Associations of 2013 and 2021 ESC definitions of left bundle-branch block with mechanical dyssynchrony and CRT-induced reverse remodeling

Abstract

Abstract Background In 2021, a new and stricter ECG-based definition of LBBB was proposed and implemented in the European Society of Cardiology (ESC) guidelines on cardiac pacing and cardiac resynchronization therapy (CRT). Aim To investigate the association between the 2021 and the 2013 LBBB definitions with CRT-induced left ventricular (LV) reverse remodeling, as well as mechanical dyssynchrony. Methods CRT patients (n=191) were retrospectively investigated. Pre-CRT digitally stored ECGs were analyzed and categorized according to the LBBB definition of 2013 (LBBB-2013) and the 2021 (LBBB-2021). Mechanical dyssynchrony (Dyss) was assessed pre-CRT using 2D-echocardiography and was defined as the presence of apical rocking and/or septal flash. CRT-induced LV reverse remodeling was measured as the relative change of left ventricular end systolic volume (LVESV) at 12 ± 6 months after CRT compared to baseline. Results Patients’ characteristics were as follows; age 70 ± 10 years, 69% males and NYHA class 2.7 ± 0.5. QRS width was 156 ± 18 ms and LVEF 33 ± 11%, and 52% had ischemic etiology. Dyss was present in 59% of the population. The percentage of the cohort that was considered to have LBBB was considerably lower according to the LBBB-2021 than according to the LBBB-2013 (18 vs. 57% respectively). Similarly, percentages of patients with LBBB+Dyss were 16 and 46% according to LBBB-2021 and LBBB-2013 respectively, with a respective Kappa coefficient of 0.16 and 0.47 (Figure A). At CRT follow up, LBBB-2013 patients showed significantly more LV reverse remodeling compared to non-LBBB patients (P < 0.001), while there was no significant difference between patients with LBBB-2021 and non-LBBB (P = 0.09, Figure B). Conclusion The LBBB definition proposed in the 2021 ESC guidelines excludes many patients from a class I indication for CRT. It is less associated with mechanical dyssynchrony and with CRT-induced LV reverse remodeling than the 2013 LBBB definition. Therefore, the new LBBB definition appears to be counterproductive with regards to selection of CRT patients.