Diurnal rhythms and clinical events in coronary artery disease.

Patients with coronary atherosclerosis present with angina, myocardial infarction and sudden death, most often caused by atherosclerotic stenosis complicated by spasm and/or occlusive thrombosis. All of these events have been shown to exhibit similar diurnal rhythms, with a peak incidence in the morning after waking and rising. Other cardiovascular parameters also show a similar diurnal rhythm associated with increased sympathetic outflow and circulating catecholamines, producing increases in heart rate, blood pressure, myocardial contractility and oxygen demand soon after waking and rising. Experimental and clinical research has recently pointed to several possible mechanisms that might be responsible for these events. In patients with atherosclerosis, dysfunction of the endothelium in the epicardial coronary arteries results in a failure to limit the constrictor response to catecholamines. Catecholamines can also alter the procoagulant nature of vascular surfaces. We speculate that the interaction between increased sympathetic activity and the procoagulant and vasoconstrictor states of atherosclerotic coronary stenoses may lead to a lower threshold to ischaemia in the waking hours, with a corresponding increase in angina, myocardial infarction and sudden death. These factors may be important considerations for the selection of suitable therapies and for future research.