Circadian variations in cardiac disease: clinical implications. Current strategies for preventing MI, dysrhythmias, sudden death.

Myocardial infarction (MI), myocardial ischemia, ventricular dysrhythmias, and sudden cardiac death (SCD) occur most frequently in the morning, especially in the first few hours after awakening. Among individual patients, however, this pattern may vary widely. Peaks in heart rate, blood pressure, and platelet aggregability and a trough in fibrinolytic activity are thought to influence the morning onset of events. beta-Blockers may blunt the peak occurrence of MI, SCD, and ischemia. Some calcium channel blockers may modify the pattern of ischemia. Alternate-day therapy with 325 mg of aspirin has been shown to blunt the morning onset of MI. The efficacy of thrombolytics may be affected by daily fluctuations in fibrinolytic activity.