Circadian variation in ST-segment elevation myocardial infarction: a nationwide analysis of onset, treatment delays, and culprit artery patterns

INTRODUCTION: ST‑segment elevation myocardial infarction (STEMI) onset follows a circadian rhythm, yet data from large contemporary national registries remain limited, particularly regarding how the onset time influences treatment delays and coronary pathology. OBJECTIVES: We aimed to examine circadian patterns of STEMI onset and their impact on treatment delays, culprit vessel involvement, and periprocedural mortality. PATIENTS AND METHODS: We retrospectively analyzed 153 543 STEMI patients from the Polish National Percutaneous Intervention Registry hospitalized between 2014 and 2022. We examined the hourly distribution of symptom onset and its associations with patient characteristics, treatment delays, and infarct‑related artery location. RESULTS: STEMI onset showed pronounced circadian variation, peaking at 8:00 AM. Although the overall pattern was similar between sexes (P for interaction = 0.15), median onset time occurred earlier in men than women (10:00 AM vs 11:00 AM; P = 0.007). Nocturnal onset (eg, 3:00 AM) was associated with substantially longer median pain‑to‑first‑medical‑contact times than daytime onset (180 vs 90 min at 1:00 PM; P