Overview of Coronary CT Angiography
Chest pain is the most common sign of coronary artery disease (CAD), which is a disease of the heart’s arteries. This pain can be hard for doctors to understand, because heart disease is still a big health problem around the world, despite improvements in medicine and procedures. This is why we need to find the problem and treat it quickly, but in a way that doesn’t cost too much.
Coronary computed tomography angiography (CCTA) is an important tool that helps us look at the heart and its blood vessels. It’s a method that doesn’t involve surgery, which can be very helpful for patients who have a low to medium chance of having heart disease that reduces the blood flow to the heart. This is especially relevant if the patient is stable and doesn’t need immediate treatment to improve the blood flow.
Although the most accurate way to diagnose CAD is through an invasive procedure known as coronary angiography, CCTA is becoming more popular because it’s non-invasive and has less risk. It also helps to make the diagnosis process quicker for patients who have a moderate risk of CAD. CCTA needs to be very precise, because the heart’s arteries are very small and always moving. It uses special technology that can take pictures quickly (this is known as temporal resolution) and can clearly show small spaces (this is known as spatial resolution).
Recent improvements in the technology used for CCTA, including 64-slice multi-detector CT (64-MDCT) systems, have made the pictures even better and they can now clearly show even the smallest and most distant parts of the coronary arteries.
Anatomy and Physiology of Coronary CT Angiography
The CCTA, or Coronary Computed Tomography Angiography, is a type of imaging test that doctors use to get a detailed view of the heart and its various parts. These include areas like the heart’s chambers, the outer layer of the heart, and the large blood vessels that carry blood to and from the heart. The test uses a special dye to make it easier to see these areas.
Although other types of heart scans can provide some details, CCTA can give doctors a lot of valuable information. It’s essential for doctors to understand the structure of the heart in detail so that they can accurately interpret the results of this test.
For instance, the heart’s blood supply comes from some major arteries. The left main artery usually originates from one of the heart valves and is typically 1 to 2 cm long. It splits into two other crucial arteries, one of which supplies the front part of the heart, and the other supplies the side of the heart. For about 0.41% of patients, however, the left main artery is absent, and instead, these two key arteries come directly from the heart valve.
The right main coronary artery comes from a different area of the heart and supplies blood to other regions of the heart.
These variations in the heart’s blood vessels can significantly influence how blood flows through the heart, making it important knowledge for interpreting the results of a CCTA scan.
Why do People Need Coronary CT Angiography
Coronary Computed Tomographic Angiography (CCTA) is a medical test that helps doctors see what’s happening inside your heart’s blood vessels. It uses advanced X-ray technology to take detailed pictures of the heart and its blood vessels. The CCTA is excellent for checking if your blood vessels (called coronary arteries) have any blockages, which could cause chest pain or a heart attack. It can find blockages over 50% better than traditional methods.
During the CCTA, some images are taken without it, but usually a contrast dye is used to improve the quality of the photos. These high-definition images can reveal minor and major heart conditions that might not be captured by other noninvasive imaging tests, such as an echocardiograph (also known as an echo) or cardiac magnetic resonance imaging (MRI).
CCTA can also detect a range of heart conditions including Adult Congenital Heart Diseases (CHD). Simple CHDs include atrial septal defects and bicuspid aortic valve, while complex conditions include Ebstein’s anomaly and transposition of great arteries. Patients with CHD often benefit from surgery, and the detailed images from a CCTA provide the vital information doctors need for successful operations.
An extra feature of the CCTA is that it can calculate calcium scores, which indicate plaque build-up in the arteries and the risk of coronary artery disease (CAD). This score, known as an Agatston score, helps to categorize patients into risk groups, and aid doctors in determine the best course of treatment.
On top of that, CCTA can be used to identify abnormalities of the coronary arteries, which occur in less than 1% of the population. These abnormalities can vary widely, from harmless conditions to causes of sudden cardiac death. CCTA gives a detailed view of these abnormalities and also allows for a full 3D assessment of the entire heart.
As per the Society of Cardiovascular Computed Tomography, CCTA has several applications including evaluating stable coronary artery disease in patients without previous CAD, CAD patients after inconclusive functional testing, symptomatic high-risk patients, and patients who had cardiac surgery previously. It may be useful for functionally assessing stenosis, which is a narrowed blood vessel condition, and screening for coronary allograft vasculopathy, a common type of heart disease in transplant patients.
When a Person Should Avoid Coronary CT Angiography
There are usually no strict rules against carrying out a CCTA, which is a type of heart scan. However, if someone has had a severe allergic reaction to iodinated contrast, a type of dye used in some scans, they should not have it again.
There are some cases where a CCTA might not be the best choice, which are:
- Acute thyroid storm: a sudden, severe worsening of hyperthyroidism symptoms.
- Pregnancy: scans should generally be avoided.
- Renal insufficiency: this means the kidneys aren’t working properly. It is defined as a creatinine clearance (CrCl) of less than 30 mL/min/1.73 m2 – a measure of how well your kidneys are clearing waste from your blood.
- Difficulty holding breath for longer than 5 seconds.
- Being on radioactive iodine therapy: a type of treatment for thyroid cancer.
- Hemodynamic instability: when blood flow is not stable enough to provide oxygen to the organs and tissues.
- Acute decompensated heart failure: sudden or worsening symptoms of heart failure.
- Patient’s height and weight above the recommended scanner thresholds: if a patient is too tall or heavy for the scanner, it might not be suitable.
Equipment used for Coronary CT Angiography
The Society for Cardiovascular Computed Tomography suggests using a 64-slice CT scanner at the very least for heart-related CT scans. This type of scanner can produce a large number of detailed images of the heart. They also recommend using dual-head power injection pumps. These pumps help in giving contrast material (a special dye used to make specific areas show up clearly on the scan) in two or three phases. This is known as biphasic and triphasic injection protocols.
All the images taken should be stored in a system called the digital imaging and communications in medicine (DICOM). DICOM is a standard for transmitting, storing, and sharing medical images. It ensures that all images and associated information are neatly organized and easy to access.
Moreover, a picture archiving and communication system (PACS) needs to be in place. PACS is a medical imaging technology that provides storage and convenient access to images from multiple modalities (source machines). This allows doctors to look at all the images gathered during the scan, which aids in providing a comprehensive review of your overall heart health.
Who is needed to perform Coronary CT Angiography?
The Society for Cardiovascular Computed Tomography suggests that scans of the heart, known as CCTAs, should be done by specially trained technologists. These professionals are skilled at using equipment that injects contrast (a special dye to make organs visible) into your body and performing heart scans. It’s important for a team member to be skilled at putting in IVs (tiny tubes inserted into your vein), usually done in your arm.
During the imaging process, a member of the team who has advanced training in cardiac (heart) life support should be nearby. Cardiac life support involves managing heart emergencies. Also, a doctor or nurse who’s trained in giving medications like beta-blockers and nitroglycerin (which help control your heart rate and relieve chest pain) should be around when the scan is done.
The doctor who reviews the scans should also have specific CCTA training. It’s a guideline given by the American College of Cardiology (ACC) and American Heart Association (AHA) to ensure the highest standard of care.
Preparing for Coronary CT Angiography
Before conducting a special type of scan known as Coronary Computed Tomography Angiography (CCTA), there are several important facts which you as the patient need to be aware of:
– Firstly, the decision to go ahead with a CCTA should only be taken if the results of the scan can potentially influence the management of your health condition or estimate of your future health (known as prognosis). It should also be certain that high-quality images can be obtained from the scan.
– Also, any possible conditions that might prevent you from undertaking the scan (known as contraindications) must be reviewed. The risks and benefits of going ahead with the scan will also be considered.
– You will be asked to give informed consent before the start of the CCTA. This means your doctor will explain the procedure to you, answer any questions you may have, and then ask for your agreement to proceed.
– Please be sure to avoid eating solid food at least 4 hours before the exam. However, you may continue to consume liquids.
– Avoiding caffeine for 12 hours before the test is also important.
For the scan, a catheter (a thin tube) will ideally be placed into a vein in the inside of your elbow on your right arm. This arrangement enables quick injection of a special dye, known as contrast, at a high speed for better images, and also lessens the chances of any image distortions. Generally, the heart rate should be lowered to 60 beats per minute or less for ideal imaging. Certain medications may be given hours before the test to achieve this.
All non-steroidal anti-inflammatory drugs should be stopped 24 to 48 hours before the study to reduce the risk of kidney damage due to the contrast dye. Similarly, a medication called Glucophage should not be taken for 48 hours after the procedure, and other types of medication may also need to be paused if nitrate drugs are expected to be used. These nitrate drugs help to widen your heart arteries and provide a clearer view of these arteries and any blockages. They are typically given 5 minutes prior to the CCTA imaging.
Lastly, you’ll need to practice holding your breath before the test as this is often required during the scan to ensure clear images are obtained.
How is Coronary CT Angiography performed
During the X-ray procedure known as CCTA, a substance called contrast dye is used to create clearer pictures of the inside of your body. Your doctor will need to inject into your bloodstream roughly about half to a full cup of this dye to make your arteries appear brighter on the X-ray. This contrast helps the doctor to see your arteries in more detail.
Doctors use two methods called ‘biphasic’ and ‘triphasic’ injection protocols. The biphasic protocol includes injecting the contrast dye first, followed by salt water (saline), while the triphasic protocol consists of contrast, a mix of contrast and saline, and finally pure saline. These methods prevent the creation of distorted images due to high concentrations of contrasting on the right side of the heart. If the doctor also needs to observe the right side of your heart, they will use the triphasic method.
The scanning process starts with taking some scout images. These are like preliminary scans that help the doctor decide the best timing for the actual X-ray to get a clear picture. Then, they set the parameters for image acquisition, which is tailored for each patient and each particular case. The X-ray machine rotates around your body while the bed you lay on is moving, which creates a spiral path – this is why this method is called ‘spiral’ or ‘helical’ CT.
The latest types of CT scanners can capture images of your heart in one rotation, which is a significant advancement from older models. The images can be captured in two ways. The ‘retrospective’ method takes images at very short intervals throughout the heartbeat cycle. The ‘prospective’ method takes images at a specific point in the heartbeat cycle. The prospective method is usually preferred because it exposes the patient to less radiation.
To minimize radiation exposure while still obtaining accurate diagnosis, the scanning range is limited only to the structures needed to be examined. The configuration of the X-ray machine is adjusted to lower radiation and maintain image clarity. If the scanner is passing through less dense tissue like lungs, the current can be adjusted to reduce radiation exposure.
Processing the images comes right after the scan. This step is crucial in evaluating the images of the coronary arteries, which supply blood to your heart, and other structures. Any abnormal heartbeats are discarded to make an accurate assessment of your heart’s health. A part of the heartbeat cycle is chosen carefully, and the appropriate parameters for reconstruction of images are determined.
If a patient has irregular heartbeats, selecting a specific part of the heartbeat cycle for image reconstruction can cause artifacts or ‘false images.’ To avoid this, a fixed point in the heartbeat cycle is chosen for image reconstruction. The phase in the heartbeat cycle where the heart muscle is at rest after contraction (late-diastole phase) is typically selected for assessing the coronary arteries. If needed, an early phase of the heartbeat cycle called systole can be selected to reduce any blurring effects due to heart movements.
Possible Complications of Coronary CT Angiography
If you’re prescribed a CCTA test, which stands for coronary computed tomography angiography, the location where the test is being conducted should have all the necessary equipment and staff to handle any unexpected allergic reactions. These reactions can be caused by the substances used during the test, although it is a very rare occurrence. If you have a known allergy to these substances, doctors can give you treatments like oral steroids and diphenhydramine (an allergy medication) before the test.
CT or computed tomography scans, including CCTA tests, use a type of radiation known as x-rays. This type of radiation can cause cell damage at a very small level. The risk associated with this radiation increases over time throughout a person’s life. This is why children and young adults have a higher risk because they have potentially more years to be exposed to radiation. Organs that produce a lot of new cells quickly are also more at risk of genetic damage from the radiation.
Although CT scans involve radiation, medical professionals strive to keep the exposure level as low as possible while still acquiring the necessary images for diagnosis. This is part of a principle called “as low as reasonably achievable,” which guides medical practice to reduce radiation exposure from medical imaging.
What Else Should I Know About Coronary CT Angiography?
Coronary Computed Tomography Angiography (CCTA) is a test that allows doctors to see your heart and blood vessels without having to perform surgery. This makes it a more comfortable and less expensive option for checking for Coronary Artery Disease (CAD), a condition that causes blockages in the heart’s blood vessels.
CCTA is not only useful in identifying CAD, but it’s also good for assessing the overall condition of your heart. Plus, it can be done relatively quickly. This tool is increasingly being used in low-risk cases to check for Acute Coronary Syndrome, a condition where blood flow to the heart muscle is suddenly blocked.
Apart from looking at the heart’s blood vessels, CCTA can explain symptoms by showing other areas in the heart or birth defects related to the heart. As technology continues to evolve and improve, there will be even more benefits to CCTA procedures. This includes lower patient exposure to radiation, which can present health risks.
