Serum albumin and atrial fibrillation: insights from epidemiological and mendelian randomization studies

Atrial fibrillation (AF) is the most common arrhythmia in clinical practice. Low serum albumin level is linked to the emergence of many cardiovascular diseases, including AF. In this study, we aim to characterize the nature and magnitude of the prospective association between serum albumin and incident AF in the Atherosclerosis Risk in Communities (ARIC) Study and investigate any causal relevance to the association between them. ARIC Study is a population-based, prospective, cohort study of cardiovascular risk factors in four US communities, initially consisting of 15,792 participants, aged 45-64 years, recruited between 1987 and 1989 (visit 1). The final sample size was 12,833 in this study. Baseline (visit 1) characteristics were compared between groups using one-way ANOVA test, Chi square test, or Kruskal-Wallis test as appropriate. We used multivariable Cox' hazard regression models to assess the association between albumin and incident AF. Two-sample Mendelian randomization (MR) based on publicly available summary-level data from genome-wide association studies was used to estimate the causal influence of the serum albumin and incident AF. During a median follow-up of 25.1 years, 2259 (17.6%) participants developed incident AF. After multiple adjustment, serum albumin was inversely associated with incidence of AF [HR = 0.90, 95% CI 0.86-0.94, per SD (0.27 g/dL) increase; HR = 0.80, 95% CI 0.71-0.91, Q4 vs. Q1]. In MR analysis, we detected no evidence for a causal relation between serum albumin level and AF in inverse-variance weighted (IVW) method (odds ratio: 0.996, 95% CI 0.980-1.012, per 1 g/dL increase of albumin; P = 0.620) without evidence of heterogeneity between estimates from individual SNPs (P_{heterogeneity} = 0.981 [MR-Egger] and P_{heterogeneity} = 0.860 [IVW]) nor pleiotropy effect (P_pleiotropy = 0.193). The serum albumin level is independently inverse associated with incident AF in a linear pattern. However, MR analyses did not support a causal role of serum albumin in the etiology of AF.