Nuclear Stress Test

What is a ‘stress test’ and why is this called a stress test?

The resting heart muscle’s blood supply needs are usually well met even in the presence of blocked arteries. When the heart is stressed either by exercise or chemicals, the demand for blood increases. The blood flow through the blocked arteries- while adequate at rest- may not be able to keep up with the demands of a stressed heart. This can show up on the pictures of the heart taken after stress. This is the principle behind all the stress tests. The term ‘stress test’ is used for any means used to increase heart muscle’s demand for blood. This can be done by exercise or by chemical means.

What is a nuclear stress test?

This is one of the tests done to look for blockages of heart arteries. During this test, a radioactive material like Cardiolyte is injected through a vein. This radioactive material attaches to the heart muscle. After the injection, you have to lie still under the camera for a few minutes so that pictures of the heart can be taken. After this, your heart is stressed. This can be done by walking on the treadmill or by chemical means. During the stress portion of the test, another injection of radioactive material is given. This is followed by another session under the camera. The pre and post stress pictures are compared to look for an evidence of blockage in heart arteries.

How do you prepare for this test?

Wear comfortable clothes and shoes. You should be fasting for four hours or more. You may be asked not to take certain medicines before the test. You may also be asked not to consume caffeine up to 24 hours prior to procedure. This test can take three hours or so to complete. There will be some wait between different steps of the test. May be a good idea to bring along your favorite book or music. 

How does this test help?

This test is very helpful for the diagnosis of coronary artery disease. This test includes looking at the EKG changes suggestive of blockages as well as pictures of the heart muscle. Unlike simple exercise treadmill test, nuclear stress test can help localize the blockage. This can also help quantify the amount of heart muscle that is in jeopardy due to blockage of heart arteries.

What are the shortcomings of this test?

This test is created to be very sensitive. It means that it should miss minimum number of cases with blockage of heart arteries. As a pay back, this test can be false positive in some cases. This means that it can be abnormal even if you do not have blockage of heart arteries that needs to be fixed by surgery or stenting.

Can radiation from the nuclear material used to do this test hurt me?

There is no evidence of clear-cut harmful effects of dosage used for the stress test. The radiation safety principle, ALARA is still followed. ALARA is an acronym for As Little As Reasonably Achievable.

What does an abnormal nuclear stress test mean?

An abnormal stress test usually means that you have blockage in heart arteries. A nuclear stress test result should be interpreted in the light of a person’s symptoms, his risk for coronary artery disease etc. The nuclear stress test has the ability to quantify the severity of abnormality. Further tests for coronary artery disease after a nuclear stress test should be considered based on several different factors. If needed, usual next step is a coronary angiogram.

I had an abnormal nuclear stress test and then underwent an angiogram that came out to be normal. Why was the stress test abnormal?

Just because you did not have artery blockage that needed to be fixed by stent or bypass surgery, it did not mean that you did not have coronary artery disease. The nuclear stress test can also be false positive in certain cases.