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.
What is the surgery like?
- 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.
The VNS implant devices are built by Cyberonics, Inc. Additional information for patients and physicians is available at their website (www.cyberonics.com).