TABLE 4711 Likelihood of Significant Coronary Artery Disease in Patients with Symptoms Suggesting Unstable Angina

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Patients at high risk of coronary artery disease, AMI, or death should be admitted to an intensive care unit (ICU). Moderate risk patients should be admitted to a non-ICU monitored setting. Patients at low risk can be treated in a non-ICU monitored setting or can be observed in an ED observation unit. Both ED observation units and non-ICU monitored settings are safe and cost-effective for patients with normal ECGs and other low-risk clinical features. Prior invasive and noninvasive assessments of cardiac function should be taken into account in making disposition decisions. Patients known to have severe coronary artery disease or depressed left ventricular function might be triaged to a more intensive setting than patients with a similar presentation without such dysfunction.

Results of prior cardiac catheterization are very useful for risk stratification. Patients who have previously been documented to have minimal (less than 25 percent) stenosis or normal coronary arteriograms have an excellent long-term prognosis. More than 98 percent of patients with this profile are free from myocardial infarction 10 years later.26 Repeat cardiac catheterizations an average of 9 years later found that approximately 90 percent of patients did not develop even single-vessel coronary artery disease. Thus, a recent (in the past 2 years) cardiac catheterization with normal or minimally diseased vessels almost eliminates the possibility of an acute coronary syndrome, due to atherosclerosis. It would not eliminate the possibility of vasospasm. Without other complicating circumstances, even observation protocols are unnecessary.

Stress tests are less useful because the precise results of such tests may not be available. When patients complete all stages of the emergency protocol, have no ECG changes, and have normal imaging studies, exercise testing can rule out acute ischemic syndromes with sensitivities in the range of 80 to 90 percent. When patients do not meet their target heart rates, exercise testing has poor sensitivity (less than 80 percent) leading to false-negative results. Unless the patient reached the maximal heart rate (220 beats per minute minus the patient's age), had no ECG changes, and had normal imaging (when done), one cannot rely heavily on the results of prior exercise testing in making disposition decisions. However, a negative maximal exercise stress predicts a favorable 1-year survival free of cardiac events.

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