Long-term multicenter experience with vagus nerve stimulation for intractable partial seizures: results of the XE5 trial.

OBJECTIVE: Intermittent stimulation of the left cervical vagus nerve trunk (VNS) with the NeuroCybernetic Prosthesis (NCP) is emerging as a novel adjunct in the management of medically refractory epilepsy. We review the safety and efficacy of VNS 1 year after completion of the E05 study, the largest controlled clinical trial of VNS to date.

METHODS: One hundred and ninety-nine patients with intractable epilepsy and at least 6 complex partial or secondarily generalized seizures per month enrolled in a randomized, double-blinded, partial crossover trial of high versus low parameters of stimulation (E05). After 3 months, all patients received high stimulation during an open-label, nonblinded extension trial (XE5). Seizure frequency, adverse events and multiple physiologic variables were monitored at regular intervals.

RESULTS: At 3 months, the mean reduction in seizure frequency among patients receiving high stimulation during E05 was 28%. Of the 199 subjects participating in this acute-phase trial, 195 continued in the long-term protocol. Among the latter patients, 21 subsequently exited the study due to lack of efficacy, and 2 others died from causes unrelated to VNS. Complete data were obtained for 164 of the remaining subjects. Using a declining N analysis, the mean and median reduction in seizure frequency at 15 months was 37 and 45%, respectively. A last visit carried forward analysis, which controls for dropouts and incomplete follow-up, yielded comparable results (34 and 45%, respectively), indicating little potential for selection bias. At 15 months, 39% of the subjects had a greater than 50% reduction in seizures, including 21% who had a greater than 75% reduction, and 2% have remained seizure free. Few serious adverse events, physiological perturbation or device failures were reported.

CONCLUSIONS: The long-term multicenter safety, efficacy, feasibility and tolerability of VNS, as well as the durability of the NCP device have been confirmed. Unlike chronic therapy with antiepileptic medication, the efficacy of VNS is maintained during prolonged stimulation, and overall seizure control continues to improve with time.