The impact of time and day on the presentation of acute coronary syndromes

Background: The frequency of acute myocardial infarction (AMI) peaks on Mondays and in the mornings. However, the distribution of the types of acute coronary syndromes (ACS), including unstable angina (UA), has not been systematically evaluated. Hypothesis: The distribution of the types of ACS and clinical presentations varies by time and day of admission. Methods: A retrospective cohort study was conducted in 1,946 consecutive nontransfer ACS admissions (1999-2004) to a tertiary-care academic center to assess presenting clinical variables in patients admitted on days versus nights (6 P.M.-6 A.M.) and weekdays versus weekends (Friday 6 P.M.-Monday 6 A.M.). Results: There were fewer ACS admissions than expected on nights and weekends (p < 0.001), but the proportion of patients with ACS presenting with ST-elevation myocardial infarction (STEMI) is 64% higher on weekends (p < 0.001) and 31% higher on nights (p = 0.022). This increased proportion with STEMI results in a greater proportion of ACS with AMI on weekends (up arrow 10%, p = 0.006) and nights (up arrow 7%, p = 0.033). Using multivariate modeling, the increase in patients with AMI on weekends was not explained by conventional risk predictors. Conclusions: Although fewer patients with ACS presented on nights and weekends, patients at those times were more likely to have an AMI, driven largely by an increased proportion with STEMI at those times. Consideration should be given to these findings when developing clinical care paradigms, health care staffing needs, and when comparing new treatment outcomes in patients with ACS.