Used to evaluate heart function, a stress test requires that a patient exercise on a treadmill or exercise bicycle so that the heart rate, breathing, blood pressure, and feeling of well being are monitored.
When the body is active, it requires more oxygen than when it is at rest, sothe heart has to pump more blood. Because of the increased stress on the heart, exercise can reveal coronary problems that aren't obvious when the body isat rest. This is why the stress test (although not perfect) is the best noninvasive "first step" in assessing the health of the heart.
The stress test helps doctors determine how well the heart handles the stressimposed by exercise. It's especially helpful in detecting coronary artery disease, 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 causinga heart attack. For this reason, a doctor needs to stand by during the exercise stress test with emergency equipment on standby.
The patient must be aware of the symptoms of a heart attack and stop the testif any of the following symptoms appear:
- An unsteady gait
- Gray or cold, clammy skin
- Dizziness or fainting
- A drop in blood pressure
- Chest pain (angina)
- Irregular heart beat (cardiac arrhythmias).
Electrodes are attached to specific areas of the patient's chest with specialadhesive patches and gel that conduct electrical impulses. Typically, electrodes are placed under each collarbone and each bottom rib, and six electrodesare placed across the chest in a rough outline of the heart. Then the technician attaches wires from the electrodes to a machine that records the heart'selectrical activity picked up by the electrodes.
The heart is first tested 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 tests performed while the patient is exercising. The patient's blood pressure is 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. If the patient is on an exercise bicycle, the resistance or "drag" is gradually increased. The patient continues exercising at higher intensities until he or she experiences severe fatigue, dizziness, chestpain, or until reaching target heart rate. (Target heart rate is usually 85%of the estimated top heart rate based on the patient's age). During this time, the patient's heart is continually monitored.
In some cases, other tests are also used together 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.
Patients are usually instructed not to eat or smoke for several hours beforethe 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 1in 100,000).
A normal result of an exercise stress test shows normal heart rate, blood pressure and no angina, unusual dizziness, or shortness of breath.
A number of abnormalities may show up on an exercise stress test, indicatingthat not enough oxygen-rich blood is getting to the heart muscle, or that there are abnormal heart rhythms or structural problems, 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 furtherevaluation and therapy.