STRESS TESTS |
It is quite common for people to have heart disease but normal results on heart tests performed under resting, relaxed conditions. However, these tests can become abnormal when the heart is made to work harder. This is the basis for stress tests.
The most common way to stress a person's heart is to have them perform exercise. Walking on a treadmill is most commonly used but a variety of stationary bicycles can also be used. Finally, for patients who are unable to exercise, intravenous medicines can be given in place of exercise to make the heart work as hard as if the person was running.
All stress tests are performed with continuous monitoring of the electrocardiogram (ECG). As the heart works harder, certain characteristic abnormalities can develop in the ECG in patients who harbor underlying heart disease.
The exercise or medication infusion is performed under the supervision of a physician.
The exercise or medication infusion is stopped immediately if:
An abnormality of the heart is detected.
The desired peak level of stress was reached.
The patient is unable to continue due to the development of any type of symptom.
The patient asks to have the test stopped.
Sometimes, pictures are taken of the heart in addition to the ECG. These can be echocardiograms or nuclear images. Echo pictures are taken just before the stress (exercise or medicine) begins and again at the peak stress level. This only adds a few minutes to the total duration of the test. The strength of contraction of the heart muscle is compared between the resting and stress echo pictures to determine if an abnormality exists.
Nuclear images are obtained by injecting a mildly radioactive substance (thallium or sestamibi (Cardiolyte or Myoview)) that has no known side effects into a vein in the arm. The blood stream carries these substances to the heart muscle in proportion to the amount of blood flow to the heart muscle. These substances emit gamma rays which are detected by a camera that constructs a picture of the heart. The injection is given and pictures taken under resting conditions and again following the stress. The pictures show the amount of blood flow to each region of the heart muscle as well as the strength of contraction of the heart muscle. As with the stress echo, the rest images are compared to the stress images to determine if a heart problem exists. The patient must lie under a camera for about 20 to 45 minutes for each picture to be acquired. Thus, this takes much longer than the other types of stress tests. For more info, please visit nuclear medicine web sites.
The only preparation for a stress test is that you must not eat or drink for the six hours preceding the test. If it is an exercise test, make sure you wear loose fitting comfortable clothes and good running shoes. High heels don't work on a treadmill! Your physician may want you to skip some of your usual medications on the day of the test. Be sure to check with your physician about this.
Why are stress tests done? Here are some of the most common reasons:
To see if an asymptomatic person has silent coronary artery disease, i.e. blockages or hardening of the arteries of the heart. (In many patients, the first manifestation of heart disease is a heart attack or death without any preceding warning symptoms.)
To determine if a person's symptoms (such as chest discomfort or difficulty breathing) are due to heart disease rather than another problem.
To check that the treatment given a patient for blocked arteries is working properly.
To assess a person's exercise tolerance before beginning an exercise or cardiac rehabilitation program.
To determine if exercise causes an abnormal heart rhythm.
Stress tests are not perfect. Sometimes they come out abnormal when the heart is really okay and sometimes they come out normal when there really is a problem with the heart. Taking echo or nuclear pictures with the stress test makes it more accurate but still not 100%. Whether further testing for blocked arteries beyond a stress test is required depends on each patient's particular circumstances.
GO BACK TO LEARN ABOUT OTHER HEART TESTS
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