CT Coronary Angiography A look at the heart arteries
CT Coronary Angiography, or CTCA, is an excellent way of assessing the coronary arteries.
Patients at a lower risk of coronary heart disease can have a CTCA as a first test and if negative, this can be very reassuring.
A computed tomograph of the coronary arteries (CTCA) is a non-invasive way of assessing the arteries of the heart. This is a common test required for patients having chest pain and provides an excellent way of assessing patients who are at low risk of very severe disease. It is not suitable for all patients – in those who are already known to have coronary disease or those with severe diabetes or kidney problems. If you have these problems, we may choose alternative tests to use instead, or alongside a CTCA.
“CTCA has really revolutionised the way we assess the coronary arteries in patients at low risk of obstructive coronary artery disease. Younger patients, with relatively few risk factors can be assessed quickly, safely and accurately. If we find there are moderate levels of artery blockage, we may need to undertake other tests to fully assess you.”
The test involves a CT (sometimes referred to as a ‘CAT scan’) and will need to be done at a specialist clinic setting, such as the Hammersmith Hospital, BUPA Cromwell Hospital or the Syon Clinic.
The Test Procedure
You will be given an appointment at one of the specialist centres and they will give you instructions relevant to their local protocols. When you arrive, the team will place a ‘drip’ or cannula in your vein. This will be used to give you a warm dye. The team will also need to ensure you are not pregnant and this is relevant for woman up to 55 years of age. You will then be invited to lie down on the bed of the CT scanner. Your heart rate will be monitored by ECG electrodes.
To get the best CTCA results its best for your heart rate to be close to 60 beats per minute. To achieve such a heart rate, we often need to give patients short acting beta-blocker medications via the drip or cannula. We often use a medication called metoprolol which is given intravenously. In some cases, you may already be on a beta-blocker and you may not need an additional dose. In other cases, particularly if you have severe asthma, we may choose to give you another drug.
Once your heart rate is controlled, the radiographer will explain what to do during the scan. In most cases, they will ask to lie still and to take a deep breath in and hold it. Its very important that you can hold your breath during the scan otherwise the information can be degraded. Try practicing breath holds before you have your CTCA.
The radiographer will then complete a series of checks and test images of your chest and heart. When they are ready, they will connect your drip to the dye that will show the heart arteries.
The dye, or contrast, contains iodine and its important to tell the radiographer if you have allergy to seafood, specifically prawns. If you ever had a reaction to contrast before, then please let us know.
The dye will be injected into your vein and give you a warm ‘hot-flush’ feeling. Many people say that they get a metallic taste in the mouth and even the sensation that they have wet themselves. This is completely normal and will not last long.
The CT table will then move through the CT scanner and you will need to hold your breath. Depending on the type of scanner, you may need to do this twice.
Once the scan is done, we will ask you take a seat and drink plenty of water. This is to help flush out the dye. If we needed to give you a drug to control your heart rate, then we will monitor your blood pressure after the scan for a short time.
CTCA involves radiation which carries an inherent long-term risk. It is known that exposure to high levels of radiation increases your risk of cancer. Quantifying the precise risk is difficult but as a principle we work very hard to ensure that the lowest level of radiation is delivered to patients. Current CTCA machines can now take very detailed images at very low radiation doses but the exposure to radiation is an important factor to consider when choosing investigations.
The contrast used in CTCA can cause some patients to develop a reaction – similar to an allergic reaction. This is relatively rare but can be unpleasant. The radiology staff are experienced in dealing with this. If it occurs, we will need to give you anti-sickness medications, anti-histamines and a small dose of steroid to calm the reaction down. Often the symptoms settle with these simple treatments.
Getting the Results
The CTCA is specialist test and I often discuss the findings with other expert Cardiologists who specialise specifically in this test. In some cases, I will report the CTCA myself alongside a Radiologist. Once we have a report issued, I will arrange an appointment in order to interpret the findings and explain them to you.
In some patients, where the coronary arteries are completely normal, we can be very reassured.
In some, we may find ‘moderate’ coronary disease and this is best assessed by undergoing a stress test. This may be an exercise tolerance test, a dobutamine stress echocardiogram or a stress perfusion MRI.
If the CTCA shows very significant or severe coronary disease, then the best way forward is to have an invasive angiogram to look at your heart arteries directly. If there is a narrowing of a coronary artery, this may be treatable by coronary angioplasty.