Used to evaluate heart function, a stress
test requires that a patient exercises on a treadmill or exercise
bicycle while his or her heart rate, breathing, blood pressure, electrocardiogram (ECG), and feeling of well being are monitored.
When the body is active, it requires more oxygen than when it is at rest, and, therefore, the heart has to pump more blood. Because of the increased stress on the heart, exercise can reveal coronary problems that are not apparent when the body is at rest. This is why the stress test, though not perfect, remains the best initial, noninvasive, practical coronary test.
The stress test helps doctors determine how well the heart handles the increased demands imposed by physical activity. It is particularly useful for evaluating possible coronary artery disease
, detecting inadequate supply of oxygen-rich blood to the tissues of the heart muscle (ischemia
), and determining safe levels of exercise in people with existing heart disease.
The exercise stress test carries a very slight risk (1 in 100,000) of causing a heart attack
. For this reason, the exercise stress test should be attended by a health care professional with a defibrillator and other emergency equipment on standby.
The patient must be aware of the symptoms of a heart attack and stop the test if he or she develops any of the following symptoms:
- an unsteady gait
- skin is grayish or cold and clammy
- dizziness or fainting
- a drop in blood pressure
- chest pain (angina)
- irregular heart beat (cardiac arrhythmias)
The technician affixes electrodes to specific areas of the patient's chest, using special adhesive patches with a special gel that conducts electrical impulses. Typically, electrodes are placed under each collarbone and each bottom rib, and six electrodes are placed across the chest in a rough outline of the heart. Then the technician attaches wires from the electrodes to an ECG, which records the electrical activity picked up by the electrodes.
The technician runs resting ECG tests while the patient is lying down, then standing up, and then breathing heavily for half a minute. These tests can later be compared with the ECG tests performed while the patient is exercising. The patient's blood pressure is taken and the blood pressure cuff is left in place, so that blood pressure can be measured periodically throughout the test.
The patient begins riding a stationary bicycle or walking on a treadmill. Gradually the intensity of the exercise is increased. For example, if the patient is walking on a treadmill, the speed of the treadmill increases and the treadmill is tilted upward to simulate an incline. If the patient is on an exercise bicycle, the resistance or "drag" is gradually increased. The patient continues exercising at increasing intensity until he or she reaches his or her target heart rate (generally set at a minimum of 85% of the maximal predicted heart rate based on the patient's age) or experiences severe fatigue
, dizziness, or chest pain. During this time, the patient's heart rate, ECG pattern, and blood pressure are continually monitored.
In some cases, other tests, such as echocardiography
or thallium scanning, are also used in conjunction with the exercise stress test. For instance, recent studies suggest that women have a high rate of false negatives (results showing no problem when one exists) and false positives (results showing a problem when one does not exist) with the stress test. They may benefit from another test, such as exercise echocardiography. People who are unable to exercise may be injected with drugs that mimic the effects of exercise on the heart and given a thallium scan, which can detect the same abnormalities that an exercise test can.
Patients are usually instructed not to eat or smoke for several hours before the test. They should also tell the doctor about any medications they are taking. They should wear comfortable sneakers and exercise clothing.
After the test, the patient should rest until blood pressure and heart rate return to normal. If all goes well, and there are no signs of distress, the patient may return to his or her normal daily activities.
There is a very slight risk of a heart attack from the exercise, as well as cardiac arrhythmia (irregular heart beats), angina, or cardiac arrest (about one in 100,000).
A normal result of an exercise stress test shows normal electrocardiogram tracings and heart rate, blood pressure within the normal range, and no angina, unusual dizziness, or shortness of breath
A number of abnormalities may show up on an exercise stress test. An abnormal electrocardiogram (ECG) may indicate deprivation of oxygen-rich blood to the heart muscle (ST wave segment depression, for example), heart rhythm disturbances, or structural abnormalities of the heart, such as overgrowth of muscle (hypertrophy). If the blood pressure rises too high or the patient experiences distressing symptoms during the test, the heart may be unable to handle the increased workload. Stress test abnormalities usually require further evaluation and therapy.
American Heart Association. 7320 Greenville Ave. Dallas, TX 75231. (214) 373-6300. http://www.americanheart.org.
National Heart, Lung and Blood Institute. P.O. Box 30105, Bethesda, MD 20824-0105. (301) 251-1222. http://www.nhlbi.nih.gov.
— Chest pain from a poor blood supply to the heart muscle due to narrowing of the coronary arteries.
— Two arteries that branch off from the aorta and supply blood to the heart.
— A device that delivers an electric shock to the heart muscle through the chest wall in order to restore a normal heart rate.
— Test results showing a problem when one does not exist.
— Dimished supply of oxygen-rich blood to an organ or area of the body.
any standardized procedure for assessing the effect of stress on cardiac function and myocardial perfusion. Stress may be induced by physical exercise or simulated by administration of a coronary vasodilator. Heart rate, blood pressure, and electrocardiogram are monitored before, during, and after the challenge. Other observations sometimes made are measurement of oxygen consumption, echocardiography, impedance cardiography, appraisal of both myocardial perfusion and cardiac wall motion by radionuclide tracer, and cardiac catheterization.
Although neither as sensitive nor as specific as invasive procedures, exercise stress testing has become a standard means of identifying and grading coronary artery disease in people with typical and atypical angina pectoris as well as in those in certain critical occupations (airline pilots, firefighters). It has been found useful for risk stratification in survivors of myocardial infarction (MI), and in planning and monitoring rehabilitation after MI, coronary bypass surgery, and balloon angioplasty. It is also used to assess the safety of exercise programs for people at risk of coronary artery disease because of age or personal or family history. The Master two-step test, based on repeated ascent and descent of a step-stool, has been superseded by more sophisticated and reproducible methods. Standard exercise testing employs graded physical exertion on an electrically driven treadmill with variable inclination and speed. Alternative methods include a mechanical stair-climbing machine, a stationary bicycle ergometer, and (for those with certain physical disabilities) an arm-exercising (hand-crank) machine. Various protocols and end-points are used to measure the outcome of stress testing. Workloads are measured in metabolic equivalents (MET), 1 MET being the amount of oxygen consumed at bed rest (3.5 mL/kg/min). In maximal (symptom-limited) stress testing, the subject continues to exercise at increasing levels of challenge until chest distress, significant hypertension or hypotension, certain arrhythmias, fatigue, gait problems, or severe dyspnea occurs. The Bruce protocol, a standard maximal exercise treadmill protocol, begins with a treadmill speed of 1.7 mph and a grade of 10°, designed to achieve a workload of 4.6 MET, and increases both speed and grade every 3 minutes. In submaximal (pulse-limited) stress testing, the subject continues exercising until reaching a target heart rate based on age, health history, and physical condition (unless the test must be stopped earlier because of symptoms). A stress test session usually lasts 6-10 minutes. Elevation or depression of ST segments by more than 1 mm during exercise is strongly suggestive of coronary artery disease. Other suggestive changes are T-wave inversion, arrhythmia, a fall in systolic blood pressure, and a marked rise in diastolic blood pressure. Exercise stress-testing protocols achieve 85-90% accuracy in identifying patients without coronary artery disease. About 5% of asymptomatic adults have positive stress test results, but only one third of these have angiographically demonstrable coronary artery disease. False positive test results occur more frequently in women. Large studies have shown that delayed return to resting heart rate, reduced chronotropic index (fraction of cardiac reserve used during exercise), and reduced age-specific functional capacity (in MET) are all potent predictors of cardiovascular mortality, regardless of etiology. Exercise stress testing is contraindicated in acute MI, severe congestive heart failure, severe hypertension, hemodynamically significant valvular disease or arrhythmia, active thromboembolic disease, and extreme obesity. As an alternative to exercise, pharmacologic challenge may be performed by intravenous infusion of dobutamine, an adrenergic agonist that increases heart rate and blood pressure in a fashion similar to physical exertion, or of dipyridamole or adenosine, which dilate normal coronary arteries but do not increase blood flow through vessels narrowed by atherosclerosis. In addition to continuous ECG monitoring, the cardiac effects of stress or pharmacologic challenge can be assessed by myocardial scintigraphy after intravenous injection of thallium 201; cineangiography after injection of technetium 99m, with or without multiple-gated acquisition bloodpool imaging; or single-photon emission computed tomography.