Generality
Myocardial scintigraphy is a diagnostic examination of nuclear medicine, which allows the state of health of the coronary arteries and myocardial blood supply to be known.
SPECT of myocardial perfusion; the arrows indicate ischemic areas
Being a nuclear medicine technique, it requires the injection of radiopharmaceuticals, ie substances containing radioactive isotopes. Once in the body, these radiopharmaceuticals are tracked using a special detection tool, which provides very clear and meaningful images.
Myocardial scintigraphy involves two moments: in a first phase, the heart is analyzed while undergoing an effort and, in a second phase, the heart is observed while it is left at rest.
In view of the examination, it is necessary to follow some important indications, which will be exposed by the doctor during a previous visit.
During or following a myocardial scintigraphy it is possible that some complications arise, however these are very rare cases.
A brief reference to the anatomy of the heart
The heart is a hollow organ, composed of four contractile cavities : two are on the right and are called right atrium and right ventricle ; the other two are on the left and are called left atrium and left ventricle .
Through the atrium and the right ventricle flows the oxygen-poor blood, which must be directed to the lungs for oxygenation; through the atrium and the left ventricle, on the other hand, passes the oxygen-rich blood from the lungs, to be pumped towards the various organs and tissues of the body.
The pumping of blood to the lungs and the rest of the body is guaranteed by the muscular structure that constitutes the atria and the ventricles and which as a whole is called myocardium .
The myocardium receives nourishment and oxygen from the coronary arteries .
Within the heart, the regulation of blood flow between the various compartments and to the outgoing blood vessels rests on four valves, also known as heart valves .
What is myocardial scintigraphy?
Myocardial scintigraphy is a diagnostic procedure for nuclear medicine, which allows the analysis of blood flow within the coronary arteries, myocardial perfusion and heart function.
In this way, it is possible to compare the blood flow of the myocardium during a stressful condition of the heart and during a moment of rest.
WHAT IS NUCLEAR MEDICINE?
Nuclear medicine is that branch of medicine based on the use of radioactive substances (so-called radiopharmaceuticals ) for diagnostic and therapeutic purposes.
A radiopharmaceutical is an injectable medicine that contains radionuclides, or radioactive isotopes .
Once injected, the radiopharmaceuticals can interact specifically with a specific biological tissue (like a normal drug) and, by virtue of their radioactive properties, they can be monitored as they spread through a special instrument for detecting radioactivity ( gamma-camera ). In this way, this complex instrumentation provides very clear images of how, over time, the radiopharmaceutical is distributed within the body.
Scintigraphy is a diagnostic examination of nuclear medicine, based on the detection of radiation emitted by an organism after the administration, in the latter, of radiopharmaceuticals. These radiations, suitably processed by an ad hoc tool, allow us to investigate the location, shape, size and functionality of various organs, including the heart, thyroid, bones, brain, liver, kidneys and lungs.
In light of what has just been stated, one can understand why radionuclides are also identified with the word " tracers ".
Please note . The distribution in a certain tissue or the interaction with a given organ by radioactive isotopes depends exclusively on the drug to which they are bound. Therefore, the choice of the pharmacological preparation is of fundamental importance for the correct execution of the examination. For example, for a thyroid analysis it is necessary to use a drug that spreads specifically in this organ of the body; the same applies to the heart.
MIOCARDIC SCANNING WITH PHARMACOLOGICAL STRESS
The stress test is not the only way to study myocardial blood supply in a stressful condition for the heart.
In fact, there is the possibility of mimicking a cardiac effort, following a certain physical activity, with the administration of particular drugs .
These pharmacological preparations induce the extension of the coronary arteries (so there is an increase in the flow of blood), just like during a physical exercise.
Cardiologists resort to so-called myocardial scintigraphy with pharmacological stress, instead of the one that involves an exercise test (also called myocardial stress scintigraphy ), when the patient is unable to practice the expected physical activity. For example, such an occurrence can occur in those cases where the patient is very old and has difficulty moving.
INVASIVE OR NON-INVASIVE?
Myocardial scintigraphy is an invasive procedure, as it involves the venous injection of radioactive isotopes.
However, it is considered less invasive than cardiac catheterization techniques, during which the cardiologist inserts a catheter into a body artery and then leads it to the heart for subsequent operations.
When you run
Usually, cardiologists use a myocardial scintigraphy when they suspect the presence of a coronary artery disease .
In medical language, coronary artery disease refers to any coronary artery disease characterized by a narrowing of these arterial vessels supplying the myocardium.
The coronary arteries may be narrowed by blood clots or so-called atheromatous plaques, or deposits consisting essentially of lipids, platelets, white blood cells and smooth muscle cells.
If coronary narrowing is greater than 70%, myocardial blood supply is insufficient to support cardiac activity; in these situations we talk about myocardial ischemia or ischemic heart disease .
Especially if left untreated, myocardial ischemia could be the prelude to myocardial necrosis or, better, areas of myocardium not adequately reached by blood; this condition is known as myocardial infarction or heart attack .
The main symptoms of coronary artery disease
The symptoms of coronary artery disease resemble those of many other heart problems, not specifically due to coronary artery disease.
However, it is worth remembering, because the sooner they recognize themselves and expose themselves to their doctor, the greater the chances of treatment.
Coronary artery disease is typical: chest pain, dyspnea (both from exertion and resting), the feeling of asthenia, heart disease, excessive sweating and distention of the veins in the neck.
OTHER CONDITIONS THAT REQUIRE MYOCARDIC SCANNING
In addition to analyzing the characteristics of a coronary artery disease in progress, myocardial scintigraphy is also practiced after:
- A heart attack . It is used to identify the precise area of the myocardium affected by the process of necrosis.
- A therapeutic treatment for the restoration of coronary flow . For example, it can be practiced after coronary bypass surgery, which is a procedure for bypassing the occluded coronary or by inserting a "new" blood vessel; or after a coronary angioplasty with stenting, which is a method for reopening the occluded coronary or by means of an inflatable balloon and a small metal cylinder ( stent ).
Preparation
Before myocardial scintigraphy, the patient must be made aware of all the pre-operative indications necessary for the correct and safe implementation of the diagnostic procedure.
The cardiologist who will take the exam or a qualified member of his staff takes care of this.
The most important pre-operative indications that must be followed can be summarized as follows:
- Notify the cardiologist (or whoever takes his place on the occasion) of any allergy to drugs, local anesthetics and the various materials used during scintigraphy.
- Complete fasting for at least 12 hours . Complete fasting means abstaining from food and liquids. Only water is an exception and can only be taken up to a few hours before the procedure.
- Avoid any medicines or substances containing theophylline or caffeine . To be precise, the intake of preparations containing theophylline should be interrupted 2-3 days before the examination; while caffeine intake should be suspended at least 12-24 hours before.
Individuals suffering from bronchial asthma are reminded that some drugs for this disorder are based on theophylline.
- Notify the cardiologist if you are (or if you suspect you are) pregnant .
- Notify the cardiologist of all the medications you are currently taking . In this regard it should be remembered that heart medicines should be suspended at least 24 hours before the exam.
- Notify the cardiologist if you have a pacemaker, or an electronic device to correct a cardiac arrhythmia.
- If you are going to undergo a myocardial exercise scintigraphy, remember to carry comfortable wear-proof clothing (shoes included) on the day of the procedure.
It is on the occasion of the preliminary meeting, in which all the aforementioned indications are exposed, that the patient can ask the doctor about the details or doubts regarding the procedure.
Procedure
Myocardial scintigraphy is an outpatient procedure that takes place in three stages:
- an initial phase, which is the same for the exercise version and for the version with pharmacological stress;
- an intermediate phase, which is specific to each version;
- a final phase, common to both procedural versions.
INITIAL PHASE
The initial phase generally involves the following steps:
- Removal of any jewel, earring and other objects, which could in some way interfere with the implementation of the procedure.
- Dressing of the patient with clothes suitable for the following stages.
- By a nurse's hand, inserting a needle-cannula into a vein in the arm or hand. The needle-cannula serves for the venous administration of the radioactive substance and, in the case of myocardial scintigraphy with pharmacological stress, also for the injection of the drug for coronary dilation.
- Also by a qualified member of the medical staff, connecting the patient to an electrocardiogram machine (ECG) and a blood pressure measuring instrument. Heart rate (via ECG) and blood pressure are two parameters that must be monitored from the beginning to the end of the procedure.
EFFORT MIOCARDIC SCANNING: INTERMEDIATE PHASE
Once the first part of the procedure is completed, the patient is asked to use the machinery for the stress test; machine that can be a treadmill (or treadmill ) or an exercise bike .
The level of activity to which it is subjected is at the discretion of the cardiologist and depends on several factors, including age, cardiac function and the patient's general health status.
Radiopharmaceutical injection takes place only after the heart rate - which is constantly monitored by ECG - has reached the most suitable exercise frequency for the characteristics of the individual under examination.
Once the radiopharmaceutical has been injected, the patient must continue exercising for a few minutes, waiting for the radionuclides to spread into the stressed heart.
MIOCARDIC SCREENGRAPHY WITH PHARMACOLOGICAL STRESS: INTERMEDIATE PHASE
During the intermediate phase of myocardial scintigraphy with pharmacological stress, the patient is seated on a hospital bed and given the drug that mimics physical effort.
As in the case of myocardial stress scintigraphy, his heart rate and blood pressure are monitored step by step.
The injection of the radiopharmaceutical occurs when the imitation of stress stress has reached the desired characteristics.
FINAL PHASE
After the radiopharmaceutical injection, it is usually necessary to wait 40-60 minutes for the acquisition of images of the heart via gamma-camera. This expectation is due to the fact that, in the first few minutes, the radiopharmaceutical also temporarily spreads to the abdominal splanchnic organs and lungs, and this could affect the quality of the images.
Acquisition by gamma-camera occurs with the patient lying on a couch connected to the equipment.
It is essential that at this time of the procedure, the individual under examination remains completely immobile.
Once the images have been collected, it is necessary to wait 3 to 6 hours before the myocardial evaluation at rest. In this period of time, unless otherwise indicated by the doctor, it is permitted to drink (water) but not to eat.
The examination at rest is very simple: the patient is seated on a hospital bed and the cardiologist (or his assistant) injects the radiopharmaceutical through the cannula needle.
Even at this juncture, image acquisition does not take place before 40-60 minutes have elapsed.
HOW MUCH HAS A MIOCARDIC SCANNING LASTS?
A myocardial scintigraphy usually takes an entire day .
However, in some special cases, it is possible to break the examination in two, so as to carry out the evaluation under stress (or with pharmacological stress) in one day and the evaluation at rest in the day immediately following.
When the procedure is broken in two, it takes about 4 hours on the first day and another 4 hours on the second day.
RADIOACTIVE ISOTOPES
There are two radioactive isotopes used for myocardial scintigraphy: thallium 201 or technetium 99 .
Thallium 201 and technetium 99 have different properties, therefore the procedural protocol varies slightly depending on whether one or the other is used.
In this article, for reasons of simplicity, the differences between the procedure with thallium 201 and that with technetium 99 will not be treated.
After the procedure
At the end of the scintigraphy, the patient may feel dizzy or dizzy as he gets up from the gamma-chamber hospital bed. To avoid this unpleasant sensation, the medical advice is to stand up very slowly.
It is also possible that the point where the cannula-needle was inserted develops redness and swelling. These two signs of inflammation generally disappear within 24-48 hours; if they go further, perhaps with the addition of pain, it is advisable to contact your doctor to make sure that an infection is not taking place.
IMPORTANT ADVICE
Cardiologists advise patients to drink plenty of water during the first 24-48 hours following myocardial scintigraphy. In fact, taking plenty of fluids favors diuresis and, through diuresis, radionuclides in the body are eliminated more quickly.
Risks and contraindications
Myocardial scintigraphy presents some risks.
First of all, the stress test could lead to the onset of chest pain, cardiac arrhythmias or, in the most unfortunate cases, myocardial infarction. This is due not so much to the intensity of physical exercise, but rather to the fact that the patient is generally a cardiopath.
Secondly, it is possible that the radiopharmaceutical and / or other medicines used for the examination give rise to an unexpected allergic reaction (NB: this generally occurs when the patient is unaware of being allergic to certain compounds or substances).
Finally, drugs that mimic cardiac stress caused by physical activity could induce dizziness, palpitations, chest pain and respiratory problems.
That said, it is important to remember that the aforementioned risks are very rare eventualities: in general, myocardial scintigraphy is a fairly safe procedure, especially when it is faithfully adhered to the pre-operative indications reported previously.
Sensations that, if felt during myocardial scintigraphy, should be reported to the doctor:
- Chest pain
- Sense of fainting
- Accelerated heart beat (heart beat or palpitations)
- Respiratory problems
CONTRAINDICATIONS
Myocardial scintigraphy is contraindicated (ie should not be conducted) in the case of:
- Pregnancy . The use of radioactive substances could affect the fetus, which could develop congenital defects.
- Woman breastfeeding her child . Radioactive substances could contaminate breast milk and have harmful effects on the baby.
- Severe myocardial infarction or heart failure . In these situations, not only myocardial stress scintigraphy but also pharmacological stress is dangerous.
- Infections characterized by fever . This is a temporary contraindication.
- Severe hypertension .
- Presence of valvular diseases and / or arrhythmias . Valvular diseases are heart valve diseases. Particularly dangerous is aortic stenosis.
Arrhythmias are alterations of the normal heart rhythm.
- Myocarditis, or inflammation of the myocardium.
- Recent intake of beverages or preparations containing caffeine or theophylline .
- Recent intake of medicines containing nitrates or drugs that slow down the heart rate (or bradycardia).
Results
Myocardial scintigraphy allows us to see how the blood spreads (perfusion) in the myocardium, both during physical exertion and at rest.
In fact, the gamma-camera provides very clear images of which are the myocardial areas adequately sprayed and which are not.
It is important to remember the following concepts: the lower the blood perfusion in a certain area of the myocardium, the greater is the narrowing of the coronary arteries destined to the spraying of the aforementioned area; the areas of myocardium where blood does not reach are those most suffering and most likely to undergo necrosis.
In light of this, a healthy heart shows a homogeneous perfusion throughout the heart muscle.
From the point of view of results, therefore, myocardial scintigraphy guarantees very useful and particularly indicative information.
