The vagus nerve, or cranial nerve X, is a part of the autonomic nervous system, which controls functions of the body that are not under voluntary control, such as heart rate and digestion. In the neck, the vagus nerve travels near the carotid artery and jugular vein. Interestingly, neurologists in the 19th century noted that applying pressure on the carotid artery in the neck, and thus the vagus nerve, could stop seizures. Recent research found that stimulation of the vagus nerve in animals decreases both epileptic activity in the EEG and the frequency and severity of seizures. After proven seizure reduction in animals using VNS, several controlled human trials demonstrated a significant reduction in seizures with minimal side effects. In 1997, the FDA approved vagus nerve stimulation in patients older than 12 with refractory partial epilepsy. Mounting clinical experience also demonstrates efficacy and safety in children and in patients with generalized epilepsies.
Vagal Nerve Stimulation is a non-drug treatment for epilepsy that utilizes the vagus nerve to send signals to the brain. The vagus nerve, the longest cranial nerve, travels from the brainstem, down the neck, into the chest and abdomen to influence activity in many organs. When a patient has a VNS device implanted, small electrical signals are sent from the device to the vagus nerve and travel up into the brain. The device is programmed by the doctor to deliver these signals (or “stimulate”) at periodic intervals.
Initially, stimulation is usually set to occur 30 seconds every five minutes. The doctor then adjusts these parameters according to patient tolerance and seizure response in follow up visits. The patient also has a degree of control over the VNS. Each patient receives a magnet that activates the device. When the patient or caregiver “swipes” over the device with the magnet, the VNS turns "on" and delivers a stimulus. This allows a patient who feels an aura coming on, or a caregiver who sees the start of a seizure, to try to stop the seizure.
Vagus Nerve Stimulation (VNS) surgery involves the surgical implantation of a stimulating device, a 6 centimeter wide disc which looks like a pacemaker. An incision is made 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 lead from the stimulator is wrapped around the vagus nerve. The brain itself is NOT surgically involved in VNS surgery. The device battery lasts for approximately 5 years, after which many patients choose to have repeat surgery to replace the battery.
Compared to standard epilepsy surgery, VNS surgery is relatively minor. The procedure takes 1-2 hours, requires general anesthesia, and most patients return home the same day of surgery.
The risks of implantation are low and mostly include the minor surgical risks of bleeding or infection (about 1-2%). Less than1% of implants cause some damage to the nerve supplying muscles in the voice box, which can result in intermittent hoarseness or a change in voice quality. This typically improves within a few months.
At first, patients may notice a tingling in the neck during the 30 or so seconds that the stimulator is “on.” In addition, when the vagus nerve is stimulated, about one third of patients have some change in their voice quality, which is reversible by reducing the amount of stimulation or adjusting other stimulation features. Even without any change in the level of stimulation, the hoarseness and changes in voice quality tend to diminish and resolve over several weeks or months. Rare side effects include change in swallowing (usually during stimulation), cough or shortness of breath.
Studies have shown that:
The vagus nerve stimulator was approved by the FDA for use in patients with refractory partial epilepsy who are 12 years of age or older. It was also approved for use in patients with refractory depression. Many centers have successfully used the device in younger children (as young as 1 year of age) and in patients with primary generalized epilepsy, Lennox-Gastaut syndrome, Landau-Kleffner syndrome, and other seizure disorders.
The NYU Comprehensive Epilepsy Program has implanted more than 500 vagal nerve stimulators. We continue to be very active and presently typically implant 2-3 devices per month. The results of our experience to date are being analyzed and are available in the surgical results section.