- A depressed or horizontal ST wave suggests some blockage and the presence of a heart disease, even if there is no angina present. (This wave pattern, however, is not very accurate, particularly in women, and can occur without heart problems).
- ST elevations and Q waves are the most important wave patterns in diagnosing and determining treatment for a heart attack. They suggest that an artery to the heart is blocked, and that the full thickness of the heart muscle is damaged. ST segment elevations, however, do not always mean the patient has a heart attack. Other factors are important in making a diagnosis.
Exercise Stress Test
Exercise stress test for evaluation of coronary artery disease may be performed in the following situations:
- Patients with possible or probable angina to help determine the likelihood of coronary artery disease being present
- Patients who were previously stable who began having symptoms
- Follow-up of patients with known heart disease or after coronary bypass surgery or percutaneous procedure
- To determine a patient's functional capacity (how well the heart can respond when extra demand is needed)
- Patients with certain types of heart rhythm disturbances
- After a heart attack, either before leaving the hospital or soon afterwards
Basic Procedure. A stress test (exercise tolerance test) monitors the patient's heart rhythms, blood pressure, and clinical status. It can tell how well the heart handles work and if parts of the heart have decreased blood supply. A typical stress test involves:
- The patient walks on a treadmill or rides a stationary bicycle. Exercise continues until the heart is beating at least 85% of its maximum rate, until symptoms of heart trouble occur (changes in blood pressure, heart rhythm abnormalities, angina, and fatigue), or the patient simply wants to stop.
- For patients who cannot exercise, the doctor may administer dobutamine or arbutamine, which are drugs that simulate the stress of exercise.
An ECG is used to monitor heart rhythms during a stress test. (An echocardiogram or more advanced imaging technique may also be used to visualize the actions of the heart and blood flow.)
Interpreting Results. To accurately assess heart problems, a variety of factors are measured or monitored using the ECG and other tools during exercise. They include:
- Exercise capacity. This is a measure of a person's capacity to reach certain metabolic rates.
- ST waves on the ECG. Doctors specifically look for abnormalities in part of the wave tracing called an ST segment. A certain type of ST segment depression may suggest the presence of heart disease. However, gender, drugs, and other medical conditions can affect the ST segment.
- Heart rate. This is how fast the heart rate goes during exercise and how quickly it returns to normal recovery. Based on age and other factors, everyone's heart rate should go up to a certain level during exercise. If it does not go up to the expected level, the patient is considered at risk for heart problems.
- Changes in systolic blood pressure. Generally, the blood pressure will go up during exercise.
- Oxygen levels may also be measured.
Using these and other measures, doctors can determine risk fairly accurately, particularly for men with chronic stable angina. The test has limitations, however, and some are significant. In patients with suspected unstable angina, normal or low risk results may not be as accurate in predicting future risk of cardiac events.
About 10% of patients, particularly younger people, will have false positive test results. In such cases, test results indicate abnormalities when there are no heart problems. In addition, for many reasons, the test is less accurate in women and an echocardiogram may be a more accurate procedure for them.
Review Date: 05/05/2011
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.