Overview of Intravascular Ultrasound
Intravascular ultrasound (IVUS) is a tool used mainly in heart-related treatments to help doctors better understand the characteristics of harmful lesions, measure the amount of plaque build-up, aid in determining the appropriate size for a stent (a small tube inserted into a narrow or blocked channel in the body), check if the stent has properly expanded, and spot any complications during the procedure.
IVUS works through a special tube with ultrasound technology that can gather images from inside an artery, creating round cross-sectional views of the entire artery. This advanced technique has a significant advantage over angiography, a type of x-ray that only produces 2-dimensional images of the inside of a blood vessel, which is actually 3-dimensional in nature.
Unlike angiography that observes the vessel from the outside, IVUS provides a view from within the vessel, offering a much detailed and accurate perspective.
Anatomy and Physiology of Intravascular Ultrasound
Intravascular ultrasound, or IVUS, is a technique used to visualize the inside of a coronary artery which is a blood vessel that provides the heart with oxygen and nutrients. This technique allows doctors to see and understand the ins and outs of the inside of your artery. The artery is made up of three layers: the inner layer (tunica intima), the middle muscle layer (tunica media), and the outer layer (tunica adventitia).
The middle layer, made of smooth muscle cells, doesn’t reflect ultrasound waves and appears dark in the ultrasound images. This makes it easy for doctors to identify it. IVUS helps doctors to understand the nature and size of plaque, which is a sticky deposit that can clog arteries. It can even distinguish between different types of plaque, like those that are hardened (calcified), made of fat (lipid), or made of new tissue growth (neointimal proliferation).
IVUS can even identify hardened plaque that might not be visible in other types of testing like angiography, which is a test that uses X-rays to view your body’s blood vessels. IVUS is especially important in understanding why a stent, which is a small tube inserted into a blocked passageway to keep it open, might have failed. Whether the stent has a blood clot (thrombosis) or has narrowed again (in-stent restenosis), IVUS can help doctors decide the best treatment plan.
Why do People Need Intravascular Ultrasound
Intravascular ultrasound (IVUS), a procedure used in patients undergoing heart-related procedures, has many useful applications. This involves inserting a small ultrasound probe into the heart’s blood vessels, allowing doctors to see images from inside the arteries.
As per the American College of Cardiology (ACC), it’s suggested for several reasons:
The first set of suggestions (termed as Class IIa):
1. IVUS could be a good way to check the left main coronary artery disease (CAD) when it’s not clear from other imaging methods (This suggestion is backed by reasonable but not the highest level of scientific evidence, termed ‘Level of Evidence: B’).
2. IVUS, with another imaging method called coronary angiography, can be used 4 to 6 weeks and 1-year post heart transplant. This is to ensure the donor didn’t have CAD, spot rapidly advancing heart transplant-related artery disease, and provide information about the patient’s prognosis (This also has ‘Level of Evidence: B’).
3. IVUS can be helpful in understanding the cause of the heart stent narrowing down or not working properly (‘Level of Evidence: C’, which means the scientific evidence supporting this is limited).
The next set of suggestions (Class IIb):
1. IVUS may be seen as a viable option in checking non-left main arteries with moderate blockages (This has ‘Level of Evidence: B’).
2. IVUS could be considered to assist in the placement of heart stents, particularly when it involves left main coronary artery (LMCA) (‘Level of Evidence: B’).
3. It may be rational to use IVUS for identifying the reason behind the formation of blood clots in the stent (‘Level of Evidence: C’).
However, a condition named CLASS III suggests that IVUS is not advised for routinely assessing a blocked artery, if a procedure to improve blood flow through the artery is not planned (‘Level of Evidence: C’).
Updated 2018 guidelines from the European Society of Cardiology (ESC) also recommend the use of IVUS for specific purposes. They suggest IVUS for assessing the severity and improving the treatment of unprotected left main coronary lesions. Furthermore, it should be considered for the detection of any issues related to stent placement leading to restenosis and considered in some patients to improve stent implementation.
When a Person Should Avoid Intravascular Ultrasound
There are generally no strict rules saying a person can’t undergo Intravascular Ultrasound (IVUS). But, in some cases, if a person’s blood vessels are excessively twisted and angled such that an IVUS catheter (a thin tube used in the procedure) can’t reach the area that needs examination, the procedure might not be advisable. This is called a relative contraindication.
Like any procedure involving the heart’s arteries, IVUS involves the use of anticoagulants, medicines that prevent blood clotting, during the process. So, if a person isn’t a good candidate for using these anticoagulants, or if they’re not suitable for angiography (an X-ray technique to see blood vessels) and cardiac catheterization (inserting a tube in the heart through blood vessels) in general, they might not be able to have an IVUS.
Equipment used for Intravascular Ultrasound
IVUS, or intravascular ultrasound, works by using a special device called a piezoelectric transducer that creates sound waves to capture pictures. There are two main types of these devices, each with a different design. The first type, called solid-state phased array, makes use of multiple piezoelectric transducers that stay in one place. The other type, rotational design, uses a single transducer.
The choice between these two types depends on where and how they are to be used. For example, the solid-state phased array design can achieve a wider range of imaging, which makes them the preferable choice when working on larger vessels often found in peripheral interventions. On the other hand, the rotational design comes with an automatic pullback feature, useful for taking measurements to determine the size and length of lesions and stents.
There are also multi-purpose IVUS devices that incorporate another type of technology in addition to ultrasound. Notably, some models available in the market can do both IVUS and near-infrared spectroscopy (NIRS), a method that uses light to scan the body. Similarly, other designs are currently being studied, combining IVUS with optical coherence tomography (OCT), an imaging technique that uses light to capture micrometer-resolution, three-dimensional images from within optical scattering media, such as biological tissue.
Who is needed to perform Intravascular Ultrasound?
A special medical device called an IVUS catheter is used to take internal pictures of your body, which are then sent to a computer for further analysis. Other medical staff in the lab may help set up the IVUS catheter. It’s a skilled heart doctor or blood vessel surgeon who controls the catheter within your body.
This online examination is used to evaluate the form and size of fatty deposits in your arteries known as plaques, assess the smallest open space in your arteries (Minimal Lumen Area or MLA), calculate the size of these plaques, and identify parts of the normal artery. This information helps doctors make the best decision for your treatment.
Preparing for Intravascular Ultrasound
The process of preparing catheters for Intravascular Ultrasound Imaging (IVUS, a test that shows the inside of your coronary arteries) changes a little depending on the creator of the catheter. However, generally, it’s a simple process where the catheter system is cleaned with saline, a type of salt solution, and then connected to a control device.
To decrease the risk of blood clotting (thrombus) or sudden narrowing of the artery (vasospasm), certain medications like anticoagulants (blood thinners) and nitroglycerin (a medicine that relaxes and widens blood vessels) should be given before inserting the catheter for IVUS.
How is Intravascular Ultrasound performed
An IVUS assessment is a type of ultrasound imaging, allowing doctors to see the inside of blood vessels. This examination can be accomplished using either a manual or automatic pullback method. The automatic pullback offers the advantage of allowing for measurements of length; this feature is helpful in determining the correct length of a stent that the doctor may need to insert.
When it comes to selecting a stent’s size, the IVUS assessment helps doctors to spot, and then measure, the areas before and after (proximal and distal) the problematic section of the vessel. After implanting the stent, IVUS also aids in assessing the smallest area inside the stent, known as the minimal stent area (MSA). This measure is vital as it is closely linked to the possibility of future issues related to the stent. The more accurate the assessment, the better the route of treatment can be planned.
Possible Complications of Intravascular Ultrasound
Side effects from the use of IVUS (a medical imaging method to see inside blood vessels) are rare, but can sometimes happen. These problems could include tearing or puncturing of the vessel (dissection and perforation), abnormal heart rhythm (arrhythmia), blood clot (thrombosis), or narrowing of the blood vessels (vasospasm). These issues could potentially happen anytime a tool is used inside a blood vessel. Therefore, when the blood vessels are very twisted (tortuous), doctors need to be especially careful.
What Else Should I Know About Intravascular Ultrasound?
IVUS, short for Intravascular Ultrasound, is a medical tech tool used by doctors to view and assess the left main coronary arteries, the ones that supply blood to your heart. This tech tool can be used to decide how serious potential blockages are and to provide guidance for clearing these blockages. This process is often called revascularization. The way the doctors approach this, also known as the PCI strategy, can change based on what the IVUS reveals.
Various clinical studies and analyses have shown that using IVUS often helps to reduce unwanted health issues related to clearing the blockages. After revascularization, IVUS can also identify factors that could increase the risk of the blockage happening again or that might impact the size of the vessel post-treatment.
Because IVUS can provide important information and help reduce future health issues, it’s surprising that it is not used more widely in the U.S. despite evidence of its benefits for many years.