A Cardiac Computed Tomography (CCT) scan is a non-invasive medical imaging procedure that uses specialized X-ray technology to produce images of the heart and its surrounding structures. This method rapidly captures multiple images as a patient passes through the scanner, which a computer then processes to create three-dimensional models of the beating heart. A CCT provides clear visualization of the heart’s anatomy, making it a powerful diagnostic tool for evaluating various forms of heart disease, particularly when other non-invasive tests have been inconclusive.
Visualizing the Coronary Arteries
The most frequent application of the CCT is Coronary CT Angiography (CCTA), which focuses on the blood vessels supplying the heart muscle. During a CCTA, an iodine-based contrast dye is injected into a vein, which travels through the bloodstream and highlights the coronary arteries on the scan. This dye allows the radiologist to visualize these arteries with high resolution.
The primary purpose of CCTA is to identify and characterize atherosclerotic plaque, which is the buildup of fatty material, cholesterol, and calcium within the artery walls. The scan can distinguish between calcified (hard) plaque and non-calcified (soft) plaque; the latter of which is often considered more prone to rupture and causing a heart attack. CCTA can determine the presence, location, and extent of Coronary Artery Disease (CAD).
Another important finding is the degree of stenosis, which is the narrowing or blockage of the artery caused by plaque. Stenosis is graded based on the percentage of obstruction. Findings may range from non-obstructive disease (mild plaque) to obstructive disease, where the narrowing is severe, often defined as 70% or greater. Detecting this narrowing helps determine if a patient’s chest discomfort is due to restricted blood flow to the heart muscle.
Assessing Heart Structure and Great Vessels
Beyond the coronary arteries, the CCT provides a view of the cardiac structure and the large vessels connected to it. The scan allows for analysis of the four heart chambers, the thickness of the heart muscle, and the function of the heart’s valves. This high-resolution imaging can detect congenital abnormalities (structural defects present from birth) or acquired conditions like tumors or scarring from a previous heart attack.
The CCT is also effective for examining the pericardium and can identify issues like pericardial thickening or fluid buildup, known as effusion. Furthermore, the scan captures the great vessels, including the Aorta and the Pulmonary Arteries. Viewing the Aorta, the body’s main artery, is useful for detecting aneurysms or aortic dissections. CCT detail is utilized for pre-procedural planning for structural heart interventions, such as transcatheter valve replacements.
Understanding the Calcium Score
The Coronary Artery Calcium (CAC) score is often performed without the contrast dye used in CCTA. This test quantifies the amount of calcified plaque in the coronary arteries, serving as a powerful predictor of future heart events. The result is reported as the Agatston score. The CAC score provides a snapshot of the total lifetime burden of atherosclerosis and helps guide preventative treatment decisions.
Interpreting CAC Scores
- A score of zero suggests a very low chance of developing a heart attack, as it indicates a lack of detectable calcified plaque.
- Scores between 1 and 99 are associated with minimal plaque and a low to moderate risk.
- A score of 101 to 400 indicates moderate plaque burden and a moderate to high risk.
- A score exceeding 400 is considered indicative of extensive disease and a high probability of significant artery blockage.
Preparation and Safety Considerations
Proper preparation for a CCT scan is necessary to ensure the clearest images possible. Patients must avoid caffeine for at least 12 hours before the procedure, as this helps maintain a slower, steadier heart rate that is easier to capture. Medications known as beta-blockers may also be administered just before the scan to slow the heart rate further, optimizing the image quality by minimizing motion blur.
When a CCTA is performed, the use of an iodine-based contrast dye requires safety considerations. Patients must report any history of allergic reactions to contrast material or pre-existing kidney issues, as the dye is eliminated by the kidneys. The procedure also involves a small dose of ionizing radiation, though modern scanners and techniques are designed to keep the exposure low while still obtaining diagnostic images.