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Cyclic and circadian variations in cardiovascular events
1Department of Preventive Medicine, RUSH Medical College of RUSH University at RUSH-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612, USA. welliott@rush.edu
Insights
Cardiovascular disease events, including heart attack and stroke, show a significant daily pattern, peaking in the morning hours after waking. This highlights the importance of understanding circadian rhythms in cardiovascular health.
Area of Science:
- Cardiology
- Chronobiology
- Public Health
Background:
- Biologic phenomena, including cardiovascular disease (CVD) incidence, exhibit reproducible cyclic variations.
- CVD is a leading cause of death, with events showing increased frequency in winter, early month, Mondays, and morning hours.
- Meta-analyses confirm a substantially higher risk of heart attack, cardiac death, and stroke in the hours following awakening.
Purpose of the Study:
- To quantify the excess risk of cardiovascular events during specific daily periods.
- To explore the implications of these temporal patterns for emergency medical services.
- To investigate potential underlying mechanisms, such as circadian variations in blood pressure and heart rate.
Main Methods:
- Review and synthesis of meta-analyses data on cardiovascular event timing.
- Analysis of risk variations based on time of day, day of week, and time of month.
- Consideration of chronobiological factors influencing cardiovascular events.
Main Results:
- A 40% increased risk of heart attack, 29% increased risk of cardiac death, and 49% increased risk of stroke between 6 AM and noon.
- These risks are significantly higher compared to random distribution throughout the day.
- Individuals with altered circadian patterns or night shift work may have different risk profiles.
Conclusions:
- The morning hours represent a high-risk period for cardiovascular events.
- Circadian rhythms, particularly blood pressure and heart rate patterns, are likely major contributors to this phenomenon.
- Further research and targeted interventions addressing early morning cardiovascular risk are warranted.
Abstract:
The incidence of many biologic phenomena displays a reproducible and cyclic variation. Cardiovascular disease, the most common cause of death in the United States and other developed countries, also has an intrinsic variation in events. These events are more common in winter, at the beginning of each month, on Mondays (in working people), and during the early morning hours of each day. Recent meta-analyses have quantitated the excess risk of cardiovascular events in the hours around and just after awakening. Between 6 AM and noon, there is a 40% higher risk of heart attack, a 29% increased risk of cardiac death, and a 49% increased risk of stroke (compared with what would be expected if these events happened at random and were evenly distributed throughout the day). These observations have major consequences for emergency medical personnel and medical transport systems. The reasons for these observations are less clear. The circadian pattern of blood pressure (BP) and heart rate may be a major contributor, and long-term "hard end-point" studies designed to test specific pharmacologic interventions targeting the early morning rise in BP and heart rate are underway. Individuals who work night shifts and those whose BP has a different circadian pattern have a higher risk of cardiovascular events, but may be less likely to have an increased risk of cardiovascular events in the morning.