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Circadian patterns of myocardial ischemia: pathophysiologic and therapeutic considerations
1Francis Scott Key Medical Center, Johns Hopkins University School of Medicine, Baltimore, Maryland.
Insights
Sudden cardiac events like heart attacks and sudden death peak in the early morning. This timing suggests shared causes, possibly related to changes in blood flow and platelet activity after waking.
Area of Science:
- Cardiovascular Medicine
- Circadian Biology
- Pathophysiology
Background:
- Acute myocardial infarctions (heart attacks) and out-of-hospital sudden death exhibit a peak incidence in the early morning hours post-awakening.
- Physiological changes upon arising, including increased heart rate and blood pressure, elevate myocardial oxygen demand.
Purpose of the Study:
- To explore the potential shared pathophysiologic mechanisms underlying early morning ischemic and arrhythmic cardiac events.
- To investigate factors beyond increased oxygen demand that may contribute to reduced coronary blood flow in the morning.
Main Methods:
- Review of existing evidence on the circadian patterns of acute myocardial infarction and sudden cardiac death.
- Analysis of physiological changes associated with waking and their impact on cardiovascular parameters.
- Consideration of vascular receptor sensitivity and platelet hyperaggregability as contributing factors.
Main Results:
- A consistent circadian pattern shows increased frequency of acute myocardial infarctions and sudden cardiac death in the early morning.
- Potential mechanisms include not only increased myocardial oxygen demand but also a paradoxical decrease in coronary blood flow.
- Early morning hours may be associated with heightened platelet aggregability, promoting coronary thrombosis and ischemic events.
Conclusions:
- Understanding the circadian rhythm of ischemic events is crucial for developing targeted therapeutic strategies.
- Continuous anti-ischemic medication regimens throughout the 24-hour day are suggested for managing these high-risk periods.
Abstract:
Recent evidence suggests that acute myocardial infarctions tend to occur most frequently in the early morning hours after awakening. In addition, the peak time of occurrence of out-of-hospital sudden death is during the same morning period, which suggests that the pathophysiologic factors influencing these acute ischemic and arrhythmic events may be similar. Although it is clear that arising from sleep is associated with an increased heart rate and blood pressure, two important determinants of myocardial oxygen demands, other factors may be responsible for a paradoxical decrease of coronary blood flow at the same time. It is possible that vascular receptor sensitivity may vary or that the early morning hours may be associated with a hyperaggregability of platelets; this would provide an additional pathophysiologic explanation for ischemic events related to platelet aggregation and coronary thrombosis, which are known to play a central role in the initiation of unstable angina, acute infarction, and sudden death. An understanding of the circadian pattern of ischemic events may be a guide for future therapeutic interventions during this period. Studies suggest that use of medications that provide continuous antiischemic activity throughout the 24-h day should be considered.