Myocardial perfusion is an imaging test. It's also called a nuclear stress test. It is done to show how well blood flows through the heart muscle. It also shows how well the heart muscle is pumping. For example, after a heart attack, it may be done to find areas of damaged heart muscle. This test may be done during rest and while you exercise.
A myocardial perfusion scan uses a tiny amount of a radioactive substance, called a radioactive tracer. The tracer travels through the bloodstream and is absorbed by the healthy heart muscle. On the scan, the areas where tracer has been absorbed look different from the areas that do not absorb it. Areas that are damaged or don't have good blood flow do not absorb the tracer. The damaged areas may be called “cold spots” or “defects.”
A stress myocardial perfusion scan assesses blood flow to the heart muscle when it is stressed. The heart is usually “stressed” from exercise. But, if you are unable to exercise, the heart can be stressed by taking a certain medicine that increases your heart rate or dilate blood vessels as would occur during exercise.
After the radioactive tracer is injected, a special type of camera is used that can detect the radioactive energy from outside the body. The camera takes images of the heart during stress and again later at rest. The two sets of images are compared.
Your doctor may order a stress myocardial perfusion scan for:
- Chest pain, either new onset or occurring over a period of days or longer
- To diagnose coronary artery disease (CAD), which is the narrowing of the coronary arteries
- After a heart attack (myocardial infarction, or MI) to assess heart muscle damage
- To assess blood flow to areas of the heart muscle after coronary artery bypass surgery, angioplasty, or stent placement.
Risks of the scan may include:
- The exercise part of the test may lead to rare instances of abnormal heart rhythms, chest pain, or heart attack due to the stress on the heart caused by the exercise.
- The needle used to put in the IV may cause some pain.
The injection of the radioactive tracer may cause some slight discomfort. Allergic reactions to the tracer are rare.
- If your heart is stressed using medicine, you may feel anxious, dizzy, nauseous, shaky, or short of breath or chest pain for a brief period.
You may want to ask your healthcare provider about the amount of radiation used during the procedure and the risks related to your particular situation.
There may be other risks depending on your specific medical condition. Be sure your healthcare provider knows about all of your medical conditions.
Make a list of questions you have about the procedure. Be sure to discuss these questions with your healthcare provider before the procedure. Bring a family member or friend to the appointment to help you remember your questions and concerns.
Certain factors may interfere with or affect the results of this test. These include:
- Use of medicines containing theophylline
- Caffeine intake within 48 hours of the procedure
- Smoking or using any form of tobacco within 48 hours of the procedure
- Certain heart medicines, such as those that slow the heart rate
Your healthcare provider will explain the procedure to you and you can ask questions.
You will be asked to sign a consent form that gives your permission to do the test. Read the form carefully and ask questions if anything is not clear.
Tell your healthcare provider if you are allergic to or sensitive to medicines, local anesthesia, contrast dyes, iodine, tape, or latex.
You may need to fast (not eat or drink) before the procedure. Your healthcare provider will give you instructions as to how long to withhold food or liquids. Do not eat or drink anything that contains caffeine for at least 48 hours before the procedure. Also, avoid any prescription and over-the-counter medicines that contain caffeine.
- If you are scheduled for a pharmacologic myocardial perfusion scan, you will need to avoid taking any medications containing theophylline or caffeine. Coffee, even decaffeinated, is not allowed, as it contains some caffeine. Medications for asthma may contain theophylline. If you have asthma, inform your healthcare provider. Theophylline medications should be stopped 48 hours prior to the test.
- Medications that contain caffeine and all food and drink containing caffeine should be held for 48 hours, too.
- If you are pregnant or think you may be, tell your healthcare provider. Radiation exposure during pregnancy may lead to birth defects.
- If you are breastfeeding, tell your healthcare provider. Radioactive tracer can contaminate breast milk.
- Tell your healthcare provider of all medicines (prescription and over-the-counter), vitamins, herbs, and supplements that you are taking.
- Tell your healthcare provider if you have a pacemaker or implantable cardioverter defibrillator.
- For an exercise scan, plan to wear loose, comfortable clothing, as well as comfortable walking shoes.
- Based on your medical condition, your healthcare provider may request other specific preparation.
You may have a stress myocardial perfusion scan on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your healthcare providers practice.
Generally, a stress myocardial perfusion scan follows this process:
- You will be asked to remove any jewelry or other objects that may interfere with the procedure.
- If you are asked to remove your clothing, you will be given a gown to wear.
- An intravenous (IV) line will be started in your hand or arm.
- You will be connected to an electrocardiogram (ECG) machine with leads that stick to your skin and a blood pressure cuff will be placed on your arm.
Exercise myocardial perfusion scan:
- You will exercise on a treadmill. The intensity of the exercise will be gradually increased by increasing the speed of the treadmill.
- Your heart rate and blood pressure will be monitored. Once you have reached your maximal exercise point (determined by the healthcare provider based on your heart rate and age), the radioactive tracer will be injected into your IV line.
- After the tracer has been injected, you will continue to exercise for several minutes.
- You will then be placed into the heart scanner so images can be taken.
Pharmacologic myocardial perfusion scan:
- You will not exercise on a treadmill. Instead, you will lie on the table in the heart scanner while a medicine is injected into your IV.
- Your heart rate and blood pressure will be monitored.
- The tracer will be injected into your IV line.
Procedure completion, both methods:
- If you have any symptoms such as dizziness, chest pain, extreme shortness of breath, or severe fatigue at any point during the procedure, let the healthcare provider or technologist know.
- You will lie flat on a table while the images of your heart are taken. About 10 to 60 minutes (depending on the type of tracer used) after the tracer is injected, the gamma camera will begin to take pictures of your heart. In this special kind of test called SPECT (single photon emission computed tomography), the scanner rotates around you as it takes pictures. The table slides into the hole of the scanner, which is a large, donut-shaped machine.
- Your arms will be on a pillow above your head. You will need to lie very still while the images are being taken, as movement can affect the quality of the images.
- After the scan is completed, you may be allowed to leave the area, but will need to return for a second set of scans. The second set of scans will be taken 3 to 6 hours after the first set. During this time, you will not be allowed to eat or use tobacco and will be allowed limited water or decaffeinated/non-calorie liquids. In some cases, your healthcare provider may decide to have you return on another day for the second set of scans.
- The second set of scans will be much like the first set, but you will not need to exercise or get the medicine. You will lie on the table as before while the scanner takes pictures of your heart.
- Once the second set of scans has been completed, the IV line will be removed, and you will be allowed to leave, unless your healthcare provider tells you differently.
Move slowly when getting up from the scanner table to avoid any dizziness or lightheadedness from lying flat for the length of the procedure.
Drink plenty of fluids and empty your bladder often for 24 to 48 hours after the test. This helps flush the remaining radioactive tracer from your body.
The IV site will be checked for any signs of redness or swelling. If you notice any pain, redness, or swelling at the IV site after you return home, tell your healthcare provider. This may be a sign of infection or other type of reaction.
Your healthcare provider may give your other instructions after the procedure, depending on your particular situation. If the perfusion scan shows you may have a serious or life threatening cardiac disease, your healthcare provider may talk to you about a same-day cardiovascular procedure.
Before you agree to the test or the procedure make sure you know:
- The name of the test or procedure
- The reason you are having the test or procedure
- What results to expect and what they mean
- The risks and benefits of the test or procedure
- What the possible side effects or complications are
- When and where you are to have the test or procedure
- Who will do the test or procedure and what that person’s qualifications are
- What would happen if you did not have the test or procedure
- Any alternative tests or procedures to think about
- When and how will you get the results
- Who to call after the test or procedure if you have questions or problems
- How much will you have to pay for the test or procedure
January 16, 2018
Fischback, Frances T. A Manual of Labaratory and Diagnostic Tests, Berman, DS. Stress-Thallium/Rest Technetuim/Sequential Dual Isotope High Speed Myocardial Perfusion Imaging. Journal of the American College of Cardiology: Cardiovascular Imaging (2009); 2(3); pp. 273-282
Kang, Steve, MD,Fraser, Marianne, MSN, RN