Key result
Circadian rhythmicity in OHCA and STEMI shows a morning incidence peak (6 a.m.–12 p.m.) and a nocturnal nadir, with worse nighttime survival driven by system delays rather than timing itself.
Why the study?
The influence of circadian rhythmicity on the time of onset and clinical outcomes of OHCA and STEMI in patients requiring prehospital emergency care and hospitalization needed synthesis.
How does circadian rhythmicity affect the time of onset of OHCA and STEMI and the related clinical outcomes of patients requiring prehospital emergency care and subsequent hospitalization?
How does circadian rhythmicity affect the time of onset of OHCA and STEMI and the related clinical outcomes of patients requiring prehospital emergency care and subsequent hospitalization?
This scoping review demonstrates that while OHCA and STEMI peak in the morning, nighttime events carry worse survival and neurological outcomes largely due to system and bystander delays rather than biological circadian effects alone.
Answers are grounded in this paper and cite their sources.
Target nighttime system delays to improve OHCA/STEMI survival; confirms circadian patterns but leaves causality open for prospective trials.
Introduction: Out-of-hospital cardiac arrest (OHCA) and ST-segment elevation myocardial infarction (STEMI) are time-critical events that exhibit circadian patterns, which influence their incidence and clinical outcomes. Objective: To determine whether circadian rhythmicity influences the time of onset of OHCA and STEMI, as well as related clinical outcomes, in patients requiring prehospital emergency care and subsequent hospitalization. Design: A scoping review. Methods: The search process included four online databases: MEDLINE Complete, CINAHL Plus with Full Text, ScienceDirect, and ProQuest. The review included original articles published between January 2010 and December 2024. Results: Eighteen studies met the inclusion criteria. These revealed that the incidence of OHCA and STEMI exhibits significant circadian variability, with the highest incidence in the morning. OHCA often has a secondary afternoon/evening peak. The nighttime hours are associated with the lowest incidence. Patients with nighttime OHCA or STEMI have a lower probability of return of spontaneous circulation and worse one-month and one-year survival and neurological outcomes. This less favorable prognosis is not due to the time of day when the event occurs but rather due to limited bystander availability, lower rates of bystander cardiopulmonary resuscitation and defibrillation, and longer times to hospital intervention. Additionally, these events were more frequently recorded in winter, while weekly variations were insignificant. Conclusion: Circadian and seasonal factors influence the occurrence and clinical course of OHCA and STEMI, with worse outcomes for nighttime cases being more a consequence of limited availability than the time of the event itself.
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Locihová et al. (2026) conducted a review in Out-of-hospital cardiac arrest (OHCA) and ST-segment elevation myocardial infarction (STEMI) (n=353,167). Circadian rhythmicity and time of symptom/event onset (morning vs. afternoon/evening vs. nighttime) vs. Daytime / regular working hours onset was evaluated on Time of onset (circadian incidence) and clinical outcomes (return of spontaneous circulation, survival, neurological outcomes, and reperfusion delays). Circadian rhythmicity in OHCA and STEMI shows a morning incidence peak (6 a.m.–12 p.m.) and a nocturnal nadir, with worse nighttime survival driven by system delays rather than timing itself.
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