Overview of Radionuclide Ventriculography
A radionuclide ventriculography scan, also known as an RNV scan, is a special type of imaging test for your heart. This procedure is a non-invasive (not cutting into body tissues) way for doctors to study how well the heart’s lower chambers (the ventricles) are working and how the blood flows within the heart.
What makes the RNV scan preferred in many cases is that it results in less variability between different observers. What does that mean to you? It basically means that more than one doctor can look at the results and they are likely to see the same thing. This makes the RNV very useful for regularly checking the heart’s function over time.
Besides, RNV scans can also help to check how different sections of the heart walls contract (tighten and relax), which could help in planning your treatment if you need something called cardiac resynchronization therapy (CRT)– a treatment for some types of heart failur.
Also, the good news is that RNV scans are a safe procedure and don’t take too much time; typically you can expect to be done within 1 to 2 hours. The process involves injecting a slightly radioactive material (tracer) into your body, and then taking images of your heart using a type of camera called a gamma camera. This camera can pick up the tracer and create images that outline the ventricles of the heart very precisely so your doctor can accurately assess how they are functioning.
There are three different ways these RNV scans can be done: a ‘first-pass’ scan, an ‘equilibrium blood pool’ scan, and a ‘Gated SPECT’. Your doctor will choose the most suitable one depending on your condition and the information needed for your care.
Anatomy and Physiology of Radionuclide Ventriculography
The RNV scan is a medical test that looks at the structure and function of your heart. It uses a radioactive marker that works on the principle that the level of radioactivity in each section of the heart relates to the volume of that section. It helps measure the volume in each part of your heart during different parts of the heartbeat – the pumping action of the heart.
For example, the volume of each heart chamber at the end of contraction (when the heart muscle tightens and pumps blood out) is called the end-systolic volume (ESV), and at the end of relaxation (when the heart muscle relaxes and allows the chambers to fill with blood) is called the end-diastolic volume (EDV). The stroke volume is the difference between EDV and ESV – usually, it is between 80 to 100 ml (milliliters). The ejection fraction (EF) is the amount of blood pumped out of the heart compared to the total amount of blood in the heart just before a beat. The heart’s output is the amount of blood pumped by the heart in a minute, calculated by multiplying the stroke volume and the heart rate.
The RNV scan can also assess the movement of the heart walls – whether they are moving normally, moving less than they should (hypokinetic), not moving at all (akinetic), or moving in the opposite direction to normal (dyskinetic).
The blood supply to the heart muscles is through three main arteries; the left anterior descending coronary artery, the left circumflex artery, and the right coronary artery. Each of these arteries provides blood to certain parts of the heart. By identifying abnormalities in the movement of different parts of the heart wall, the RNV scan can help pinpoint which artery might be affected, which is particularly useful for diagnosing heart conditions like ischemia (lack of blood supply to the heart) or heart attack.
Why do People Need Radionuclide Ventriculography
Radionuclide ventriculography is a type of imaging test that is used to check how well the heart is pumping blood. It’s often used to check the function of the left and right ventricles, the two lower chambers of the heart that receive blood from the top chambers and pump it out to the body. This test can be used in several situations:
- It can help doctors assess how well the heart is working in patients with different heart conditions. These could include coronary artery disease, where the blood vessels supplying the heart are narrow or blocked; valvular heart disease, a condition affecting the valves that control blood flow in the heart; atrial arrhythmia, an irregular heart rate; congenital heart disease, which is present from birth; and myocardial disease, which affects the heart muscle. This test could also be used before starting a type of chemotherapy (cancer treatment) that can harm the heart.
- It can be used to assess how well the left ventricle is filling with blood and pumping it out in patients with congestive heart failure. Congestive heart failure is a condition where the heart doesn’t pump blood as well as it should. Even if the heart’s pumping action (ejection fraction or EF) is preserved, this test can be used to check its function.
- For patients on chemotherapy that can harm the heart, this test can be used to keep a check on how well the heart is functioning over time.
- If a patient has a moderate chance of having coronary artery disease, and other imaging tests aren’t available, this test can be used to check the movement of the heart wall
- Before a device called a cardiac resynchronization therapy (CRT) device is implanted in the heart to correct its rhythm, this test can check how evenly timed the pumping action in the different areas of the heart is – this is known as ventricular synchronicity.
When a Person Should Avoid Radionuclide Ventriculography
There are a few reasons why certain individuals, such as pregnant or nursing ones, may need to avoid medical procedures. One such reason is to prevent exposing an unborn baby or nursing infant to potentially harmful radiation.
Similarly, if a person has previously had an allergic reaction to a radioactive tracer, (a special substance used to track processes within the body) getting such a procedure might not be safe for them.
Equipment used for Radionuclide Ventriculography
Here is a list of equipment your doctor might use during a heart scan:
* Heart monitor: This machine measures the electrical activity of your heart to check how well it’s working.
* Blood pressure machine: This device measures how hard your blood is pushing against the walls of your arteries as it’s pumped around your body.
* Radioactive tracer (TI-201 or Tc-99m-labelled): This is a safe, small amount of radioactive material that’s injected into your bloodstream. It helps the doctors to see your heart more clearly on a scan.
* Gamma camera: This camera captures images of the radioactive material in your body, helping your doctor see how your heart is functioning.
* Treadmill or stationary bike: You may be asked to exercise on one of these pieces of equipment. This exercise makes your heart work harder, allowing the doctors to see how it functions under stress.
* Computer system with special software: This computer processes the images captured by the gamma camera, and allows the doctor to analyze them.
Who is needed to perform Radionuclide Ventriculography?
The RNV scan, a special type of test used to look at your heart, should be done by a trained professional in nuclear medicine. This person knows how to get and work with the images that come from the scan. During the scan, there will also be a heart doctor, a radiologist (a doctor who specializes in medical imaging), or a doctor who specializes in nuclear medicine watching over the process.
Preparing for Radionuclide Ventriculography
For the rest RNV scan, there’s no special preparation necessary.
However, if you’re having an exercise RNV scan, you’ll need to not eat anything 4 to 6 hours before your scan. Also, for your comfort, make sure to avoid drinks with caffeine for 12 hours prior to the scan and wear comfortable clothes and shoes.
How is Radionuclide Ventriculography performed
The patient is comfortably positioned on the examination table, hooked up with sensors that can detect the electrical activity of the heart (EKG or electrocardiogram) and a blood pressure cuff on the arm. The resting heart rate, the EKG reading, and blood pressure are recorded before starting the test and are monitored at all times during the exam.
The procedure involves marking, or ‘tagging’, the patient’s red blood cells (RBC) with a radioactive substance called technetium-99m. This tagging can be done in two ways – inside the body (in vivo) or outside the body (in vitro), before being injected back into the patient via an IV. The dosage given will depend on the patient’s weight, but it’s typically around 20mCi.
The procedure can be conducted using three methods – first-pass study, gated equilibrium ventriculography, or gated SPECT image acquisition. All these methods use the EKG readings to coordinate the scanning with the heartbeat. The EKG readings help break up the heart’s cycle into frames, with each heartbeat being the ‘trigger’ for sequencing these frames. Stable heart rhythm is crucial to get accurate data; too much variation or irregularities can distort the results. The test may involve physical activity like riding a stationary bike or taking medication (dobutamine) to stimulate the heart.
In the first method, the first-pass study, a special camera takes quick sequence images of the heart, lungs, and large blood vessels immediately after the radioactive substance is injected.
In the second method, gated equilibrium ventriculography, images are taken only after the radiotracer evenly spreads throughout the bloodstream. It captures images from three different angles – front view, a 45-degree view to visualize the heart’s inner wall, and a side view. During exercise, only the 45-degree view is captured at different exercise stages.
The third method, gated SPECT image acquisition, allows for the precise visualization of the blood flow to specific heart segments. It can generate more detailed images of the heart from multiple angles, including 3D images. This method gives a more accurate measurement of the heart’s pumping efficiency (ejection fraction) compared to simpler methods that may not account for all parts of the heart.
Both visual (qualitative) and numeric (quantitative) assessments are made from the images. Visual assessment involves watching the movement of the heart on a screen to check for potential irregularities in the heart’s contractions and wall movements. In the numeric assessment, a computer measures the changes in radioactivity in the heart region during a heartbeat. The radioactivity level changes correspond to changes in blood volume in the heart, allowing for accurate measurements of the heart’s blood-holding capacity both at rest and during contractions. The heart’s pumping efficiency in different parts is also analyzed.
Possible Complications of Radionuclide Ventriculography
The Renal Nuclear Venogram (RNV) scan is a safe test that doesn’t have serious side effects. It makes use of a small amount of a substance called a radiotracer, which leaves your body through your kidneys within a day. The amount of radiation you’re exposed to during an RNV scan is about the same as what you’d get from a CT scan, a common imaging test.
During the scan, a medicine called dobutamine might be used. This could cause some minor discomfort like nausea, a headache, a racing heartbeat, or chest discomfort, but these symptoms usually go away after a few minutes.
What Else Should I Know About Radionuclide Ventriculography?
The RNV scan is a top-of-the-line test used to check how well the left side of your heart is working before and during treatment with chemotherapy that could damage your heart. It’s also known to be a cost-effective way to keep a tab on heart function during such treatments.
A previous research suggests that this scan is useful in evaluating the risk of heart-related complications and death during surgery. If the scan shows abnormal movements of your heart’s walls, this could be a sign of lack of blood supply to your heart or a heart attack. It can also help provide more information on your risk of heart disease and give warning signs of a serious heart event like a heart attack.
Moreover, the scan can assist in figuring out the type of heart muscle disease you may have – whether it’s dilated, hypertrophic, or restrictive cardiomyopathy. In simpler terms, it helps doctors determine whether your heart is enlarged, abnormally thick, or stiff. RNV scan results can also be helpful before starting CRT, a therapy used to improve the heart’s efficiency, as the commonly used heart scan methods have not been consistently reliable in predicting the success of the treatment.