Painless ST-segment depression in patients with angina pectoris. Correlation with daily activities and cigarette smoking.

Ambulatory electrocardiographic monitoring was employed in 33 patients with angina pectoris and abnormal stress tests to determine the frequency with which myocardial ischemia manifested by painless ST-segment depression occurred during normal activity. ST-segment depression occurred in 24 patients during the monitoring period; and in 21, it occurred either solely in the absence of pain or both with and without pain. Of 109 recorded episodes of ST-segment depression, 61 percent were painless. The frequency of painless ST-segment depression was independent of activity other than automobile driving, during which all episodes were painless. In patients who smoked cigarettes, ST-segment depression was more common while smoking, but the incidence of painless ST-segment depression was not altered. The study indicates that ST-segment depression occurs more commonly in the absence than in the presence of chest pain and that ambulatory electrocardiographic monitoring is a useful method of determining the frequency of myocardial ischemia during normal daily activity.