Stress tests are functional tests to determine if the heart is able to get adequate blood and oxygen to meet its needs. They are usually the first test for evaluation of symptoms suggestive of angina.
They are also appropriate as a screening test for sedentary people with multiple cardiac risk factors before they begin an exercise program. Another use is to determine whether a particular treatment (medications, angioplasty, stents, surgery or others) is successfully controlling a person's angina.
The most common stress test is the exercise treadmill test. In the basic exercise test, the patient walks on a treadmill, while blood pressure, heart rate, and the heart's electrical activity are monitored continuously.
The speed and incline of the treadmill are gradually increased until the patient reaches a predetermined exercise level (based primarily on his or her age) or becomes too tired to continue. The test may also be stopped if the patient experiences angina-like symptoms or if typical abnormalities are seen on the ECG.
The test is positive (meaning the heart isn't getting enough oxygen) if such ECG changes occur, especially if angina symptoms also occur. The test is negative (normal) if the person completes the test without generating any ECG abnormalities. If the person doesn't reach the target heart rate, or if the ECG changes are relatively minor, the result may be inconclusive.
If someone's resting ECG is already abnormal, that can make it hard to interpret a standard exercise treadmill test. One alternative in this situation is a thallium (or sestamibi) stress test. The thallium stress test involves injecting a small bit of contrast agent into the patient's veins and then measuring blood flow to the heart at rest, immediately after exercise, and after the patient has recovered from the exercise.
The test is positive if there is an area that appears to get blood flow at rest and in recovery, but not during exercise. Sometimes breast tissue or fat on the chest wall can obscure the view of the heart and make this test inconclusive.
Another option is a stress echocardiogram. This test uses ultrasound to show live images of the heart before and during exercise. If part of the heart is not getting enough oxygen, those muscles won't contract properly.
For people who are physically unable to walk on a treadmill, medications can be given to make the heart speed up and imitate the physical exertion of the basic exercise test. These induced stress tests can be carried out with sestamibi, thallium, or echocardiographic imaging.
With such a wide variety of options, we can perform a stress test on just about anybody. These functional heart tests are the best way to tell if a person may need additional diagnostic testing, medication, or treatment for coronary artery disease.
