue and ensure resynchronization. However, LBBP capture could fail to achieve adequate resynchronization [1] in some patients, in whom biventricular pacing should be attempted. Electrocardiographic imaging (ECGI) [2]—a new noninvasive technique—may be of help in assessing electrical resynchronization during LBBP implant. ECGI may provide beat-to-beat live mapping of the heart with the electrical and location data from a vest or a belt and the cardiac anatomy obtained from an imaging technique or an artificial intelligence-derived geometric model. Electrocardiographic imaging could be a new tool for a successful resynchronization strategy with LBBP. It can be valuable at different stages: during implantation, to assess resynchronization, and dyssynchrony correction (Figures 1 and 2), and select the best configuration and optimization (Figure 3); and in future selection of implant candidates, by disclosing the pattern of activation, conduction velocity, and scar location. Could ECGI prove useful during LBBP implantation to optimize device settings and assess whether true resynchronization is achieved, thereby helping to reduce the incidence of non-response? We present two clinical cases. A 73-year-old woman with a history of hypertension, diabetes, and chronic renal disease was referred to our center for CRT implant. She presented with ischemic cardiomyopathy (chronic occlusion of the mid anterior descending artery and interventricular posterior artery) with acute pulmonary edema 3 months before CRT implantation. Echocardiography showed left ventricular ejection fraction (LVEF) 27% under guideline-directed medical therapy (GDMT) and left bundle branch block (LBBB) according to Strauss criteria, with QRS 170 ms. Baseline ECGI showed interventricular and intraventricular dyssynchrony with delayed activation of the lateral wall of the left ventricle with left ventricular activation time (LVAT) of 92 ms (Figure 2). Could ECGI help to assess correction of intraventricular and interventricular dyssynchrony? A 58-year-old woman with medical history of asthma, hypertension, and right breast cancer treated with surgery and radiotherapy, with no recurrence at 8 years, presented with non-ischemic cardiomyopathy under GDMT with LBBB (QRS 154 ms) and LVEF 38%. Left bundle branch pacing was applied, achieving non-selective capture, spike-R in V6 60 ms, qR morphology in V1, and QRS 125 ms. However, while programming various atrioventricular (AV) intervals within the fusion band we observed different QRS widths (from 119 to 140 ms) (Figure 3). Could ECGI help to further reduce ventricular activation time and select the best configuration? Patients with CRT indication typically show intraventricular and interventricular dyssynchrony. Postimplantation, correction of dyssynchrony usually is measured with echocardiography on a deferred basis, which prevents taking action during the implantation if dyssynchrony is not corrected, such as crossover to biventricular pacing or the left bundle branch-optimized cardiac resynchronization therapy (LOT-CRT) strategy. An imageless, beat-by-beat technique that assesses ventricular dyssynchrony in real time (Figure 1) could help implanters to achieve the best possible resynchronization. ECG imaging may help during the lead-screwing process to assess intraventricular resynchronization (change in activation pattern, early activation of the septal area and LVAT shortening) [3]. Interventricular dyssynchrony can be measured with ventricular electrical uncoupling (VEU). Patient 1 obtained a correction of both types of dyssynchrony with LBBP (Figure 2). The patient was a CRT responder with LVEF of 50% at 12-month follow-up. Optimization with fusion obtains better LV remodeling with biventricular pacing [4]. However, usefulness of AV interval optimization with LBBP has not been evaluated. We offer an example of the possible value of fusion to achieve the best possible resynchronization (Figure 3). Usually a short AV interval is programmed with LBBP, not the nominal AV. However, looking for the shorter LVAT and better pattern of activation obtained within the fusion band could improve the degree of resynchronization achieved. With fusion-optimized LBBP, Patient 2 achieved super-response with LVEF of 57% at 12-month follow-up. Electrocardiographic imaging may be a useful technique to help the electrophysiologist and the multidisciplinary cardiac resynchronization team to improve implant, programming, and optimization of our patients who are candidates for LBBP. The authors thank Andreu M. Climent and Jana Reventós-Presmanes for their work developing ACORYS technology; Josep Boqué, Paz Garre, and Elisenda Ferró for their support with electrocardiographic imaging (CardioInsight Medtronic system); and the Arrhythmia nursing team for their work in the Device Clinic. All patients provided written informed consent. M. Pujol-Lopez has received speaker honoraria from Medtronic. M. Regany-Closa, B. Pellicer-Sendra, and R. Molero are shareholders of Corify Care SL. J. M. Tolosana has received honoraria as a lecturer and consultant from Abbott, Boston Scientific, and Medtronic. L. Mont has received unrestricted research grants, fellowship program support, and honoraria as a lecturer and consultant from Abbott, Biotronik, Boston Scientific, Livanova, and Medtronic; he holds stock in Galgo Medical and Corify Care SL. M. S. Guillem is a shareholder of Corify Care SL. All remaining authors have declared no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.