EPILEPSY AND VAGAL NERVE STIMULATORS 

INTRODUCTION: 

An estimated 0.5 to 1% of the overall population has seizures. As many as 50% of patients with epilepsy lack adequate control of their seizures or experience unacceptable side effects from medications. The Neurocybernetic Prosthesis (NCR), a vagal nerve stimulator, was developed by Cyberonics for the treatment of human epilepsy. Over 2,000 patients worldwide have had implantation. This advance in management of epilepsy is an additional form of therapy that helps the patient with seizures that are difficult to control or require so much medication to control them that the side effects interfere with normal life. The significant advantage of the vagal nerve stimulator is that it avoids intracranial surgery, which most parents appreciate. 

COST-BENEFIT OF VAGUS NERVE STIMULATION: 

Boon and co-workers have demonstrated the cost effectiveness of this instrumentation in the treatment of patients with refractory epilepsy, This is demonstrated by a 50% reduction in the yearly cost of epilepsy medication and a four fold reduction of hospital admission days. Therefore, though the up front cost is present, the long-term cost benefit ratio far outweighs the initial up front cost. As a consequence, though initial approval may be difficult for some insurance carriers and/or Medicaid, approval can be obtained when clinically justified.

VAGUS NERVE STIMULATION IN CHILDREN: 

There are well documented studies on the effectiveness of the vagus nerve stimulation and limited side effects of the same in children as demonstrated by Murphy and the Pediatric VNS Study Group. In that reported series, the vagal nerve stimulator was placed in patients with  refractory epilepsy (age range 3.5 to 18 years). At 18 months, a significant seizure control with reduction of medication was obtained in a large number of patients. More importantly, the control was enhanced over a progressively increasing period of time. Therefore, the longer the patient was treated with a vagal nerve stimulator, the further progression of the control of seizures was noted. In addition to seizure control, some patients report improvement in alertness, mood, verbal skills, and sense of control.

BRIEF DEVICE DESCRIPTION: 

The NCP system consists of an implantable pulse generator and bipolar lead and an external programming system used to change stimulation settings. The pulse generator is a multiprogrammable bipolar pulse generator that delivers electrical signals to the vagus nerve. It is hermetically sealed in a titanium case and is powered by a single battery. The new 101 systems have a battery life of approximately six to eight years. The bipolar lead and the pulse generator make up the implantable portion of the system. The external programmable system includes a programming Wand, programming software, and an IBM compatible personal computer for programming. The software allows physicians to place the programming Wand over the pulse generator to read and change device settings. In addition, external magnets are provided to the patient that can give brief stimulation as they are passed over the generator located on the chest. This provides an on demand stimulation as an attempt to abort or de‑intensify an oncoming seizure or to temporarily inhibit stimulation, or to reset the pulse generator in combination with the programming Wand. Finally, it allows for tests of daily function of the pulse generator.

BRIEF DESCRIPTION OF THE SURGICAL IMPLANT: 

There are two incisions made on the patient, one at the level of the left neck in its mid portion and another one in the left upper chest just in front of the pectoralis muscle. The generator is housed in the chest incision and hidden in the chest wall. A small mass is noted, when the generator is in place, according to the body habitus and size of the patient. In females, it can be hidden significantly by the proximity of the superior aspect of the breast and therefore can be incorporated in the bra. The neck incision is where the placement of the electrodes is done on the vagus nerve itself. The operative procedure takes between one and one and a half hours and is performed under general anesthesia.

CONTRAINDICATIONS OF VAGAL NERVE STIMULATORS: 

Vagal nerve stimulators cannot be used in patients after bilateral or left cervical vagotomy. That is the only absolute contraindication.
 

POTENTIAL SIDE EFFECTS: 

Larynx irritation may occur with some coughing and hoarseness upon stimulation of the device. Difficulty breathing is very rarely noted but has also been documented. Patients with pulmonary disease may have an increased risk of breathing problems. Infection may occur in the placement site which will require removal and appropriate antibiotic treatment in most circumstances.

MAGNETIC RESONANCE IMAGING SAFETY: 

The MRI can be performed but it is recommended that the unit be turned off for the procedure and/or rechecked immediately following the MRI. An MRI can be done of the head but not of the body because heat induction may occur on the electrodes and that could lead to damage of the tissues.

COMPUTED TOMOGRAPHY AND VAGAL NERVE STIMULATORS: 

There are no contraindications for CT scanning with vagal nerve stimulators in place. However, the metal in the system will create significant computer overload and scatter and, as a consequence, the images may not be clear.

ELECTROMAGNETIC SAFETY: 

Although the antenna inside the generator is controlled by radio-frequency signals, neither the generator nor the electrode leads are affected by microwave transmission, cellular telephone, or airport security systems. On the other hand, the patient should not be close to powerful magnets or powerful transmitting antennas. Hair clippers, vibrators, and loudspeaker magnets with strong static or pulsing magnetic fields can cause accidental magnet activation. These devices should be kept away from the pulse generator by at least 15 cm.

MANAGEMENT OF THE PROGRAM AND FOLLOW-UP: 

The trained pediatric neurosurgeon will install the equipment and confirm its function at the operative intervention. The follow-up will be done by the trained pediatric neurologist, who will then adjust as needed and change the programming externally in follow‑up visits in the office.