Clinical evaluation of transient myocardial ischemia during daily life

Ambulatory ST-segment monitoring has been introduced in an attempt to obtain an objective measure of transient myocardial ischemia during daily life. Serial observations conducted out of the hospital have produced a picture of the nature and activity of ischemic heart disease that differs markedly from that obtained by conventional assessment. Episodes of transient ischemia appear to be more frequent and prolonged than is suggested by the occurrence of chest pain. Furthermore, only a minority of episodes are associated with tachycardia, and most occur at heart rates well below those achieved during exercise testing. This suggests that mechanisms other than an excessive increase in myocardial oxygen demand may be responsible for the many episodes occurring outside the hospital. Accurate interpretation of this new information depends on the reliability of transient ST-segment depression as a marker of ischemia. In 100 normal volunteers, episodes of significant ST-segment depression similar to that observed in patients with angina were rare (2 percent). Positron emission tomography with rubidium-82 was used to study regional myocardial perfusion during transient ST-segment depression with and without pain in patients with angina and coronary disease. All episodes of painless ST-segment depression and 97 percent of episodes with angina were accompanied by tomographic evidence of ischemia. This much broader view of ischemic heart disease, revealed by studies performed out of the hospital during patients' ordinary daily activities, has important implications for the objective assessment of symptoms, the relief of ischemia, and the prevention of myocardial damage.