MYOCARDIAL SCINTIGRAPHY WITH PERSANTINE
The myocardial scintigraphy with persantine or “mibi persantine” is an imagery test done at the nuclear medicine department.
An oxygen detective in the heart muscle
The test is done with a radioactive substance injected in the body to allow for the doctor to see the oxygen activity in your heart muscle.
This substance marks the active muscular cells of the heart as soon as it is injected in the blood system.
It remains in the body for a short moment, but long enough for pictures to be taken with the equipment that records the myocardial radioactivity.
The screening test helps determine if thoracic pains or other suspicious symptoms originate from the heart.
It is also useful to follow the evolution of the patient with known for having a stable coronary disease, that is, someone carrying stable atheroma plaques on his or her coronary arteries.
It is not used to see the coronary arteries as such, or to know the percentage the arteries may be blocked.
An indirect way to see the coronaries at work
This test helps determine, indirectly, if there are significant obstructions in the coronary arteries.
In other words, it allows to verify if cholesterol plaques are sufficiently important to limit the oxygen distribution in the heart muscle.
Alternative to the treadmill test
It is prescribed to patients who are incapable of passing a treadmill test conveniently. The effort test is replaced by an injection of a medication, the persantine (dipyridamole). This medication is capable of dilating the coronary arteries that do not have considerable cholesterol plaques.
Done as an out patient
This test is done at the external department.
You must have an appointment for this exam.
Easy test with a particular preparation
The myocardial scintigraphy with persantine is an easy test.
There is a particular preparation to be done before the exam, however. The indications are explained when you take your appointment. Some hospitals sent the instructions by mail or email. A questionnaire is also sent to be filled out.
If the preparation is not completed properly, the exam will be cancelled.
· You must have your complete list of medication with you as these will be revised before starting the exam.
· You must have an empty stomach (no food or drinks other than water is permitted) at least 4 hours before your appointment.
· Stop taking any over-the-counter medication (not prescribed by your doctor) 48 hours before your appointment.
· Continue taking prescribed medication, except if you are told to stop. Verify with your doctor.
· The day before and the day of the exam, do not take any form of caffeine.
- Coffee, tea, even decaffeinated coffee
- Soft drinks and energizing drinks (Red Bull, for example)
- Chocolate (cookies, cake, pudding, chocolate milk, etc.)
· Some medication containing theophylline, the antidote of persantine, cannot be taken in the days prior to the exam. However, do not stop these types of medication without advice from your doctor. It is possible that your lung condition does not allow the persantine test to be done (important asthma or COPD) or other medical conditions. This will be evaluated by the doctor supervising the test.
The marking substance does not have any secondary effect other than weak radioactivity that lasts a few hours and that is harmless for your surroundings.
Persantine can cause certain secondary effects that quickly disappear since an antidote is administered at the end of the exam. The most frequent unwanted effects are headaches, dizziness or nausea.
STEP 1: RESTING PERIOD
The receptionist at the nuclear medicine department will greet you and ask for the request paper if he or she does not already have it.
The technologist present will make sure that you adequately prepared for the test and if your questionnaire is completely filled out.
Remove upper-body clothing
You must remove all upper-body clothing and put on a hospital gown.
Plastic catheter in a vein
A catheter will be installed in vein in your arm. It is a small plastic tube that remains in place during the whole exam. It allows for rapid injection of the necessary medication for the two steps of the test.
Injection of the marking substance at rest
At this moment, a lightly radioactive substance will be injected in your body.
This marker follows that traces of the oxygen in the heart muscle and will allow seeing the oxygenation level in the heart at rest.
Next, you will go to the waiting room because a 45-minute to one hour period is necessary to optimize the distribution of the marker in your body. During this time, you must continue de fast (water is however permitted).
Images of your heart are taken
Once the waiting period is over, your name will be called and it is time for the images of your heart at rest be taken.
To correctly take these images, you will lay on an examination table and a few electrodes, or electricity produced by the heart sensors, are placed on your chest to record the cardiac rhythm.
A camera revolves around your chest for approximately 15 minutes. You must remain stable during all the time the images are taken.
Afterwards, you will return to the waiting room while the technologist checks if the technical part of the exam is of good quality. You are then asked to proceed to the next step.
It is possible that a retake of the images be necessary (approximately 15% of the time) either because of movements while the images were being taken or because the heart is not seen well enough.
It is possible that you are asked to drink a little water and to walk before the second set of pictures is taken.
It is important to understand your heart at rest. For example, if you already experience a heart attack, we perceive, on the images of the heart at rest, an area where oxygenation is diminished or absent.
STEP 2: PERSANTINE
For the second phase of the exam, we once again call your name and have you lay on a stretcher. Ten electrodes are placed on your thorax and a pressure band is installed around the arm opposite the one with the catheter. The technologist will explain to you the procedure of this second step.
An electrocardiogram is done.
We measure the blood pressure and your heart rate.
A doctor will analyse the information, depending on your health and on the questionnaire that you have previously filled out. It is possible that he or she asks more questions and that he or she does a short lung exam.
Injection of the substance that simulates an effort
The exam starts with the injection in the vein, over a 4-minute span, of persantine (dipyridamole).
The persantine is a vasodilator; it dilates the arteries.
This substance is administered to simulate an effort done by your heart.
During this phase of the exam, your blood pressure and your heartbeat are observed and noted and electrocardiograms (ECG) are recorded.
Injection of the marked
Between six and seven minutes after the beginning of this injection, a new injection is done as the lightly radioactive marker is sent in your system so new images of your heart can be taken.
Injection of the antidote to counter effect the persantine
Two to three minutes later, a third substance is frequently injected. It is called aminophylline, an antidote for persantine. This substance blocks the persantine and stops its effect and, consequently, possible side-effects.
Persantine secondary effects are numerous, but the most frequent ones are headaches, dizziness and nausea.
Some patients may feel thoracic pain as if they were doing great efforts, others will be out of breath. Usually, these effects disappear with the injection of the antidote. Supplementary aminophylline doses may be administered if needed.
In all, this phase lasts approximately 20 minutes.
Waiting period number two
When this phase is finished, there is another waiting period of about one hour.
During this time, you must eat a light meal. It is important to not eat a heavy meal because a full stomach prevents the doctors from seeing your heart conveniently.
Caffeine and other medication restrictions demanded for the exam are now lifted.
Period for taking images of your heart during effort
After the wait, you will be once again called to the examination room for the second sequence of images.
Just like the first time, a camera revolves around your chest for approximately 15 minutes.
When these images are obtained, you will once again return to the waiting room while the technologist confirms the quality of the images.
When everything is confirmed, you may leave.
The images obtained after the injection of the persantine are compared to those taken at rest. If there isn’t any difference between the two phases, the exam will be considered negative for significant coronary obstructions.
If there is a diminished perfusion zone noticeable only on the images taken after the injection of persantine, but with a normal perfusion on the images taken at rest, this is suspicious of a lack of oxygen in an area of your heart at effort. Depending on how much it is spread and on the severity of the differences in the two sets of pictures, other exams may be necessary.
Your heart specialist will discuss this with you.
The exam is not perfect and may require complementary studies using different methods (ultrasound, coronary angiography or other).