Pathophysiology and triggers of acute myocardial infarction: clinical implications.

A new approach to identification of the triggering mechanisms of acute myocardial infarction has been provided by the observation that the disease occurs more frequently during the morning hours compared to other times of day. This circadian variation results primarily from an increased relative risk during the initial 2-3 h after awakening and arising. The precise relationship between the onset of myocardial infarction and external factors such as activity and meal patterns needs to be determined in controlled epidemiologic studies. The possible underlying pathophysiologic mechanisms responsible for the circadian pattern of myocardial infarction include acute variations of blood pressure, heart rate, platelet aggregability and fibrinolytic activity, leading to an increased risk of plaque rupture and intracoronary thrombosis. Clinical implications of these findings include the need to design preventive regimens to provide maximum protection at the time of peak risk of myocardial infarction.