BACKGROUND: Evidence linking an elevated white blood cell count (WBCC), a marker of inflammation, to the development of atrial fibrillation (AF) after an acute coronary syndrome (ACS) is limited. We examined the association between WBCC at hospital admission, and changes in WBCC during hospitalization, with the development of new-onset AF during hospitalization for an ACS.

METHODS: Development of AF was based on typical ECG changes in a systematic review of hospital medical records. Increase in WBCC was calculated as the difference between maximal WBCC during hospitalization and WBCC at hospital admission. Multiple logistic regression analysis was used to adjust for several potentially confounding demographic and clinical variables in examining the association between WBCC, and changes over time therein, with the occurrence of AF.

RESULTS: The median age of study patients (n=1325) was 60years, 31.8% were women, and 80.1% were non-Hispanic whites. AF developed in 7.3% of patients with an ACS. Patients who developed AF, as compared with those who did not, had a similar WBCC at admission, but a greater increase in WBCC during hospitalization (6.0x10(9)cell/L vs. 2.7x10(9) cell/L, p < 0.001). After adjusting for several potentially confounding factors, an increase in WBCC was associated with the development of AF. This association was observed in patients with different ACS subtypes, types of treatment received, and according to time of acute symptom onset.

CONCLUSION: Increase in the WBCC during hospitalization for an ACS should be further studied as a potentially simple predictor for new-onset AF in these patients.