Biorhythms and chronotherapy in cardiovascular disease

Recent findings about the effects of biorhythms on cardiovascular disorders are reviewed, and their implications for drug therapy are discussed. The chronobiological approach to physiology evaluates time-dependent changes in biological functions and considers those changes to be multifactorial. Characterization of disease states with this approach allows more accurate determination of the times when patients are at highest risk and therefore in greatest need of preventive measures; it also provides a mechanism for designing optimal drug regimens. There is evidence of circadian variations in the occurrence of myocardial ischemia, acute myocardial infarction, ventricular tachycardia, and sudden cardiac death. Many cardiovascular disorders occur with greatest frequency between 0600 and 1200 in the general population. Blood pressure, too, follows a distinct circadian pattern. Factors affecting circadian variations in cardiovascular disorders include physiological determinants, such as heart rate, catecholamine release, and platelet aggregation--which themselves vary cyclically--and exogenous factors, such as mental stress, anxiety, and physical activity. In chronotherapy, circadian variations in disease states and in the pharmacodynamic properties of drugs are exploited to improve prevention and treatment. Conditions in which research suggests a chronotherapeutic approach may be advantageous include thromboembolism, hypertension, stable exertional angina, variant angina, sustained ventricular tachycardia, and acute myocardial infarction. Information on circadian patterns in the occurrence of many cardiovascular disorders is enabling clinicians to tailor treatment in ways that may lead to improved patient outcomes.