Coronary Artery Calcification (CAC, Hardened Heart Arteries)
With the prevalence of coronary artery disease in the developed world, we are all accustomed to serious conditions whenever these arteries are diseased or damaged. The coronary arteries carries blood to the heart muscle. If it is diseased in any way then the heart will ultimately be affected to some degree. Most of us are well aware of the narrowing of the coronary artery that occurs with the build up of fatty plaques, a condition known as atherosclerosis. When it occurs in the coronary arteries then we refer to it as coronary artery disease. It may be linked to calcium deposits in the plaques which can cause hardening of the arteries and are more likely to lead to a heart attack (myocardial infarction) or sudden cardiac death.
What is CAC?
Coronary artery calcification is where calcium accumulates and hardens (mineralization) a portion of the coronary artery. It is not dissimilar from the way bones use calcium to become hard and strong. While calcification is necessary for healthy bones, the same does not apply to the arteries. These blood vessels are soft and elastic despite being relatively strong. These properties ensure that the artery can maintain its required function, irrespective of where it is located in the body.
The plaques seen in atherosclerosis are usually referred to as fatty plaques and associated with different types of fats in the blood. However, these plaques may also contain calcium. Once it hardens the plaque narrows. A heart scan can detect this calcification of the coronary artery even before there is any symptoms. It means that invasive procedures like an angiogram does not have to be done in every case to identify narrowing of the coronary artery.
Meaning and Causes
The presence of coronary artery calcification is indicative of coronary artery disease. Usually calcification is seen in more advanced atherosclerotic lesions but small amounts can appear in early lesions. In fact the calcification may be detectable from as early as the twenties since coronary atherosclerosis starts early in life although symptoms appear much later in life once there is significant narrowing. Understandably the calcified lesions are usually smaller in younger adults and in early stages of coronary artery disease.
The exact reason for and purpose of coronary artery calcification is not understood. It was thought of as being a passive process that occurred over a long period of time, especially since it is more commonly observed in elderly patients. However, this may not always be the case since it is sometimes observed in younger people with relatively early atherosclerotic lesions and does not affect arteries with no atherosclerosis. In this regard, the degree of calcification may be associated with more serious outcomes in younger adults than in the elderly.
Location and Risks
The location of the calcification can also determine the severity of the outcome. Calcified deposits found in the tunica media (middle layer) of the artery are more likely to lead to serious outcomes as it causes the artery to stiffen, as compared to calcification in the tunica intima (inner layer) of the artery. It has been found that while certain risk factors known to be linked to coronary artery disease may also contribute to calcification, some factors are more likely to cause calcification in the middle layer or inner layer specifically.
For example, advancing age, diabetes mellitus and hyperphosphatemia (high blood phosphate levels) are associated with calcification in the middle and inner layers. Hypertension (high blood pressure), hyperlipidemia (high blood lipids), and cigarette smoking are more often associated with calcified deposits in the inner layer only. However, this should not detract from the fact that calcification may be linked to all risk factors associated with coronary artery disease.
Signs and Symptoms
Coronary artery calcification is not usually associated with any specific signs and symptoms beyond coronary artery narrowing, even without any evidence of calcification. Unlike with large arteries such as the aorta where calcification may cause a bruit (abnormal sound heard with a stethoscope), the coronary arteries are too small to present with such noticeable signs.
- Chest pain (angina) with physical and psychological stress
- Shortness of breath associated with chest pain
- Excessive and sudden sweating
- Dizziness and even fainting
- Radiated pain to the jaw, arm or upper abdomen
The differentiation between cardiac chest pain and non-cardiac chest pain needs to be made on a case by case basis. However, coronary artery disease should always be suspected in a person with high risk factors.
Diagnosis of CAC
The popularity of scanners to detect coronary arterial calcification does not mean that it is a conclusive indicator for coronary artery disease. It is important to note that the absence of calcification with diagnostic investigations does not mean that atherosclerosis is not present. However, the presence of coronary artery calcification is indicative of coronary artery disease (atherosclerotic narrowing). A person with high risk factors should not solely depend on a calcification scan to confirm or exclude coronary artery disease, especially younger adults.
Tests and Scans
The preferred method for detecting coronary artery calcification is through the use of computed tomography (CT) scan. It is non-invasive when compared to a CT angiogram that requires the administration of dyes. It is highly sensitive and specific for calcium deposition and can also quantify the degree of calcification. However, CT scans do not preclude the need for a traditional angiogram especially in high risk and symptomatic patients.
The multislice or helical CT scan to detect coronary artery calcification, also known just as the heart scan, uses beams of electrons to create a 3D image of structures within the body. Not all structures can be detected with this technique but calcifications like bone tissue can be clearly visualized. Deposits of calcium appear as white spots and in the healthy coronary artery this should be absent whereas it would be expected in healthy bones.
Although the scans are sometimes marketed as quick and accurate ways of testing for coronary artery disease, it is not always accurate for younger adults, especially those without symptoms and without high risk of coronary artery disease. A stress ECG may sometimes be a more accurate test for coronary artery disease and an angiogram is still the preferred investigation when there is no calcification. A heart scan should be requested by a medical professional based on a patient’s family and medical history as well as the results of clinical findings.
References:
- circ.ahajournals.org/content/94/5/1175.full
- www.sciencedirect.com/science/article/pii/S0735109714003283
