What Is Stress Testing?
Stress testing provides information about how your heart works during physical stress. Some heart problems are easier to diagnose when your heart is working hard and beating fast.
During stress testing, you exercise (walk or run on a treadmill or pedal a stationary bike) to make your heart work hard and beat fast. Tests are done on your heart while you exercise.
You might have arthritis or another medical problem that prevents you from exercising during a stress test. If so, your doctor may give you medicine to make your heart work hard, as it would during exercise. This is called a pharmacological (FAR-ma-ko-LOJ-ih-kal) stress test.
Doctors usually use stress testing to help diagnose coronary heart disease (CHD). They also use stress testing to find out the severity of CHD.
CHD is a disease in which a waxy substance called plaque (plak) builds up in the coronary arteries. These arteries supply oxygen-rich blood to your heart.
Plaque narrows the arteries and reduces blood flow to your heart muscle. The buildup of plaque also makes it more likely that blood clots will form in your arteries. Blood clots can mostly or completely block blood flow through an artery. This can lead to chest pain called angina (an-JI-nuh or AN-juh-nuh) or a heart attack.
You may not have any signs or symptoms of CHD when your heart is at rest. But when your heart has to work harder during exercise, it needs more blood and oxygen. Narrow arteries can't supply enough blood for your heart to work well. As a result, signs and symptoms of CHD may occur only during exercise.
A stress test can detect the following problems, which may suggest that your heart isn't getting enough blood during exercise:
- Abnormal changes in your heart rate or blood pressure
- Symptoms such as shortness of breath or chest pain, especially if they occur at low levels of exercise
- Abnormal changes in your heart's rhythm or electrical activity
During a stress test, if you can't exercise for as long as what is considered normal for someone your age, it may be a sign that not enough blood is flowing to your heart. However, other factors besides CHD can prevent you from exercising long enough (for example, lung disease, anemia, or poor general fitness).
Types of Stress Testing
The two main types of stress testing are a standard exercise stress test and an imaging stress test.
Standard Exercise Stress Test
A standard exercise stress test uses an EKG (electrocardiogram) to detect and record the heart's electrical activity.
An EKG shows how fast your heart is beating and the heart's rhythm (steady or irregular). It also records the strength and timing of electrical signals as they pass through your heart.
During a standard stress test, your blood pressure will be checked. You also may be asked to breathe into a special tube during the test. This allows your doctor to see how well you're breathing and measure the gases that you breathe out.
A standard stress test shows changes in your heart's electrical activity. It also can show whether your heart is getting enough blood during exercise.
Imaging Stress Test
As part of some stress tests, pictures are taken of your heart while you exercise and while you’re at rest. These imaging stress tests can show how well blood is flowing in your heart and how well your heart pumps blood when it beats.
One type of imaging stress test involves echocardiography (echo). This test uses sound waves to create a moving picture of your heart. An exercise stress echo can show how well your heart's chambers and valves are working when your heart is under stress.
A stress echo also can show areas of poor blood flow to your heart, dead heart muscle tissue, and areas of the heart muscle wall that aren't contracting well. These areas may have been damaged during a heart attack, or they may not be getting enough blood.
Other imaging stress tests use radioactive dye to create pictures of blood flow to your heart. The dye is injected into your bloodstream before the pictures are taken. The pictures show how much of the dye has reached various parts of your heart during exercise and while you're at rest.
Tests that use 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 considered safe for you and those around you. However, if you're pregnant, you shouldn't have this test because of risks it might pose to your unborn child.
Imaging stress tests tend to detect CHD better than standard (nonimaging) stress tests. Imaging stress tests also can predict the risk of a future heart attack or premature death.
An imaging stress test might be done first (as opposed to a standard exercise stress test) if you:
- Can't exercise for enough time to get your heart working at its hardest. (Medical problems, such as arthritis or leg arteries clogged by plaque, might prevent you from exercising long enough.)
- Have abnormal heartbeats or other problems that prevent a standard exercise stress test from giving correct results.
- Had a heart procedure in the past, such as coronary artery bypass grafting or percutaneous coronary intervention, also known as coronary angioplasty, and stent placement.
- Exercise echocardiogram or exercise stress echo
- Exercise test
- Myocardial perfusion imaging
- Nuclear stress test
- PET stress test
- Pharmacological stress test
- Sestamibi stress test
- Stress EKG or ECG
- Treadmill test
Who Needs Stress Testing?
You may need stress testing if you've had chest pains, shortness of breath, or other symptoms of limited blood flow to your heart.
Imaging stress tests, especially, can show whether you have coronary heart disease (CHD) or a heart valve problem. (Heart valves are like doors; they open and shut to let blood flow between the heart's chambers and into the heart's arteries. So, like CHD, faulty heart valves can limit the amount of blood reaching your heart.)
If you've been diagnosed with CHD or recently had a heart attack, a stress test can show whether you can handle an exercise program. If you've had percutaneous coronary intervention, also known as coronary angioplasty, (with or without stent placement) or coronary artery bypass grafting, a stress test can show how well the treatment relieves your CHD symptoms.
You also may need a stress test if, during exercise, you feel faint, have a rapid heartbeat or a fluttering feeling in your chest, or have other symptoms of an arrhythmia (an irregular heartbeat).
If you don't have chest pain when you exercise but still get short of breath, your doctor may recommend a stress test. The test can help show whether a heart problem, rather than a lung problem or being out of shape, is causing your breathing problems.
For such testing, you breathe into a special tube. This allows a technician to measure the gases you breathe out. Breathing into the tube during stress testing also is done before a heart transplant to help assess whether you're a candidate for the surgery.
Stress testing shouldn’t be used as a routine screening test for CHD. Usually, you have to have symptoms of CHD before a doctor will recommend stress testing.
However, your doctor may want to use a stress test to screen for CHD if you have diabetes. This disease increases your risk of CHD. Currently, though, no evidence shows that having a stress test will improve your outcome if you have diabetes.
What To Expect Before Stress Testing
Stress testing is done in a doctor’s office or at a medical center or hospital. You should wear shoes and clothes in which you can exercise comfortably. Sometimes you’re given a gown to wear during the test.
Your doctor might ask you to fast (not 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 the 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 prescription medicines also may interfere with some stress tests. Ask your doctor whether you need to avoid certain drinks or food or change how you take your medicine before the test.
If you use an inhaler for asthma or other breathing problems, bring it to the test. Make sure you let the doctor know that you use it.
What To Expect During Stress Testing
During all types of stress testing, a doctor, nurse, or technician will always be with you to closely check your health status.
Before you start the "stress" part of a stress test, the nurse will put sticky patches called electrodes on the skin of your chest, arms, and legs. To help an electrode stick to the skin, the nurse may have to shave a patch of hair where the electrode will be attached.
The electrodes will be connected to an EKG (electrocardiogram) machine. This machine records your heart's electrical activity. It shows how fast your heart is beating and the heart's rhythm (steady or irregular). An EKG also records the strength and timing of electrical signals as they pass through your heart.
The nurse will put a blood pressure cuff on your arm to check your blood pressure during the stress test. (The cuff will feel tight on your arm when it expands every few minutes.) Also, you might have to breathe into a special tube so the gases you breathe out can be measured.
Next, you'll exercise on a treadmill or stationary bike. If such exercise poses a problem for you, you might turn a crank with your arms instead. During the test, the exercise level will get harder. You can stop whenever you feel the exercise is too much for you.
If you can't exercise, medicine might be injected into a vein in your arm or hand. The medicine will increase blood flow through your coronary arteries and make your heart beat fast, as it would during exercise. You can then have the stress test.
The medicine may make you flushed and anxious, but the effects go away as soon as the test is over. The medicine also may give you a headache.
While you're exercising or getting medicine to make your heart work harder, the nurse will ask you how you're feeling. You should tell him or her if you feel chest pain, short of breath, or dizzy.
The exercise or medicine infusion will continue until you reach a target heart rate, or until you:
- Feel moderate to severe chest pain
- Get too out of breath to continue
- Develop abnormally high or low blood pressure or an arrhythmia (an irregular heartbeat)
- Become dizzy
The nurse will continue to check your heart functions and blood pressure after the test until they return to normal levels.
The "stress" part of a stress test (when your heart is working hard) usually lasts about 15 minutes or less.
However, there's prep time before the test and monitoring time afterward. Both extend the total test time to about an hour for a standard stress test, and up to 3 hours or more for some imaging stress tests.
Exercise Stress Echocardiogram Test
For an exercise stress echocardiogram (echo) test, the nurse will take pictures of your heart using echocardiography before you exercise and as soon as you finish.
A sonographer (a person who specializes in using ultrasound techniques) will apply gel to your chest. Then, he or she will briefly put a transducer (a wand-like device) against your chest and move it around.
The transducer sends and receives high-pitched sounds that you probably won’t hear. The echoes from the sound waves are converted into moving pictures of your heart on a screen.
You might be asked to lie on your side on an exam table for this test. Some stress echo tests also use dye to improve imaging. The dye is injected into your bloodstream while the test occurs.
Sestamibi or Other Imaging Stress Tests Involving Radioactive Dye
For a sestamibi stress test or other imaging stress test that uses radioactive dye, the nurse will inject a small amount of dye into your bloodstream. This is done through a needle placed in a vein in your arm or hand.
You’ll get the dye about a half-hour before you start exercising or take medicine to make your heart work hard. The amount of radiation in the dye is considered safe for you and those around you. However, if you're pregnant, you shouldn't have this test because of risks it might pose to your unborn child.
Pictures will be taken of your heart at least two times: when it's at rest and when it's working its hardest. You'll lie down on a table, and a special camera or scanner that can detect the dye in your bloodstream will take pictures of your heart.
Some pictures may not be taken until you lie quietly for a few hours after the stress test. Some patients may even be asked to return in a day or so for more pictures.
What To Expect After Stress Testing
After stress testing, you'll be able to return to your normal activities. If you had a test that involved radioactive dye, your doctor may ask you to drink plenty of fluids to flush it out of your body. You shouldn't have certain other imaging tests until the dye is no longer in your body. Your doctor can advise you further.
What Does Stress Testing Show?
Stress testing shows how your heart works during physical stress (exercise) and how healthy your heart is.
A standard exercise stress test uses an EKG (electrocardiogram) to monitor changes in your heart's electrical activity. Imaging stress tests take pictures of blood flow throughout your heart. They also show your heart valves and the movement of your heart muscle.
Doctors use both types of stress tests to look for signs that your heart isn't getting enough blood flow during exercise. Abnormal test results may be due to coronary heart disease (CHD) or other factors, such as poor physical fitness.
If you have a standard exercise stress test and the results are normal, you may not need further testing or treatment. But if your test results are abnormal, or if you're physically unable to exercise, your doctor may want you to have an imaging stress test or other tests.
Even if your standard exercise stress test results are normal, your doctor may want you to have an imaging stress test if you continue having symptoms (such as shortness of breath or chest pain).
Imaging stress tests are more accurate than standard exercise stress tests, but they're much more expensive.
Imaging stress tests show how well blood is flowing in the heart muscle and reveal parts of the heart that aren't contracting strongly. They also can show the parts of the heart that aren't getting enough blood, as well as dead tissue in the heart, where no blood flows. (A heart attack can cause heart tissue to die.)
If your imaging stress test suggests significant CHD, your doctor may want you to have more testing and treatment.
What Are the Risks of Stress Testing?
Stress tests pose little risk of serious harm. The chance of these tests causing a heart attack or death is about 1 in 5,000. More common, but less serious side effects linked to stress testing include:
- An arrhythmia (irregular heartbeat). Often, an arrhythmia will go away quickly once you're at rest. But if it persists, you may need monitoring or treatment in a hospital.
- Low blood pressure, which can cause you to feel dizzy or faint. This problem may go away once your heart stops working hard; it usually doesn't require treatment.
- Jitteriness or discomfort while getting medicine to make your heart work hard and beat fast (you may be given medicine if you can’t exercise). These side effects usually go away shortly after you stop getting the medicine. Sometimes the symptoms may last a few hours.
Also, some of the medicines used for pharmacological stress tests can cause wheezing, shortness of breath, and other asthma-like symptoms. Sometimes these symptoms are severe and require treatment.
The National Heart, Lung, and Blood Institute (NHLBI) leads or sponsors many studies aimed at preventing, diagnosing, and treating heart, lung, blood, and sleep disorders.