How does the brain control heart rate, digestion, sweating, speech, chewing and the gag reflex? Though these functions seem unrelated, they’re all controlled by the vagus nerve – a long fiber that connects the brain to the throat, heart and digestive system.
How does vagus nerve stimulation suppress seizures?
Stimulating this nerve — using an implanted device that controls the vagus nerve much like an artificial pacemaker controls the heart — can suppress seizures after they start and can reduce seizure frequency by 45 to 80 percent. VNS devices stimulate this nerve by sending mild electrical impulses to it, which are then are carried up to the brain to the areas where seizures begin.This technique, known as vagal nerve stimulation (VNS), is most effective in people with atonic and focal seizures. The device tends to be least effective in individuals who experience generalized tonic-clonic and complex partial seizures.
Surgery to implant a VNS device takes one to two hours under general anesthesia and can be performed on an inpatient or outpatient basis. The VNS unit is typically placed on the left side of the body so that it can control the heart rate before or during a seizure, but in some cases it may be repositioned to the right side. The amount of stimulation and frequency can be adjusted by the doctor using a wireless wand, but the device is not activated until 2 weeks after surgery to avoid affecting the heart. The patient receives a magnet that can be used to activate the VNS to help control oncoming seizures. The device’s battery lasts about 6 years.
What are the seizure control rates of VNS devices?
It is important to remember here that VNS is a palliative procedure – this means that it is not intended to stop the seizures, although a very small percentage of children do have seizure freedom after VNS device implantation.
Generally, the greatest benefits are seen in children older than 12 years, when VNS is applied at high frequencies and for extended periods of time. One study reported that 1 to 2 percent of these children became seizure free 2 years after implantation, while 25 to 40 percent of the children reduced seizure frequency by half. Children younger than 12 years also benefit from VNS, but the safety and effectiveness of VNS is unclear because VNS is not FDA-approved for this age group.
In adult studies, 49% of patients responded to VNS therapy 0 to 4 months after implantation with a greater than 50% reduction seizure frequency). 5.1% – 8% of patients were seizure-free and 63% of patients were responders at 24 to 48 months, with 8.2% achieving seizure freedom. In these adult studies, positive factors for seizure freedom were age of epilepsy onset >12 years with predominantly generalized seizure type and nonlesional epilepsy.
How soon before we see results?
A child’s response to VNS is not immediate – rather, seizures typically improve over a period of 12-18 months after the device is implanted. Though the device does not typically eliminate seizures, it can boost the effectiveness of other treatments and may be a good alternative to surgical procedures such as corpus callosotomy. VNS may also help improve the quality of life in children with other neurological challenges and developmental delays, and can help improve alertness, mood, academic success and memory.
What are the side effects of VNS device implantation?
Children with cognitive impairments often pick at or place fingers on wounds, increasing the chance of infection. About 10 percent of patients needed the external hardware removed and reinserted because of this. To help these children, doctors have implanted the device in alternate locations, including under the pectoral muscles.
One of the most common side effects is voice hoarseness, which can affect 40 percent of children with VNS devices. These effects typically disappear within 5 years of implantation. Changing the location of the implant using a lower neck incision may reduce the risk of this side effect. Children who have difficulty swallowing and are less alert before surgery are more likely than others to aspirate food and may need close supervision after VNS implantation. Other side effects include sleep apnea, torticollis, inappropriate laughter, involuntary movement, urinary retention and lower facial paresis.
Vagus Nerve Stimulation, Deep Brain Stimulation, and Responsive Neurostimulation (Neuropace)
Dr. Taylor Abel, MD, FAANS, is the Director of the Pediatric Epilepsy Surgery Program at UPMC Children’s Hospital of Pittsburgh and Dr. George M Ibrahim, MD, PhD, FRCSC, FAANS, is a pediatric neurosurgeon at The Hospital for Sick Children in Toronto, Canada, Assistant Professor at the Institute of Biomaterials and Biomedical Engineering, and Institute of Medical Science, Department of Surgery at the University of Toronto, and Associate Scientist Program in Neuroscience and Mental Health at SickKids Research Institute. Here, Drs. Abel and Ibrahim discuss vagus nerve stimulation, deep brain stimulation, and responsive neurostimulation (NeuroPace).