Clinical problems in coronary disease are caused by wide variety of ischemic episodes that affect patients out of hospital.

Transient ischemia arising from proximal events in epicardial coronary arteries causes important symptoms, such as angina pectoris, and is usually studied in the hospital with provocative tests. However, Holter monitoring of ST-segment disturbances in patients out of the hospital has shown frequent asymptomatic evidence of ischemia that is surprisingly prolonged and that is not associated with the obvious tachycardia of exercise or stress. Positron emission tomography has been developed to measure the regional myocardial uptake of a cation (rubidium-82) in order to assess repeatedly the directional changes in regional coronary blood flow during these events. This method has been used to show that both symptomatic and asymptomatic episodes of ST depression are reliably associated with disturbances in regional myocardial perfusion. The daily activities of patients have been analyzed and reproduced in the hospital to assess the effects of cold stimulation, mental arithmetic, cigarette smoking, and exercise. Physical exercise was associated with angina, ST-segment change, and regional abnormalities of myocardial perfusion, including decreased perfusion in poststenotic segments. The other tests caused the same disturbances in myocardial perfusion; these perfusion disturbances were mostly asymptomatic and surprisingly prolonged, with periods of recovery that were two to five times longer than the ST-segment disturbance and the pain. Current studies using a structured diary indicate that the episodes of transient ischemia occurring out of the hospital are more frequently associated with different levels of mental arousal than with any other activity. Physical exercise is a relatively infrequent cause of transient ischemia. The examination of coronary blood flow using provocative tests derived from the patients' own activities out of the hospital have confirmed that, irrespective of the pattern of angina, patients have frequent episodes of asymptomatic transient ischemia that are surprisingly prolonged and that these episodes occur in response to previously unsuspected ordinary daily activities. The disturbances in coronary blood flow usually include a regional decrease in myocardial perfusion that can only be explained by pathophysiologic events in the proximal epicardial coronary arteries.