Exercise stress testing is an invaluable tool for examining the cardiovascular (i.e., the heart and blood vessels) system's response to exercise. It provides important diagnostic and prognostic information that cardiologists and internists use to effectively evaluate and manage patients with heart disease. When performed by trained physicians in appropriately selected patients, exercise stress testing is a safe procedure that poses minimal risks and can provide a wealth of information.
Who Needs a Stress Test?
Although there are many reasons for your doctor to order a stress test, the most common reason is to evaluate the cause of chest pain. Because chest pain can come from areas other than the heart, such as the esophagus or the chest wall, a stress test can be helpful in determining the likelihood of whether or not you have heart disease. Sometimes a physician may ask you to have a stress test in the absence of chest pain if he or she suspects you are at increased risk of having coronary artery disease (also referred to as atherosclerosis or hardening of the arteries). You may be at increased risk if you smoke; have diabetes; high blood pressure or elevated levels of cholesterol; or if one of your parents or siblings had a heart attack at a young age. I have occasionally ordered stress tests for my patients who are asymptomatic, but who have important jobs that could put others at risk if they were to have a heart attack, such as airline pilots, police officers, and firefighters.
If you have coronary artery disease, chances are that you either have had, or will have, a stress test. Stress tests are commonly performed in patients who have already suffered heart attacks. The test allows doctors to assess the patient's risk of having another heart attack in the near future. They are also helpful in determining the effectiveness of medical therapy in preventing chest pain and limiting ischemia (a reduction in blood flow and oxygen to the heart muscle). Stress tests can also aid in the diagnosis and management of arrhythmias, which are abnormal and potentially harmful heart rhythms.
If you happen to be one of those individuals who is planning to begin an exercise routine, but haven't worked out for many years, your physician may advise you to have a stress test before you begin. That way, your doctor can gauge how much exercise you can safely do and provide you with a training program to help you get back in shape.
Details of a Stress Test
Following a brief physical exam, you will be connected to an electrocardiogram (EKG) so that your heart rate and rhythm can be monitored throughout your exercise and recovery (rest period). Although some centers prefer to have patients exercise on a stationary bicycle, most will ask you to walk on a treadmill. The test begins at a slow pace and is designed to make the heart work progressively harder by gradually increasing the speed and the incline of the treadmill. A physician and a nurse or trained assistant will be with you throughout the test. In addition to monitoring your heart rate, they will check your blood pressure and frequently ask you how you feel. You should immediately tell them if you feel chest pain, shortness of breath, or lightheadedness, as these are reasons to stop the test. Of course, you should also tell them if you feel too tired to go on, so they can turn off the treadmill. After you have finished exercising, you will be asked to lie down for several minutes. Once your heart rate returns to its baseline, the test is concluded.
Test Interpretation
In order to interpret the test results, physicians will look at your exercise performance and compare it with that of people your own age. They will observe how your blood pressure and pulse changed with increasing exercise and they will examine the EKG for any changes suggestive of ischemia. Although stress tests are important diagnostic procedures, they cannot definitively determine whether or not a person has coronary artery disease. Rather, what they do is help physicians determine the likelihood of whether or not significant coronary artery disease is present.
To improve its predictive value, stress testing is frequently combined with either echocardiography (stress echo) or nuclear scanning (exercise thallium). By performing an echocardiogram (an ultrasound of the heart) before and immediately following exercise, cardiologists can identify ischemic regions of the heart that may not have been detected by the EKG alone. Exercise thallium testing involves the injection of a small amount of radioactive liquid into a vein before and during exercise. This liquid is then absorbed by the heart muscle except in areas that are ischemic or have been scarred by a heart attack. A special camera is used to image the heart muscle and requires you to lie under it for several minutes before and after you exercise.
Inability to Exercise
Many patients are not able to exercise vigorously enough due to other underlying medical conditions. These conditions may include peripheral vascular disease, arthritis of the knees or hips, severe emphysema, or a previous stroke that impairs their ability to walk. In spite of these limitations, stress testing can still be performed using an infusion of medicine in place of exercise (pharmacologic stress testing). Pharmacologic stress testing involves the intravenous administration of medicines such as adenosine or dipyridamole (Persantine) that cause the arteries of the heart to dilate (get bigger) as they would during exercise. Some patients may feel chest pressure or a headache while these medicines are being administered, which takes several minutes, but these effects go away shortly after the infusion is discontinued. Occasionally, a patient's heart rate may slow down quite dramatically and cause lightheadedness, but this effect is only short-lived. Another intravenous medicine, dobutamine, is frequently used in patients with lung disease who cannot receive adenosine or dipyridamole, as these drugs can cause wheezing and shortness of breath. Dobutamine is a medicine that is similar to adrenaline and simulates exercise by stimulating the heart to beat faster and stronger. This drug is used cautiously because it has the ability to cause a tachycardia (an excessively fast heart rhythm) or an arrhythmia.
Stress Test Safety
Exercise and pharmacologic stress tests are safe procedures, but, like all tests, they carry some risk. An estimated one out of every 1,000 people who complete a stress test will suffer a heart attack, and two out of every 10,000 patients will die as a result of exercise during a stress test. In order to minimize these risks, cardiologists avoid stressing people who have ongoing chest pain, advanced heart failure, or severe valvular heart disease, as these patients may be more likely to suffer a complication. Although we understand that it is highly unlikely that an emergency will occur during a stress test, we always prepare ourselves for this occurrence. We stock the stress lab with emergency medications, a defibrillator, and breathing equipment, just in case a heart attack does occur.
How to Prepare for a Stress Test
Relax. Get a good night's sleep. There are no complicated preparations for the test, but there are a few things you should remember:
- Avoid eating anything the morning of your test.
- It's OK to take your pills with some water, but check with your doctor first to see which of your medicines you should or should not take before the test.
- Do not drink any coffee, tea, or colas, especially if you will be having a pharmacologic stress test, as caffeine may inhibit the effects of the intravenous medications.
- Remember to bring rubber-soled shoes (e.g., jogging shoes or tennis shoes) and wear comfortable, loose-fitting clothes. You may also want to bring a towel to use after you exercise.
- If you experience chest pain, have trouble breathing, or simply don't feel well, please inform your doctor before getting on the treadmill.
A stress test is usually interpreted within a day. To find out your final result, consult with your referring physician.
Conclusion
When performed in appropriately selected individuals, stress testing is a safe, reliable tool that allows your doctor to gauge your risk of having heart disease and provides a measure of your physical fitness. Remember, if you have any questions or concerns surrounding your stress test, please consult your doctor or a healthcare professional.
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