Plaque

The problem with plaque

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Plaque contains a number of different substances. The most important are the fatty substances or lipids – the "athero" part of the word atherosclerosis. The other contents – calcium, muscle cells and fibrous tissue – are the "sclerosis" part. Most heart attacks occur because an atherosclerotic plaque has become unstable.

Unstable plaque

Unstable plaque contains large amounts of lipids covered by a thin coating called a fibrous cap. Inflammatory cells in the plaque may eat away this fibrous cap, causing the content of the plaque to spill into the bloodstream. These cells interact with blood elements and clotting factors to cause a blood clot. If the clot is large enough to completely obstruct blood flow through a coronary artery, a heart attack will occur.

Narrowing plaque

Plaque may narrow the blood vessel enough to limit blood flow through the vessel. This usually causes symptoms only during exercise or stress.

Plaque and heart attacks

The likelihood that a plaque will rupture and cause a heart attack is not related to the severity of the narrowing. A plaque that narrows a vessel by only 30 percent may cause a heart attack, while a larger one that narrows a blood vessel by 90 percent may remain stable for years, perhaps causing chest pain during exercise, but not resulting in a heart attack. The chance of a plaque erupting has nothing to do with its size, but its stability.