A computed tomography (CT) heart scan is a sophisticated, non-invasive medical imaging procedure that uses specialized X-ray equipment and advanced computer processing to generate detailed, three-dimensional images of the heart and its surrounding blood vessels. The primary purpose of a CT heart scan is to visualize the coronary arteries, the vessels supplying blood to the heart muscle. By clearly imaging these arteries, the scan helps medical professionals detect the presence and extent of atherosclerotic plaque buildup, which is a major indicator of heart disease.
Distinguishing Types of CT Heart Scans
The term “CT heart scan” encompasses two primary procedures that serve distinct clinical purposes: Coronary Artery Calcium (CAC) Scoring and CT Coronary Angiography (CTCA). CAC scoring is a quick, low-dose scan designed specifically to measure the amount of calcified plaque in the coronary arteries. Calcium deposits are a marker for hardened plaque, and this scan yields a single numerical value assessing a person’s future risk of a heart event. The procedure is fast, typically completed in minutes, and does not require contrast dye injection.
Conversely, CT Coronary Angiography (CTCA) is a more comprehensive diagnostic tool used to visualize the artery walls and the vessel lumen in detail. This scan is capable of identifying both calcified and non-calcified, or “soft,” plaque, which may not yet contain enough calcium to register on a CAC score. To achieve this detail, an iodine-based contrast dye is injected intravenously, highlighting the coronary arteries as blood flows through them. CTCA is generally reserved for patients experiencing symptoms such as chest pain, or those requiring precise visual mapping of existing blockages.
The fundamental difference lies in their objective: CAC scoring is a screening tool focused on quantifying plaque burden as a predictor of risk, while CTCA is a diagnostic tool focused on visualizing the degree of narrowing, or stenosis, within the arteries. Because the CTCA requires a clear image of the moving heart, it often necessitates preparation to ensure a slow and steady heart rate. This is not a requirement for the simpler CAC scoring procedure, which captures a static image of the calcium deposits.
The Patient Experience: Step-by-Step Procedure
The initial steps for both types of CT heart scans involve minimal preparation, though CTCA requires more specific logistical planning. Patients are often instructed to avoid caffeine and smoking for several hours before the scan, as these substances can elevate the heart rate, potentially blurring the resulting images. For a CTCA, a medical professional may administer medication, such as a beta-blocker, either orally or intravenously, to temporarily slow the heart rate to an optimal level, usually below 60 to 70 beats per minute.
Once in the scanning room, the patient lies on a movable table, and small electrode patches are affixed to the chest. These electrodes connect to an electrocardiogram (EKG) machine, which continuously monitors the heart’s electrical activity. This EKG monitoring is synchronized with the CT scanner, allowing the machine to capture images at the precise moment in the cardiac cycle when the heart is stillest, thereby minimizing motion artifacts.
For a CTCA, an intravenous (IV) line is inserted, typically in the arm, through which the contrast dye will be injected during the scan. As the table slides into the CT gantry, the patient is asked to remain still. During the brief scanning period, the technologist will communicate through an intercom, instructing the patient to take a breath in and hold it for a few seconds. This breath-hold prevents the movement of the chest and lungs from distorting the images of the heart.
If contrast dye is administered during a CTCA, the patient may experience a brief, intense sensation of warmth spreading through the body and sometimes a metallic taste in the mouth. The entire scan acquisition is rapid, often lasting only a few seconds, though the total time in the exam room, including preparation, is usually between 10 and 15 minutes. Following the scan, the EKG electrodes and the IV line are removed, and the patient can typically resume normal activities.
Interpreting the Scan Results
The interpretation of a CT heart scan depends entirely on the type of procedure performed, yielding either a quantitative score or a detailed anatomical report. Coronary Artery Calcium (CAC) Scoring results are reported using the Agatston score, a number derived from the size and density of the detected calcium deposits. A score of zero signifies the absence of any detectable calcified plaque, which correlates with a very low risk of a heart event.
Scores between 1 and 100 suggest a minimal to mild plaque burden, indicating a slight elevation in risk compared to a zero score, often prompting a focus on lifestyle modifications. A moderate score, ranging from 101 to 400, suggests a high plaque burden and is associated with a significantly increased risk. The highest scores, exceeding 400, indicate extensive calcified plaque and severe disease, which typically require aggressive medical management and further diagnostic testing.
In contrast, the results of a CT Coronary Angiography (CTCA) are interpreted visually, focusing on the degree of narrowing, or stenosis, within the coronary arteries caused by plaque. The radiologist or cardiologist assesses whether a blockage is categorized as mild, moderate, or severe based on the percentage of the vessel lumen that is obstructed. CTCA reports also provide information about the characteristics of the plaque, noting whether it is composed of soft, non-calcified material, hard calcified material, or a mix of both. This detailed visual assessment helps determine the need for interventions or specific medical therapies to manage the identified blockages.