MYOCARDIAL SCINTIGRAPHY DOBUTAMINE

MYOCARDIAL SCINTIGRAPHY DOBUTAMINE

 

The treadmill is a cardiology exam that assesses whether the heart receives enough oxygen during effort.
However, for various reasons, some people have difficulty walking on the treadmill and therefore cannot provide adequate effort for the results to be conclusive.

In this case, your doctor may ask for a different exam to substitute the treadmill. One of these tests is called the dobutamine myocardial scintigraphy.

 

A detective of oxygen in the heart muscle

The exam is done with the help of a radioactive marker that "follows the tracks" of oxygen in the heart muscle.

This marker colors the active muscle cells of the heart when injected in the blood.

It remains fixed for a little while, the time to take the photos using a device for recording myocardial radioactivity.

 

Its use


This is a screening test that helps determine if chest pain or other suspicious symptoms are of cardiac origin.

It is also useful to follow the evolution of a patient known for a stable coronary disease, or in other words, carrier of stable atheromatous plaques on his coronary arteries.

However, it does not allow to see the coronary arteries as such, or to know the percentage of blockage of these arteries.

 

An indirect way to see how coronaries work

This examination helps to determine, indirectly, whether there are significant obstructions of the coronary arteries.

In other words, it allows verifying if cholesterol plaques are large enough to limit the oxygen distribution in the heart muscle.



Make an appointment


This exam is done externally and asks for an appointment.

 


 

 

Easy exam

Myocardial effort scintigraphy is a relatively easy test.



 

 

The instructions;


·        You will need to bring the list of medications you are taking as they will be reviewed before you start the exam.

 

·        You must be fasting (without eating or drinking anything other than water) at least 3 hours before your appointment.

 

 

 

Taking medication


Pills in the beta-blocker class should be stopped 24 to 48 hours prior to this test because they counteract the effect of dobutamine on your heart. Your doctor will give you instructions.
 

These pills are relatively easy to find on your medication list as their names all end with the letters "lol".

For other medication, if you have not been given any different indications, take them as usual.
 


Possible side effects
 

The marker has no side effects, except low radioactivity present for a few hours, but without any danger for others around you.

 

How is the exam done?


The exam consists of two parts: A series of photos at rest and another series of photos taken once the dobutamine is taken.

Depending on the hospital, the two phases can be done the same day or be done on two different days.

This will be mentioned to you.

 

PHASE 1: INJECTION AT REST

Preparation:

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.

 

Reception

The receptionist at the nuclear medicine department will greet you and ask for your request if it isn’t in his or her possession.

 

Usual verifications

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, wear a hospital gown and lay down on a stretcher.

 

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.

 

Installation of the electrodes

The electrodes are also installed.

These sensors, well attached to the skin, record the electricity emitted by your heart throughout the examination.

 



For a better electrical contact
The surface of our skin can attenuate the amplitude of the heart's electricity. To help better capture this electricity, it is necessary to lightly scratch the skin with small sandpaper.


Around a blood pressure device

Finally, a monitor is installed on the opposite arm of the catheter to record your blood pressure at different times during the examination.

 


 

We are ready

Once all this installation done, we are ready to start the next step

 

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” the resting heart’s oxygenation.

 

 

Waiting period


After the injection, you will return to the waiting room because a 45-minute to three hour pause is necessary to optimise the distribution of the tracer in your body.

During this time, you must continue to fast if the waiting period is short.

However, a small snack is allowed if the waiting time is too long.

It is important to follow the instructions relative to this subject.

 

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.

 

 

STEP 2: INJECTING THE TRACER UNDER DOBUTAMINE

This step can be done the same day as the first step or a separate day for the reasons described above.

The case where the second part of the exam is on a different day, the preparation for this day has to be redone.

You are asked to remove all upper body clothing, to put on a hospital gown and to sit on a stretcher.

The technologist needs your list of pills to complete his information. You should plan to bring an up-to-date list of your medications.



Plastic catheter in a vein

A catheter will be installed on one arm to allow the injection of the radioactive tracer during the treadmill test. The technologist will explain the progress of this second step.


Electrode installation

The electrodes are also installed. These sensors, well attached to the skin, record the electricity emitted by your heart throughout the examination.



For a better electrical contact

The surface of our skin can attenuate the amplitude of the heart's electricity. To help better capture this electricity, it is necessary to lightly scratch the skin with small sandpaper.

 

Blood pressure device

Finally, a monitor is installed on the opposite arm of the catheter to record your blood pressure at different times during the examination.

 

We are ready

Once all this installation done, we are ready to start the next step.


An electrocardiogram is done. We measure your blood pressure and your heart rate.

A doctor will check your information. Depending on your health and the questionnaire that you have completed previously, it is possible that more questions are asked and that a short examination of your lungs be done.

 

We are now ready for the "simulation of the effort" part

 

Intravenous dobutamine -2nd part

To perform the second phase of the examination, we use a drug, dobutamine, to simulate physical activity (replacing the treadmill).

 

Gradual injection of dobutamine.


Dobutamine is a medication that is administered through the veins with progressive doses while evaluating its effect on your blood pressure and your heart rate.

This medication is given using the catheter installed in your arm.

Throughout this phase of the exam, your blood pressure and heart rate are monitored and noted, and electrocardiograms (ECG) are recorded.

 

The purpose of the exam is to speed up the heart


The purpose of the exam is to have your heart rate boosted by dobutamine enough for the test to be valid.

This heart rate is based on your age.

 

 

The infusion of dobutamine begins

The administration of dobutamine begins. The dose is gradually increased every 3 minutes.

The duration of each period offers the time necessary for your heart to respond to the medication. In other words, it will accelerate and pump harder.

Once this "response" is obtained, we move to the next level until we get the heart rate needed to complete your exam.

 

Do not be afraid

It is likely that during the medication administration, you feel your heart beat faster and faster. Do not worry because this is the purpose of the exam, as if you are gradually climbing a hill.


When the desired heart rate for the examination is reached, the dobutamine is stopped and the technician injects the lightly radioactive tracer through the same catheter.

This radioactive marker "follows the paths" of the oxygen in the heart muscle in which the effort has just been simulated.

 

It remains attached to living heart cells for a little while, the time to take pictures using a myocardial radioactivity recorder.

 

Short term effects

The effects of dobutamine take a few minutes to disappear completely. Medication may be given to you to slow your heart back to the rate it had at the beginning of the test.

 

Waiting period # 2


When the dobutamine phase is over, there is another waiting period of approximately one hour.

You will be directed to the nuclear medicine department to take the pictures.

During this waiting time, you may be asked to eat a light meal. It is important not to take a large meal because a full stomach limits the quality of the pictures.

It is important to follow the instructions given to you.

 

Time for the pictures of your heart during effort to be taken


After the wait, we call you again for the second series of photos.

As for the first time, a camera rotates around your chest for about 15 minutes.

After these images are obtained,  you will have to return to the waiting room so that the technologist validates the quality of the images before your departure.

 

 

And it's over

 

After the exam, you can get dressed and after a moment of observation in the waiting room, you can leave.

 

The results are sent to your doctor

The results will be communicated to the doctor who requested the examination.

 

You can request a copy for another doctor

You may request that a copy of the result be sent to another doctor.

All you need to do is give the name and contact details of this doctor to the staff.

You can ask for it at any time.

 

What we are looking for in your photos

The images obtained after the tracer injection during dobutamine will be compared to those taken at rest. If there aren’t any differences between the two sets of photos, the exam will be considered negative. In other words, the arteries of the heart do not seem to have any significant coronary obstructions. The heart does not seem to be “blocked”.

If there is a diminished perfusion zone seen only on the effort images, but with a normal infusion on the resting photos, this is suspicious of a lack of oxygen in a region of your heart during effort. Depending on the extent and / or severity of the difference between the two sets of photos, further examinations may be necessary. Your cardiologist will discuss this with you.

 

The examination is not perfect and may require further studies by other methods afterwards (ultrasound, coronarography or others).

 

 

 

 

 

 

 

 

If there is a diminished perfusion zone seen only on the effort images, but with a normal infusion on the resting photos, this is suspicious of a lack of oxygen in a region of your heart during effort. Depending on the extent and / or severity of the difference between the two sets of photos, further examinations may be necessary. Your cardiologist will discuss this with you.

 

The examination is not perfect and may require further studies by other methods afterwards (ultrasound, coronarography or others).

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