Presentation Times of Myocardial Infarctions to the Emergency Department: Disappearance of the Morning Predominance

Background: Previous studies show that myocardial infarctions (MIs) occur most frequently in the morning. Objectives: We hypothesized that there no longer is a morning predominance of MI, and that the timing of ST-elevation myocardial infarction (STEMI) vs. non-ST-elevation myocardial infarction (NSTEMI) presentation differs. Methods: We reviewed MI, STEMI, and NSTEMI patients (2013–2017) from a multiple-hospital system, identified by diagnostic codes. Daily emergency department arrival times were categorized into variable time intervals for count and proportional analysis, then examined for differences. Results: There were 18,663 MI patients from 12 hospitals included in the analysis. Most MIs occurred between 12:00 PM and 5:59 PM (35.7%), and least between 12:00 AM–5:59 AM (16.3%). After subdividing all MIs into STEMIs and NSTEMIs, both groups continued to have the greatest presentation between 12:00 PM and 5:59 PM (33.1% and 36.0%, respectively). STEMIs (17.2%) and NSTEMIs (16.2%) were least frequent between 12:00 AM and 5:59 AM. We found the second most common presentation time for MIs was in the 6 PM–11:59 PM time period, which held true for both subtypes (MI 26.7%, STEMI 26.4%, NSTEMI 26.7%). Conclusions: These data suggest a potential shift in the circadian pattern of MI, revealing an afternoon predominance for both STEMI and NSTEMI subtypes.