Comparison of the relation of the ESC 2021 and ESC 2013 definitions of Left Bundle Branch Block with clinical and echocardiographic outcome in cardiac resynchronization therapy.

AIMS: We aimed to investigate the impact of the 2021 ESC guideline changes in left bundle branch block(LBBB) definition on cardiac resynchronization therapy(CRT) patient selection and outcomes.

METHODS: The MUG(Maastricht-Utrecht-Groningen) registry, consisting of consecutive patients implanted with a CRT device between 2001 and 2015 was studied. For this study, patients with baseline sinus rhythm and QRS duration >130ms were eligible. Patients were classified according to ESC 2013 and 2021 guideline LBBB definitions and QRS duration. Endpoints were heart transplantation, LVAD implantation or mortality(HTx/LVAD/mortality) and echocardiographic response(LVESV reduction >15%).

RESULTS: The analyses included 1.202, typical CRT patients. The ESC 2021 definition resulted in considerably less LBBB diagnoses compared to the 2013 definition(31.6% vs 80.9%, respectively). Applying the 2013 definition resulted in significant separation of the Kaplan Meier curves of HTx/LVAD/mortality(p<0.0001). A significantly higher echocardiographic response rate was found in the LBBB compared to the non-LBBB group using the 2013 definition. These differences in HTx/LVAD/mortality and echocardiographic response were not found when applying the 2021 definition.

CONCLUSION: The ESC 2021 LBBB definition leads to a considerably lower percentage of patients with baseline LBBB then the ESC 2013 definition. This does not lead to better differentiation of CRT responders, nor does this lead to a stronger association with clinical outcomes after CRT. In fact, stratification according to the 2021 definition is not associated with a difference in clinical or echocardiographic outcome, implying that the guideline changes may negatively influence CRT implantation practice with a weakened recommendation in patients that will benefit from CRT. This article is protected by copyright. All rights reserved.