Vagus nerve stimulation (VNS) is an FDA-approved treatment for medically intractable, partial onset epilepsy in patients over 12 years of age.
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How safe and effective is vagus nerve stimulation?
Efficacy and safety issues have been addressed in several large clinical trials. The current device is manufactured by Cyberonics (Houston, TX) and includes a pair of helical electrodes (2mm or 3mm diameter), a battery-powered generator (models 101/102), a tunneling tool, software and programming tools, and supplies for the patient. The model 102 generator is smaller and incorporates a single pin electrode design to avoid incorrect lead connections.
What conditions does vagus nerve stimulation treat?
Indications for vagus nerve stimulation include patients with medically intractable, partial epilepsy without resective surgical options or those where surgery is contraindicated for medical reasons. Contraindications include patients with history of previous left neck surgery or prior cervical vagotomy.
Are there patients who should not receive vagus nerve stimulation treatment?
Relative contraindications may include: pregnancy, asthma, chronic pulmonary disease, active peptic ulcer disease, and insulin-dependent diabetes mellitus.
Are there side effects associated with vagus nerve stimulation treatment?
Common adverse effects include coughing, hoarseness, dyspnea, and headache. These effects are seen during vagus nerve stimulation and tend to habituate with time. Serious adverse effects have been reported and include vocal cord paralysis, infection, Horner's syndrome, lower facial muscle paresis, and cardiac arrest. Sudden unexplained death has also occurred, but not at a rate different than the epileptic population. Other mechanical complications can occur such as lead fracture or generator malfunction.
Who is a good candidate for vagus nerve stimulation?
Patients with epilepsy uncontrolled by anticonvulsant medications may be candidates for vagus nerve stimulation. The definition of an individual being considered as medically intractable generally includes a description of an adequate drug trial without unacceptable side effects. The exact definition of an adequate drug trial is not clear. At our institution, most candidates for vagus nerve stimulation have been on many medications without appreciable benefit. Because the efficacy of vagus nerve stimulation is not much higher than that of a new medication trial, it is the author's opinion that vagus nerve stimulation candidates should exhaust medication options prior to consideration for vagus nerve stimulation therapy.
Although not FDA approved for treatment in the pediatric population, there is growing evidence that vagus nerve stimulation is safe and similarly effective in this population.
What is the anatomy of the vagus nerve?
The vagus nerve is a mixed cranial nerve containing approximately 80% sensory fibers. Efferent fibers innervate the larynx and provide parasympathetic control to the heart, lungs, and abdominal viscera. The right vagus nerve innervates the sinoatrial node of the heart while the left innervates the atrioventricular node. In the dog model, vagus nerve stimulation of the right vagus nerve caused more cardiac slowing then the left. For this reason, the left human vagus nerve is implanted. Adverse cardiac complications have not been seen, perhaps because vagus nerve stimulation of the nerve can be done on a segment away from the origin of the cardiac branches.
What happens during vagus nerve stimulation treatment?
On the day of surgery, after the patient receives preoperative antibiotics and a general anesthetic, the patient's neck and chest are prepped with betadine scrub and paint solutions. The electrodes for the vagus nerve stimulation are implanted in the patient's neck.
Surgeons expose the vagus nerve, then make an incision in the chest to accommodate the generator for vagus nerve stimulation. Electrodes are implanted on the vagus nerve by gently winding the electrode spirals around the nerve.
Once the electrodes are implanted and the system tested, some doctors turn on the system at the lowest setting, while most prefer to wait one or two weeks before initiating stimulation therapy.
Once the system is tested, the generator is sewn to the pectoralis fascia with a permanent suture.
What happens after vagus nerve stimulation surgery?
Patients should be counseled to observe the wound for signs of infection following the vagus nerve stimulation procedure. The sutures are self-absorbing and need not be removed. Return to normal preoperative activities is allowed after 48 hours. Patients should be warned that this therapy will not result in cessation of seizures and they should continue to practice seizure precautions. A return to care in two weeks with the treating neurologist is indicated to begin or increase vagus nerve stimulation.
