Better Treatment? – Evaluating Vagus Nerve Stimulation (VNS) Therapy
Jennifer Lee
For over a hundred years, medical professionals have been seeking a new way to prevent uncontrolled seizures in individuals with epilepsy. Following the extensive research on brain wave patterns when vagus nerve is stimulated, Dr. Jacob Zabara performed studies on seizure control by using this technique. In 1988, VNS was first performed on real patients with medically intractable epilepsy by Dr. Kiffin Penry; and since then, many clinical studies have taken place. The Food and Drug Administration (FDA) approved the use of the Vagus Nerve Stimulator (VNS) for the treatment of refractory epilepsy in 1997.
VNS Therapy was developed mainly to improve seizure control in patients with refractory epilepsy. Usually, a patient with epileptic seizures could be treated with anti-epileptic drugs (AEDs). However, 20-40% of epileptic patients continue to experience seizures: these patients are said to have refractory or intractable epilepsy. In addition, about 40% of patients with refractory epilepsy are also not suitable for surgery, either because seizure control could not be achieved or that it is attainable only at the expense of severe adverse effect. Fortunately, new options for treatment of refractory epilepsy have been developed including new AEDs and vagus nerve stimulation (VNS) therapy.
The secret of VNS therapy lies, as the name suggests, in the left vagus nerve. It was considered the best candidate because 1) it is a primary communication line between major organs in the body and the brain; and 2) it has very few pain fibers. Its ideal nature means no brain surgery and very little discomfort. At the beginning of the treatment, a pulse generator is implanted in the upper left chest and connected to a bipolar lead attached to the left vagus nerve through a wire to the lower neck, where a generator (sometimes called an "epilepsy pacemaker") delivers intermittent electrical stimulation to the vagus nerve. The surgical procedure usually takes about 45 minutes to 2 hours, under anesthesia. After the system is fully implanted, all of the stimulation parameters (i.e. current intensity, pulse width and frequency, on/off cycles) can be adjusted externally by the physician. Although the foundation of VNS was established about 60 years ago, a significant amount of additional research is necessary in order to fully understand its exact mechanism.
Over many years of practice, VNS has proven to be a safe and effective add-on treatment to many refractory epileptic patients in terms of reduction in frequency of partial-onset seizures. It also appears that the benefits from VNS treatment do not fade out over the long run.
Right now in Canada, eleven of the twelve Ministries of Health cover the VNS procedure and device through their medical insurance programs and medical budgets. Seven of them provide the operation within their provinces, while three provinces and one territory provide coverage for patients to carry out the procedure elsewhere in Canada.
VNS Update: On June 24, 2002, U.S. Food and Drug Administration approved a new vagus nerve stimulator model called the Cyberonics Pulse Generator Model 102 System. This model is significantly smaller in size, lighter-weight, less visible and more comfortable than previous models used in VNS therapies.!
References:
(1) Corabian, Paula and Leggett, Patricia; Vagus Nerve Stimulation for Refractory Epilepsy; Alberta Heritage Foundation for Medical Research, Edmonton, 2001; P.ii, 3-7
(2) "Epilepsy Foundation Says New VNS Therapy More Patient-Friendly" Epilepsy Foundation, 2002; https://www.efa.org/epusa/media/n062402.html
(3) J. Engel, Jr. and T.A. Pedley; Epilepsy: A Comprehensive Textbook; Lippincott-Raven Publishers, Philadelphia, 1997; P.1353, 1358
(4) "Vagus Nerve Stimulation, Biomedical Engineering Seminar I" University of Rhode Island, 2001; http://www.ele.uri.edu/Courses/ele282/S01/Morgann_2_Vagus.pdf
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