What is a stress test?
There's nothing like a good workout to find out how fit you really are. You may feel like a champion in your armchair fantasies, but playing a set of tennis can tell a different story. Likewise, you don't know how well your heart is working until you put it to the test. Almost everybody's heart beats in the same monotonous rhythm when they're resting. But during exercise, sick hearts and healthy hearts act very differently.
If you're at risk for heart trouble, your doctor may want to check your heart by monitoring it while you exercise. This type of exam is called a stress test or an exercise tolerance test. Your doctor will have you walk on a treadmill or ride an exercise bike for about 10 to 20 minutes. The workout will start at a slow pace and gradually grow more intense. By the end of it, you'll feel like you're walking or riding a bike up a small hill. During the test, electrodes on your chest that are hooked up to an electrocardiograph (ECG or EKG) machine will measure the flow of electricity in your heart. You'll also have a blood pressure cuff on your arm.
Often, a stress test is done in conjunction with other diagnostic tests, such as an echocardiogram, which uses sound waves to create a moving picture of the heart, or a nuclear stress test, which uses a harmless, radioactive substance called thallium to show how well blood flows to the heart.
What can a stress test tell about my heart?
First and foremost, a stress test can measure how much strain your heart can take. If the arteries to your heart are clogged with fatty plaque -- a condition called coronary heart disease -- your heart will struggle to keep up during your workout. Your blood pressure may drop, and your ECG will probably show irregular patterns. You may also feel extremely tired and short of breath.
While the stress test correctly identifies roughly 75 percent of all people with coronary heart disease, people in the early stages usually sail through the exam without a hint of trouble. In general, the test works if the arteries are already more than halfway clogged. So if the stress test shows that your arteries are blocked, watch out: Unless you and your doctor take action, it's likely that a heart attack is on the way.
Newer research has demonstrated that stress tests can also aid doctors in determining the likelihood of coronary heart disease even for those without signs of it. In 2005, doctors from Johns Hopkins reported in a study, published in the journal Circulation, that 90 percent of those who died from coronary heart disease and had no early signs of the illness, scored below average 10 to 20 years earlier on stress tests. The research teams analysis showed that study participants who scored below average were two to four times more likely to die from coronary heart disease. More than 6,000 men and women participated in the study from 1972 to 1995.
Doctors may also prescribe light exercise tests if someone has already had a heart attack or has been diagnosed with heart disease. The exercise is often done in a supervised medical setting, and the results can help doctors devise a safe exercise program. The test may also be used to tell whether a patient is responding to treatment, or how well a pacemaker is working.
Who needs a stress test?
If you've already had a heart attack, a stress test can be important to your recovery strategy. Ideally, however, most people would have a stress test BEFORE they ever had a heart attack. With this in mind, the American College of Cardiology recommends the test for the following groups:
- Men over 45 and women over 55, and people with diabetes, who are about to start vigorous exercise programs, especially if they've been inactive.
- Men over 45 and women over 55 who are involved in occupations in which impairment might impact public safety, or who are at increased risk of coronary artery disease due to other diseases (e.g. chronic renal failure).
- People with several risk factors for heart disease, including smoking, obesity, high blood pressure, diabetes, high cholesterol levels, advanced age, male gender, and a family history of heart trouble.
- Anyone who has symptoms of coronary artery disease, especially chest pain (angina pectoris).
Is the stress test safe?
The procedure is quite safe. Your doctor will watch you very closely during the test. If you get extremely tired or show any other signs of coronary artery disease, the physician will stop the exam immediately. As a further safeguard, a person trained in cardiac life support will be in the room at all times. It's not entirely risk-free, however: About one patient in every 2,500 has a heart attack during the test. But with the proper screening beforehand, there should be little chance of a problem.
Who shouldn't take a stress test?
Some people aren't healthy enough to withstand a stress test. You shouldn't take the test -- or engage in any other vigorous exercise -- if you have recently had a heart attack or if you have high-risk unstable angina; uncontrolled symptomatic heart failure; severe hypertension (systolic pressure over 200 or diastolic pressure over 110); inflammation of the heart (pericarditis, endocarditis, or myocarditis); acute aortic dissection; uncontrolled arrhythmia (unusual rhythms in the heartbeat); or blood clots in the lungs or deep veins. You may also be unable to take the test if you have severe physical disabilities or if you're extremely heavy. (The equipment usually can't support more than 350 pounds.)
Some cases call for extra caution. Patients with advanced diabetes, Parkinson's disease, mitral valve prolapse, frequent arrhythmia, thyroid problems, or certain other illnesses may have trouble enduring the test. If you have one of these conditions, your physician will give you a thorough checkup before ordering the test.
In addition, many medications can make the stress test hard to interpret. If you're taking digoxin, anti-arrythmia drugs (such as quinidine or procainamide), blood pressure medications, or tricyclic antidepressants, the test may be less accurate than usual.
Alternative methods to assess your heart are available if for some reason the treadmill test can't be done. If a stress test isn't right for you, your doctor may suggest cardiac catheterization, which uses a special dye and x-rays to show the inside of your arteries. Another test, a computed tomography (CT) scan, uses electron beams to find calcium deposits in heart arteries, which may be an indication of heart disease.
Darrow, M.D. Ordering and understanding the exercise stress test. American Family Physician. January 15, 1999.
Driggers, DA and Marchant D. Maximizing the exercise stress test. Postgraduate Medicine. May 1, 1999.
ACC/AHA guidelines for exercise testing. Journal of the American College of Cardiology. July, 1997. http://www.acc.org/clinical/guidelines/exercise/jac5074fla51.htm#who
ACC/AHA 2002 guideline update for exercise testing. Circulation 2002; 106:1883-1892.
Johns Hopkins University. Exercise Stress Testing Helps Identify Coronary Heart Disease Risk. September 2005. http://www.jhu.edu/~gazette/2005/26sep05/26stress.html
National Heart, Lung, and Blood Institute. How Is Coronary Artery Disease Diagnosed? http://www.nhlbi.nih.gov/health/dci/Diseases/Cad/CAD_Diagnosis.html
American Heart Association. Thallium Stress Test. http://www.americanheart.org/presenter.jhtml?identifier=4743