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A transient ischemic attack (TIA) is an ischemic stroke in which the blood flow is restored quickly and the symptoms disappear within 24 hours. In other words, it's a mini-stroke that you recover from quickly. For most patients with a TIA, the symptoms last less than one hour. The longer the symptoms last, the more likely that there will be permanent brain tissue injury.
TIAs affect 1 in 15 persons over age 65 years, but often go undiagnosed if the symptoms are not recognized. Approximately 15% of strokes are preceded by a warning TIA. Therefore, recognition of TIA symptoms is important because preventative treatment may help to reduce the chance of an impending stroke.
The risk of stroke is highest within the first 3 months following a TIA, especially within the first few days. Within the first month, the average risk of stroke after a TIA ranges from 1 in 20 to 1 in 10. TIAs and strokes generally occur in people with atherosclerosis (hardening of the arteries) or coronary artery disease. In fact, people who have suffered TIAs are even more likely to die of heart attack than of stroke.
A TIA is caused by the same factors that cause ischemic stroke. Ischemia is the medical term for a reduction of blood and oxygen to the cells.
Ischemic stroke occurs when the arteries feeding the brain become blocked. This may result from narrowing (stenosis) of the arteries, which disturbs blood flow, creating areas of turbulence that can lead to blood clot (thrombus) formation. Such a clot may occur in a brain-feeding artery, or it may occur elsewhere in the body, travel up to the brain, and lodge in a narrowed section of a brain artery.
A free-floating particle in the blood is called an embolus, and a free-drifting clot is called a thromboembolism. Local and travelling blood clots are the leading causes of stroke and TIA. The most common sources of brain emboli that cause stroke are the carotid arteries in the neck and the heart.
The risk factors for TIA are exactly the same as those for stroke:
There are other risk factors that aren't preventable:
The symptoms of a TIA vary depending on which arteries are obstructed. The most common location of blockage is in the carotid artery system. The two carotid arteries supply blood to the two sides of the brain. If one of them is blocked, there may be symptoms in the eye on the side of the blocked arteries, or symptoms affecting the opposite side of the body.
A blockage in the left carotid artery, for example, could cause temporary blindness in the left eye or paralysis of the right side of the face and the right arm and leg, or a loss of speech (inability to speak normally or understand speech).
Instead of complete blindness, many people suffer blurring or dimming of vision like a shade or veil slowly descending across their field of vision (the medical term for this is amaurosis fugax).
Another common location of blockages is the vertebrobasilar system. These strokes and TIAs can sometimes cause symptoms on both sides of the body or in both eyes. The balance control centre of the brain may be affected, causing symptoms of vertigo, dizziness, imbalance, and poor coordination, as well as double vision and slurred speech.
TIAs may come alone or in a series. Some people get several in a year, and a few get them daily. The more TIAs you get, the more likely you are to suffer a full-scale stroke.
The symptoms of TIA are identical to the symptoms of stroke, for the very good reason that a TIA is a stroke. When it happens, there's no way of knowing if the blockage will dissolve quickly (meaning a TIA) or stay in place long enough to cause cell death (meaning a stroke). According to statistics, it's far more likely to be a real stroke. Rush to the hospital (not the doctor's office) immediately - every minute of delay is risky. Even if you are having a TIA, you need immediate treatment, for a large stroke may follow within hours. Never attempt to drive yourself, because there's a major risk of sudden blindness, paralysis, or blackout.