Heart attacks and circadian rhythms

Aims: This study has two main aims. First, to confirm a peak incidence of heart attacks (acute myocardial infarction or AMI) occurring in the early hours of the morning and second, to explore the links between acute myocardial infarction and circadian rhythms. Circadian rhythms control a host of biochemical, biological and behavioural patterns in humans. There is an internal mechanism for circadian rhythms known as the biological clock and external factors such as the light/dark cycle that ensures that our internal clock is synchronized with the environment. Methods: This is a quantitative study collating data from patients attending a district general hospital with a diagnosis of ST-segment elevation MI as part of the Myocardial Ischaemia (formerly Infarction) National Audit Database (MINAP). Results: The results of the study show that there is a significant peak in incidence of AMI in the morning hours between 6 am and 12 noon. This peak accounts for 34% of all patients presenting with AMI which is statistically significant (P<0.001). The review of the literature suggests a link between the peak in incidence of AMI and circadian rhythms. Conclusions: An understanding of circadian rhythms is important to understand how patients with AMI and other acute coronary syndromes can be treated but also how to prevent their occurrence.