A Coronary Artery Calcium (CAC) score is a diagnostic measurement used to assess the amount of calcified plaque in the arteries supplying the heart. This non-invasive test helps clinicians stratify a person’s risk for future cardiovascular events by providing a direct measure of established atherosclerosis. The true significance of a zero result requires understanding what the test measures and its inherent limitations regarding the full scope of heart disease.
What Does the Coronary Artery Calcium Score Measure?
The CAC score is determined using a specialized, non-contrast computed tomography (CT) scan of the heart. This imaging technique quantifies the amount of calcified plaque present within the coronary arteries. Plaque is a buildup of fats, cholesterol, and other substances.
When plaque hardens, it becomes calcified plaque, a definitive marker of atherosclerosis, or hardening of the arteries. The resulting measurement is reported in Agatston units, named after the cardiologist who developed the scoring method. The score is calculated by multiplying the area of the calcification by a density factor derived from the CT image’s Hounsfield units. A score of zero indicates the absence of any detectable calcified plaque at the time of the scan.
The Significance of a Zero Score
A Coronary Artery Calcium score of zero is a highly favorable finding associated with an extremely low risk of experiencing a heart attack or other major cardiovascular event. This result can reclassify an individual who might otherwise be considered at intermediate risk based on traditional factors like cholesterol or blood pressure. Individuals with a zero score have a very low annual risk of a major event, often less than 1% over the next five to ten years. Studies have demonstrated that this low-risk prognosis holds true across different age groups, even in older adults, indicating a significantly lower risk of death from any cause compared to those with even the lowest measurable calcium score.
Why Zero Doesn’t Guarantee Absence of Disease
Despite the positive prognosis, a zero CAC score does not guarantee the complete absence of all heart disease. The fundamental limitation of the test is that it only detects calcified, or hard, plaque. It cannot visualize non-calcified plaque, often referred to as “soft plaque,” which can still be present in the coronary arteries.
Soft plaque is composed primarily of lipids and can be unstable, meaning it is susceptible to rupture, the mechanism that commonly triggers an acute heart attack. Non-calcified disease is more prevalent in younger patients, who can have significant obstructive disease despite a zero score. Furthermore, the CAC score does not assess issues related to the smallest blood vessels, known as microvascular disease. This condition can cause chest pain and serious cardiac events, particularly in individuals with diabetes or in women, even when the major coronary arteries appear clear.
Maintaining Health After a Zero Score
Receiving a zero CAC score offers an excellent opportunity to maintain a long-term, low-risk status through consistent lifestyle measures. The result is not a permanent shield against future disease, as the development of new plaque can begin years later.
This involves focusing on a diet rich in whole foods, such as the Mediterranean pattern, and limiting processed foods and saturated fats. Regular physical activity, aiming for at least 150 minutes of moderate exercise each week, helps prevent the future formation of plaque. Individuals should continue to manage traditional risk factors like blood pressure and cholesterol, in consultation with a healthcare provider. Depending on individual risk factors, a physician may recommend retesting the CAC score after five to ten years to monitor for any new plaque development.