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Chest discomfort is a common symptom of heart concerns, so your doctor may request Myocardial Perfusion Imaging (MPI) to investigate the cause. MPI is a non-invasive way to examine how well blood flows through (perfuses) your heart muscle (myocardium). It can assess whether your symptoms are caused by lack of blood flow to the heart muscle due to narrowed or blocked heart arteries.
MPI looks at the amount of blood in your heart muscle at rest and during exercise, evaluating if arteries are blocked and how many. It can also indicate whether you’ve previously had a heart attack and how much heart muscle has been damaged from that attack.
Sometimes called a nuclear stress test, during MPI a radioactive material (radiopharmaceutical) is injected intravenously and taken up by your heart muscle as it flows through the heart arteries. Areas of the heart with good blood flow take up more radiopharmaceutical than areas which have poor blood flow or have been damaged by a heart attack. This allows a special gamma camera to take pictures of your heart and assess blood flow at rest and exercise.
MPI is a two-part exam, performed over two days. On the first day, you will need to fast for four hours prior to the appointment and then the radiopharmaceutical is injected into your arm vein while seated. You will rest for about 45 minutes and will even have a small snack, then you will be positioned so that the gamma camera can take images that show the blood flow to your heart while resting. The appointment takes two hours, and afterwards you may return to your daily activities.
On the second day, you will again need to fast for four hours prior to the appointment. You will also need to wear exercise clothing for the exercise or stress portion of this study. Electrodes will be placed on your chest and an intravenous (IV) line is inserted into your arm. After an internal medicine physician discusses your medical history and symptoms with you, you will be asked to walk on a treadmill as it gradually increases in speed and inclination. Once your heart rate reaches a certain point (calculated according to your age) and you feel tired, the radiopharmaceutical is injected into the IV. You will continue walking for approximately one minute to circulate the radiopharmaceutical to your heart muscle before ceasing exercise.
After the injection, you will rest for about 20 minutes and then lie under the nuclear medicine gamma camera for another set of images. These images show the blood flow to your heart muscle at stress. The appointment takes two hours, and afterwards you can return to your daily activities. Please note, it you’re unable to exercise on the treadmill, you can be given a medication (through your IV) that dilates your heart’s arteries to “mimic” a stress condition.
The radiopharmaceutical is excreted from the body through your urine. Keeping hydrated and voiding frequently will help eliminate it from your body. Your rest and stress studies will be processed and then reviewed by a specialized nuclear medicine radiologist and your health care practitioner will receive a copy of the following within a few days of your exam:
MPI exams are generally safe for most people. To determine whether this exam is appropriate for you, you will need to discuss your symptoms and medical history with your health care practitioner, who would then provide you with a requisition for this imaging if recommended. Your requisition, and any lab work and resting ECG, are sent to Mayfair for triaging. Our contact centre will then be in touch to coordinate booking and explain how to prepare for your exam.
You are injected with a radioisotope and exposed to low-dose X-rays during the scans. In most cases, the benefits of this exam outweigh the small increased risk from radiation exposure
Please visit the Myocardial Perfusion Imaging exam page, for more information about what happens during this exam and how to prepare.
REFERENCES
American Heart Association (2018) “Myocardial Perfusion Imaging (MPI) Test.” www.heart.org. Accessed November 22, 2018.
Government of Alberta (2017) “Cardiac Perfusion Scan.” www.myhealth.alberta.ca. Accessed November 22, 2018.
Heart and Stroke Foundation (2018) “Thallium or Cadiolite scan.” www.heartandstroke.ca. Accessed November 22, 2018.
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