White blood cell count and risk of incident atrial fibrillation (from the Framingham Heart Study)

Several studies have reported that inflammatory markers are associated with atrial fibrillation (AF). The white blood cell (WBC) count is a widely available and broadly used marker of systemic inflammation. We sought to investigate the association between an increased WBC count and incident AF and whether this association is mediated by smoking, myocardial infarction, and heart failure. We examined the participants in the Framingham Heart Study original cohort. Cox proportional hazard regression analysis was used to examine the relation between the WBC count and incident AF during a 5-year follow-up period. We adjusted for standard AF risk factors, smoking, previous myocardial infarction, and interim myocardial infarction and heart failure before the incident AF. Our sample consisted of 936 participants (mean age 76 ± 6 years and 61% women). The median WBC count was 6.4 × 10(9)/L (25th to 75th percentile 5.6 × 10(9)/L to 7.8 × 10(9)/L). During a median 5-year follow-up period, 82 participants (9%) developed new-onset AF. After adjusting for standard risk factors for AF, an increased WBC count was significantly associated with incident AF, with a hazard ratio per SD (0.26 × 10(9)/L) increase of 2.22 (95% confidence interval 1.10 to 4.48; p = 0.03). We found no substantive differences adjusting for smoking, previous myocardial infarction, interim myocardial infarction, or heart failure. In conclusion, in our community-based sample, an increased WBC count was associated with incident AF during 5 years of follow-up. Our findings provide additional evidence for the relation between systemic inflammation and AF.