Coronary Artery Calcium Score – CAC Scoring Explained

Estimated reading time: 8 minutes

Measurements of coronary artery calcium score (CAC scoring) are commonly used to assess future heart disease risk.

When we age, calcium deposits can be found in many parts of our bodies. Calcification in the arterial walls is common in people aged 65 and older.

Coronary Calcium Score

So, to some degree, calcification of arteries can be regarded as a normal part of aging.

Due to their metallic nature and density, calcium deposits are easily detected by X-ray images.

Today, a heart scan, also known as a coronary calcium scan, is used to assess the amount of calcium in the coronary arteries.

Coronary Artery Disease

To be able to function normally, the heart needs a continuous supply of oxygen and other nutrients. The coronary arteries play an essential role in delivering these nutrients to the heart muscle.

Unfortunately, the coronary arteries are prone to a disease called atherosclerosis.

Atherosclerosis is a chronic inflammatory condition in which plaque builds up inside the arteries. A plaque is made up of inflammatory cells, cholesterol, calcium, and other substances.

Plaques in the coronary arteries may block blood flow to the heart muscle, leading to chest pain symptoms.

Furthermore, plaques may rupture, leading blood clotting at the plaque site. This may cause a sudden disruption of blood flow, leading to a heart attack.

In the early 1960s, several risk factors for coronary artery disease were defined. Since then, it has repeatedly been documented that smoking, high LDL-cholesterol, and high blood pressure are associated with increased risk.

Examples of other conditions that predispose to coronary artery disease are family history, insulin resistance, physical inactivity, mental stress, and depression.

Coronary heart disease remains the most common cause of death in the Western world. Hence, identifying individuals at risk is a significant step to reduce the burden of this disease.

Measuring the amount of calcium in the coronary arteries by CT scan may provide important information about the presence of coronary artery disease.

Coronary Artery Calcification

Most of us will ultimately get calcification in our arteries as we age. Hence, calcification of the coronary arteries can be regarded as an aging phenomenon.

However, if the amount of calcium is higher than expected by age, it may reflect an increased heart attack risk.

Coronary calcification can be seen in adolescents, although it usually starts later in life.

For many years, arterial calcification was thought to result from a degenerative process associated with aging. However, recent evidence suggests a more active process, likely arising from inflammation of the vessel wall.

Coronary Calcium Score

In the 1980s, US cardiologists lead by Dr. Arthur Agatston studied how to assess the amount of calcium in the coronary arteries.

Using an ultrafast CT scan technique, Agatston defined a method to calculate coronary artery calcium score (CAC score).

Initially, the CAC score was called the Agatston score,

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The coronary arteries supply oxygen-rich blood to the muscle of the left ventricle of the heart. The amount of calcium in the walls of the coronary arteries, assessed by calculating the coronary calcium score, appears to be a better predictor of risk than standard risk factors

CAC score is an important tool to predict heart attack risk and other vascular events (2).

Furthermore, it may help to detect the presence and extent of coronary artery disease.

Nonetheless, the CAC score does not reflect the presence or absence of blockages or impaired blood flow in the arteries.

Still, a patient with a high CAC score is more likely to block a coronary artery than a patient with a low CAC score.

An individual with a CAC score of zero is very unlikely to have a severe blockage of a coronary artery.

Coronary Calcium Score Interpretation

The following definitions are used to relate the CAC score to the extent of underlying coronary artery disease (3):

  • Coronary calcium score 0: No identifiable coronary artery disease. 
  • Coronary calcium score 1-99: Mild coronary artery disease. 
  • Coronary calcium score 101-400: Moderate coronary artery disease.
  • Coronary calcium score > 400: Extensive coronary artery disease.

When interpreting the CAC score, it is essential to consider age and gender. Women, in general, have lower calcium scores than men.

A calcium score calculator is available here that provides CAC score distribution based on age, gender, and ethnicity.

Using CAC Score to Assess Arterial Age

CAC score increases with age. Hence, at a certain age, we will be expected to have a specific CAC score that would be considered normal for that age. This score would then reflect the age of our arteries or the arterial age.

If everything is normal, we would expect our arterial age to be the same as our observed age.

However, if the CAC score is high, our arterial age may be higher than our observed age. Conversely, if our CAC score is low, the arterial age may be lower than our observed age.

The table below shows how arterial age can be predicted from the CAC score (4).

Calcium Score and Arterial Age

Let’s take an example.

A 60-year-old man has a CAC score of 500. According to the table above, his arterial age will be 84 years.

Hence, this 60-year-old man has arteries that are consistent with the arteries of an 84-year-old man.

Arterial age based on the CAC score can also be calculated here.

When Should CAC Scoring Be Performed?

Coronary calcium score guidelines don’t recommend routine use of CAC scoring in asymptomatic individuals (5).

However, the CAC score may be useful for individuals at increased risk based on the ASCVD score.

The ASCVD score is based on several parameters such as gender, race, cholesterol levels, blood pressure, smoking, and the presence of diabetes.

ASCVD score can be calculated here.

Hence, if ASCVD score is between 5-20 percent, CAC scoring may help to guide further therapy.

CAC scoring is not recommended in individuals with ASCVD risk below 5 percent.

Coronary Calcium Score

How Is Coronary Calcium Assessment Performed?

Lately, ultrafast spiral CT has been used to assess coronary calcium. This technique, often called heart scan, makes the scanning time very short.

The patient usually needs no specific preparation. Fasting is not necessary.

As high heart rate may reduce imaging quality, patients are often asked to refrain from smoking and drinking coffee before the scan. Sometimes beta-blockers are administered to slow heart rate.

Many experts have expressed concerns about the radiation involved with the CT scan. It has been estimated that there may be an increase in cancer risk with repeated procedures (6).

What to Do About Extensive Coronary Calcification?

There is no specific treatment available that lowers coronary calcium.

Treatment of individuals with high calcium scores should aim at reducing risk. This involves treating lipid disorders, high blood pressure, and diabetes if present.

Due to the overwhelming evidence of benefit in individuals with coronary artery disease, treatment with aspirin and statins is often advised.

Refraining from smoking is essential, and regular, moderate exercise is advised.

Further evaluation may be needed if extensive calcification is present.

Coronary Calcium Score and Statins

Treatment with statins is often advised for patients with a high CAC score. This is based on their ability to reduce plaque size and improve clinical outcomes.

Interestingly, however, statins do not reduce calcifications in the coronary arteries. In fact, some studies suggest that statins may promote coronary calcification (7).

The fact that the CAC score is associated with increased risk does not prove that calcium itself is harmful. It is simply a marker of underlying coronary artery disease.

Patients with high CAC scores have simply had their coronary artery disease detected by the high amount of coronary calcium. The calcium itself is not the problem. Indeed, it has been suggested that the calcium may represent shrinkage and stabilization of plaques (8).

Statins are often recommended if the CAC score is above 100.

Conversely, statin therapy is not recommended in patients with a CAC score of zero.

The Role of Calcium and K2 Supplements

Inadequate calcium intake can lead to decreased bone density, thereby increasing the risk of osteoporosis and bone fractures.

Supplemental calcium can increase bone mineral density and bone strength. However, recent data suggests that high consumption of calcium supplements may increase calcification of the arteries (9).

Hence, it has been suggested that elevated consumption of calcium supplements may raise the risk of heart disease.

Vitamin K2 deficiency is associated with an increased risk of calcification of the blood vessels. Furthermore, researh indicates that the use of vitamin K2 supplements is associated with decreased arterial calcification (10).

Hence, increased intake of vitamin K2 might help to reduce the health risks associated with coronary calcium.

However, further studies are needed to establish the role of K2 supplements in people with high CAC score.

The article was initially published August 19, 2014.

It was revised, updated and republished on December 20th, 2020.

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