Repolarization changes following conduction system pacing evaluated by ultra-high-frequency electrocardiography

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: Public hospital(s). Main funding source(s): This work was supported by the National Institute for Research of Metabolic and Cardiovascular Diseases project (Programme EXCELES, ID Project No. LX22NPO5104) — Funded by the European Union — Next Generation EU and a personal grant from the Dutch Heart Foundation (2021T016). BACKGROUND: On the surface electrogram (ECG) of a normal heart, the polarity of the T-wave is concordant with the QRS complex. This phenomenon could be explained by the presumption that regions that depolarize first repolarize last. Acute changes in ventricular activation can lead to abnormal T-waves. Conduction system pacing (CSP) leads to a more physiological ventricular activation compared to conventional right ventricular pacing (RVP), but little is known about repolarization changes following CSP. PURPOSE: To compare repolarization changes following CSP with those during RVP and normal intrinsic activation in patients requiring bradycardia treatment. METHODS: Ultra-high-frequency electrocardiographic (UHF-ECG) measurements were acquired at time of implantation during normal intrinsic rhythm (narrow QRS [nQRS], n=199), selective His bundle pacing (sHBP, n=50), left ventricular septal pacing (LVsp, n=87), non-selective left bundle branch pacing (nsLBBP, n=47), and RVP (n=102). Activation and repolarization times were calculated for leads V1 and V6 from the time position of the QRS negative and from the T-wave positive derivative maxima respectively. Dyssynchrony (e-DYS) was defined as the time difference between leads V6 and V1. Differences between e-DYS depolarization (e-DYS-dpt) and repolarization (e-DYS-rpt) was evaluated by Kruskal Wallis tests. RESULTS: The left panel of Figure 1 demonstrates that during both nQRS and sHBP, e-DYS-dpt is small and slightly positive, while e-DYS-rpt is negative. RVP leads to a positive and increased e-DYS-dpt and e-DYS-rpt. LVsp and nsLBBP create negative e-DYS-dpt and e-DYS-rpt values. e-DYS-dpt and e-DYS-rpt was significant different between the groups (p-values <0.001). The middle and right panel of Figure 1 shows that during nQRS and sHBP, the activation-repolarization relationship is negative (~ first depolarized regions repolarize last). RVP, LVsp, and nsLBBP leads to a positive activation-repolarization relationship (~ first depolarized regions repolarize first). CONCLUSION: sHBP preserves the physiological negative activation-repolarization relationship. RVP, LVsp, and nsLBBP reverses the activation-repolarization relationship, though smallest changes are present during LVsp. LVsp (after nQRS and sHBP) leads to the most synchronous activation and repolarization of the three. [Figure: see text]