Circadian variation--increased morning incidence of acute myocardial infarction in patients with coronary artery disease.

OBJECTIVE To examine whether a circadian variation exists in the onset of symptoms of Acute Myocardial Infarction (AMI) in patients with Coronary Artery Disease (CAD) and to review the characteristics of such variation. SETTING Patients with AMI admitted to the coronary care units of two teaching hospitals in the city of Karachi, Dr. Ziauddin Medical University Hospital and National Institute of Cardiovascular Disease. METHOD The study population included patients admitted to the coronary care unit. The diagnosis was based on the onset of AMI signs and symptoms and ECG changes. The inclusion criterion was an age less than 76 years. RESULTS The incidence of Myocardial infarction assessed by the onset of clinical symptoms exhibited a marked circadian variation. Myocardial infarction occurred 2.8 times more frequently during morning hours (period of maximum incidence) as compared to evening (period of minimum incidence). CONCLUSION This result extends previous observation of the circadian variation in the incidence of AMI onset. This study also helps in searching the potential triggers to physiological changes that may occur during morning hours. Design and timing of cardioprotective medication may play a crucial role in improving circadian variation and prevention of AMI.