Circadian variation and triggering of cardiovascular events

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 cardiovascular events has convinced many that they may be triggered by morning activities. It is of note, however, that cardiovascular events occur throughout the day--even if at lower frequency compared with the morning. There is a strong association between external triggers and the onset of myocardial infarction and sudden cardiac death beyond what is to be expected by chance alone. The magnitude of this association (relative risk two- to threefold) is comparable with the 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, bursts of anger and sexual activity have been proved 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 the onset of cardiovascular events are important in addressing the question of a causal relationship between triggers and disease onset and in perhaps improving preventive strategies.