As with the stress echo, nuclear imaging provides additional information to stress alone. Specifically, the nuclear camera evaluates the squeezing strength of the heart and determines the amount of decreased blood flow to the heart.
Preparing for the Test
Your doctor may ask you to prepare for the test by avoiding some medications and adjusting your diet for 24 to 48 hours prior to the test. More information on preparing for the test is found here.
What Happens During the Test?
The protocol for the exercise nuclear test is similar to that for exercise without imaging. You will require an IV (intravenous) line, however, for this test.
The nuclear stress test takes longer than either the treadmill stress test without imaging or the stress echo, mainly due to imaging time; plan on spending two to four hours if the entire nuclear stress test is done on one day (see below).
As opposed to the stress echo, there is a recovery time of several minutes while walking slowly on the treadmill after the stress injection.
The nuclear images can take up to 20 minutes per set of images (20 for rest and 20 for stress). There are also several required delays between the different stages of the test.
If your nuclear stress images are done first, there is a chance that the doctor will tell you that rest pictures are not required. This is good news, and obviously saves you time. You should know that some labs follow such a protocol routinely, while others never do. In other words, don’t get too upset if you are asked to stay for both sets of pictures. It does not mean that anything is necessarily wrong.
In some cases. the rest and stress images are done on different days. Again, this may be part of the lab’s protocol, or due to a need for higher doses of the isotope, which cannot be given on the same day. In other words, if more isotope needs to be injected for good quality images, the doctors may decide that they prefer to spread the two injections over two days.
Is There Radiation, and is it Dangerous?
As described above, you will be injected with a radioactive material (isotope) twice during the test; during rest and at peak exercise. The exact timing of which comes first varies among different centers. For example, in some settings the rest injection and imaging are done before the stress test, while in other places the order may be reversed.
You should not feel any discomfort when the isotope is injected into your IV. If you feel any discomfort at the IV site, let the staff know.
Although many people worry about radioactivity injected into their body, the small dose of isotope almost completely disappears with 24 hours. There has been no documented increase in cancer among those undergoing nuclear stress tests.
Nevertheless, a small amount of radioactivity will stay in your body after the test. As a precaution, it’s recommended that you avoid prolonged close contact with pregnant women and children for at least 12 hours after the test. It's ok to say hello or even give them a hug, but prolonged contact such as sleeping in the same bed is best avoided. Also, if you are planning on flying, airport radiation detectors may sense the leftover radiation in your body. I recommend that my patients carry a letter explaining the situation to airport security staff.
After the Test
Once your test is over, a doctor will review the rest and stress images. Your doctor will discuss these with you and provide further instructions.
Sources:
American College of Cardiology Appropriateness Criteria for a Nuclear Stress test.
ACC/AHA 2002 Guideline Update for Stress Testing
ACC/AHA/ASNC 2003 Guidelines for the Clinical Use of Cardiac Radionuclide Imaging