The Facts
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 brain tissue injury.
TIAs affect one 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.
Causes
A transient ischemic attack 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 obstructed. This may result from narrowing (stenosis) of the arteries,
which disturbs bloodflow, 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 traveling 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/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, that figure
increases further. Quitting smoking reduces stroke risk; over five 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.
There are other risk factors that aren't preventable:
- Age naturally increases the risk of stroke and TIAs.
- Diabetes increases the risk of cardiovascular and cerebrovascular events.
Controlling blood sugar levels may also reduce the risk.
