An embolus is a clot (or a piece of plaque that acts in the same manner as a clot) that travels from the site where it formed to another location in the body. The embolism can lodge in an artery at the new location and block the flow of blood there.
The blockage deprives the tissues in that location of its normal blood flow and oxygen (lack of blood and oxygen is called "ischemia"). This can result in damage or even death of the tissues (necrosis) in that organ.
Arterial embolism may be caused by a single embolus or multiple emboli.
Arterial emboli can affect the extremities -- especially the legs and feet. Some may involve the brain, causing a stroke, or the heart, causing a heart attack. Less common sites include the kidneys, gut (intestines), and the eyes. A major risk for emboli is atrial fibrillation because the blood flow through the atria can be slow enough to trigger clots to form, which can then travel (embolize). The risk of an embolism increases when factors that tend to form clots are increased. These may include injury or damage to an artery wall, hematologic (blood component) conditions associated with increased clotting (such as increased platelet count), and other disorders. Another condition that poses a high risk for embolization (especially to the brain) is mitral stenosis. Endocarditis may also cause arterial emboli (paradoxical embolization), if a clot travels through a hole in the heart called the foramen ovale.
If an embolism involves the arteries supplying blood flow to the lungs, it is called pulmonary embolism, rather than arterial embolism, and it is a different condition (that is, clots originated in the veins, not the arteries). Endocarditis can also cause pulmonary embolism.
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