Introduction to Vagus Nerve Stimulation
Seizures are caused by electrical events in the brain that occur when there is a brief disturbance in the way the brain's electrical system works. Vagal nerve stimulation (VNS) is a surgical treatment that reduces the frequency and duration of seizures in certain patients diagnosed with epilepsy. VNS was first introduced experimentally in 1988. By the mid 1990's, the safety and efficacy of VNS was firmly established through numerous clinical trials across North America and Europe. In March of 1997, the use of VNS, specifically for patients over the age of twelve with partial onset seizures that are refractory to anti-epileptic medications, was officially sanctioned by The Canadian Health Protection Branch.
VNS uses regular pulses of electrical energy to prevent or interrupt the electrical disturbances in the brain, thus decreasing the frequency and duration of seizures. The vagus nerve originates in the brainstem (where the brain becomes the spinal cord) and travels through the neck into the chest and abdomen. It is one of the longest nerves in the human body, and it affects a large number of bodily functions including speech, swallowing, heart rate, and digestion. Every person has two vagal nerves, one for each side of the body. VNS therapy involves the left vagus nerve, and the stimulation is applied to the nerve as it passes through the middle of the neck or "mid-cervical" region.
The electrical signals to the vagus nerve come from a thin, round pulse generator — a battery — about the size of a pocket watch. The device is usually implanted under the skin on the upper left side of the chest. A flexible, insulated plastic tube, containing electrodes runs under the skin from the little generator and connects to the left vagus nerve on the left side of the neck.
VNS has been found effective in controlling some epilepsies when anti-epileptic drugs have been inadequate, their side effects intolerable, or neurosurgery has not been an option. In some cases, VNS has also been effective in stopping seizures.
VNS is approved for use in Canada as an adjunctive therapy for some people with epilepsy. VNS is currently approved in more than twenty countries.
How Does Vagal Nerve Stimulation Control Seizures?
The exact mechanism by which VNS prevents or inhibits seizure formation is currently unknown. However, what is known is that VNS works by interfering with the electrical activity of the brain. Epileptic seizures are associated with highly synchronized, characteristic patterns of brain wave activity. The vagus nerve disrupts these synchronized brain wave patterns by providing a sudden stimulation to the vagal nerve, which carries the impulse from the neck back up to the brain. Therefore, with every stimulation from the pulse generator, epileptic electrical activity may be interrupted, thus preventing a seizure before it occurs. This would explain why manually activating the pulse generator (with a hand-held magnet) at the onset of an aura is often effective at preventing progression to a seizure.
VNS Surgery
Implanting the VNS battery in a patient and connecting it to the vagus nerve takes approximately an hour. The procedure is usually done under general anesthesia, and can be done on an in-patient or out-patient basis. Two incisions are required, one in the neck to gain access to the vagal nerve, and one below the collarbone in the chest wall or armpit. A 5-6 cm incision is made below the collarbone where the pulse generator is inserted into a pocket of fat between the surface of the skin and the ribs of the chest wall. After the pulse generator is in place, the surgeon threads a plastic tube containing the electrodes from the neck to the generator in the chest. Then, the surgeon gently wraps the flexible ends of silicone-coated electrodes around the vagus nerve.
Programming the Device
The device is programmed to begin stimulation at one to two weeks after surgery. Programming is performed with the aid of a computer and a "programming wand." The wand is held above the chest directly over the pulse generator (the procedure is completely non-invasive). Doctors program the device to deliver pulses of electrical stimulation automatically, 24 hours a day. The device can be re-programmed as many times as necessary. It is important to note that the system is not designed to provide constant stimulation, but rather to generate a series of short, repeated electrical impulses. The device usually gives the patient a stimulation for about thirty seconds on and five minutes off, but settings may vary. This occurs automatically throughout the day during both wake and sleep. The device continues the cycle until the neurologist re-programs it or until the battery runs out, usually in about six years. In addition, the patient can manually trigger a stimulus at any time, or turn the device off altogether, by holding a hand-held magnet over the pulse generator. When the battery runs out, another surgical procedure is required, which involves the chest only.
Monitoring Treatment
After the surgery, the doctor schedules a series of follow-up visits. At first, a person with a new VNS implant may see the doctor every two weeks. Later, if everything is going well, the doctor may schedule the visits every two to six months, or as needed.
The manufacturer of the device recommends that people being treated with VNS visit their doctors at least every six months throughout the life of the device.
Also, people who have the VNS implant should let their doctor know if at any time the device becomes uncomfortable, if the stimulation seems to be coming on too often, if it seems to have stopped altogether, or if they have any concerns about its operation or effects.
Some people worry that their body may reject the VNS device; however, rejection is not a problem because the device is made of titanium. Titanium is a material that is widely used for pacemakers and does not trigger an immune response. If the device has to be removed, it is usually because it is not effective or, in about one percent of cases, it is due to malfunction or infection.
How Well Does VNS Work?
The efficacy of VNS varies widely from patient to patient. It is hard to know in advance how someone with epilepsy will respond to the VNS therapy. In some people with epilepsy, their seizures are eliminated completely, but in others the device may have no effect.
Studies have shown that one-third of VNS patients will experience a major improvement in seizure control (i.e. greater than fifty percent reduction in seizure frequency), one-third will experience a moderate improvement in seizure control, and one-third will continue to have seizures as before the device was implanted.
Please remember that improvement may not happen over night, it usually takes time. Several months may go by before there is any change, followed by a slow but steady improvement.
Safety and Side Effects
The VNS implant has not yet been officially approved for use in children less than twelve years old, pregnant women, or the elderly (more than sixty years of age).
The most common side effects associated with the VNS implant are hoarseness, breathlessness, voice change, coughing, and sore throat. These side effects only occur when the stimulator is "on." Most of the side effects usually become less noticeable with time. In addition, smoking has been shown to worsen the hoarseness, sore throat and inflammation. As well, patients with chronic obstructive pulmonary disease may have an increased risk of shortness of breath.
Other less common side effects reported in clinical trials include: incoordination of voluntary muscles, difficulty swallowing, aspiration (inhaling fluid into the lungs), insomnia, indigestion, infection, inflammation of the throat, twitching, nausea, vomiting, pain, and prickling or decreased skin sensation.
There are also side effects associated with the surgery itself. These are rare, and include: blood clots, damage to nerves or blood vessels in the neck, facial paralysis, foreign body reaction to the implant, scarring or infection at the incision site, fever, muscle pain, and ringing in the ears.
Furthermore, after the device is implanted, any trauma to the chest or neck may result in damage to the pulse generator or disconnection of the leads. This can damage the vagus nerve, and/or inactivate the device, resulting in increased seizure frequency.
The mode of action of VNS is still unknown. It is, therefore, difficult to determine which medications (if any) might cause adverse reactions for VNS patients.
Summary Chart of The Major Advantages and Disadvantages of VNS
The following chart is a brief summary of the major benefits and concerns associated with vagal nerve stimulation. Please note that important issues of safety and risk associated with the surgery itself are not included in the table, and should be discussed with your physician. No two patients are the same, and actual benefits and side effects experienced will vary greatly from patient to patient.
| ADVANTAGES | DISADVANTAGES |
| A potentially effective therapy for the treatment of partial seizures (with or without generalization) or generalized seizures. | Surgical procedure required (involves a general anesthesia and overnight stay at the hospital) |
| Non-pharmacological option for patients with intractable or inoperable seizures. | Contraindicated in patients after a bilateral or left cervical vagotomy, or in patients with cardiac conduction defects. |
| May generally reduce frequency or duration of seizures, and shorten the length of the post-ictal period. | Two thirds of patients will experience light or no reduction in frequency or duration of seizures. |
| May eliminate the need for anti-epileptic medications (AEDs), and/or reduce the required dose. | Most patients still require AEDs for optimal control of seizures (all AEDs continue for at least three months following implantation). |
| Improvement is both short-term (months) and long-term (years). | Long term commitment may be required to see improvement. |
| The device maintains its constant stimulation cycle without any effort or assistance from the patient. | Stimulation pulses are often noticeable, and may lead to hoarseness of voice, breathlessness or swallowing difficulties. |
| For patients who experience auras, seizures may be averted at onset by use of the hand-held magnet. | The magnet may have no effect. |
| The magnet may be used to stop stimulation momentarily (i.e. to prevent hoarseness while singing) or to inactivate the device continuously (i.e. if patient experiences stimulation induced pain or discomfort). | Continuous or frequent magnet use will use up the battery and could potentially cause damage to the left vagus nerve. |
| The pulse generator is not affected by microwave ovens, power lines, metal detectors or cellular phones. | The pulse generator is adversely affected by MRI, therapeutic radiation, external defibrillation, strong magnets, and hair clippers. The unit may interfere with transistor radios, hearing aids, cardiac pacemakers and defibrillators. |
| A special "magnet guard" will be provided for the hand-held horseshoe magnet. |
The magnet may damage televisions, computer disks and credit cards, and should be kept away from these items at all times. |
| An irregular stimulation will alert the patient that the battery is approaching exhaustion. | The pulse generator will require surgical replacement when the battery runs out, at significant cost to the patient. |
| The intensity of the stimulation can be individualized to the needs and tolerance of each patient. | Programming of the device will require several follow-up appointments, and should only be performed by a qualified, experienced physician. |
The above summary chart of the major advantages and disadvantages of VNS was compiled by Epilepsy Kingston, Ontario, Canada. Reproduced with permission.
Technical Questions
What will the VNS Implant Cost?
The implant device alone costs $14,000 dollars (Canadian), and it is not covered by OHIP. It is important to note that the implant has to be replaced when the batteries run out, and the replacement is as expensive as the original implant. The full implant including the entire surgical procedure and hospital stay costs approximately $29,000 (Canadian). [Information provided by Irene Elliot at the Hospital for Sick Children in Toronto, Ontario, Canada].
Using the Magnet
The magnet involved in the VNS treatment allows the patient some control over the device and how it works. The special, thin blocked magnet is attached to a strap. It can be worn on the wrist like a watch, or clipped to a belt like a pager. Although the VNS system delivers stimulation automatically in regular pulses all the time, the magnet can be used to deliver extra electronic stimulation in between cycles. The patient does this by passing the magnet over the area of the chest where the VNS device is implanted.
Tips on Handling the Magnet
- Don't place or store the magnet near credit cards, televisions, computers, computer disks, microwave ovens or other magnets. Keep it at least 10 inches away from these items.
- Do not drop the magnet. It can break if it falls on a hard surface.
- Carry the magnet with you. If your seizures stop or are shorter when the extra stimulation is turned on, show family members or caregivers how to use the magnet when you have a seizure.
- Ask your doctor about how much and for how long you can safely use the magnet to activate the device.
Who is Using VNS?
The VNS system was approved for people with partial onset seizures - seizures that begin in one part of the brain. VNS is intended for people whose seizures do not respond to medications and who are either not good candidates for brain surgery or don't want to have brain surgery. People who are considering VNS must not have any other medical conditions that might be affected by the device. For example, VNS should not be used in people who have had certain throat operations or disorders affecting the throat.
Currently, about 10,000 people have received the VNS system, including about 33 percent under the age of eighteen. A registry system that tracks about 5,000 people living with VNS includes about 60 percent with partial seizures;15 percent with Lennox Gastaut Syndrome (mixed seizures); and 25 percent with generalized seizures.
Where Can I learn More about the VNS implant and hear about other people who have had the procedure?
There are a variety of resources that share patient experiences, provide technical information, or allow people to ask questions in an electronic bulletin board format. Some of the more useful sources of information about the Vagal Nerve Stimulator are:
Epilepsy Ontario
1 Promenade Circle, Suite 308
Thornhill, Ontario L4J 4P8
800-463-1119
<http://www.epilepsyontario.org>
e-mail: <info@epilepsyontario.org>
Epilepsy Canada National Office,
1470 Peel St. Suite 745,
Montreal Quebec H3A 1T1
800-860-5499
<http://www.epilepsy.ca>
e-mail: <epilepsy@epilepsy.ca>
Both of the above organizations offer objective information and their web sites contain valuable lists of frequently asked questions, newsletters and links to other resources.
Cyberonics, Inc. (The manufacturer of the VNS unit)
The Cyberonics Building, 16511 Space Center Blvd.
Houston, Texas USA 77058
888-VNS-STIM (867-7846)
<http://www.cyberonics.com>
E-mail: various departments accessed through their website
Contact the Canadian distributor of the device by visiting their web site:
<http://www.xycorpmed.com>
Cyberonics is not an impartial resource because they are selling the VNS unit, but their Web site does have a large number of very useful information sources. The VNS bulletin board is a great place to browse through postings of other people's experiences, problems and success stories about the implant. Cyberonics will also provide you with a "patient information bag" at your request. They have many links to independent organizations and personal Websites of varying quality.
This handbook is designed to provide the reader with a patient-oriented introduction to vagal nerve stimulation, or "VNS". The handbook is written exclusively for the education of patients with intractable epilepsy. Accordingly, the information herein pertains only to the use of VNS as a therapy for reducing or eliminating the occurrence of epileptic seizures. The information presented in this pamphlet was up-to-date at the time of writing. However, keep in mind that VNS is a relatively new technique being studied; thus, information regarding the use, outcomes, safety and side effects of VNS may change as new research becomes available. Before deciding that VNS is suitable for you, please contact your physician to discuss the treatment as it pertains to you.
This handbook was created in August of 2002
The support of Epilepsy Canada and Epilepsy Kingston for the use of their information on VNS is acknowledged. HRDC (Human Resource Development Canada) Summer Career Placement Program is also acknowledged. Thanks to Theresa Sargeson for her work in researching and creating this project.
