Circadian Variations in Myocardial Ischemia

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Abstract
Extended ambulatory electrocardiographic monitoring in the patient's customary environment provides clear evidence of circadian patterns in myocardial ischemic episodes. In patients with effort angina, the highest activity occurs between 6 AM and noon. This coincides with peaks in diurnal variation of frequency of acute myocardial infarction, stroke, and sudden death. A number of potential underlying common triggering mechanisms, including catecholamine secretion, sympathetic nervous system activity, blood pressure, heart rate, cortisol secretion, and aggregability of platelets, exhibit similar surges. As a result of these coinciding morning peaks, myocardial oxygen demand is increased and oxygen supply reduced after a person arises in the morning. Attention to this vulnerable period is merited in the timing and choice of medication, both to prevent or reduce ischemia and to modify potential disease-triggering mechanisms. (JAMA. 1991;265:386-390)