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Seen and Unseen Plaque

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Issue 30 - July 1999
Bypassing Heart Surgery

An understanding of vulnerable plaque now allows us to comprehend why some people with little or no blockage can have a heart attack while others with almost completely blocked arteries may never experience any of the symptoms of cardiovascular disease.

All arterial plaques are actually thought to be the body’s way of repairing damage to the arterial wall. Small tears might be caused by high blood pressure from stress, the effects of smoking, or a number of other factors. In response, collagen, clotting proteins, and a number of other substances are released into the bloodstream. These adhere to the injured site and attract platelets, special cells responsible for clotting. The core of the plaque contains many lipid-rich (fat-laden) cells derived from white blood cells (leukocytes), which in turn contain a large amount of tissue factor, a powerful coagulant. This core is separated from the bloodstream by a fibrous cap. It is the integrity of the cap that determines the stability of the plaque.

The body has a tendency to treat the build-up of soft cholesterol in vulnerable plaque as an infection. It sends in germ-fighting blood cells that inflame the plaque, and enzymes called metalloproteinases that eat away at the fibrous cap.  Vulnerable plaque is a lethal combination of powerful thrombogenic material (clotting substances) stored in the artery wall, separated from the bloodstream only by a weak cap that is being attacked by the body’s defense mechanism. Biomechanical studies have shown that it can take no more stress than that caused by a normal heartbeat to rupture these plaques.