Circadian Variability and Its Influence on Infarct Size and Clinical Outcome Among Japanese Patients With Acute Myocardial Infarction.

Background: There is significant circadian variation in the frequency of myocardial infarction onset, with a notable increase during the early morning. However, it remains unclear whether this circadian rhythm influences post-acute myocardial infarction (AMI) clinical outcomes and infarct size. Methods and Results: This study included 2,251 patients enrolled in the Japan AMI Registry (JAMIR) who had ST-elevation myocardial infarction (STEMI) with a documented time of onset, stratified into 4 time periods: 00:00-06:00, 06:00-12:00, 12:00-18:00, and 18:00-00:00 h. The primary outcome measure, used as an indicator of infarct size, was peak creatine kinase (CK) level. The median peak CK level among patients was 1,978 IU/L. No significant differences in peak CK levels were observed among the 4 time period groups (P=0.117). Similarly, the relationship between onset time and peak CK levels was not significant (P=0.215). There were no significant differences among the 4 time period groups in secondary endpoints of in-hospital mortality (P=0.788) and 1-year clinical outcomes, including all-cause mortality (P=0.544), myocardial infarction (P=0.636), stroke (P=0.943), stent thrombosis (P=0.344), and a composite endpoint (cardiovascular death, non-fatal myocardial infarction, or non-fatal stroke; P=0.430). Conclusions: Circadian variation had no effect on infarct size or clinical outcomes in patients with STEMI.