Vagal Nerve Stimulation for Drug Refractory Epilepsy
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.302458
Source of Support: None, Conflict of Interest: None
Keywords: Drop attacks, drug refractory epilepsy, Lennox Gastaut syndrome, neuromodulation, non focal epilepsy https://www.youtube.com/watch?v=h4_oZLEai8A
The primary goal of epilepsy surgery is attainment of seizure freedom followed by reduction in the antiepileptic drug requirement and overall improvement in the quality of life. Epilepsy surgery, whenever possible should be directed towards definitive resection of the epileptogenic zone localized through comprehensive preoperative epilepsy workup. However, such localization may not be possible in all cases of drug-refractory epilepsy (DRE), even after exhausting preoperative investigations and hence are candidates for either disconnection or neuromodulation procedures.
Vagal nerve stimulation (VNS) is among one of the widely used procedure in the management of patients with generalized epilepsy or focal seizures with no localization. It is often compared with corpus callosotomy (CC) in terms of indications and seizure outcomes, however preferred to CC owing to its less invasive and complication profile in the developed nations. Children with “drop attacks” especially benefit from these procedures. It is crucial to adequately prime these patients regarding the expected benefits in terms of seizure freedom, as to approximately 50% of reduction in seizures in about 50% of cases. The other important benefit being in terms of mood elevation and improved quality of life with time.
We present a step by step technique of implantation of a left-sided vagal nerve stimulator for DRE in a patient with bilateral seizure onset on preoperative workup [Video 1].
The procedure is carried out under general anesthesia to offset the risk of patient developing intraoperative seizures. The stimulator is implanted on the left side, as the right vagus nerve supplies the sinoatrial node, which might lead to bradycardia on stimulation. The patient's head is turned to the right by thirty degrees, with shoulder roll placed to extend the neck. A horizontal skin crease incision is given along the anterior border of the sternocleidomastoid at a point midway between the line joining the mastoid process and the medial end of the clavicle. Doing so avoids the cardiac branches of the vagus nerve and the risk of resultant bradycardia/asystole.
A subcutaneous pocket is made about two to three finger breadths inferior to the left clavicle is created. The pulse generator/battery should fit snugly into the pocket. It should neither be loose so as to allow unnecessary movement, nor be so tight as to cause postoperative tissue necrosis.
A subcutaneous tunnel is made connecting the neck and the chest incisions. Leads are passed through the tunneler and connected to the battery.
The electrodes comprise of three helices with the inferior most helix called the anchor tether to hold the electrode in place. The middle helix is the positive electrode and the superior most is the negative electrode. The electrodes are gently wrapped around the exposed nerve, taking care to maintain the orientation. Inadvertent placement of the negative electrode inferiorly leads to failure of delivery of stimulation to the brain and may cause cardiac complications. The connecting wire is then tethered to the surrounding soft tissue after making a strain-free loop to allow for neck movement postoperatively. After connecting the lead with the battery, the integrity of the connection is confirmed using a programming device placed over the chest pocket with the stimulator in situ. The incisions are then closed after thorough antibiotic (vancomycin) saline irrigation.
Programming of the stimulation parameters is usually done two weeks after implantation. The final current strength is decided after assessing the patient for side effects.
Video link: https://youtu.be/h4_oZLEai8A
Video timeline with audio transcript:
00:00-00:08 – This video demonstrates the placement of vagal nerve stimulator in a pediatric case of DRE.
00:09-00:29 – A 16 years old boy presented with DRE beginning at the age of 4 years with multiple seizure semiology predominated by drop attacks, on multiple antiepileptic drugs.
00:30-00:43 – Video electroencephalography (VEEG) revealed bilateral onset of seizures recorded at the time of head drop.
00:44-00:56 – MRI axial FLAIR sequence revealed bilateral parietooccipital gliosis.
00:57-01:13 – Magnetoencephalography (MEG) and single-photon emission computerized tomography (SPECT) revealed bilateral onset of seizures concordant with the VEEG findings suggesting a diagnosis of Lennox Gastaut syndrome.
01:14-03:45 – Under general anesthesia, the patient is positioned supine, head turned slightly to the right and neck extended with the help of a roll placed underneath the shoulder blades. A skin crease neck incision midway between mastoid and sternal notch along the anterior border of sternocleidomastoid muscle on the left side and another incision below the left clavicle are marked.
01:46-03:39 – The skin incision in the neck is deepened, platysma is cut, the omohyoid is isolated and retracted medially and downwards. The carotid sheath is opened in the carotid triangle and the two roots of the Ansa cervicalis are identified along the anterior carotid sheath. The internal jugular vein (IJV) is seen on opening the carotid sheath, further deeper sharp dissection exposes the left vagus nerve beneath and between the IJV and the carotid. Approximately 3 cms of the vagus nerve is exposed by circumferential dissection ensuring minimal damage to the nerve by leaving a sliver of adventitial tissue around the nerve.
03:40-03:54 – Infraclavicular subcutaneous pocket is created, so as to snugly allow the pulse generator placement.
03:55-04:18 – Subcutaneous tunnel is created connecting the neck and the chest incisions followed by introduction of the lead accordingly.
04:19-05:10 – The VNS device has two components, the lead and the pulse generator. The lead consists of three helical coils with the distal coil representing the negative, middle positive terminal and the proximal being an anchor coil. The distal end of this lead is to be inserted into the slot in the pulse generator. There are multiple variants of pulse generators: the 102 basic variant, 103 well suited for pediatric/lean adult patients, the autostim is specially designed for aborting the seizure at the beginning by picking up the ictal tachycardia.
05:10-05:38- It is prudent to practice the lead placement on the dummies especially for the beginners so as to get acquainted with technique.
05:39-07:18 – The helical coils are wrapped around the vagus circumferentially. A strain free loop is created in the neck using adequate length of the lead and secured to the surrounding connective tissue with silk suture.
07:19-08:32 – The distal end of the lead inserted into the slot provided in the battery, ensuring the tip of the distal end to be clean and free from blood prior insertion. The device is then interrogated for proper functioning with the help of an external wand wrapped in a sterile cover. On confirmation, a test stimulation is done to check for appropriately functioning device. This is followed by placement of the battery into the infraclavicular subcutaneous pocket. The lead wire is coiled and placed underneath the battery. Repeat device interrogation system diagnostics are done to reconfirm the functionality of the VNS device after closure.
Outcome: The patient is relieved of drop attacks with a seizure frequency of 1-2 seizures per month from the preoperative frequency of 4-5 seizures per day.
VNS as a neuromodulation therapy was approved by the Food and Drug Administration of USA in 1997 after randomized controlled trials proved its efficacy and safety., Although initially approved for patients older than 12 years of age, it has been used successfully in younger children as well. The response rate to VNS has been seen to improve with time, from 36.8% after one year to 42.7% after three years., VNS has been shown to decrease the incidence of sudden unexpected death in epilepsy, owing to its cardioprotective role. Over the years, an improvement in mood has also been observed in patients with VNS and it has recently been FDA approved for the treatment of major depression. The most common side effects are related to stimulation and include cough, hoarseness of voice and neck pain seen initially in nearly half of the patients. But the severity and incidence has been seen to reduce with time.,
A comprehensive preoperative epilepsy workup, especially in a specialized epilepsy care center, involving a multidisciplinary team of experts is imperative. In carefully selected patients of DRE, VNS surgery is a simple, safe and effective procedure to alleviate disabling seizures, with excellent long-term seizure-free outcomes.
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Conflicts of interest
There are no conflicts of interest.