Morning increase of onset of myocardial infarction. Implications concerning triggering events.

During the past 5 years it has been clearly established that there is a prominent morning increase in the frequency of onset of acute myocardial infarction. Similar increases have also been observed for the related conditions of sudden cardiac death, stroke and episodes of transient myocardial ischemia. The period from 6 a.m. to noon is also a time when a number of physiologic processes that could contribute to the onset of coronary thrombosis are intensified. Arterial pressure, which could lead to plaque rupture, rises; coronary tone increases; and platelet aggregability, which could contribute to a hypercoagulable state, increases. The immediate significance of these observations is the emphasis that should be placed on pharmacologic protection of patients during the morning hours. The primary longer-term significance of the recognition of the morning increase of onset of acute cardiovascular disease is the contribution it makes to the concept that onset of coronary thrombosis at any time of the day is frequently triggered by the activities of the patient. Investigation of this possibility may yield more information about the mechanism of disease onset and facilitate design of more effective preventive therapy.