A Computed Tomography Coronary Angiogram (CTCA) is a non-invasive imaging test designed to visualize the coronary arteries, the vessels that supply blood to the heart muscle. The procedure involves injecting an iodine-based contrast dye to highlight the arteries. The primary purpose of a CTCA is to look for blockages or narrowing, which indicates Coronary Artery Disease (CAD). An “abnormal” result means the scan has detected evidence of this disease, initiating a process to understand its extent and determine appropriate management steps.
What Defines an Abnormal CT Coronary Angiogram
An abnormal CTCA result is defined by the physical detection of atherosclerosis, the buildup of plaque within the artery walls. Even the smallest amount of plaque (fatty material and calcium) is considered abnormal because it signifies underlying disease. The CTCA provides a detailed view of the entire vessel wall and lumen, distinguishing it from a simple calcium score.
Findings are categorized into two main types based on plaque obstruction. Non-obstructive coronary artery disease is identified when plaque is present but narrows the artery by less than 50%. This detection confirms the disease process has begun, regardless of whether the plaque is soft or calcified.
Obstructive coronary artery disease is diagnosed when plaque causes a significant narrowing of 50% or more, substantially restricting blood flow. Stenosis, the medical term for this narrowing, is the most concerning finding and often correlates with symptoms like chest pain. Any result showing plaque is classified as abnormal.
Grading the Severity of Coronary Artery Disease
Once an abnormal result is confirmed, the severity of the coronary artery disease is graded to determine prognosis and guide treatment. Severity is determined by measuring luminal stenosis; the most severe narrowing in any vessel dictates the overall grade. Radiologists use a standardized system, such as the Coronary Artery Disease–Reporting and Data System (CAD-RADS), to communicate these findings.
The CAD-RADS system assigns a numerical score, typically ranging from 0 (no plaque) to 5 (total occlusion), reflecting specific degrees of stenosis. For example, a score of 2 indicates mild stenosis (25-49% narrowing), while a score of 3 represents moderate stenosis (50-69% narrowing). The system also incorporates plaque burden (P1 mild to P4 extensive) to account for the total amount of plaque, contributing to risk stratification.
Plaque location is a significant factor; a moderate blockage in the left main coronary artery is considered more serious than a severe blockage in a smaller vessel. This detailed grading translates anatomical findings into a clinical prognosis, determining the patient’s immediate and long-term risk of a heart attack. Higher CAD-RADS scores and plaque burden indicate a greater atherosclerotic burden and urgency for intervention.
Management and Follow-Up After Diagnosis
Management following an abnormal CTCA is tailored to the diagnosed severity and the patient’s clinical picture. For patients with non-obstructive or mild disease (CAD-RADS 1 or 2), the primary focus shifts to aggressive preventative therapy. This involves intensive lifestyle modifications, such as dietary changes, regular exercise, and smoking cessation.
Pharmacological treatment is often initiated or intensified, even for mild disease, to stabilize the plaque and prevent progression. High-intensity statin therapy is commonly prescribed to lower cholesterol and reduce cardiovascular risk. The goal is to aggressively manage risk factors to prevent non-obstructive plaque from becoming a significant blockage.
When the CTCA reveals moderate (CAD-RADS 3) or severe (CAD-RADS 4 or 5) obstructive disease, further functional testing is required to assess if the narrowing is causing a lack of blood flow to the heart muscle. This might involve a stress echocardiogram or nuclear stress test. If functional testing confirms significant ischemia, the patient may be referred for an invasive coronary angiogram. This procedure allows for immediate intervention, such as placing a stent to open the blocked artery and restore normal blood flow.