Increased mortality among acute MI patients admitted during weekends, but not by time of day

Background/Introduction Hospitals typically operate with reduced staffing and service availability during weekends compared with weekdays. Previous studies have reported higher mortality among patients admitted during weekends, but the extent to which this association persists after adjusting for case mix remains uncertain. Emergency admissions are fewer during weekends, and clinical experience suggests that some patients may delay seeking care until weekdays. Hospital service availability also varies by time of day. Purpose To examine whether admission during weekends is associated with increased 30-day mortality among patients hospitalized with acute or subsequent myocardial infarction (MI), and to assess whether time of day modifies this association. Methods Using data from the Norwegian Patient Registry, we identified all acute admissions for MI (ICD-10: I21–I22) to public hospitals in Norway from 2018 through the first tertile of 2025. In total, 90,440 episodes were included, of which 7,817 resulted in death within 30 days. Mortality was attributed only to the final episode in each patient’s care sequence. Logistic regression was used to estimate the association between weekend, public holiday, or bridge day admission and 30-day mortality, compared with weekday admission. Models were adjusted for age, sex, diagnosis-related groups, diabetes, hypertension, other cardiac comorbidities, and time of admission (07:01–16:00, 16:01–22:00, 22:01–07:00). Results The overall 30-day mortality rate was 8.6%. Admission during weekends, public holidays, or bridge days was consistently associated with higher mortality across all models. The association was significant in the basic model adjusting for age and sex (p < 0.001), remained significant after adjustment for diagnosis-related groups (p = 0.01), and persisted in the fully adjusted model (p = 0.02). The fully adjusted odds ratio was 1.09, indicating approximately 9% higher odds of death for patients admitted during weekends or equivalent days. Adjustment for time of admission did not materially change the effect, and time of day itself was not significant (p = 0.07). Excluding Monday admissions, which had markedly higher volumes, reduced the effect size, but the association remained significant. Conclusion Admission during weekends, public holidays and bridge days is associated with increased 30-day mortality among MI patients, independent of patient characteristics and time of day. Further studies using clinical quality registries with detailed MI subtype information are warranted.Figure1Figure2