Stress Testing Using Imaging
Some stress tests take pictures of the heart when you exercise and when you’re at rest. These imaging stress tests can show how well blood is flowing in the different parts of your heart and/or how well your heart squeezes out blood when it beats
One type of imaging stress test involves echocardiography, which is a test that uses sound waves to create a moving picture of your heart. An echocardiogram stress test can show how well your heart’s chambers and valves are working when your heart is under stress. The test can identify areas of poor blood flow to your heart, dead heart muscle tissue, and areas of the heart muscle wall that aren’t contracting normally. These areas may have been damaged during a heart attack or may be getting too little blood.
Other imaging stress tests use a radioactive dye to create images of the blood flow to your heart. The dye is injected into your bloodstream before pictures are taken of your heart. The pictures show how much of the dye has reached various parts of your heart during exercise and at rest.
Tests that use a radioactive dye include a thallium or sestamibi stress test and a positron emission tomography (PET) stress test. The amount of radiation in the dye is safe and not a danger to you or those around you. However, if you’re pregnant, you shouldn’t have this test because of risks it might pose to your unborn child.
Some doctors may use magnetic resonance imaging (MRI) to take pictures of the heart when it’s working hard. This test doesn’t use a radioactive dye or sound waves. Instead, it uses radio waves and magnetic fields to create images that show blood flow in the heart and whether all parts of the heart wall are contracting strongly.
Imaging stress tests tend to be more accurate at detecting CAD than standard (nonimaging) stress tests. An imaging stress test may be done first if you:
- Can’t exercise for enough time to get your heart working its hardest. (Medical problems, such as arthritis or leg arteries clogged by plaque, may prevent you from exercising enough.)
- Have abnormal heartbeats or other problems that will cause a standard exercise stress test to be inaccurate.
- Are a woman. Standard stress tests are less accurate in women than in men. If you’re a woman and live far from a testing facility, your doctor may want you to skip a standard stress test and get an imaging stress test instead. That way, you don’t have to make a second trip for the imaging stress test if there are any questions about the results from the standard stress test.
What To Expect Before Stress Testing
Standard stress testing can often be done in a doctor's office. But imaging stress testing is usually done at a hospital. Be sure to wear athletic or other shoes in which you can exercise comfortably. You may be asked to wear comfortable clothes in which you can easily exercise, or you may be given a gown to wear during the test.
Your doctor may ask you not to eat or drink anything but water for a short time before the test. If you're diabetic, ask your doctor whether you need to adjust your medicines on the day of your test.
For some stress tests, you can't drink coffee or other caffeinated drinks for a day before the test. Certain over-the-counter or prescribed medicines also may interfere with some stress tests. Ask your doctor whether you can take all your medicines as usual and whether you need to avoid certain drinks or foods.
If you use an inhaler for asthma or other breathing problems, bring it to the test and be sure to let the doctor know that you use it.
What To Expect During Stress Testing
During all types of stress testing, a technician will always be with you to closely monitor your health status.
Before you start the “stress” part of a stress test, a technician will put small sticky patches called electrodes on the skin of your chest, arms, and legs. To help an electrode stick to the skin, the technician may have to shave a patch of hair where the electrode will be attached.
The electrodes are connected to a machine that records the electrical activity of your heart. This recording, which is called an EKG (electrocardiogram), shows how fast your heart is beating and the heart’s rhythm (steady or irregular). The machine also records the strength and timing of electrical signals as they pass through each part of your heart.
The technician will put a blood pressure cuff on your arm to monitor your blood pressure during the stress test. (The cuff will feel tight on your arm when it expands every few minutes.) In addition, you may be asked to breathe into a special tube so the gases you breathe out can be monitored.
After these preparations, you will exercise on a treadmill or stationary bicycle. If such exercise poses a problem for you, you may instead turn a crank with your arms. During the test, the exercise level will get harder. But you can stop whenever you feel the exercise is too much for you.