What Is Atherosclerosis?

Atherosclerosis -- hardening and narrowing of the arteries -- gets a lot of bad press, with good reason. This progressive process silently and slowly blocks arteries, putting blood flow at risk.

Atherosclerosis is the usual cause of heart attacks, strokes, and peripheral vascular disease -- what together are called "cardiovascular disease." Cardiovascular disease is the No. 1 killer in America, with more than 900,000 deaths last year.

How does atherosclerosis develop? Who gets it, and why? Atherosclerosis is a mouthful, but it doesn't need to be a mystery. This deadly process is preventable and treatable. Read on, and get to know your enemy.

Atherosclerosis: How It Happens

First, an Anatomy 101 review:Arteries are blood vessels that carry blood from the heart throughout the body. They're lined by a thin layer of cells called the endothelium. The endothelium works to keep the inside of arteries toned and smooth, which keeps blood flowing.

"Atherosclerosis starts when high blood pressure, smoking, or high cholesterol damage the endothelium," says Richard Stein, MD, national spokesperson for the American Heart Association. "At that point, cholesterol plaque formation begins."

Cholesterol invasion. Bad cholesterol, or LDL, crosses damaged endothelium. The cholesterol enters the wall of the artery.

Plaque formation. Your white blood cells stream in to digest the LDL cholesterol. Over years, the accumulating mess of cholesterol and cells becomes a plaque in the wall of the artery.

"It's a jumble of lipids, or cholesterol, cells, and debris, and it creates a bump on the artery wall," explains Stein. As the process of atherosclerosis continues, "the bump gets bigger." A big enough bump can create a blockage.

Atherosclerosis tends to happen throughout the body. "So if you have plaque in your heart, you're at a higher risk for stroke, and vice versa," says Stein.

Atherosclerosis usually causes no symptoms until middle or older age. Once narrowings become severe, they choke off blood flow and can cause pain. Blockages can also suddenly rupture, causing blood to clot inside an artery.

Atherosclerosis: Plaque Attacks

Plaques from atherosclerosis can behave in different ways.

• They can stay within the artery wall. There, the plaque grows to a certain size and stops. "Because they don't block blood flow, these plaques may never cause any symptoms," says Stein. 
• They can grow in a slow, controlled way into the path of blood flow. Eventually, they cause significant blockages. Pain on exertion (in the chest or legs) is the usual symptom. 
• The worst-case scenario: plaques can suddenly rupture, allowing blood to clot inside an artery. In the brain, this causes a stroke; in the heart, a heart attack.

The plaques of atherosclerosis cause the three main kinds of cardiovascular disease:

• Coronary artery disease: Stable plaques in the heart's arteries cause angina (chest pain on exertion). Sudden plaque rupture and clotting causes heart muscle to die. This is a heart attack, or myocardial infarction. 
• Cerebrovascular disease: Ruptured plaques in the brain's arteries causes strokes, with the potential for permanent brain damage. Temporary blockages in an artery can also cause transient ischemic attacks (TIAs), which are warning signs of stroke; however, there is no brain injury.
• Peripheral artery disease: Narrowing in the arteries of the legs caused by plaque. Peripheral artery disease causes poor circulation. This causes pain on walking and poor wound healing. Severe disease may lead to amputations.