Circadian variation in cardiovascular events.

Prospective studies have shown not only that there is a greater incidence of acute myocardial infarction during the morning waking hours but also that transient myocardial ischemia, unstable angina, sudden cardiac death, complex ventricular arrhythmieas, and strokes have a greater incidence at a similar time. Studies of the physiologic responses that occur throughout the day have shed much light on why such a pattern in the timing of cardiovascular events is seen. It has been shown, for example, that blood pressure and heart rate surge on waking and at the start of daily activities, as does release of catecholamine. It appears that delaying the time of arising and of commencing activities simply shifts the risk of cardiovascular events rather than negating it. The most important clinical message obtained from the study of circadian variation in cardiovascular disease is that protection should be offered to cover the morning waking hours in addition to other times of the day. This need is being addressed with the increasing use of long-acting therapeutic agents.