The Vagus Nerve Stimulator (VNS) is an Implantable Medical Device for Epilepsy.
The NeuroCybernetic prosthesis, NCP, system manufactured by Cyberonics Inc of Houston Texas is the only system available commercially for stimulation of the vagus nerve. The system, which is implanted within the body, comprises a lead, placed on the left vagus nerve in the neck, and a pulse generator, placed in the upper chest area similar to a cardiac pacemaker. Pulses from the generator are sent to the vagus nerve via the lead. The generator, which is programmed from outside the body, delivers stimulation pulses, as programmed by your physician, 24 hours a day regardless of your seizure activity or whether you are awake or asleep. You can deliver additional stimulation if you can feel the onset of a seizure by placing a magnet over the generator for a short time. A colleague or carer may also do this for you if a seizure has already commenced.
Once implanted, the generator is usually programmed to deliver 30 pulses per second to the vagus nerve for 30 seconds every 300 seconds. However, a physician can fine-tune the programming of the system specifically. The level of stimulation is dependent upon comfort and tolerance that varies from patient to patient.
When was vagus nerve stimulation first used for the treatment of epilepsy?
Following extensive studies by many researchers that showed changes in the brain wave patterns, EEG, when the vagus nerve was stimulated, Dr. Jacob Zabara applied the technique to prevent seizures or to reduce the number, intensity and/or duration. The first implant in man took place on a patient under the care of Dr. Kiffin Penry in 1988 in the United States of America. Many clinical studies have since taken place and current evidence indicates that vagus nerve stimulation is an effective and safe adjunctive (add-on) treatment for patients with refractory epilepsy.
Is there an age range for VNS?
Patients as young as 18 months have been implanted and patients over 60 years of age have also been implanted. Your physician will discuss this with you, if necessary.
What does the operation to implant the vagus nerve stimulation entail?
Admission to hospital usually on the day before surgery and discharged a few days after the operation, depending on the surgeon’s preference. The operation to implant the system is carried out under general anesthesia. The incision for the lead is made on the left side of the neck through which the vagus nerve is exposed and the lead placed around it. The other end of the lead is taken under the skin to second incision in the left upper chest area below the collarbone and connected to the pulse generator. The NCP system will not be switched on until several weeks after the operation.
What happens after the operation?
Depending upon the preference of the physician, the level of stimulation to the vagus nerve is gradually increased over the weeks following implantation. The level of stimulation is very individual and will only be increased to the patients own specific level of tolerance. Programming is done externally using a computer and a programming wand without any discomfort to the patient.
The surgeon will wish to see the patient in the days following discharge from hospital to have the incisions checked and any sutures removed. There will be regular appointments with the physician after the programming is complete and the patient will probably be asked to complete a seizure diary card so that an assessment of the effect of VNS on the epilepsy can be reliably made. The physician may reprogram the generator depending on the effect of VNS on the seizures.
Can a patient or carer deliver stimulation?
The implanted system will deliver stimulation 24 hours every day according to the programming that the physician made at the last visit. If the physician’s instruction to the magnet to command additional stimulation has been programmed accordingly, the patient will be able to deliver additional stimulation when he experiences an aura. This is achieved by placing the magnet over the generator for about 2 seconds. If the patient is having a seizure, a companion or carer can deliver additional stimulation by using the magnet in the same way.
Will the vagus nerve stimulation effect anti-epileptic drugs?
The clinical results on VNS have shown no effect an anti-epileptic drug blood levels or body chemistry.
Will the vagus nerve stimulation have a effect on other systems in the body?
Mild side effects may occur with VNS such as voice changes, hoarseness, throat irritation and cough, breathing problems, snoring, difficulty swallowing, nausea, abdominal pain and tingling of the skin. For most people, side effects are mild and can be minimised by adjusting the stimulator.
Who is a suitable patient for VNS?
The doctor responsible for treating the patient’s epilepsy will have the answer to this question.
Are there any special precautions to take if implanted with a stimulator?
Yes. If medical treatment is needed for epilepsy or any other conditions, a reminder is required to the physician and/or surgeon of an implanted system. If the patient requires an MRI scan, the physician and/or surgeon will need to know of an implanted system. If a general anesthetic is required, the stimulator should be programmed to ‘off’ for the duration of the procedure. The stimulator can be reprogrammed to `on’ once the patient has fully recovered from the anesthetic.
Is the NCP System approved for use in epilepsy?
Vagus nerve stimulation has been approved for patient use in Australia by the Therapeutic Goods Administration.
Information reviewed by Professor David Reutens, Royal Brisbane & Women’s Hospital. Updated August 2013. To be reviewed August 2015.