Overview of Nuclear Medicine SPECT Scan Cardiovascular Assessment, Protocols, and Interpretation
A Myocardial Perfusion Single-Photon Emission Computed Tomography (MPS) is a type of special and cost-effective imaging test. This test is used widely for early detection of “coronary artery disease,” which is a disease where the blood vessels supplying the heart muscle become narrow or blocked. This test is conducted about 9.1 million times annually in the United States alone.
This scan is particularly important as it helps in diagnosing heart disease, predicting future heart problems, and checking the effectiveness of heart treatments. The accuracy of this test is always improving, thanks to better technology, new software, and better scanning materials.
Here’s how MPS works: A special imaging machine, known as a gamma camera, detects a safe radioactive substance that is injected into your veins. This substance helps to show how blood is flowing in your heart. The gamma camera takes several images from different angles, creating a 180-degree arc view of your heart.
The success of the MPS scan depends on two factors. Firstly, the injected substance must be transported to the surface of the heart cells, which relies on the blood flow. Secondly, the cell membranes of the heart must be healthy to take in the substance. The amount of this substance that heart cells take up is directly related to the blood flow in the heart. Your doctor can use these images to evaluate which parts of your heart have reduced blood flow.
This scan can identify the problem areas in your heart, and can also help doctors pinpoint which specific blood vessel is causing such problems. By comparing the amount of the injected substance taken up by heart cells at rest and during stress, doctors can tell whether the heart problem is permanent or can be reversed.
Anatomy and Physiology of Nuclear Medicine SPECT Scan Cardiovascular Assessment, Protocols, and Interpretation
Your heart muscle, also referred to as the myocardium, can be thought of as being divided into 17 sections. These sections are based on viewing the heart from the front (short axis) and from the side (long axis). In the front view, your heart has different parts, or walls: septal (separating the two pumping chambers), anterior (front), lateral (side), and inferior (bottom). When viewed from the side, your heart again shows septal and lateral walls.
On a different view from the side, there’s also an anterior (front) and an inferior (bottom) wall. Different arteries supply blood to these different areas. The left anterior descending artery provides blood to the front and septal wall, the left circumflex artery to the side wall, and the right coronary artery to the bottom wall.
Doctors use a scale from 0 to 4 to rate how well each part of the heart muscle is receiving blood, with 0 meaning normal and 4 meaning no circulation of blood is taking place. If the test results show that all parts of your heart muscle are getting enough blood both at rest and under stress (like during exercise), this means your heart muscle is healthy.
However, if your heart is not getting enough blood while under stress but does during rest, this could signal that a part of your heart muscle is at risk (ischemic). If your heart muscle shows signs of not getting enough blood both at rest and under stress, then part of the heart muscle may have scar tissue or may be ‘sleeping’ (hibernating), a condition which may occur if the heart is not getting enough blood supply over time. If the heart enlarges during stress, this could mean significant disease in the heart’s arteries, potentially affecting multiple areas or the main artery leading away from the heart (left main artery).
Why do People Need Nuclear Medicine SPECT Scan Cardiovascular Assessment, Protocols, and Interpretation
If you are suspected to be at a moderate risk for coronary artery disease (CAD), which is a type of heart disease, your doctors will want to understand how severe the condition might be and where there might be restrictions in your heart’s blood supply. This can help them work out how serious your heart disease might be, and guide them in how to treat it.
If you’ve had a moderate score between 4 and -11 (indicating an intermediate risk) on what is known as the Duke Treadmill Test (a heart stress test), this will also mean they want to find out more. If you have already been diagnosed with heart disease, and your symptoms of chest pain or discomfort (ischemic symptoms) have changed, you might need to be tested again.
Also, you may need to have your heart condition checked again in 1 to 3 years if you’re highly likely to have coronary artery disease. If you had a CT scan and it showed a lot of hardness (calcification) in your coronary arteries, further testing might also be needed. An ECG (a test that measures the electrical activity of your heartbeat) might not provide predictable results in this case.
Even if you don’t have symptoms, but have jobs with high risks, like being a firefighter or pilot, you may need a test. However, these tests aren’t recommended for people who have no symptoms and a low chance of having coronary artery disease.
For people already diagnosed with ischemic heart disease, it is advisable to check on their condition 3 to 5 years after having procedures done to restore blood flow to the heart. These procedures include coronary artery bypass graft surgery (CABG), where a blood vessel from another part of your body is used to bypass a blocked artery, or coronary angioplasty, where a tiny balloon is inserted and inflated to widen a narrow or blocked artery. Repeat tests can also be helpful to check if treatments for heart disease are working. Note that routine checks are not recommended for all patients after these procedures.
Before any non-cardiac (non-heart related) surgery, if your operation falls into the ‘intermediate-risk’ category or if it’s vascular surgery (related to the blood vessels), and you have heart risk factors and low physical capability (measured as less than 4 METS which is the ability to do physical activities), you may need testing. However, for those undergoing low-risk or intermediate-risk non-cardiac surgeries, or vascular surgeries and are in a good functional health condition, such tests may not be necessary.
When a Person Should Avoid Nuclear Medicine SPECT Scan Cardiovascular Assessment, Protocols, and Interpretation
MPS, which is a type of medical test used to evaluate your heart’s health, should not be done in certain situations. This includes if you are pregnant or breastfeeding, had a recent heart attack (less than 2 days ago), or have various severe health conditions like specific heart conditions, lung clot, a tear in a major blood vessel, severe lung blood pressure, certain types of chest pain, heart failure, severe high blood pressure, or irregular heart rhythms.
Additionally, MPS is not usually recommended if you have a severe condition affecting the main blood vessel leading out of your heart, certain severe valve conditions, a specific type of heart disease that causes a thickened heart muscle, severe blockages in the blood flow from the left side of your heart, or a total blockage in the electrical signals in your heart.
Also, MPS is not favorable if you are suffering from severe illnesses like metastatic cancer. Metastatic cancer is a type of cancer that has spread from the place where it first started to another place in the body.
Each of these conditions can make this test less accurate or riskier for your health. This is why your doctor will evaluate your medical history and current condition before recommending MPS.
Equipment used for Nuclear Medicine SPECT Scan Cardiovascular Assessment, Protocols, and Interpretation
To carry out a test called a myocardial perfusion scan, which checks the blood flow to your heart, the doctor will use specific equipment. This includes:
A treadmill machine you’ll need to walk or run on. This is because the test often involves making your heart work harder through exercise.
Various drugs, including vasodilators and Ionotropes. Vasodilators help widen blood vessels to improve blood flow, and Ionotropes help strengthen your heart’s contractions.
An antidote. This might be needed to counteract any potential side effects from the vasodilator and inotropes.
A radioactive substance called a radiotracer. This is injected into your body and can be picked up by a special camera to create images of your heart.
A specific camera called a myocardial perfusion gamma scan machine. It captures images of the radioactive tracer in your body, providing a clear picture of the blood flow to your heart.
Who is needed to perform Nuclear Medicine SPECT Scan Cardiovascular Assessment, Protocols, and Interpretation?
A myocardial perfusion scan is a procedure that is done by a team of medical experts. It includes a doctor known as a nuclear cardiologist or radiologist, who specializes in using radioactive substances to diagnose or treat diseases. There’s also a nuclear technologist who helps operate the special equipment used during the procedure. Lastly, a nurse is there to provide care and ensure your comfort.
Preparing for Nuclear Medicine SPECT Scan Cardiovascular Assessment, Protocols, and Interpretation
Before the test, you will need to avoid eating any food or drinking liquids for 3 hours. This is called ‘fasting’. Additionally, avoid food and drinks that contain caffeine for at least 12 hours. This includes coffee, tea, chocolate, and some types of soda. If you’re taking blood pressure medication that also helps with chest pain (like a beta-blocker, calcium channel blocker, or nitrates), you should stop taking them 12 hours before the test. These preparations are necessary to get accurate results from the test.
How is Nuclear Medicine SPECT Scan Cardiovascular Assessment, Protocols, and Interpretation performed
There are two main methods to perform stress testing, which helps doctors determine how the heart responds to exertion or strain:
1. Exercise
2. Drugs or ‘Pharmacological’
1. Exercise-Based Stress Testing:
The most favored kind of stress testing is exercise-based. This method uses the Bruce protocol, which involves walking on a treadmill until you reach 85% of your maximum predicted heart rate. It’s important to note that reaching this heart rate doesn’t mean you should stop the test right away.
In this test, a radioactive tracer is injected to visualize the heart as close to peak exercise as possible, and you are encouraged to exercise for at least one minute after the injection. However, the exercise should be stopped right away if you’re experiencing severe chest pain, extreme tiredness, loss of balance, dizziness, or a significant drop in blood pressure. If these symptoms occur, or if the machines are unable to monitor the heart activity accurately, the exercise is stopped.
2. Pharmacologic Stress Testing:
When you can’t exercise or can’t exercise adequately, pharmacologic stress testing is used. In this process, different drugs like dipyridamole, adenosine, and regadenoson serve as agents, prescribed to expand your blood vessels — much like what occurs during exercise.
However, some conditions like severe lung disease and consuming caffeine-containing drinks can be contraindications for using these drugs. If these drugs are used, aminophylline (a drug that counters the effects of the vasodilators) can be given to reverse their effects.
In more specific cases where performing exercise and using vasodilators are both not possible, we use a type of drug that stimulates the heart called an inotrope. Dobutamine is a popular inotrope used. However, it’s important to note that this is not suitable for patients with certain conditions like severe hypertension and heart disease.
Both these tests utilize radioactive substances known as radiotracers for creating clear imaging. The commonly used ones are Thallium-201 and Technetium–99. They function differently in the body, each possessing different sets of pros and cons that doctors consider when prescribing stress tests.
Possible Complications of Nuclear Medicine SPECT Scan Cardiovascular Assessment, Protocols, and Interpretation
Problems from a heart scan, known as a myocardial perfusion scan, don’t happen often. However, there are a few things that could possibly occur:
* You could be exposed to a small amount of radiation during the scan.
* There’s a small chance of a heart attack (or ‘myocardial infarction’) happening.
* Rarely, you might experience an irregular heartbeat, also known as an arrhythmia.
* Some people might have chest pain that isn’t caused by a lack of blood flow to the heart (non-ischemic chest pain), especially if you’ve taken certain medications like dipyridamole and adenosine.
* Some people might start wheezing, which is when you make a whistling sound while breathing due to narrow or blocked airways.
What Else Should I Know About Nuclear Medicine SPECT Scan Cardiovascular Assessment, Protocols, and Interpretation?
A myocardial perfusion scan is a specific kind of heart test that plays a critical role in diagnosing heart diseases that are caused by blocked or narrowed arteries, such as ischemic heart disease. It is also helpful in checking how well treatments for these types of heart diseases are working.
This scan helps doctors examine the blood flow to the heart muscle, which is essential for its normal function. This test is noninvasive, meaning it doesn’t involve any surgical procedures, making it a practical choice.
It can also be incredibly beneficial before surgery for assessing potential heart risks, especially for patients who have other health issues and are scheduled for intermediate-risk surgeries. A myocardial perfusion scan can highlight areas where the blood flow might be weak or not reaching at all, guiding the doctors in managing the condition effectively.
The extent of the risk associated with the heart during surgery is directly linked to the severity of the blood flow abnormalities revealed in the myocardial perfusion scan. This means that any problems with blood supply to the heart seen on the scan could indicate a higher risk during surgery.