Most commonly, exercise testing is used to aid in the diagnosis of coronary artery disease in patients (1) who have chest pain or (2) who are thought to be at risk for coronary disease because of the presence of risk factors, such as family history or hypertension. In patients known to have cardiopulmonary disease, exercise testing is often used to assess therapeutic interventions (e.g., medications, surgery, angioplasty) and in following symptoms related to the disease. In addition, exercise testing can be helpful in determining a prognosis in patients with recent myocardial infarction, valvular heart disease, or known congestive heart failure.
How reliable is an exercise test for the diagnosis of coronary artery disease?
The reported sensitivity of exercise electrocardiography (ECG) ranges from 55-85%, and the specificity ranges from 70-90%. An exercise test clearly is an imperfect study, and interpretation of the results is best thought of in terms of the predictive value” of an abnormal test result, which depends heavily on factors related to the patient and to the study itself. The following table illustrates some of these factors and describes how they influence the predictive value of a test result.
According to the table, a patient having an abnormal exercise ECG is more likely to have obstructive coronary artery disease if one or more of the ‹“ ‹“better’ ‘ factors are present, and less likely if the ‹“ ‹“worse’ ‘ factors are present. For example, a 45-year-old man with typical angina and 2 mm of horizontal ST-segment depression on exercise ECG has a 95% chance of having obstructed coronary arteries, whereas a 45-year-old asymptomatic woman with the same exercise ECG has only a 10% likelihood of obstructive coronary disease.
What is the Bruce protocol?
The Bruce protocol specifies how the intensity of exercise progresses during the test. Protocols have been developed by many investigators. The one developed by Bruce and coworkers is the most popular, both because it is the most extensively validated and because it can be performed relatively quickly. In the Bruce protocol, each stage lasts 3 minutes. During Stage I, the patient walks at 1.7 mph up a 10% grade. Energy expenditure for the average person is estimated to be 4.8 METS during this stage. Both speed and grade rise with each stage. It is unusual for a patient to complete Stage V (5.0 mph, 18% grade).