Of the more than 5 million persons who present to emergency departments each year with chest discomfort suggesting myocardial ischemia, 75 percent or more have no objective evidence of an unstable coronary syndrome. Evaluation of these “low-risk” patients with hospitalization is very expensive, necessitating the development of rapid “rule-out” protocols in short-stay observation areas to reduce costs. Lindsay and associates point to the need for an effective and accurate protocol in these short-stay situations and examine some of the data that support a protocol calling for routine stress testing.
Virtually all triage protocols include a period of observation for recurrent ischemic pain and electrocardiographic (ECG) changes, as well as testing for serum markers of myocardial necrosis. Some protocols include routine stress testing if there is no evidence confirming active ischemia during the observation period.
The stress test most often used, exercise ECG, has important disadvantages as a screening test in acute ischemia triage situations. First, many patients cannot exercise adequately for reasons other than heart disease. Second, exercise ECG results can be misleading when the resting ECG is abnormal. Patients with left ventricular hypertrophy, left bundle branch block or resting ST-T wave segment abnormalities cannot be accurately evaluated. The false-positive rate in a low-risk population such as those with negative findings after initial screening for unstable coronary disease is unacceptably high.
Echocardiography, stress echocardiography and myocardial scintigraphy have all been advocated as ways to recognize patients with unstable coronary artery disease. These studies provide higher sensitivity and specificity than exercise ECG and can be used in more diverse patients. Although these procedures are more accurate and improve the triage procedure, they increase the cost of chest screening tremendously.
The authors concur with the view of the National Heart Attack Alert Coordinating Committee's Working Group on Evaluation of Technologies for Identifying Acute Cardiac Ischemia in the Emergency Department, which found that data supporting the routine use of stress testing to be limited and inconclusive. Newer biochemical assays including troponin levels combined with clinical markers such as age, history of prior coronary artery disease and the presence of cardiac risk factors such as diabetes may be the most effective way to triage patients with chest pain.