Triggers of transient myocardial ischemia: circadian variation and relation to plaque rupture and coronary thrombosis in stable coronary artery disease. The phenomenon of transient myocardial ischemia is common in patients with stable coronary disease and appears to be due both to increases in myocardial demand and to episodic coronary vasoconstriction. The circadian variation of transient ischemic episodes closely parallels the circadian variation of acute coronary syndromes associated with plaque rupture, such as myocardial infarction and sudden death. These concordant temporal patterns of transient ischemia, myocardial infarction and sudden cardiac death probably represent independent manifestations stemming from the consequences of increased sympathetic activity. 