Daylight Savings Time and Acute Myocardial Infarction.

Importance: Previous data suggest that the time changes associated with daylight savings time (DST) may be associated with an increased incidence of acute myocardial infarction (AMI). Objective: To determine whether the incidence of patients presenting with AMI is greater during the weeks during or after DST and compare the in-hospital clinical events between the week before DST and after DST. Design, Setting, and Participants: This cross-sectional study examined patients enrolled in the Chest Pain MI Registry from 2013 to 2022. The study included patients who presented 1 week before DST, during the week of DST, or 1 week after DST (spring or fall) and assessed incidence of AMI, in-hospital mortality, stroke, and clinical outcomes during those times and compared the DST weeks with the week before or after. Data were analyzed from March 2024 to May 2025. Main Outcome and Measure: The main outcome was in-hospital mortality rate. The incidence ratio (IR) of AMI cases was calculated using the observed number of patients with AMI in the DST week divided by the number of patients with AMI who arrived 1 week before or after DST. Results: The final cohort included 168 870 patients (median [IQR] age, 65 [56-75] years, 57 023 females [33.8%]; 111 847 males [66.2%]) at 1124 hospitals during the study period. There were 28 678 patients (17.0%) with AMI treated during spring DST, 28 596 (16.9%) the week before, and 28 169 (16.7%) the week after. There were 27 942 patients (16.5%) with AMI treated during fall DST, 27 365 (16.2%) the week before, and 28 120 (16.7%) the week after. Patient characteristics were similar for the spring and fall DST analyses (spring and fall DST median [IQR] age across groups: 65 [56-74] years and 65 [56-75] years, respectively), and there were 28 725 females (33.6%) in the spring and 28 298 females (33.9%) in the fall. There was no significant difference in the incidence of AMI for the following time periods: spring DST week vs 1 week prior, spring DST week vs 1 week after, fall DST week vs 1 week prior, and fall DST week vs 1 week after. There were no significant differences in adjusted in-hospital outcomes for the 1 week before or after fall or spring DST. Conclusions and Relevance: This study found no significant difference in the incidence rates of AMI in DST weeks compared with the week before or after. Additionally, there were no differences in in-hospital clinical outcomes.