Vagus nerve stimulator

(vagal stimulator)

 

Electrical stimulation of the vagus nerve for the control of epilepsy (seizures).

Device successfully used in Europe for treatment of some kinds of depression.

The vagus nerve is one of the twelve cranial nerves.  The nerve originates in the brainstem from several collections of neurons (nerve cells) called “nuclei”.  The nuclei of the vagus nerve send axons (extensions of nerve cells) out of the brainstem, through the subarachnoid space, out a hole in the base of the skull called the jugular foramen, and then alongside the carotid artery in the neck, as the “vagus nerve”.  Because of its proximity to other neurons in the brainstem that have axons that communicate with other areas of the brainstem, thalamus, cerebral cortex, etc. stimulation of the vagal nuclei can produce reactions in many parts of the brain.  Some of these other brain areas are involved in seizure activity.  Electrical current applied to the vagus nerve in the neck travels back along the axons into the nucleus where it can then exert influences on other parts of the brain (including those that control seizures).  A vagal stimulator is a device with electrodes that are surgically wrapped around the vagus nerve in the neck.  The electrodes get their electric current from a generator placed below the skin over the chest mucles at about the level of armpit (axilla).  Wires run under the skin from the generator to the stimulating electrodes.
Placement of a vagal stimulator is done with the patient under general anesthesia.
The patient is placed in the supine position.  The hair over the neck or chest incisions is shaved.
The neck incision is made along the anterior border of the sternocleidomastoid muscle about halfway between the mastoid process (the bony prominence low and behind the ear) and the clavicle (breast bone) where it ends at the junction of the chest and neck.
The chest incision is variable: the simplest is a straight line incision parallel to the clavicle about half way between this bone and the nipple.   For cosmetic or other considerations the surgeon and patient may elect to put the incision (and therefore the generator as well) in a different location.
A metal tube with blunt end is used to open a “tunnel” in the space below the skin and above the muscle fascia of the neck and chest.  After the electrodes are placed the wires that will connect it to the generator are fed through the tunnel.  A “pocket” large enough to accomodate the electrical generator (approximately 4 by 4 by 2 inches, 1/4 pound) is made and the generator is “interrogated” by a computer (used later in the outpatient clinic to make adjustments) prior to placement in the pocket.
Both incisions are closed with sutures to the deep tissue layers, staplels, tape, or glue can be used to close the skin.  The patient is taken to the recovery room post operatively and can usually go home the next day.
Risks of vagal stimulator placement include those associated with surgery:  injury to the vagus nerve (which then becomes unusable for stimulation), injury to the carotid artery or internal jugular vein (neither a fatal problem but either can be difficult to manage and can require terminating the procedure before the electrodes have been placed).  Injury to the vagal nerve can result in hoarseness or difficulty swallowing (hoarseness is actually an indicator that the vagal stilulator is working and is frequent at the time the device is turned on).  Complications that may not be apparent at the time of surgery include: infection (either wound) — a bad problem because it frequently requires removal of all hardware, a course of antibiotics and then starting all over again in a few months.  The generator is large enough that it may be cosmetically disfiguring.  Sometimes the generators move over time to a position that is uncomfortable.  In addition to surgical complications are potential problems with the device itself: if the device fails another surgery may be necessary to replace it.
The battery in the generator has a life of three to five years (approximately) depending on the year the device was made (battery life gets longer with each new generation).  When the battery runs down the generator must be replaced — requires another surgery to reopen the chest incision.

Epilepsy – Neuropathophysiology

 

Vagal nerve stimulator insertion – Procedure

 

Vagal nerve stimulator insertion – Risks and complications

 

Functional neurosurgery Specialty Center