Background: Elevated C-reactive protein (CRP) was shown to be associated with an increased risk for new-onset atrial fibrillation (AF) in ST elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (PCI); however, the optimal time frame to measure CRP for risk stratification is not known.

Objectives: To evaluate the relation between the change in CRP over time (CRP velocity [CRPv]) and new-onset AF among STEMI patients treated with primary PCI.

Methods: We included 801 STEMI patients who underwent PCI between 2007 and 2017 and had their CRP measured with a wide range assay (wr-CRP) at least twice during the 24 hours after admission. CRPv was defined as the change in wr-CRP concentration (mg/l) divided by the change in time (in hours) between the two measurements. Patient medical records were reviewed for occurrence of new-onset AF.

Results: New onset AF occurred in 45 patients (6%). Patients with new onset AF had significantly higher median CRPv (1.27 vs. 0.43 mg/l/h, P = 0.002). New-onset AF during hospitalization occurred in 3.4%, 4.5 %, and 9.1% of patients in the first, second and third CRPv tertiles, respectively (P for trend = 0.006). In a multivariable logistic regression, adjusting for clinical variables the odds ratios for new onset AF was 1.93 (95% confidence interval 1.0–3.59, P = 0.04) for patients in the third CRPv tertile.

Conclusion: CRPv might be an independent and rapidly measurable biomarker for new-onset AF following primary PCI in STEMI patients.