68 Presentation Times of STEMIs and Acute Myocardial Infarctions to the Emergency Department: Disappearance of the Morning Predominance

Abstract

A number of previous studies have demonstrated a peak incidence of STEMI or acute myocardial infarction occurring in the morning between 6AM - 12PM. We hypothesized that there is no longer a morning predominance of STEMIs and acute myocardial infarctions based on the time of presentation to the emergency department. A retrospective review of patients with acute myocardial infarctions presenting to a multiple-hospital system were retrieved from electronic medical records for the years 2013-2017. We identified cases of STEMI and acute myocardial infarction by diagnostic codes and also collected their times of arrival to the emergency department. They were categorized into 4 time periods (12AM - 5:59AM, 6AM - 11:59AM, 12PM - 5:59PM, 6PM - 11:59PM). Chi-Square test for goodness of fit was used to compare presentation times of patients with STEMIs, and separately for all acute myocardial infarctions. We identified 18,663 myocardial infarctions which included 2,395 STEMIs from 11 hospitals. We found that 33.1% of STEMIs presented between 12PM - 5:59PM (χ2 = 124.6, p < 0.001), and 35.7% of myocardial infarctions during the same time period (χ2 = 1,534.8, p < 0.001). The second most prevalent time of presentation (6PM - 11:59PM) had 26.4% of the STEMIs and 26.7% of the myocardial infarctions. In the past 4 decades there have been significant changes in medical therapy and lifestyles that may have contributed to a shift in the circadian pattern of STEMIs and acute myocardial infarctions. This cohort demonstrates there may be a shift in this circadian pattern to later in the day, with the highest prevalence occurring between 12PM - 5:59PM, followed by 6PM - 11:59PM. This is significantly different from what was previously reported.