Morphology of ambulatory ST segment changes in patients with varying severity of coronary artery disease. Investigation of the frequency of nocturnal ischaemia and coronary spasm.

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Abstract
The frequency and magnitude of objectively determined myocardial ischaemia during normal daily activities of patients with varying severity of coronary artery disease are unknown. Furthermore, the incidence of nocturnal resting myocardial ischaemia and frequency of coronary spasm in patients with normal coronary arteries and chest pain are also not known. One hundred consecutive patients with chest pain referred for coronary angiography were therefore investigated with exercise testing and ambulatory ST segment monitoring. Fifty two of 74 patients with significant coronary artery disease and six of 26 with no significant coronary narrowing had episodes of ST segment change during 48 hours of ambulatory monitoring. Two patients, one with normal coronary arteries and localised spasm and one with three vessel disease, had episodes of ST segment elevation, whereas all other patients had episodes of ST segment depression. The frequency, duration, and magnitude of ST segment changes were greater in patients with more severe types of coronary artery disease. Thus more than six episodes of ST segment change per day occurred in patients with two or three vessel disease or left main stem stenosis and in the only patient with coronary spasm and normal coronary arteries. Nocturnal ischaemia occurred in 15% of patients with coronary artery disease and was almost an invariable indicator of two or three vessel coronary artery disease or left main stem stenosis. Episodes of ST segment change occurred most commonly during the morning hours and least commonly during the night, in parallel with changes in basal hourly heart rates. The heart rate at the onset of ST segment change tended to be lower in patients with coronary artery disease than in those with normal coronary arteries. The duration of exercise to ST segment depression tended to be shorter in patients with more severe disease, but it could not predict patients with nocturnal myocardial ischaemia, left main stem stenosis, or coronary spasm, whereas ambulatory ST segment monitoring was able to identify most of these patients.