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    Understanding Stroke -- the Basics

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    What Is a Stroke? continued...

    Because of improved treatment and greater public awareness of the dangers of high blood pressure, the overall death rate from stroke is declining. Nonetheless, stroke remains the fourth leading cause of death in the U.S., behind heart disease, cancer, and lung disease. It is also the leading cause of disability and second only to Alzheimer's disease as a cause of dementia.

    Recovery from stroke depends on the extent and location of brain damage. Although about 25% of patients die within the first year of having their first stroke, some stroke victims recover fully. But in the vast majority of cases, there is lasting physical or mental disability. Weakened stroke victims are also more vulnerable to infectious diseases such as pneumonia. In addition, depression often follows a stroke; unless treated, it can significantly hinder recovery.

    What Causes Stroke?

    An ischemic (or clot) stroke occurs when a blood clot obstructs blood flow to a portion of the brain. The blocked vessel is already narrowed by years' worth of plaque buildup due to atherosclerosis (hardening of the arteries). The clot that serves as the final plug may be either a stationary blood clot created on the spot (thrombus), or an embolus composed of blood, plaque, or some other substance that formed elsewhere and traveled to the site.

    Embolic blood clots. Emboli are blood clots that start in one location and travel to the brain to do their damage. Stroke-triggering blood clots may be produced when blood flow is sluggish. After a heart attack, for example, clots may form on the damaged heart wall because of slower blood flow there before traveling to the brain. A common cause of blood clots is an irregular heart rhythm called atrial fibrillation. In atrial fibrillation, the upper chambers of the heart beat rapidly and irregularly. This increases the risk of a blood clot forming in the upper chambers of the heart (atria), which could break off and block an artery of the brain.

    Bleeding. Bleeding (or hemorrhagic) strokes may be caused by aneurysms in the brain that rupture or arteries that become weak under the strain of long-term high blood pressure. Bleeding strokes can also result from a leaking arteriovenous malformation, a tangle of overgrown blood vessels in the brain that some people are born with.

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