Myocardial Perfusion Imaging (MPI) Stress Test is also known by other names:
- Cardiolite stress test
- Nuclear medicine stress test
- Sestamibi (MIBI) stress test
- Stress SPECT
What is it?
The test is basically a noninvasive way to assess the blood flow to the muscle of the heart. We inject a nuclear tracer into the blood stream and the tracer is taken up by the heart muscle cells that receive good blood flow. We image the heart with a camera that senses gamma rays released by the tracer. This basically provides us with a map of where the blood flow to the heart is adequate.
We will scan your heart once at rest to produce a baseline image. You will then undergo some type of stress that increases the workload of the heart (either with you on the treadmill or receiving IV medication such as dobutamine or adenosine) followed by a second scan that shows the quality of blood supply at peak exertion. We compare the two images to determine if there are any areas where the blood flow worsens with physical stress. Such a finding would suggest the presence of blockage in the coronary arteries.
What are the indications for the procedure?
We generally use the MPI stress test as the first step in evaluating any patient we suspect of having coronary artery disease. Symptoms such as chest pain or discomfort, shortness of breath, and exertional intolerance are common reasons for which we perform this study. We often do this test on patients with no symptoms if they are found to have an EKG abnormality or are anticipating a major surgery. We can also use nuclear stress testing evaluate the status of a previously placed coronary stent.
How is it done?
Upon arrival in the office our nurse will place an IV in your arm. You will start by receiving the first dose of radiotracer followed by a period of time when you lie on a table under the gamma camera (see illustration). Since the radiotracer is inert you won’t feel anything when it goes in. You will then undergo either exercise or chemical stress testing while you are attached to EKG leads and monitored by our nurses. At some point near the completion of the stress portion we will administer the second dose of radiotracer. We’ll give you a light snack while you wait to go under the scanner for a second time. After this you are free to go. We process the images and one of our cardiologists interprets the study. You should expect to receive a phone call within a day or so notifying you of the results of the test. If the test is abnormal we’ll let you know what sort of further testing or therapy we recommend.
How do you prepare for the test?
We do the MPI stress tests at our Bergan, Immanuel, Midlands and Lakeside offices during the weekdays, both mornings and afternoons. Our schedulers will tell you when and where to come for the test. You should have nothing to eat 4-6 hours prior to the study and have no caffeine of any type (coffee, tea, cola) within 12 hours of the test. We want you to take all your usual medications with a small amount of water on the day of the test unless we specify otherwise. Wear comfortable clothing that would be suitable for exercising.
What are the risks of the test?
The risks of stress testing, in the form of exercise or chemical stress testing, are addressed in other articles on this web site (Lexiscan, treadmill testing, dobutamine, adenosine). The nuclear medicine portion of this test involves the use of a radioactive material that allows us the ability to image the heart. While there is a theoretical risk of adverse effects from radiation, the amount of exposure you as a patient will receive is well within established safety guidelines. The radioactive tracer (technetium-99m) is attached to a biologically inactive compound (sestamibi) that is selectively taken up by the mitochondria in healthy heart muscle. The technetium-99m has a very short lifespan and exhibits no detectable radiation activity after 24 hours. Your kidneys eliminate the tracer within hours after the study ends.
An alternative to the MPI stress test is the stress echocardiogram. This study uses ultrasound technology to image the heart at rest and stress and it provides much of the same information we obtain from the MPI. The utility of the stress echocardiogram is limited in patients who are obese, have emphysema, or have certain EKG abnormalities
