The Coronary Artery Calcium (CAC) score is a non-invasive imaging test used to assess heart disease risk. The scan uses a computed tomography (CT) machine to look for calcium deposits (calcified plaque) within the walls of the coronary arteries supplying the heart muscle. A high score indicates a significant amount of calcified plaque, which is a definitive sign of coronary artery disease (CAD). This distinction is crucial because a high CAC score signals a high risk for a future event, even if the arteries are not currently obstructed.
Understanding the Coronary Artery Calcium Score
The CAC score quantifies the total amount of calcified plaque present in the coronary arteries. This measurement is performed using a specialized, non-contrast chest CT scan. The results are reported using the Agatston score, which factors both the size and the density of the calcium deposits detected in the artery walls.
A score of zero signifies that no calcified plaque was found, which is generally associated with a very low risk of a heart attack over the next decade. Scores increase in parallel with the amount of calcified plaque burden; for instance, a score between 101 and 300 suggests moderate calcification, while a score over 400 indicates extensive plaque. The score serves as a direct measure of the cumulative disease burden, reflecting years of atherosclerosis progression. The CAC score is a measure of plaque quantity, not a direct assessment of how much blood flow is currently being impeded.
The Difference Between Calcification and Obstruction
The core reason a high CAC score can exist without a severe blockage lies in the different forms of plaque and how arteries adapt. Atherosclerotic plaque is classified as soft (non-calcified) or hard (calcified). The CAC scan specifically detects the hard, calcified plaque, which is typically older and more stable.
This calcified plaque is often stable because the body has attempted to wall off the unstable deposits that formed earlier. In many cases, the artery wall has remodeled outward, a process known as positive remodeling, to accommodate the growing plaque. This outward expansion keeps the central channel, or lumen, relatively open, preventing a significant, flow-limiting obstruction (stenosis).
Conversely, soft plaque is newer, composed primarily of fatty material and inflammatory cells, and is highly unstable. This soft plaque is far more dangerous in the short term because it is prone to sudden rupture, which can trigger a blood clot and cause an acute heart attack, even if it has not caused a major blockage. Since the CAC scan only highlights calcium, it misses this non-calcified, vulnerable plaque entirely. Therefore, a high CAC score indicates significant wall damage, but it does not necessarily mean the artery is narrowed enough to restrict blood flow, a condition that usually requires a stress test or a CT angiogram to evaluate.
What a High Score Signals: Future Risk Assessment
Even in the absence of an immediate flow-limiting blockage, a high CAC score is a powerful predictor of future cardiovascular events. The score quantifies the total atherosclerotic burden built up over a lifetime, making it an excellent prognostic tool. A score above 100 indicates established coronary artery disease and significantly elevates the risk for a major cardiac event, such as a heart attack or cardiac death, over the next five to ten years.
For individuals with a CAC score of 400 or higher, the risk of a major adverse cardiac event is substantially increased compared to those with a zero score. Studies have shown that even patients with a high CAC score but no evidence of significant artery narrowing have a mortality risk that is more than double that of individuals with a zero score. The CAC score provides risk information that is independent of traditional risk factors like cholesterol or blood pressure.
Next Steps After a High Score Diagnosis
A diagnosis of a high CAC score, regardless of current symptoms or blockages, necessitates aggressive preventative action to mitigate future risk. The primary focus shifts to intensive management of all traditional cardiovascular risk factors, including strict control of blood pressure, achieving optimal blood sugar levels, and managing cholesterol. Physicians frequently use the high CAC score to initiate or intensify preventative medications, particularly high-intensity statin therapy. The goal of statins is to stabilize the plaque and reduce cholesterol levels, helping to transform soft, unstable plaque into more stable, calcified plaque.
Lifestyle modifications are equally emphasized, including adopting a heart-healthy diet, regular physical activity, and completely stopping smoking. In some cases, if a patient is symptomatic or the score is extremely high (e.g., over 1000), further testing, such as a stress test or a Coronary CT Angiogram (CCTA), may be ordered to definitively rule out a flow-limiting obstruction or to assess the volume of soft, non-calcified plaque.