[Circadian rhythms and cardiovascular diseases: clinical perspectives]

Chronobiology is a branch of biomedical sciences devoted to the study of biological rhythms. Biological rhythms exist at any level of living organisms and, according to their cycle length, may be divided into: a) circadian rhythms (period of approximately 24 hours), b) ultradian rhythms (period shorter than 24 hours), c) infradian rhythms (period longer than 24 hours). The cardiovascular system is organized according to an oscillatory pattern, and most cardiovascular functions exhibit circadian changes. Most evidence suggests that occurrence of cardiovascular events is not evenly distributed in time, but shows peculiar temporal patterns varying with time of the day, day of the week, and month of the year. These patterns coincide with the temporal variation in the (a) pathophysiological mechanisms that trigger cardiovascular events, and (b) physiological changes in the body rhythms. We will here briefly review the temporal aspects in occurrence of myocardial ischemia and infarction, as well as underlying triggering factors and possible applications in therapy.