Abstract Body (Do not enter title and authors here): Background:
Although left (LBBB) and right (RBBB) bundle branch blocks play a critical role in cardiovascular pathogenesis, the associations of LBBB and RBBB with cardiovascular (CV) outcomes, especially in patients with HFpEF is understudied compared with normal QRS.

Aim:
We assessed clinical outcomes of LBBB and RBBB in patients with HFpEF who were admitted for acute decompensated heart failure compared with those without bundle branch blocks.

Method:
A cross-sectional study was conducted using the National Inpatient Sample (NIS) database from 2019. We only included adult hospitalizations with HFpEF admitted for acute decompensated heart failure in the study. Hospitalized records were categorized into three groups (LBBB, or RBBB, and those with normal QRS). Clinical outcomes included atrial fibrillation (AF), ventricular fibrillation (VF), complete heart block (CHB), sick sinus rhythm (SSR), cardiac arrest (CA), length of stay (LOS) and in-hospital mortality. Propensity score (PS) inverse probability of treatment weighting and matching were applied to determine the association between BBB types and CV outcomes and validated associations in sensitivity analyses.

Results:
A total of 334511 hospitalizations with HFpEF included LBBB (6818, 2%) and RBBB (7948, 2.4%) were analyzed. Compared to normal QRS, LBBB was associated with VF (odds ratio [OR]=2.47, p<0.001), SSR (OR=1.72, p<0.001), CHB (OR=2.77, p<0.001) and longer LOS (relative risk [RR]=1.15, p<0.001) after adjusting for covariates in PS analysis. Similarly, RBBB was associated with AF (OR=1.30, p<0.001), VF (OR=1.59, p=0.033), SSR (OR=1.72, p<0.001), CHB (OR=2.81, p<0.001), CA (OR=1.19, p<0.001), and longer LOS (RR=1.08, p<0.001) [Table 1]. These associations remained consistent in multiple validation analyses including after additionally adjusting for obesity, hypertension and diabetes.

Conclusion:
In hospitalized records with acute decompensated HFpEF, BBB was associated with increased risk of CV outcomes and longer hospital length of stay. The extent of association with multiple CV outcomes varied according to RBBB and LBBB.