What is Coronary Artery Calcification?
Calcium is the most common mineral in the human body. While the majority of calcium is found in our teeth and bones, about 1% is dissolved in our blood. As we grow older, calcium starts to collect in various parts of our body, including our arteries. This buildup of calcium in the arteries, also known as arterial calcification, is often linked to vascular or artery injury, inflammation, and repair.
This buildup often starts with the onset of atherosclerosis, a disease where plaque builds up inside your arteries. This disease and calcium buildup usually become detectable through medical imaging after the age of 40 and is quite common among those older than 60.
It’s also important to know that all patients with confirmed coronary artery disease (CAD), a condition that affects the arteries supplying blood to your heart, show signs of coronary calcification. Despite not all plaques being calcified, there remains a strong link between the amount of calcium in the coronary arteries and atherosclerosis. Before, coronary artery calcification (CAC) was attributed to age-related decay, however, today, it’s seen to stem from CAD.
CAC might present differently based on a patient’s heart condition: with unstable angina, a chest pain or discomfort that generally occurs while resting, typically having smaller, scattered calcium deposits, while stable angina, chest pain typically triggered by physical activity or emotional stress, tends to have fewer but larger deposits. Artery blockages with no calcium accumulation tend to be less severe. This is why CT angiography, a type of imaging test, is effective at imaging CAC, potentially predicting significant atherosclerosis.
What Causes Coronary Artery Calcification?
Calcification, or the accumulation of calcium in body tissues, can occur in different layers of our blood vessels. If it occurs in the middle layer, it could result in peripheral arterial disease and is often related to kidney failure, high levels of calcium or phosphate, and overactive parathyroid glands. But if calcification happens in the inner layer, it may be linked to heart diseases and atherosclerosis (hardening of the arteries) which we are focusing on in this piece.
Atherosclerosis is believed to start with fat deposits on the inner lining of a blood vessel. Immune cells called macrophages get into the fat core of the plaque (fat deposit), which could die and decay. Coronary artery calcification (CAC) is thought to begin when smooth muscle cells, that have moved towards the inner layer from the middle layer of the blood vessel, start dying off. Apart from this, macrophages dying off can cause larger spots of calcification.
Small scale calcifications happen deeper in the decaying core, close to the internal elastic layer. As these small calcifications join together, they form fragments and specks of calcium. As this process continues, the calcification spreads into the surrounding tissue, forming calcified sheets or plates. These sheets can fracture and form calcium nodules, which can distort the lining of the blood vessel and may cause acute blood clots. These calcified nodules contribute to 2% to 7% of coronary artery blood clots.
The calcification and decay of the fat core can happen separately. If the decaying core increases in size, a thin-cap fibrous plaque may form, which is likely to rupture. In healed plaque ruptures and fibrocalcific plaques, calcification increases a lot more compared to the decaying core areas.
Risk Factors and Frequency for Coronary Artery Calcification
Coronary artery calcification, which can lead to heart problems, is more common in certain groups of people. Age, gender, and race all play a role in how likely a person is to have this issue, and other health conditions can increase the risk.
- Coronary artery calcification is found in 90% of men and 67% of women over 70.
- Women who haven’t gone through menopause tend to have lower levels of calcification, thanks to the protective effect of estrogen.
- After menopause, a woman’s calcification can reach three times what it was before.
- Men generally have more calcification than women until they reach their sixties.
In addition, research shows differences in coronary artery calcification among different racial groups. After accounting for common risk factors, the study found that whites had the highest levels of calcification, followed by Chinese, Hispanics, and African Americans. This was true for both men and women.
Some health issues can also increase the risk of calcification. People with diabetes, for example, are prone to higher levels, which can lead to more severe health problems.
- Higher HbA1C, which is a marker for long-term blood sugar control, is linked to both new and worsening calcification.
- Other risk factors that can increase calcification include metabolic syndrome, abnormal cholesterol levels, smoking, high blood pressure, chronic kidney disease, and high levels of the inflammation marker C-reactive protein.
Signs and Symptoms of Coronary Artery Calcification
Coronary artery calcification is a condition that happens when calcium builds up in the arteries of your heart. While it doesn’t cause noticeable symptoms, it’s important because it can independently predict future heart health issues and allow doctors to more accurately categorize a patient’s cardiovascular risk level.
Testing for Coronary Artery Calcification
Computed tomography, or CT scans, have been used to detect coronary artery calcium (CAC) since the 1980s. They have become faster and more accurate over time, which makes them a popular choice for this kind of diagnosis. The CT scans are typically performed without needing to insert an IV or prepare the patient in a specific way.
Once the CT scan images are captured, a measurement called the Agatston score is calculated. This score is determined by multiplying the area of calcification by its density. This score is a well-established way of measuring the amount of coronary artery calcium. A higher score implies larger and denser areas of calcification, which could be an indication of increased risk of heart disease.
The American College of Cardiology and American Heart Association recommend this test for people who are asymptomatic but have a moderate risk of cardiac events, as well as for individuals aged 40 and older with diabetes. However, the test is generally not recommended for people at a very low or very high risk of cardiac events.
CAC can be categorized as:
- No disease: 0
- Mild disease: 1-99
- Moderate disease: 100-399
- Severe disease: >400
It’s important to note that while CAC can help in predicting the existence of coronary artery stenosis, it better indicates the extent of coronary atherosclerosis rather than the degree of stenosis. Severe coronary calcification is often linked with advanced obstructive coronary disease.
Another point to consider is that the presence and extent of CAC should always be documented on all CT chest scans, even if they are being performed for other reasons. Sometimes, these calcifications can be picked up incidentally.
On the subject of radiation exposure, men generally get exposed to about 0.7 to 1.5 mSv and women to about 0.9 to 1.9 mSv during a CT scan. To give some context, the average annual background radiation in the United States is around 3.0 to 3.6 mSv.
In people without symptoms, zero Agatston score is a strong predictor of low risk when compared to a normal level of hs-CRP, or lack of carotid plaque.
You may also have heard of the coronary calcium detected by chest radiography, but it is not recommended because it has poor sensitivity in detecting CAC.
Usually, the gold standard for imaging heart vessels is cardiac catheterization, an invasive procedure that involves injecting dye into the blood vessels for visual evaluation. Non-invasive tests like exercise stress testing, stress echocardiography, SPECT, and PET are being studied for their potential in spotting patients who need catheterization. These tests currently have a sensitivity and specificity of 70% to 90%, which results in many unnecessary invasive cardiovascular tests.
Research has shown that combined with a negative coronary CTA, a low chance of having coronary artery disease before testing holds a large negative predictive value. This means that it’s very unlikely for a patient to have coronary artery disease. In particular, patients with diabetes had significantly fewer heart events in the CTA group than those in the Functional Stress Testing (FST) group.
In conclusion, CTAs, which are anatomical studies that can directly visualize the coronary vessels, seem to be the best imaging option for evaluating coronary artery calcium.
Treatment Options for Coronary Artery Calcification
In many large studies, fewer heart problems are reported than anticipated. This is generally because participants in these studies are actively being treated for risk factors like high blood pressure, high cholesterol levels, and smoking. It’s also crucial to effectively manage conditions like diabetes and chronic kidney disease to maintain good heart health.
Measuring coronary artery calcification (CAC), or the buildup of calcium in the arteries, is used in the prevention of atherosclerotic diseases, which are conditions where the arteries harden due to plaque buildup. Current guidelines recommend using a CAC score to make decisions about using cholesterol-lowering medications, known as statins. If a patient’s CAC score is 0 and they don’t smoke, have diabetes, or have a family history of early heart disease, then they generally don’t need to start on a statin. However, if their CAC score is between 1-99 and they’re older than 55, statins are generally recommended. If they’re younger than 55, they can wait and reassess their need for statins in 3-5 years. For those with a CAC score over 100, it’s recommended to start on statins. Aspirin may also be considered for prevention in patients younger than 70 and with a CAC score over 100. There’s no need for regular repeated CAC testing to monitor the effectiveness of treatment.
The progress in treating coronary artery calcification has been significant. Intravascular lithotripsy (IVL), a procedure that breaks up severe calcium buildup in the coronary arteries, was found effective in a particular study. The presence of coronary artery calcification can also make procedures during heart catheterization more difficult. To address this, several techniques can be applied during the procedure, in addition, to placing stents into the artery. These include using special balloons or lasers, or performing other procedures to remove the calcifications.
What else can Coronary Artery Calcification be?
When doctors try to diagnose coronary artery calcification (CAC), they have to differentiate it from other conditions that might look like calcification. These include:
- Noises in the background that could be wrongly read as tiny areas of calcification
- Calcification of pericardium, which is the tissue surrounding the heart, particularly near blood vessels on the heart’s surface
- Movements creating misleading signals or noise
- Calcification of the middle layer of the artery wall, the tunica media, which can be mistakenly interpreted as calcification of the innermost layer, the intima. These two have different causes and prognoses.
In other words, while trying to diagnose CAC, doctors need to correctly identify and interpret the signals and images they observe.
What to expect with Coronary Artery Calcification
According to multiple major studies, the presence of calcium in the coronary arteries (CAC) can indicate a higher chance of future heart-related problems. This measure is so effective that it can enhance prediction models in terms of anticipating patient risk, performing better than other indicators. CAC helps doctors categorize patients into low-risk and high-risk groups. In essence, if no calcium accumulation is detected in the coronary arteries (CAC score of 0), the risk is incredibly low for heart disease or related incidents.
For instance, among patients classified as low-risk due to their medical history or Framingham risk score, a CAC of 100 correlates with roughly a 10% chance of heart disease events over the next decade. On the other hand, the same high-risk patients with a CAC score of 0 have just a 3% risk of heart disease events over this period.
People with no symptoms but categorised as medium-risk are typically assessed by measuring CAC, according to medical guidelines. A CAC score over 400 implies deteriorating health outcomes. This shows how effective the CAC score can be in redefining patient risk and predicting future heart-related incidents.
Possible Complications When Diagnosed with Coronary Artery Calcification
The complications of coronary artery calcification (CAC) can include narrowing of the arteries, which reduces blood flow to the heart, chest pain (angina), and heart attacks (myocardial infarction). The decision to send a patient for a heart catheterization procedure is usually based on whether they are likely to have a blockage that can be treated. This decision depends on the size, location, and appearance of the blockage. If a blockage reduces the size of an important blood vessel by more than 50% or if it affects more than 50% of the left principal artery, it’s usually deemed significant and likely to impact blood flow negatively. However, excessive testing for CAC can lead to unnecessary heart catheterization procedures, which may have risks like bleeding, infection, artery tearing, and sudden tightening of the coronary arteries.
Risks of CAC Testing and Associated Procedures:
- Narrowing of arteries leading to reduced heart blood flow
- Chest pain (angina)
- Heart attacks (myocardial infarction)
- Unnecessary heart catheterization procedures
- Bleeding from procedures
- Infection from procedures
- Artery tear during a procedure
- Sudden tightening of the coronary arteries