Vagal Nerve Stimulation
Vagal Nerve Stimulation
Morbidity and mortality rates
Vagal nerve stimulation is a treatment for epilepsy in which an electrode is implanted in the neck to deliver electrical impulses to the vagus nerve.
Vagal nerve stimulation is an alternative to medication or surgical removal of brain tissue in controlling epileptic seizures. The seizures of epilepsy are caused by uncontrolled electrical discharges spreading through the brain. Antiseizure drugs interrupt this process by reducing the sensitivity of individual brain cells to stimulation. Brain surgery for epilepsy either removes the portion of the brain where seizures originate, or cuts nerve fibers to prevent the nerve impulses that occur during a seizure from spreading to other parts of the brain. Vagal nerve stimulation uses a different approach: It provides intermittent electrical stimulation to a nerve outside the brain—the vagus, or tenth cranial nerve, which influences certain patterns of brain activity.
The vagus nerve is a major connection between the brain and the rest of the body. It carries sensory information from the body to the brain, and motor commands from the brain to the body. The vagus is involved in complex control loops between these destinations; its precise pathways and mechanisms are still not fully understood. It is also not known how stimulation of the vagus nerve works to reduce seizure activity—it may stimulate inhibitory pathways that prevent the brain’s electrical activity from getting out of control, interrupt some feedback loops that worsen seizures, or act in some other fashion.
Vagal nerve stimulation has been effective in reducing seizure frequency in patients whose seizures are not controlled by drugs, and who are either not candidates for other types of brain surgery or who have chosen not to undergo these procedures.
About 2.7 million people in the United States have been diagnosed with epilepsy. Ten percent of patients who are newly diagnosed with epilepsy do not respond well to medications, however, and so may be candidates for surgical treatment. Vagus nerve stimulation was first performed in the United States in 1988 and received final approval by the United States Food and Drug Administration (FDA) in July 1997. As of 2007, approximately 32,000 people worldwide are being treated with vagus nerve stimulation. One registry of patients who are being treated with vagus nerve stimulation shows that 60% were performed for patients with partial seizures, 15% were performed for patients with Lennox-Gastaut syndrome (also known as mixed seizures), and 25% were performed for patients with generalized seizures.
The vagal nerve stimulator (VNS) has two parts: an electrode that wraps around the left vagus nerve in the neck, and a pulse generator, which is implanted under the skin below the collarbone. The two parts are connected by a wire. Stimulation is performed only on the left vagal nerve, as the right vagal nerve helps control the heartbeat.
Surgery to implant a VNS device takes about two hours. A neurosurgeon implants the electrode and generator while the patient is under general anesthesia. A vertical incision is made in the left side of the neck, and the helical electrode is attached to the nerve itself. A second incision is made on the left side of the chest below the collarbone, and the pulse generator (a disc about 2 in [5 cm] in diameter) is implanted under the skin. The connecting wire is threaded around the muscles and bones to join the electrode and generator.
The generator makes a small bulge under the skin, but is hidden by clothing after the operation.
Before the neurosurgeon closes the incisions, he or she tests the VNS device to make sure it is working, and programs it to deliver the lowest amount of stimulation. The device is usually timed to stimulate the vagus nerve for 30 seconds every five minutes.
A candidate for vagal nerve stimulation will have had many tests already to determine the focal point of seizure activity. Preoperative tests include neuroimaging, as well as psychological tests to determine the patient’s cognitive (thinking) strengths and weaknesses.
The patient must be fully informed about VNS— how it works, its advantages and disadvantages, what will happen during surgery—before the operation is scheduled. A video as well as written material about VNS is available to view and discuss with the doctor.
Implantation of the stimulator in an adult may be performed as either an outpatient or inpatient procedure. In the latter case, the patient will remain in the hospital overnight for monitoring of heart function and other vital signs. Children who are receiving a VNS are usually scheduled for an overnight stay. Pain medication is given as needed.
Epilepsy— The name for a group of syndromes characterized by periodic temporary disturbances of brain function. The symptoms of an epileptic seizure may include loss of consciousness, abnormal movements, falling, emotional reactions, and disturbances of sight or hearing.
Helical— Having a spiral shape.
Neurologist— A physician who specializes in diagnosing and treating disorders of the nervous system.
Seizure— A single episode of epilepsy. Seizures are also called convulsions or fits.
Vagus nerve— The tenth cranial nerve, running from the head through the neck and chest into the abdomen. Intermittent electrical stimulation of the vagus nerve can help to control epileptic seizures.
The stimulation parameters are adjustable, and the neurologist may require several visits to find the right settings. Settings are adjusted with a magnetic wand that delivers commands to the stimulator’s computer chip. The patient will be taught how to use a magnet to temporarily increase stimulation, to prevent a seizure, or to abort it once it begins.
The VNS generator is powered by a battery that lasts several years. It is replaced during an outpatient procedure under local anesthesia.
The most common adverse effects from vagal nerve stimulation are a hoarse voice, cough, headache, and ear pain. These side effects can be reduced by adjusting the stimulation settings, and may subside on their own over time. Infection and device malfunction are possible, though rare.
Patients who have had a VNS implanted must avoid strong magnets, which may affect the stimulator settings. Areas with warning signs posted regarding pacemakers should be avoided. The patient should consult with the neurologist and the neurosurgeon about other hazards.
Approximately half of all patients who have received vagal nerve stimulation experience about a 50% reduction in seizures. Another 9% of patients obtain complete relief from seizures. Most patients who continue to take antiseizure medications can
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
The implanting of a VNS device is performed by a neurosurgeon in a hospital, in consultation with a neurologist.
QUESTIONS TO ASK THE DOCTOR
- What will the procedure cost? Will my insurance cover the cost?
- How often will I need to return to have the stimulator adjusted?
- Will my medication dosages be reduced after this procedure?
- How long will the procedure take?
- How many VNS devices have you implanted? What is your success rate?
reduce their dosage, however, which offers some relief from the side effects of these drugs.
Morbidity and mortality rates
Vagal nerve stimulation is a relatively safe procedure. Pilot studies of 300 patients that were done prior to FDA approval of VNS reported the following complication rates: hoarseness, 37% of patients; coughing, 14%; voice alteration, 13%; chest pain, 12%; and nausea, 2%.
Some candidates for vagal nerve stimulation are also likely to be candidates for a corpus callosotomy, temporal lobectomy, or other surgical procedures.
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DeGiorgio, C. “Vagus nerve stimulation for intractable seizures in children.” Pediatric Neurology 35 (November 2006): 323–326.
Rielo, Diego, MD, and Selim R. Benbadis, MD. “Vagus Nerve Stimulation.” eMedicine, April 12, 2002 [June 10, 2003]. http://www.emedicine.com/neuro/topic559.htm (accessed April 16, 2008).
Saneto, R. P. “Vagus nerve stimulation for epilepsy: randomized comparison of three stimulation paradigms.” Neurology 65 (July 2005): 317–319.
American Association of Neurological Surgeons (AANS). 5550 Meadowbrook Drive, Rolling Meadows, IL 60008. (847) 378-0500. http://www.neurosurgery.org (accessed April 16, 2008).
Epilepsy Foundation. 4351 Garden City Drive, Landover, MD 20785-7223. (800) 332-1000. http://www.epilepsyfoundation.org (accessed April 16, 2008).
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