Vagus Nerve Stimulation (VNS)

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Vagus Nerve Stimulation (VNS)

Definition

The vagus nerve is part of the autonomic nervous system, which controls bodily functions that are not under conscious control (for example, heartbeat, breathing, and sweating). The vagus nerve passes through the neck as it travels between the chest and abdomen and the lower part of the brain . Vagus nerve stimulation (VNS), also known as vagal nerve stimulation, is a procedure whereby the vagus nerve is stimulated by means of a surgically implanted electrical device. The VNS device is sometimes referred to as a “pacemaker for the brain.” It is placed under the skin on the chest wall and a wire runs from it to the vagus nerve in the neck.

Purpose

The goal of VNS is to change the functioning of various brain and somatic systems, by lessening of the numbers of seizures in the case of epilepsy or by inducing a more positive mood in the case of treatment refractory depression (TRD). In epilepsy, treatment has been concurrent with pharmaceuticals used to reduce seizures. Although approved by the FDA in 2005 for use in treating major depression that has not responded to at least four depression treatments, solid evidence for the efficacy of VNS in depression has yet to be established.

Description

Research has not been able to establish exactly how VNS works, except to note a multiplicity of effects on the brain and body by stimulating the vagus nerve. The

vagus nerve, the tenth cranial nerve, originates in the brain and travels through the mid-brain. Branching into left and right vagus nerves, it runs down the neck and to the thorax and abdomen. The functions of the vagus nerve are many and various, ranging from the stimulation and release of neurotransmitters in the brain to issues related to breathing, swallowing, and the vocal chords, to the functioning of the digestive tract. The vagus nerve has been shown to create changes in the functioning of the hypothalamus, the amygdale, and the cingulate gyrus—brain structures that affect neurotransmitter output and reuptake, mood, and seizure activity, among other things. Because the vagus nerve runs through the middle of the brain, it influences many areas of the brain indirectly, so that while some brain cells increase their activity with VNS, others decrease in synaptic activity. The manufacturers of the only FDA-approved VNS treatment in the United States for epilepsy and depression have used the omnipresent effects of vagus nerve stimulation to bolster their claims as to its efficacy as a treatment for those two disorders.

VNS is the name for the procedure that implants an electrical stimulation device alongside the vagus nerve in the area of the carotid artery, located in the neck. The pulse generator device, which is about the size of a pocket watch, is surgically implanted on the left side of the body, just below the collarbone. Electrodes from the pulse generator are then implantedon the left side of the neck and wrapped around the left vagus nerve. The electrodes are connected to the pulse generator by a wire. The surgical procedure takes about an hour and is usually done as an outpatient procedure.

After implantation, the surgeon tests the device and closes the incisions. Further changes are made with the use of a special “wand” a software package, and a portable computer, so patients need not undergo any more invasive procedures related to adjusting the electrical “dose.” As an additional control, patients are provided with a strong, hand-held magnet that, when held over the skin that covers the pulse generator, prevents it from operating. If patients experience problems with the pulse, they can use the magnet until they get to the physician. The patented collection of pulse generator, leads, software, and programming devices are called the NeuroCybernetic Prosthesis System, or NCP, and are currently sold by only one company, Cyberonics.

The pulse generator, which contains a battery with a lifespan of six to eight years, sends out an electrical impulse whose strength, frequency, and duration are determined by the physician. The impulse travels through the wire to the electrodes, which transmit the pulse to the vagus nerve. VNS was originally used for patients with refractory episodic epilepsy who were deemed unsuitable for epilepsy surgery, but it has been increasingly prescribed for patients whose illness is less severe.

The first VNS implant for treatment-resistant depression was done in the United States in 1998. Physicians using VNS for patients with epilepsy had reported that patients seemed more alert, and combining anecdotal observations with the fact that some anticonvulsant drugs have also been used in depression treatment, the manufacturer of the VNS system decided to test its efficacy as a treatment for treatment-resistant depression.

The reported VNS depression research to date has had low numbers of participants, and much research has been directly or indirectly funded by Cyberonics, leaving reported findings somewhat open to debate. In fact, in May of 2006, the Public Citizen’s Health Research Group sent a letter to the FDA requesting that the organization require Cyberonics to withdraw its advertisement from WebMd.com and issue a corrective statement. The Public Citizen’s Health Research Group said that the Cyberonics ad “greatly exaggerated” the findings from the clinical studies, and called the advertisement “false and misleading.” The nonprofit then pointed out 10 items in a two-paragraph advertisement, explaining why they were false, exaggerated, or both. In another case, one journal editor resigned over having failed to disclose that he and eight other researchers had been funded by Cyberonics in regards to a published study on VNS. Other researchers have included statements in their published papers on VNS acknowledging that they received funding from the company.

Precautions

The physician’s manual published by the VNS manufacturer contains in the introduction a document subtitled Indications, Contraindications, Warnings and Precautions. This 20-page document must be considered the primary resource for precautionary information, as there is not yet much research available beyond that which has been funded by the manufacturer, Cyberonics. Precautionary information for this section has been taken from this document, which can be found online at http://www.vnstherapy.com/depression/hcp/Manuals/default.aspx.

The difference between “contraindications, warnings, and precautions” as published by the manufacturer seem unclear, as they combine VNS requirements, pre-existing health conditions, procedures that cannot be performed on people using VNS, age limitations,

and therapeutic devices that cannot be used in conjunction with VNS. The VNS system is only to be used on the left vagus nerve, and is approved for children over the age of 12 in cases of epilepsy and patients over the age of 18 for depression.

Procedures and devices that can damage the implant, the patient’s tissue, or both and consequently that should not be used with VNS:

Diathermy, or cauterization. Diathermy causes a concentration of heat in the implant, which can damage the implant, destroy tissue, and even lead to death.
Radiation therapy.
External and internal defibrillation devices.
Electrosurgery.
Therapeutic ultrasound.
Full-body MRI.

Pre-existing conditions under which VNS should not be prescribed:

Having only one vagus nerve.
Having metal plates or other implants such as pacemakers.
Pregnancy.
Dysphagea (problems with swallowing).
Obstructive sleep apnea (OSA) (A condition that causes patients to stop breathing while asleep).
Previous heart attacks and other cardiac abnormalities.
Respiratory illness such as asthma or dyspnea.
Brain injury.
Injury to the central nervous system (CNS).
Dysautonomis (disease of the autonomic nervous system).
Vasovagal syncope (a condition in which the blood vessels dilate and the heart rate slows, causing fainting).
Ulcers.
Hoarseness.
Having other concurrent forms of brain stimulation treatments.
Suicidal thoughts or ideas.
Bipolar disorder.
Schizophrenia or schizoaffective disorders.
Delusional disorders.

Preparation

Patients have to be informed of risks, and those with contraindicated health conditions must be ruled out before surgery. Patients who elect to have VNS

KEY TERMS

Central nervous system —The brain and spinal cord.

Diathermy —The use of heat to destroy abnormal cells; cauterization.

should have the procedure and equipment thoroughly explained, and will be taught the use of the handheld magnet in case it is needed.

Aftercare

The surgical procedure takes about an hour, but there are two incisions and, as with any implant, risk of infection. Wound care must be addressed, and patients require follow-up appointments with their physicians to monitor the effects of the treatment and adjust the electrical “dose.” Changes in patients’ health also need to be monitored, as so many conditions are contraindicated in the use of VNS. For example, in the case of treatment-resistant depression, if a depressed patient becomes suicidal or experiences a manic episode, use of VNS is contraindicated.

Risks

Because the device is surgically implanted, along with the risk of infection there is the potential for breakage, migration, or corrosion. Other issues may have to do with irritation to the vagus nerve, which can result in hoarseness or in permanent nerve damage. It is imperative that the surgeon receives specialized training for implanting the VNS.

People who have cardiac arrhythmia are at risk, and occurrences of bradycardia (slowed heartbeat) or asystole (heart stoppage) during or after implantation have been reported. The manufacturer states that safety has not been established for patients who suffer bradycardia or asystole during implantation. Although there is implant information for cardiac patients, it is listed under the heading of contraindications.

Patients should be warned to avoid anything that may generate a strong electrical or magnetic field, as the field could affect the functioning of the VNS system. This includes strong magnets, hair clippers, and anti-shoplifting tag deactivators. The magnet used with the VNS can affect televisions, credit card strips, and computer disks. The pulse generator in the VNS is said to affect pocket transistor radios and hearing aids.

Resources

PERIODICALS

Chae, Jeong-Ho, et al. “A Review of the New Minimally Invasive Brain Stimulation Techniques in Psychiatry.” Review of Brazilian Psychiatry 23.2 (2001): 100–109.

Cyberonics, Inc. “Introduction to the VNS Therapy System: Indications, Contraindications, Warnings, and Precautions.” Physician’s Manual for the VNS Therapy System 26-0006 (July 2006): 1–20.

George, Mark S., et al. “Vagus Nerve Stimulation: A New Tool for Brain Research and Therapy.” Society of Biological Psychiatry 47.1 (2000): 287–95.

Husain, Mustafa M., and others. “Pregnancy and Delivery While Receiving Vagus Nerve Stimulation for the Treatment of Major Depression: A Case Report” Annals of General Psychiatry 4.16 (2005): http://www.annals-general-psychiatry.com/content/4/1/16

Lurie, Peter, MD. “Letter to FDA Requesting the Immediate Halt of Cyberonics Ads for Vagus Nerve Stimulation Devices.” HRG Publication #1770. May 2006: http://www.citizen.org/publications/release.cfm?ID=7434&catID=126&secID=1163.

Nemeroff, Charles B., and others. “Corrigendum VNS Therapy in Treatment-Resistant Depression: Clinical Evidence and Putative Neurobiological Mechanisms.” Neuropsychopharmacology 31.2329 (2006): 1345–55.