Adding Insult to Injury: When Atrial Fibrillation Encounters Left Bundle Branch Block.

Background: It is not uncommon that atrial fibrillation (AF) coexists with left bundle branch block (LBBB). Whether LBBB is an independent predictor of poor prognosis in AF patients remains undetermined. This study aims to investigate the impact of LBBB on the AF-related outcomes in non-valvular AF patients.

Methods: The clinical data of AF patients were collected from the Medical Information Mart for Intensive Care-III (MIMIC-III) database. The frequencies of acute arterial embolism events (AEE) and in-hospital cardiac death were compared between the non-LBBB and LBBB groups. And, their 1-year mortality was assessed through a survival analysis model. Additionally, the two groups were matched in a 1:2 ratio by a propensity score matching (PSM) method according to the CHA₂DS₂VASc score and AF type.

Results: 5051 patients diagnosed with non-valvular AF without apparent structural heart disease were enrolled in this study, among them, there were 65 with LBBB which had more AEE (13.8% vs 6.8%, p = 0.04). After PSM, with balanced CHA₂DS₂VASc score and AF type, LBBB was still related with AEE (13.8% vs 3.8%, p = 0.02) significantly, and it was also independent of heart failure (HF) (odds ratios (OR) 6.38, 95% confidence intervals (CI) [1.10, 36.93], p = 0.04). LBBB was also correlated with in-hospital cardiac death (OR 5.33, 95% CI [1.01, 28.28], p = 0.04). And, the LBBB patients had a lower 1-year survival rate in the subgroup of HF (67.6% vs 83.0%, p = 0.06).

Conclusions: The LBBB was an independent risk factor of AEE and related to in-hospital cardiac death and 1-year all-cause mortality in this non-valvular AF cohort from MIMIC-III.