Vagal nerve stimulation (VNS) is a new treatment for patients with refractory partial seizures that are not amenable to surgery because no resectable focus or lesion is identifiable. While the FDA only first approved its use in 1997, VNS had already demonstrated anticonvulsant effects in a number of seizure types. In children, some have advocated the use of VNS for Lennox Gastaut syndrome and atonic seizures though overall these patients tend to not do as well as following corpus callosotomy. For the subpopulation of children who do well, and avoid surgery, it has been recommended, similar to a drug trial, a VNS trial prior to palliative surgery. While the mechanism of action of VNS is unknown at this time, it has been proposed that electrical stimulation of the vagus nerve decreases the brain’s sensitivity to the conditions or stimuli that can trigger seizures, possibly increasing the degree of inhibition or decreasing the degree of excitation in the CNS.

The VNS system consists of an implantable pulse generator and stimulation leads with unique helical electrodes that, together, deliver programmable pulse trains to the left vagus nerve 24 hours a day. A hand-held magnet may be used to instantaneously activate the generator transcutaneously if the patient experiences an aura or if an observer witnesses the patient having a seizure. The generator may be programmed externally with a programming wand attached to a standard personal computer to adjust frequency, output current, pulse width, signal time on, signal time on, and magnet parameters. The stimulation pulse is ramped up or down for patient comfort. After battery depletion (current generations are expected to last 7-10 years), the pulse generator can be replaced without changing the vagal nerve leads.

The surgical procedure for implantation is fairly straightforward for anyone familiar with the carotid sheath area. The procedure takes less than 2 hours and is usually performed under general anesthesia on an outpatient or inpatient basis. Inpatient stays have been recommended due to the uncommon complication of bradycardia in the first 24 hours. These patients can be observed and discharged from the monitored bed. The pulse generator is placed in a subcutaneous pocket below the left clavicle. A second incision, transverse in the neck, extending across the anterior border of the sternocleidomastoid muscle allows for the placement of the helical electrodes around the vagus nerve. The connector pin end of the stimulation lead is tunneled subcutaneously from the neck to the chest pocket, where it is attached to the generator. Generator replacement upon battery depletion is usually done on an outpatient basis with local anesthesia requiring about 30-45 minutes.

Outcomes with the VNS have been good, with over 50% reduction in seizure frequency in 50-75% of patients. Adverse events are mild and occur mainly during stimulation, the most significant being hoarseness, throat paresthesias, and coughing. Minor complications have included wound infections, ipsilateral vocal cord paralysis, hoarseness, and temporary left facial hyperesthesia.