At what time of day do most ST-Elevation Myocardial Infarction (STEMI) events in men occur?

Circadian Pattern of ST-Elevation Myocardial Infarction in Men

Most STEMI events in men occur during the early morning to early afternoon hours, with peak incidence around late morning (approximately 11:30 AM to 1:00 PM). 1

Circadian Variation of STEMI

The circadian pattern of STEMI has been well-documented in multiple studies and guidelines:

• According to the European Society of Cardiology guidelines, there is a clear circadian variation of STEMI with a higher incidence in the early morning hours 2
• This pattern is explained by physiological factors that occur upon waking:
  • Increased β-adrenergic stimulation
  • Elevated vascular tone and blood pressure
  • Hypercoagulability of the blood
  • Heightened platelet reactivity 2

Recent Evidence on Timing Patterns

Recent research has provided more specific data on the timing of STEMI events:

• A 2013 study examining 519 STEMI patients found a significant circadian pattern with a peak at approximately 11:30 AM 1
• The National Cardiovascular Data Registry analysis of 45,218 STEMI patients showed that 41% of events occurred between 6 AM and 2 PM, compared to 32% between 2 PM and 10 PM, and only 26% between 10 PM and 6 AM 3
• A 2020 study suggests a potential shift in this pattern, with the highest frequency now occurring between 12 PM and 6 PM (33.1% of STEMIs) 4

Factors Affecting Circadian Pattern

The morning predominance of STEMI is not universal and can be modified by several factors:

• Medication use:

  • Beta-blockers significantly abolish the circadian pattern 1
  • Statin and aspirin use may attenuate but not eliminate the pattern 1

• Medical conditions:

  • Diabetes mellitus abolishes the circadian pattern 1
  • Patients with more severe cardiovascular disease (prior heart failure, 3-vessel disease) have higher rates of overnight events 3

• Demographics:

  • The morning peak is more pronounced in older patients, males, and those of white race 3
  • Younger age and female gender may attenuate the pattern 1

• Lifestyle factors:

  • Smokers tend to experience STEMI earlier in the day compared to non-smokers 1

Clinical Implications

Understanding the circadian pattern of STEMI has important implications for healthcare systems:

• Resource allocation in emergency departments and catheterization laboratories should account for higher STEMI volumes during morning to early afternoon hours
• Preventive medications (particularly beta-blockers) may be timed strategically to provide maximum protection during vulnerable morning hours
• Patient education should include awareness of increased morning risk, especially for those with multiple risk factors

Conclusion

While the classic circadian pattern shows a morning predominance of STEMI in men, recent evidence suggests this pattern may be shifting toward a later peak in the day. Regardless, the lowest incidence consistently occurs during overnight hours (10 PM to 6 AM). This pattern is significantly modified by medication use (particularly beta-blockers), presence of diabetes, and other patient characteristics.