CIRCADIAN VARIATION AND TRIGGERS OF ACUTE CORONARY SYNDROMES

Myocardial infarction and sudden cardiac death demonstrate a marked ci rcadian variation with an increased risk during the morning after awak ening and arising. The recognition of the morning increase of acute co ronary heart disease has convinced many that morning activities can 't rigger' its onset. It is of note, however, that coronary events may oc cur throughout the day-even if at lower frequency compared with the mo rning. There is a strong association between external triggers and ons et of myocardial infarction and sudden cardiac death beyond that expec ted 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 frequentl y and may play a causative role in up to 20% of cases of acute coronar y syndromes. Physical exertion, burst of anger and sexual activity hav e been proven to have triggering potential. Other possible triggers in clude external and environmental events such as earthquakes, war threa t and climatic factors. The pathophysiological links between external triggers and onset of coronary syndromes are important in addressing t he question of a causal relationship between triggers and disease onse t and, perhaps, in improving preventive strategies.