Cardiac Nuclear Imaging
What is a stress myocardial perfusion scan?
A myocardial perfusion scan is a type of nuclear medicine imaging test. This means that a tiny amount of a radioactive substance, called a radioactive tracer is injected during the scan to help show the tissue under study, in this case, the heart.
A stress myocardial perfusion scan is used to assess 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 medication that increases your heart rate as it would 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.
On the scan, the areas of heart muscle that do not absorb the radioactive tracer look different from the areas that do absorb it. The areas that absorb the tracer are healthy. The areas that do not absorb the tracer are damaged due to decreased blood flow. The damaged areas may be called “cold spots” or “defects.”
Why might I need a stress myocardial perfusion scan?
Possible reasons a stress myocardial perfusion scan may be done include, but are not limited to:
- Chest pain, either new onset or occurring over a period of days or longer
- A diagnosis of 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 or other procedures that are done to improve blood flow to the heart muscle
There may be other reasons for your healthcare provider to recommend a stress myocardial perfusion scan.
What are the risks of a stress myocardial perfusion scan?
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 medication, 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 to discuss any concerns with your healthcare provider prior to the procedure.
Certain factors may interfere with or affect the results of this test. These include, but are not limited to, the following:
- Use of medications 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 medications, such as those that slow the heart rate
How do I prepare for a stress myocardial perfusion scan?
- Your healthcare provider will explain the procedure to you and ask if you have any 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 medications, local anesthesia, contrast dyes, iodine, tape, or latex.
- Fasting (not eating or drinking) may be required before the procedure. Your healthcare provider will give you instructions as to how long you should withhold food and/or liquids.
- 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. Some over-the-counter medications that contain caffeine include Anacin, Excedrin, and NoDoz. Consult your healthcare provider for specific instructions.
- If you are pregnant or think you may be pregnant, tell your healthcare provider. Radiation exposure during pregnancy may lead to birth defects.
- If you are lactating, breastfeeding, tell your healthcare provider due to the risk of contaminating breast milk with the radioactive tracer.
- Tell your healthcare provider of all medications (prescription and over-the-counter), vitamins, herbs, and supplements that you are taking.
- Tell your healthcare provider if you have a pacemaker.
- 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.
What happens during a stress myocardial perfusion scan?
A stress myocardial perfusion scan may be done 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.
Pharmacologic myocardial perfusion scan:
- You will not exercise on a treadmill. Instead, you will lie on the table while a medication 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.
What happens after a stress myocardial perfusion scan?
Be sure to move slowly when getting up from the scanner table to avoid any dizziness or lightheadedness from lying flat for the length of the procedure.
You will be instructed to drink plenty of fluids and empty your bladder frequently for 24 to 48 hours after the test to help 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, and/or swelling at the IV site after you return home, you should notify your healthcare provider as this may be a sign of infection or other type of reaction.
Your healthcare provider may give you additional or alternate instructions after the procedure, depending on your particular situation. If the perfusion scan indicates 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
- The risks and benefits of the test or procedure
- When and where you are to have the test or procedure and who will do it
- When and how will you get the results
- How much will you have to pay for the test or procedure