Heart Disease Health Center

Stages of Atherosclerosis

Although the exact biological process is not completely understood, scientists have described three different stages of atherosclerosis that lead to the "clogging" of your arteries.

• The fatty streak: The first evidence of atherosclerosis can be found in children 10 to 14 years of age. The "fatty streak" appears as a yellow streak running along the major arteries, such as the aorta. The streak consists of smooth muscle cells, which are filled with cholesterol, and macrophages (a type of immune system "scavenger" cell that removes harmful substances, such as excess cholesterol particles, from the bloodstream). The fatty streak alone does not cause any symptoms but, over time, can develop into a more advanced form of atherosclerosis called fibrous plaque.
• Fibrous plaque: A fibrous plaque forms in the inner layer of the artery. The plaque consists of large numbers of smooth muscle cells, macrophages, and lymphocytes (a type of white blood cell that typically responds to an infection or injury). These cells are all filled with cholesterol. As the fibrous plaque grows, it projects into the space inside the artery where the blood is flowing.
• Complicated lesion: The last stage of atherosclerosis occurs when the fibrous plaque breaks open, exposing the cholesterol and connective tissue underneath. This rupture provokes a strong clotting reaction from your blood, such as when you have a cut. The combination of fibrous plaque and the blood clot is called a complicated lesion.

What does atherosclerosis do to arteries?

• It narrows your arteries. When the fibrous plaque grows large enough, it begins to narrow your arteries. This narrowing process happens slowly over many years. In time, the plaque growing into your arteries can limit blood flow to such a degree that parts of your body that depend on the arteries for blood begin to suffer from lack of oxygen, a condition called ischemia. When fibrous plaque in your coronary arteries causes your heart muscle to suffer from lack of oxygen, you may experience chest pain (angina).
• It hardens your arteries. When hard plaque forms in the walls of an artery, it can restrict the artery's ability to widen (dilate) so that more blood can flow through when needed, such as when you physically exert yourself. This "hardening" of your coronary arteries can also cause chest pain, usually during exertion.
• It blocks your arteries. When a blood clot forms around a crack or rupture in the fibrous plaque, this complicated lesion can completely block the flow of blood through the artery. Such an abrupt loss of blood supply causes lack of oxygen to or actual death of tissue (infarction), which can then damage tissues or organs that normally receive blood from that artery. Men who smoke and/or have high cholesterol have a greater chance of having a plaque rupture, causing a heart attack or sudden death.

The role of smoking

Smoking plays a large role in the development of atherosclerosis. The carbon monoxide and nicotine contained in tobacco smoke affect blood flow through your arteries by:

• Making it easier for cholesterol-carrying lipoproteins to enter the walls of your arteries.
• Promoting the formation of fibrous plaque.
• Promoting the formation of blood clots that can completely block your arteries.

Reversing atherosclerosis

If you think of atherosclerosis as a response to injury, the buildup of fibrous plaque can be reversed by removing the source of injury. In the case of high cholesterol, by reducing the amount of LDL cholesterol in your arteries and increasing the amount of HDL, which removes cholesterol that is already in your artery walls, you can actually reverse atherosclerosis. The ability to reverse atherosclerosis helps explain why treating high cholesterol can reduce the risk of further complications from atherosclerosis.