Understanding Stroke -- the Basics
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.
The vast majority of strokes afflict people over the age of 60. Men are more often affected than women, and African Americans -- possibly because of a greater incidence of high blood pressure -- more often than whites. A more recent trend also shows that Hispanics are also more likely than whites to suffer strokes. A younger person is more apt to have a bleeding stroke, while older people usually suffer clot strokes.
The main controllable risk factors for stroke are:
- High blood pressure
- Heart disease
- High cholesterol levels (specifically, high LDL or "bad" cholesterol)
- Type 2 diabetes
- Abuse of stimulant drugs such as amphetamines and cocaine
- Excessive alcohol use