A Coronary CT Angiography (CTCA) is a non-invasive medical imaging test that provides detailed, three-dimensional pictures of the coronary arteries, which supply blood to the heart muscle. The procedure uses a specialized Computed Tomography (CT) scanner and X-rays to capture cross-sectional images. To visualize the arteries, a contrast material containing iodine is injected into a vein, temporarily highlighting the blood vessels. This allows physicians to assess the structure of the coronary arteries without surgical catheter insertion.
Why Coronary CT Angiography is Performed
The primary purpose of a CTCA is to evaluate patients for Coronary Artery Disease (CAD), which involves plaque buildup in the heart’s arteries. It is often recommended as a first-line diagnostic test for people with symptoms like unexplained chest pain, especially those with a low to moderate likelihood of obstructive CAD. A clear result reliably excludes significant blockages, often preventing the need for more invasive procedures.
The test also assesses patients with inconclusive results from other non-invasive tests, such as a stress test. For individuals with known CAD, a CTCA can check the patency of coronary bypass grafts or evaluate certain coronary stents. It can also visualize unusual formations of the coronary arteries, known as congenital anomalies.
Patient Preparation for the Scan
Patients are typically instructed to fast from food for a few hours before the scan, though they can drink clear liquids. It is important to avoid stimulants like caffeine, including coffee, tea, and energy drinks, for at least 12 hours prior, as these increase the heart rate and can blur the images.
Controlling the heart rate is necessary for optimal image acquisition, with the target often below 65 beats per minute (bpm). To achieve this, patients may receive a beta-blocker, either orally or intravenously upon arrival. Patients with diabetes taking certain medications, such as Metformin, may need to stop them temporarily due to the iodine contrast.
What Happens During the Imaging Procedure
The CTCA procedure begins with a healthcare professional placing an intravenous (IV) line, typically in the arm, for the contrast dye injection. Electrodes are attached to the chest for an electrocardiogram (ECG), which monitors the heart’s electrical activity. The ECG synchronizes the X-ray pulses with the moment the heart is moving the least, ensuring sharp, clear images.
The patient lies on a motorized table that slides into the CT scanner. Before the main scan, nitroglycerin may be administered under the tongue to widen the coronary arteries. The contrast dye is then rapidly injected through the IV line, which may cause a temporary sensation of warmth or a metallic taste.
During imaging, the patient is asked to hold their breath briefly, usually for about 10 to 12 seconds, to prevent blurring. The scanner rotates around the chest, capturing hundreds of cross-sectional images quickly. A technologist controls the process from an adjacent room but communicates with the patient through an intercom system.
Understanding the Scan Results
The resulting CTCA images reveal detailed information about the coronary arteries, allowing physicians to identify, locate, and assess the severity of any plaque buildup or narrowing. The scan visualizes both calcified (hard) and non-calcified (soft) plaque within the vessel walls. Plaque presence can be quantified using a Coronary Artery Calcium (CAC) score, which is sometimes acquired during the protocol.
A CAC score of zero suggests a very low short-term risk for cardiovascular events. If the CTCA shows no evidence of plaque or significant narrowing, it reliably excludes obstructive CAD. Conversely, if the images show significant stenosis (narrowing), the severity is measured to determine the degree of blockage. Based on the findings, the doctor will discuss next steps, which may range from lifestyle and medication adjustments for mild disease to a recommendation for further testing if a severe blockage is found.