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:
- High blood pressure is the number one risk factor. Even people with borderline high blood pressure have a higher TIA or stroke risk than people with normal blood pressure. Higher pressures mean increased risk. Even a small (6 mm Hg) reduction in diastolic blood pressure leads to a 42% reduction in the risk of stroke.
- Smoking is the number two risk factor in most strokes. Tobacco consumption of up to a pack a day may double your risk. Beyond a pack a day, the figure increases further. Quitting smoking reduces stroke risk - over 5 years, the risk falls to the same level as that of people who have never smoked.
- Heart disease and arrhythmias are often due to risk factors, but some are congenital (present from birth). The type of arrhythmia known as atrial fibrillation is closely associated with stroke. Most people with atrial fibrillation are treated with blood thinners to prevent this complication.
- Heavy alcohol use is a modifiable risk factor. Reducing how much alcohol you consume in a day to the maximum recommended amount can reduce your risk for developing a TIA or stroke.
There are other risk factors that aren't preventable:
- age naturally increases the risk of stroke and TIAs
- diabetes increases the risk of cardiovascular (heart- and blood vessel-related) and cerebrovascular (brain-related) events - controlling blood sugar levels may also reduce the risk
Symptoms and Complications
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.
Making the Diagnosis
The diagnosis of TIA depends on a detailed review of the symptoms, medical history, and neurological examination, and consideration of other conditions that may mimic a TIA (such as migraine, seizure, brain tumour, or non-neurological conditions).
To confirm the diagnosis and exclude other conditions, a brain scan such as computed tomography (CT) or magnetic resonance imaging (MRI) may be performed. Doppler ultrasound tests may be performed to see if there are blockages in the arteries. In some circumstances, an angiogram (a procedure in which dye is injected into the carotid artery via a small tube inserted into a blood vessel) may be done to investigate further.
Treatment and Prevention
The first thing to do after a recent TIA is to be assessed by a physician to confirm the diagnosis, and to begin treatments to lower the risk of having a stroke. Basically, this involves use of antiplatelet medications to minimize the chance of further clot formation. Acetylsalicylic acid* (ASA), ticlopidine, clopidogrel, and a combination of ASA and dipyridamole are medications that are commonly used to "thin" the blood, break up existing blood clots, and inhibit blood clot formation
In special circumstances, an anticoagulant medication called warfarin or heparin may be prescribed for stroke prevention. Other medications such as blood pressure-lowering agents and cholesterol-lowering agents may be considered for long-term stroke risk reduction.
Surgery for blockages in the carotid artery may be recommended for stroke prevention if there is severe (more than 70%) blockage. It's important to heed the warning given by a TIA, especially when many of the risk factors for stroke can be reduced. Stop smoking, reduce excess weight, and keep alcohol intake to a minimum. It is even more important to control high blood pressure.
*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.