Delayed ventricular conduction alters ventricular repolarization in patients with heart failure: an electrocardiographic imaging study
Authors: Nguyen U , Stoks J , Cluitmans M J M , Strik M , Van Rees B , Meiburg R , Mihl C , Volders P G A , Vernooy K , Prinzen F W 
Published: May 2023

Abstract

Funding Acknowledgements
Type of funding sources: Public hospital(s). Main funding source(s): Personal grant from the Dutch Heart Foundation.

Background
In the normal human heart, the polarity of the T-wave is concordant with the QRS complex. This phenomenon is often explained by longer repolarization of earlier activated regions. Patients with delayed ventricular conduction often have discordant T-waves, but the link to regional repolarization is unknown.

Aim
To compare epicardial repolarization-activation (RT-AT) relations in patients with heart failure and reduced ejection fraction (HFrEF) with those having a structural normal heart.

Methods
14 patients with HFrEF and delayed ventricular conduction and 11 patients no history of structural heart disease and a normal surface ECG (nQRS) were analyzed using electrocardiographic imaging (ECGI). HFrEF patients were subcategorized as left bundle branch block (LBBB, n=6) or non-specified intraventricular conduction disturbance (IVCD, n=8). Noninvasive ECGI was used to assess epicardial activation (ATs) and repolarization times (RTs). RT-AT relationships were evaluated for 24 epicardial segments using linear regression analysis. Interventricular repolarization dispersion (inter-RTD) was defined as the difference between average left-ventricular (LV) and right-ventricular RT, while total epicardial repolarization dispersion (total-RTD) was defined as the standard deviation of all epicardial RTs. The maximum of the local RT gradients (RTG) was defined as their 95th percentile. RT parameters were described as median±IQR and Kruskal Wallis tests were used to evaluate the differences between the groups.

Results
An HFrEF patient’s representative 24-segment AT and RT bullseyes with a positive RT-AT relation (~depolarize last, repolarize last) is provided in Figure1A. A positive RT-AT slope was present in the majority of HFrEF patients (1.14±0.17 for LBBB and 1.16±0.55 for IVCD), whereas the nQRS group (-0.25±2.16) demonstrated an overall slightly negative slope with high variability (Figure 1B and 1C). Individual (thin lines) and group-averaged (thick lines) RT-AT slopes normalized for the earliest AT and earliest RT (in case of a positive RT-AT slope) or latest RT (in case of a negative slope) are visualized in Figure 1C. Both inter-RTD (41±25 for LBBB, 32±13 ms for IVCD, and 8±20 ms for nQRS) as well as total-RTD (34±9for LBBB, 34±12 ms for IVCD, and 24±8 ms for nQRS) was significantly higher in the LBBB and IVCD group compared to the nQRS group, whereas RTG did not differ between the groups (Figure 1B). RT-AT slopes, inter-RTD, total-RTD, and RTG did not significant differ between the LBBB and IVCD subgroup.

Conclusion
This ECGI study shows that in patients with HFrEF, later activated regions also have a later completion of repolarization, regardless of conduction delay, whereas a variable RT-AT relation is present in subjects with structural normal hearts. HFrEF additionally initiates a higher degree of interventricular and total repolarization dispersion.