MYOCARDIAL SCINTIGRAPHY ON TREADMILL
Myocardial scintigraphy perfusion imaging on treadmill or MIBI on treadmill
The treadmill is a test done in cardiology that indirectly evaluates if there are blockages in the coronary arteries.
Some exams can be inconclusive. Your doctor may ask for a complementary exam afterwards. One of these complementary exams is another treadmill test, but accompanied by a radioactive tracer injection to verify through images the circulation condition of the cardiac muscle. This test is called the “Myocardial scintigraphy perfusion imaging at exercice”, “MIBI at exercice” or “MIBI with a treadmill”.
An oxygen detective in the heart muscle
The exam takes place with a radioactive tracer present in the body, allowing the oxygen to be “seen” in the cardiac muscle.
The tracer enters the active muscular cells of the heart once it is injected in the body. It remains in the cells for a long enough period allowing for images to be taken by a radioactive myocardial recording instrument.
This screening test helps determine if thoracic pains or other symptoms originate from the heart.
It is also useful to follow the evolution of a patient with a stable coronary disease, or, in other words, coronary arteries containing stable atheroma plaques.
It does not allow to see the coronary arteries, or to evaluate the blockage percentage in these arteries.
An indirect method to see the coronaries at work
This exam helps determine, indirectly, if there are any significant obstructions of the coronary arteries. In other words, it verifies if cholesterol plaques are sufficiently important in size to limit the distribution of oxygen to the heart muscle.
Done in extern
This exam takes place in the extern department.
You must call for an appointment for this exam.
The myocardial scintigraphy is an easy exam.
· You must bring along the list of medication that you take, as these will be revised before beginning the test.
· You must fast (no food and no drinks other than water) for at least three hours before your appointment.
· Continue taking the medication prescribed by your doctor, unless otherwise advised. Check with your doctor prior to the exam.
Possible secondary effects
The tracer does not have any side effects other than weak radioactivity in the next few hours. It is harmless to you and others around you.
What happens during the exam?
The test consists of two phases: study at rest and study during effort. Depending on the protocols in your hospital, the two phases can take place the same day or on different days. You will be informed of the procedure.
PHASE 1: INJECTION AT REST
You must have an empty stomach for the injection. We will inform you how long you must fast prior to the exam, but it is generally three to four hours. You must take all your medication. No other preparation is needed.
The receptionist at the nuclear medicine department will greet you and ask for your request if it isn’t in his or her possession.
The nuclear medicine technologist will verify with you if your preparation is done and will make sure you filled out a questionnaire appropriately.
Remove upper body clothing
You must remove all upper body clothes and wear a hospital gown.
Sensors on your skin
You will be asked to lie on a bed for the installation of electrodes. These sensors placed on your skin record the electricity produced by your heart during the examination.
.Plastic catheter in a vein
A catheter, a small plastic tube, is installed in a vein in an arm and remains in place during the whole exam. The injection of the radioactive tracer will be done through the catheter.
Tracer injection at rest
The radioactive substance is injected at this moment. It is this substance that marks the oxygen in the heart muscle and it allows the technologist to “see” it in the resting heart.
After the injection, you will return to the waiting room because a period is necessary to optimise the distribution of the tracer in your body. During this time, you must continue to fast.
Taking the images of your heart
After this waiting period, you will be called to the exam room. Images of your heart at rest will be taken.
To ensure the quality of the images, you will be asked to lie on an examination table, little electricity sensors called electrodes will be installed on your chest to record the heart rate.
A camera will rotate around your chest for about 15 minutes. You must lie still during all this time while the images are taken.
After the exam, you will return to the waiting room while the technologist confirms the technical quality of the exam before moving on to the next step.
It is possible that a retake of the images be necessary (approximately 15% of the time), possibly because of movements occurred during the exam or because the heart was not seen in a high enough quality.
You may be asked to drink some water or fat milk and to walk before the test is redone.
It is important to evaluate your heart at rest. For example, if you have already had a heart attack, the images of your resting heart will reveal an area where oxygenation is diminished or absent.
PHASE 2: INJECTION DURING AN EFFORT ON THE TREADMILL
This phase can take place the same day as phase 1 or on a different day. For phase 2, you must pass a treadmill test, generally in cardiology.
The day of your exam, you must bring your comfortable shoes to the hospital. Sandals and high-heel shoes are not permitted for security reasons.
You will be asked to remove all clothing that covers your thorax and to wear a hospital gown.
The technologist needs your list of medication to complete your papers. Therefore, you must carry your updated list with you.
You will lay on a bed for the installation of the electrodes. These sensors, well attached to your skin, record the electricity produced by your heart throughout the exam.
For a better electrical contact
Keratin on our skin can reduce the amplitude of the electricity of your heart. To prevent this, your skin is lightly scratched with sandpaper before the electrodes are installed.
A catheter will be installed on your arm to allow an easier injection of the radioactive tracer (MIBI) during the treadmill test. Ten electrodes are placed on the thorax as well as an armband for the pressure on the arm without the catheter. The technologist will explain the procedure for the second phase.
An electrocardiogram is then done. Your blood pressure and your heart rate are measured.
A doctor will verify the information, depending on your health and the questionnaire you previously filled out. Your doctor may ask you more questions and might have you pass a test for your lungs.
During this phase, your blood pressure and heart rate are checked upon and noted and the electrocardiogram (ECG) is recorded.
We then move to the treadmill. When the doctor will feel it is the right moment, generally at maximum effort or close to it, the injection of the radioactive tracer will be done. We continue with the treadmill test after the injection, typically for one more minute.
Second waiting period
When this step comes to an end, there is an approximately one-hour waiting period. You will be sent to the nuclear medicine department for the images to be taken.
During this waiting period, you will be asked to eat a light meal. It is important to keep it light as a full stomach prevents the technologist from seeing your heart adequately.
LAST PHASE; SECOND ROUND OF PICTURES
Taking the images of your heart during an effort
After this waiting period, you will be called a second time to the examination room for more images to be taken.
As per the first time, a camera will rotate around your chest for another 15 minutes.
After these new images are obtained, you must return to the waiting room once again while the technologist checks the quality of the images before you leave.
The images obtained after the injection of the radioactive tracer during an effort are compared to those taken while at rest. If there are no differences between the two phases, the exam will be considered negative for the presence of significate coronary obstructions.
If there is a reduced perfusion zone noticeable only on the post effort images, but with normal perfusion on the resting images, this is suspicious of a lack of oxygen in a region of the heart during effort. Depending on the size and/or severity of the difference between the images, other exams may be necessary. Your cardiologist will discuss this with you.
Example of oxygen déficit at exercice:
The exam is not perfect and may require further complementary tests using different instruments (echography, coronary angiography or others).