Vagus nerve stimulation for complex partial seizures: surgical technique, safety, and efficacy

Abstract

Electrical stimulation of the vagus nerve has shown efficacy in controlling seizures in experimental models, and early clinical trials have suggested possible benefit in humans. Eleven patients with complex partial seizures were subjected to implantation of vagus nerve stimulators. Electrode contacts embedded in silicone rubber spirals were placed on the left vagus nerve in the low cervical area. A transcutaneously programmable stimulator module was placed in an infraclavicular subcutaneous pocket and connected to the electrode. One patient required replacement of the system due to electrode fracture. Another patient developed delayed ipsilateral vocal-cord paralysis; the technique was then modified to allow more tolerance for postoperative nerve edema. A third patient showed asymptomatic vocal-cord paresis on immediate postoperative laryngoscopy. Vagus nerve stimulation produces transient vocal-cord dysfunction while the current is on. Nine patients were randomly assigned to receive either high- or low-current stimulation, and seizure frequency was recorded. The high-current stimulation group showed a median reduction in seizure frequency of 27.7% compared to the preimplantation baseline, while the low-current stimulation group showed a median increase of 6.3%. This difference approached statistical significance. The entire population then received maximally tolerable stimulation. The high-current stimulation group showed a further 14.3% reduction, while the low-current stimulation group showed a 25.4% reduction compared to the blinded period. The efficacy of vagus nerve stimulation seemed to depend on stimulus parameters, and a cumulative effect was evident. These results are encouraging, and further study of this modality as an adjunct treatment for epilepsy is warranted.

Vagus Nerve Stimulation in the Treatment of Refractory Epilepsy

“…In fact, one trial noted a 6% median increase in seizure frequency with low VNS. 8 There were also significant differences in the percentage of patients considered responders (Ն50% reduction in seizure frequency), consisting of 22 to 39% of patients in the high VNS group versus only 13 to 19% of those in the low VNS group. The use of the hand-held magnet by patients and caregivers to activate the NCP generator directly in response to auras or simple-partial seizures has also reduced the severity of evolving seizures.…”

“…8,21,50,51 These trials demonstrated a mean or median seizure frequency reduction of 24 to 31% over 3 months of follow-up in patients receiving the high VNS treatment paradigm (i.e., VNS at therapeutic stimulatory parameters, such as 30 Hz, 30 s on, 5 min off, and 500-ks pulse width). This improvement was significantly greater than that found in patients in the low or subtherapeutic VNS group (e.g., 1 Hz, 30 s on, 90 -180 min off, 1.30-ks pulse width); these patients experienced a mean or median seizure frequency reduction of only 6 to 15%.…”

“…[3][4][5][6][7][8][9][10] Additional details regarding the surgical procedure have been published previously. 11 Due to potentially higher risks of bradycardia and arrhythmias with right VNS, the left vagus nerve has been targeted in the majority of cases.…”

“…The incidence of electrode fracture is low, and device failure was uncommon in recent trials. 8 Electrode removal is not required for generator or battery replacement, and the electrode is typically left in place in the event of device, removal except in the setting of infection. If required, electrode removal can be accomplished with minimal risk of nerve injury, even several years after implantation and despite the presence of fibrosis.…”

Estimulación eléctrica vagal en el tratamiento de la epilepsia rebelde: Situación actual

“…Esto es importante porque los parámetros eléctricos constituyen una variable fundamental relacionada con el control de las crisis y otros aspectos fisiológicos 40 .…”