Understanding CT Scans for Heart Assessment

What is a CT Scan?

A CT scan, or Computed Tomography scan, is a non-invasive imaging test that uses X-rays and computer technology to create detailed cross-sectional images of the body. For heart assessment, cardiac CT scans specifically target the heart and its blood vessels.

There are two main types relevant to heart evaluation:

• Coronary Calcium Scan (also called Calcium Scoring): This is a quick, low-radiation scan without contrast dye. It detects and measures calcium deposits in the coronary arteries, which are signs of plaque buildup. (FIGURE 1)

• CT Coronary Angiography (CTCA): This involves injecting a contrast dye into a vein to highlight blood vessels. It provides 3D images of the coronary arteries, allowing doctors to see blockages or abnormalities in detail. (FIGURE 2)

These scans are performed using a CT scanner, which captures multiple slices of the heart in seconds. They are particularly useful for patients at risk of heart disease.

What Information Does a CT Scan Provide?

CT scans offer valuable insights into heart health by revealing the condition of your coronary arteries—the blood vessels that supply oxygen to the heart muscle.

• From a Coronary Calcium Scan: This test calculates a "calcium score" (often called the Agatston score) based on the amount of calcium in your arteries. A score of 0 indicates no detectable calcified plaque, while higher scores (e.g., over 100) suggest moderate to severe atherosclerosis, increasing the risk of heart attacks. It's an excellent screening tool for asymptomatic patients to assess CAD risk early. Please note that a calcium score of zero does not completely exclude disease, as a small number of patients may have early-stage plaques that have not yet calcified.

• From CT Coronary Angiography (CTCA): CTCA is more comprehensive than calcium scoring. This provides detailed visuals of the arteries, showing narrowed areas (stenosis), more detailed plaque characterisation (soft or hard), and can detect blockages that might cause chest pain or other symptoms. It also highlights other issues like enlargement of vessels or heart chambers, and abnormalities of the valves. (Figures 3-5 fused to each other)

Overall, these scans improve risk prediction beyond traditional factors like cholesterol levels or blood pressure, especially for those with intermediate risk.

·         Planning Procedures: For transcatheter procedures (like TAVI) or minimal access cardiac surgery, CT angiography provides precise 3D images of your heart and blood vessels. This helps surgeons plan the best approach, choose the right device size, and navigate safely, reducing complications.

Role in Informing Procedures

CT scans play a crucial role in cardiovascular screening and planning interventions by providing precise data to guide medical decisions.

• For Screening: In patients without symptoms but with risk factors (e.g., family history, smoking, or high cholesterol), a calcium scan can stratify risk—low scores may mean lifestyle changes suffice, while high scores might prompt further tests like CTCA or stress testing. CTCA is ideal for those with low to intermediate pre-test probability of CAD, helping avoid unnecessary invasive procedures.

• For Planning Interventions: If blockages are detected, CT results inform treatments like angioplasty, stenting, or bypass surgery. CTCA maps artery anatomy, assesses plaque stability, and even evaluates fractional flow reserve (FFR) non-invasively to determine if a blockage is significant enough to require intervention. This aids in personalised planning, reducing risks during procedures.

By enhancing risk discrimination and reclassification, these scans help doctors tailor preventive strategies or urgent care, potentially preventing heart events.

What Happens on the Day of the Scan?

Preparing for and undergoing a cardiac CT scan is straightforward, but details vary between calcium scoring and CTCA.

• Preparation: Wear comfortable clothes without metal (e.g., no jewellery). For CTCA, you may need to fast for 4-6 hours and avoid caffeine for 12 hours. Inform your doctor of allergies, especially to iodine contrast, or conditions like kidney issues. Beta-blockers might be given to slow your heart rate for clearer images.

• During the Procedure: You'll lie on a table that slides into a doughnut-shaped scanner. Electrodes monitor your heart rhythm. For calcium scoring, it's quick (5-10 minutes).

• For a CTCA scan, a small tube is placed in your arm to give contrast dye, which may cause a brief warm feeling. You’ll be asked to hold your breath for a few seconds during the pictures to help them come out clearly. The machine may make some whirring sounds, but the test itself does not hurt. Most of the time in the room is spent on preparation and the actual scan takes only a fraction of a second.

• After the Scan: Most people can return to their usual activities right away. If contrast dye was used, drinking plenty of water will help flush it from your system. Your results are usually ready within 24-48 hours and will be reviewed with your doctor.