What is a Stress Test?
The Exercise Stress Test
Hopping on a bike or treadmill can help your doctor find the source of your symptoms.
By Arthur Agatston, MD
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What is it?
The primary purpose of an exercise stress test is to determine your ability to increase blood flow through your coronary arteries to your heart muscle when your heart is beating faster and/or harder, demanding two to five times the blood flow it gets at rest.
If you have been feeling symptoms such as chest pain or shortness of breath with exertion, an exercise stress test will help your doctor figure out whether these symptoms are coming from sluggish blood flow due to a blockage in one or more of your coronary arteries. The stress test will also indicate how severely the blockage is limiting the blood flow, which is crucial information in deciding whether to recommend an invasive or noninvasive approach to treatment.
Doctors also get other valuable information from a stress test. From watching a patient exercise, we get a good sense of whether the person's symptoms are heart or lung related. For instance, some patients complain of shortness of breath even while they are demonstrating outstanding exercise capacity on the treadmill or bike. And yet they don't appear short of breath to me. These people may have the benign "sighing" type of shortness of breath. Other patients demonstrate limited exercise capacity with extreme shortness of breath, and yet they still insist they are doing fine. These are the patients I look at much more closely.
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Studies from Steven N. Blair, PED, of the Cooper Institute in Dallas, as well as others, have indicated that overall exercise capacity is an excellent predictor of future health and longevity. The blood pressure response to exercise is a helpful sign of the risk of future complications from hypertension, such as heart attack and stroke. The two most common types of exercise stress tests are theplain EKG testand thenuclear (or thallium) test. During both tests, you walk on a treadmill or ride a bike, which increases in elevation and/or speed every few minutes. In the plain EKG stress test, leads are applied to your chest, as they are for the basic EKG, and tracings are similarly produced. We look for changes on the tracings that indicate compromised blood flow to the heart muscle. This test takes about 20 minutes.
In the nuclear exercise stress test, two sets of images are taken. The first is taken after a small amount of a radioactive tracer (such as thallium) is injected when you are at rest. This is not a dye, so allergic reactions are not a problem. The second set is done after the tracer is re-injected when you are at peak exercise on the treadmill or bike. The radioactive substance travels to the heart muscle in proportion to the flow of blood. If there is a blockage in one or more of the coronary arteries supplying blood to the bottom of your heart, this area will accumulate less thallium during exercise than other areas with normal blood flow. The resting and exercise images are then compared and significant blockage will almost always be apparent.
In younger patients in whom I do not suspect heart disease, I use the plain EKG exercise stress test. In older patients, in those with abnormal resting EKGs, and in patients in whom I strongly suspect coronary artery disease, I prefer the nuclear stress test because it gives a better quantification of heart muscle areas with compromised blood flow. For patients who cannot exercise, there is a third type of stress test called apharmaceutical stress test. In this test, a drug is injected to dilate the coronary arteries, which allows increased blood flow unless there is a blockage. Nuclear images are obtained in the same manner described for the nuclear stress test to reflect relative blood flow during rest and during exercise.
A stress test is a good indicator of the state of a patient's coronary blood flow at the time of the test. But its ability to predict the future does have limitations. You can accumulate a lot of plaque in your coronary arteries, and even have blockages, yet still maintain normal blood flow at rest and during exercise. This is because your body may have produced the protective network of collateral blood vessels.
While a stress test is valuable for women as well as men, studies have shown that women have more abnormal stress tests without necessarily having obstructive coronary disease. These women may have a disease of their smaller vessels, which can limit blood flow and cause chest pain but not necessarily cause a heart attack. Having a nuclear stress test rather than a plain EKG stress test helps to reduce the number of false positives for women.
If a patient's initial stress test is fine, I normally do not repeat it unless there is a change in the person's symptoms or risk factors. In high-risk patients, including those with known coronary artery disease, I repeat a stress test on a more regular basis.
Video: What is a Treadmill Stress Test?
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