by Elizabeth Heubeck, MA
Anatomy and Physiology
The heart is a muscular pump weighing between 10 and 12 ounces and consisting of four chambers. The left chambers pump oxygen-rich blood throughout the body, while the right chambers pump blood that lacks oxygen to the lungs for replenishment.
During exercise, your muscles require additional oxygen-rich blood. Your heart supplies this extra blood by contracting more frequently and more forcefully. This increases your cardiac output, which is the volume of blood your heart pumps out to the rest of your body per minute.
Like other muscles in the body, your heart also requires a steady supply of oxygen-rich blood, which it receives through the coronary arteries.
Reasons for Procedure
If the blood supply to the heart muscle is compromised, it may not receive enough oxygen to meet its demand during exercise. Coronary heart disease, also referred to as CHD, is the most common reason for an imbalance between oxygen supply and demand. In CHD, cholesterol plaques block the flow of oxygen-rich blood through one or more coronary arteries.
Insufficient oxygen reaching the heart muscle results in a condition called myocardial ischemia. By measuring the heart's electrical activity during physical activity, an exercise tolerance test helps determine if myocardial ischemia is present.
Your doctor may recommend an exercise tolerance test to: screen for CHD if you are at high risk but have no symptoms, evaluate chest pain, which is often produced by myocardial ischemia, identify an irregular heart rhythm occurring during activity, monitor your heart's response to cardiac treatment, develop a safe exercise regimen, plan a rehabilitation program if you have had a heart attack.
The exercise tolerance test is useful because the electrical activity of the heart is often quite sensitive to myocardial ischemia. An electrocardiogram, or EKG, can detect this electrical activity on the surface of the body. Certain changes in the electrical pattern of the EKG during exercise could indicate insufficient supply of oxygen to the heart muscle at times of high demand.
Your doctor may recommend another test closely related to the exercise tolerance test called a myocardial perfusion scan. In this test, which is described later, a special radioactive substance is used to help determine which parts of the heart muscle are receiving blood.
In addition, your physician may recommend these other studies to evaluate the blood supply to your heart muscle: a resting electrocardiogram, testing with certain drugs that put strain on the heart's supply and demand; stress echocardiography, which uses high pitched sound waves to create images of the beating heart during exercise; coronary angiography, which uses x-rays and a special dye to look for atherosclerotic plaques in the coronary arteries; testing your blood to see if the heart muscle has recently been damaged.
Before your exercise tolerance test, your physician will perform a physical exam and a resting EKG. He or she will also review your medical history and any medications you are taking.
To prepare for your exercise tolerance test: avoid caffeinated beverages or foods for 12-24 hours prior to the test, avoid consuming anything other than water for four hours before the test, avoid smoking for several hours before the test, wear comfortable clothing and walking shoes, bring a list of any medications, herbs, or dietary supplements that you are taking.
Immediately before the test begins, a technician will: check your blood pressure; attach small adhesive patches called electrocardiogram electrodes to your chest and arms. These electrodes contain wires that connect to an EKG machine. Perform an EKG test to record your heart's electrical activity while at rest. Throughout the procedure, the technician will closely monitor your blood pressure, heart rate, EKG, and symptoms. Monitoring will continue after the test until levels return to baseline.
During the test, which takes place on a treadmill or stationary bike, you will be asked to: Begin walking or riding slowly. Gradually exercise more strenuously as the technician increases the speed and elevation, or resistance, of the machine every 2-3 minutes. Continue exercising until you are exhausted, or have reached your target heart rate.
During the test, you will be asked to report any of the following symptoms: chest pain, dizziness or lightheadedness, pounding in your chest, extreme shortness of breath, other bothersome symptoms.
If your doctor recommends a myocardial perfusion scan, a technician will inject a small amount of radioactive material into your vein while your heart is working as hard as it can during your exercise tolerance test.
You will then be asked to lie under a special camera while a technician takes pictures of your heart from different positions. About an hour later, after you have rested, the technician will take a second set of pictures.
Risks and Benefits
Possible complications of exercise tolerance testing include: chest pain, shortness of breath, dizziness, or lightheadedness, abnormal heart rhythm, and/or heart attack.
Benefits of exercise tolerance testing include: early detection of heart disease, guidance in planning treatment for heart disease, monitoring the effectiveness of treatment, and/or assessing the risk of future cardiac events.
In an exercise stress test, or any procedure, you and your doctor must carefully weigh the risks and benefits to determine whether it's the most appropriate procedure for you.
After the Procedure
After the test is complete, you will be able to go home and resume normal activity, unless you experience any complications or worrisome symptoms. Once your doctor receives the test results, he or she will discuss with you the need to further testing or treatment.
Once home, call your doctor if any of the following symptoms occur: chest pain, pounding in the chest, dizziness or lightheadedness, excessive fatigue or shortness of breath.
- American College of Cardiology Foundation, American Heart Association. ACC/AHA guideline update for exercise testing. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Exercise Testing). American College of Cardiology Foundation. Available at: http://www.guideline.gov/summary/summary.aspx?ss=15&doc_id=3427&nbr=2653#s26. Accessed June 22, 2004.
- Fowler-Brown A, Pignone M, Pletcher M, Tice JA, Sutton SF, Lohr KN. Exercise Tolerance Testing to Screen for Coronary Heart Disease: A Summary of the Evidence for the U.S. Preventive Services Task Force. February 2004.
- Agency for Healthcare Research and Quality, Rockville, MD. Available at: http://www.ahrq.gov/clinic/3rduspstf/chd/chdsum1.htm. Accessed June 22, 2004.
- Ordering and Understanding the Exercise Stress Test. American Family Physician website. Available at: http://www.aafp.org/afp/990115ap/401.html. Accessed June 21, 2004.
- The Normal Heart and How it Works. American Heart Association website. Available at: http://www.americanheart.org/presenter.jhtml?identifier=770. Accessed June 21, 2004.
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