Coronary artery disease is the most common type of heart disease in the United States, with 785,000 people having a first coronary attack each year, according to the Centers of Disease Control and Prevention (CDC). Another 470,000 people who have already had a coronary attack are likely to experience a second one.
One of the ways that doctors diagnose coronary artery disease is through a nuclear stress test, which measures blood flow to the heart while a person is resting or when there is stress on the heart.
What Is It?
A nuclear stress test is one of many stress tests available to cardiologists that allow an image to be created of the heart both at rest and under stress. This allows the doctor to see if the heart is working as efficiently as it should and to see if there are any areas of the heart that are being deprived of blood or oxygen. With this information, the cardiologist can then formulate a treatment plan.
Because nuclear stress testing does involve low level exposure to radiation, doctors will only use this test if other tests are not an option or in the event that a stress electrocardiogram (ECG) was unreadable or unclear.
Like other stress tests, the nuclear stress test involves obtaining two sets of images of the heart muscle, one at rest and one while, or immediately after, exercise. This will give the doctor two images to compare to evaluate how well the heart works under stress.
There are many names that a nuclear stress test can be called including:
- Thallium stress test
- Exercise scintigraphy
- Sestamibi stress test
- MIBI stress test
- Myocardial perfusion scintigraphy
Like other forms of stress testing, nuclear stress testing is used for a few different reasons:
- Diagnose coronary artery disease
- Look at the heart to ensure that it is the right size and shape
- Evaluate the effectiveness of treatment for coronary artery disease
There are some risks associated with nuclear stress testing, but these are rare. Nuclear stress testing is considered very safe. There are also always qualified medical personnel present in the event of a problem so it can be dealt with quickly.
- Allergic reaction to the radioactive dye
- Blood pressure drop
- Abnormal heart rhythms (arrhythmias)
- Heart attack
What Happens During The Test?
Like other stress tests, the patient will be asked to give a complete medical history upon arrival. The doctor will also want to know about things like daily activity levels and what of those activities causes problems such as chest pain or difficulty breathing. This will give the doctor an idea of how much exercise is necessary for the stress test.
Patients will then be hooked up to an ECG with sticky electrodes on their chest. They'll feel a little cold, and some people say that they itch, but they are not uncomfortable. The ECG monitors the heart's rhythms throughout the test, both for a resting baseline reading as well as during exercise.
An intravenous (IV) line will also be started. This is so that the doctor can inject the radioactive dye. The dye is a radioactive substance called thallium or sestamibi and it is specifically used for medical imaging purposes. There will be a period of time after the dye is injected that the patient will be required to lie down and wait while the dye works its way through the circulatory system to the heart, usually between 15 and 45 minutes. A special camera will then take pictures of the heart to look for signs of a problem.
After the baseline scan, it's time to exercise, which is typically done on a treadmill or exercise bike. The exercise period is usually fairly brief (between 10 and 15 minutes). It will be challenging, similar to walking briskly or riding a bicycle uphill.
If someone is not able to exercise for some reason, a medication called dobutamine can be used to mimic the effects of exercise on the heart by speeding up the heart rate. Once the heart has reached its target rate the radioactive dye will then be injected again and the scan of the heart will be performed again.
Vital signs such as heart rate, heart rhythms and blood pressure will be monitored throughout the test.
Preparing For The Test
Before the test, the patient should:
- Avoid caffeine for 24 hours, including coffee, tea, sodas (even those labeled caffeine free), chocolate, pain relievers that contain caffeine as well as any weight loss aids that contain caffeine.
- Don’t eat or drink after midnight, except for a few sips of water to take medications.
- Wear comfortable clothing and athletic shoes with non-skid soles.
Generally, patients are not advised to stop taking medications in preparation for a nuclear stress test, but there are some exceptions. Patients should discuss withholding medication if they take any of the following because they can interfere with test results:
- Vasodilators such as Viagra, Cialis, Levitra
- Medications for congestive heart failure like Digoxin
Also, if a patient has breathing problems, such as asthma, he should be sure to bring his rescue inhaler with him to the test, in case he needs it. Exercise is a common asthma trigger.
The results of the nuclear stress test are usually available a few days after the test is completed and the results will be reviewed with the patient at a follow-up appointment with the doctor who ordered the test.
Test results will include both the baseline measurements and pictures of the heart's function as well as the measurements and pictures of the heart's function under stress. The differences between these two will give the doctor a picture of the heart's health and allow the doctor to prescribe or modify treatment.