What is a Wada Test or Amytal Study?
After video EEG (electroencephalograph) monitoring, a Wada (WAH-dah) test is often done first. This test is officially known as the intracarotid sodium amobarbital procedure (ISAP), but the nickname "Wada test" is commonly used. The name comes from the doctor who first performed it, Dr. Juhn Wada.
- The Wada test looks at language and memory on one side of the brain at a time.
- Language (speech) is controlled by one side of the brain (in most people, the left side). The Wada will help doctors find out which side controls language in your brain.
- Memory can be controlled by both sides of the brain. The Wada can help figure out which side of your brain is more responsible for helping you remember (make and store memories).
- If the side that controls language or memory is where your seizures may be coming from, the surgeon may consider doing another test called a functional MRI (magnetic resonance imaging) or other brain mapping tests before surgery.
Who can have a Wada test?
The Wada test can be done in both adults and children. Children must be old enough to cooperate with the testing.
Who performs the test?
Three doctors are usually involved in performing a Wada test:
- Neuroradiologist (an expert in taking and interpreting pictures of the brain and it blood vessels)
- Epileptologist (a neurologist who specializes in epilepsy)
- Neuropsychologist (a specialist in the relationship between the brain and how we think and behave)
What's an angiogram?
Right before the Wada test, a cerebral angiogram is done.
- The angiogram looks at blood flow in the brain to make sure no problems are seen.
- The neuroradiologist places a catheter (a long, narrow tube) into an artery, usually in the leg.
- The catheter is directed to a major artery (called the internal carotid artery) in one side of the neck.
- Once the catheter is in place, a dye is injected. Some people report a warm sensation when this happens.
- The dye can be seen on a special x-ray machine. This machine takes pictures of the dye as it flows through the blood vessels of the brain. Once the angiogram is done, the catheter will stay in place for the Wada.
What happens during the Wada test?
Before the test, EEG leads are put on to record brain activity. The epileptologist will watch the EEG during the Wada test. The neuroradiologist then gives medicine to put one side of your brain to "sleep" for a few minutes.
- This is done by putting a medicine into the right or left internal carotid artery. A medicine called sodium amobarbital or sodium amytal has been used. Other similar medicines can be used.
- If the right carotid artery is injected, the right side of the brain goes to "sleep" and can't communicate with the left side. The EEG can show if activity on that side has slowed down enough or if enough medicine is given.
- Once the doctors are sure one side of your brain is asleep, the neuropsychologist tests your ability to speak and remember. They will show you words, objects, and pictures on a card.
- The awake side of the brain tries to recognize and remember what it sees.
- After just a few minutes, the medicine wears off. The side that was asleep starts to wake up.
- Once both sides of your brain are fully awake, the neuropsychologist will ask you what was shown. If you don't remember what you saw, items are shown one at a time and asked whether you saw each one before.
- Then the other side of the brain is put to sleep.
- To do this, the catheter is withdrawn part of the way and threaded into the internal carotid artery on the other side.
- A new angiogram is done for that side of the brain.
- Different word, object, and picture cards are shown, and the awake side (which was asleep before) tries to recognize and remember what it sees.
- Once both sides are awake again, you will be asked what was shown the second time. Then you are shown items one at a time and asked whether you just saw each item.
How long does the test take?
- The Wada test can vary between medical centers. At some centers, both sides of the brain are tested in one day. Usually, there is a wait of 30 to 60 minutes before the second side is tested. Other centers test one side on one day, and test the other side the following day. Generally speaking, the time a person will spend in the testing room will be about 3 to 4 hours.
- Usually this test is done as an outpatient test. You come and leave the same day. Other times, the test may be done when you are admitted to the hospital or you stay overnight after the test.
Is the Wada safe?
A Wada test is generally a safe procedure with very few risks. General risks like pain, bleeding, or infection where the catheter is inserted may happen. There is a small risk of some complications with the Wada test.
- These complications can be as minor as pain where the catheter is inserted or as serious as a potential stroke.
- Since the Wada involves entering arteries, there is a chance that fat inside an artery may come loose and cause a blockage in the brain, leading to a stroke. This risk of stroke is less than 1% overall. It is greater (but still relatively low) if you are older or if you have atherosclerosis (hardening of the arteries) or a history of high cholesterol.
Is there a recovery period?
- You will be on bedrest for several hours after the test.
- The nurses and doctors will check the site where the catheter was inserted to be sure there is no bleeding. They will also check the pulses and sensation in the leg.
- Usually, a person is sent home after several hours with information about what to do at home. Heavy lifting and other strenuous activity or exercise is usually avoided for a few days after the test.
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