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Atherosclerosis (narrowing of arteries)

What is atherosclerosis?

Atherosclerosis (or arteriosclerosis), is the disease process of 'hardening' of the arteries. Fatty deposits build up over time in the walls of the arteries, forming lumps (atheroma) which extend into the artery and reduce the blood flow. Atherosclerosis increases the risk of conditions such as angina, stroke and heart attack. Treatment includes medication, medical procedures (eg, angioplasty) or heart surgery, in conjunction with lifestyle changes.

How does atherosclerosis occur?

When we are born, our blood vessels are flexible and elastic, and the blood is able to flow through them with ease. As we age, fatty deposits start to develop in the walls of our arteries and gradually they build up, forming lumps which extend into the middle of the artery, reducing the ease of blood flow through the artery. This process can be broken down into three stages:

Fatty streaks
Damage to the inner wall of the artery allows infiltration of fatty substances. At this stage artery damage is minimal and the blood flow is not seriously affected.

Soft plaque
Repeated injury at the site of the fatty plaques results in a thickening of the artery's middle layer. Deposits of cholesterol, fatty substances, connective tissue and blood products form a soft cap or plaque. This bulges into the channel of the artery, restricting the flow of blood.

Hard plaque
All three layers of the wall of the artery are affected. The artery's channel is now almost blocked.

1 Healthy blood flow in an artery 2 Mild atherosclerosis (plaque)
3 Severe atherosclerosis 4 Artery blocked by a clot

This process can affect any organ. Atheroma of the arteries to the brain can lead to a stroke; to the legs, gangrene; and, in the case of the heart, angina or a heart attack.

Treatment depends on area affected

The narrowing of the artery can be in one area, multiple areas, or affect an artery throughout its length. This is important for your doctor to know as it will affect his/her decision regarding what treatment is best for you.

Doctors often talk about one, two or three vessel disease; this refers to how many and which of the main branches of the coronary arteries are affected. In general, one or two vessel disease may be treated with medicines or angioplasty, whereas three or more vessel disease usually requires bypass surgery.

What is thrombosis?

Thrombosis is the medical term for a clot, the natural process that stops us bleeding when we injure ourselves. In coronary artery disease a clot forms, not as a result of an outside injury, but as a result of damage to the inner lining of the artery wall, caused by the fatty build-up (atheroma) in the wall of the artery.

Normally the lining of the artery is smooth, but when atheroma builds up, the walls are no longer smooth and sometimes the protruding plaques crack open. When this happens, platelets (blood cells that help with clotting) stick to these cracks to seal them, and, providing the artery is not very narrowed, then no harm occurs.

If the narrowing is already severe, then even a small clot forming on the top of a plaque can have a serious effect on the blood's ability to flow through the artery.

The formation of a thrombus is one of the main problems in coronary heart disease. It is the cause of most cases of sudden deterioration in angina and most heart attacks.

Related topics 

Heart attack - minimising heart risks
Heart risk - do you need a heart risk assessment?

Original material provided by the Heart Foundation of New Zealand, 2005. Reviewed and edited by everybody, January 2011. Latest review by Health Navigator, August 2014.

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