There are several ways to treat epilepsy. How well each treatment works varies from one person to another. Vagus Nerve Stimulation therapy is a form of treatment for people with epilepsy whose seizures are not controlled with medication.
Vagus nerve stimulation (VNS Therapy) is designed to prevent
seizures by sending regular, mild pulses of electrical energy to the brain via
the vagus nerve. These pulses are supplied by a device something like a
pacemaker.
·
The VNS device is sometimes referred to as a "pacemaker for
the brain." It is placed under the skin on the chest wall and a wire runs
from it to the vagus nerve in the neck.
·
The vagus nerve is part of the autonomic nervous system, which
controls functions of the body that are not under voluntary control, such as
the heart rate. The vagus nerve passes through the neck as it travels between
the chest and abdomen and the lower part of the brain.
·
The surgeon first makes an incision along the outer side of the
chest on the left side, and the device is implanted under the skin.
A second incision is made horizontally in the lower neck, along a crease
of skin, and the wire from the stimulator is wound around the vagus nerve in
the left side of the neck. The brain itself is not involved in the surgery.
·
The device (also called an implant) is a flat, round battery,
about the size of a silver dollar—that is, about an inch and a half (4 cm)
across—and 10 to 13 millimeters thick, depending on the model used. Newer
models may be somewhat smaller.
·
The procedure usually lasts about 50 to 90 minutes with the
patient under general anesthesia. Usually the person can go home later the same
day. Sometimes you may need to stay overnight in the hospital for
observation.
How is VNS used?
· The neurologist (or licensed professional) programs the
strength and timing of the impulses according to each patient's needs. The
settings can be programmed and changed by placing a wand over the generator on
the left side of the chest. The wand is connected to a handheld computer.
·
For all patients, the device is programmed to go on (give
stimulation) for a certain period (for example, 7 seconds or 30 seconds)
and then to go off (stop stimulation) for another period (for example, 14
seconds or 5 minutes). The device is set to give stimulation at regular
intervals during the day, usually with 30 seconds of stimulation alternating
with 5 minutes of no stimulation. The patient is usually not aware that it's
operating.
·
Holding a special magnet near the implanted device
(generator) triggers the device to deliver another burst of
stimulation, outside of the programmed intervals. For people with warnings
(auras) before their seizures, activating the stimulator with the magnet when
the warning occurs may help to stop the seizure.
·
Settings (also called stimulation parameters) set by the
neurologist typically include a stimulation amplitude of 1.0 to 3.0 mA
(milliamperes), a stimulation frequency of 20 - 30 Hz (hertz), and a pulse
width of 130 - 500 microseconds. By adjusting these settings, the doctor
not only may be able to control more of the patient's seizures, but often can
also relieve side effects. One study, for instance, found that changing the
pulse width eliminated pain that some patients were experiencing.
·
The battery for the stimulator lasts approximately 5-10 years,
depending on the settings used.
What can VNStherapy do during a seizure?
Some people have a warning or aura
which is a simple focal (or 'simple partial') seizure that tells them that they
are going to have a further seizure. When this happens, they can pass a special
magnet over the stimulator to give extra stimulation. This may stop the aura
from developing into another seizure or may reduce how long it takes to recover
afterwards.
The magnet can be worn on their
wrist like a watch or on their belt. For people who have no warning before a
seizure, someone else could use the magnet when a seizure happens.
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