Circadian rhythm and cardiovascular disease.

The demonstration of a circadian variation in frequency of onset of myocardial infarction, sudden cardiac death, and stroke provides an opportunity to gain insight into the mechanism of transformation from chronic stable to acute unstable manifestation of cardiovascular disease. Contributing physiologic changes that exhibit a morning peak include arterial pressure, heart rate, and vascular tone, which promote plaque rupture, together with increased platelet reactivity and reduced fibrinolytic activity. The study of circadian rhythm also has implications for triggering of disease onset by external stressors. Further study of this area will provide insight into new approaches to prevent disease onset.