Circadian variation and triggers of acute coronary syndromes.

Myocardial infarction and sudden cardiac death demonstrate a marked circadian variation with an increased risk during the morning after awakening and arising. The recognition of the morning increase of acute coronary heart disease has convinced many that morning activities can 'trigger' its onset. It is of note, however, that coronary events may occur throughout the day--even if at lower frequency compared with the morning. There is a strong association between external triggers and onset of myocardial infarction and sudden cardiac death beyond that expected by chance alone. The magnitude of this association (relative risk two- to threefold) is comparable to that of other known long term risk factors of cardiac disease. Trigger factors occur relatively frequently and may play a causative role in up to 20% of cases of acute coronary syndromes. Physical exertion, burst of anger and sexual activity have been proven to have triggering potential. Other possible triggers include external and environmental events such as earthquakes, war threat and climatic factors. The pathophysiological links between external triggers and onset of coronary syndromes are important in addressing the question of a causal relationship between triggers and disease onset and, perhaps, in improving preventive strategies.