Introduction: Vagus nerve stimulation (VNS) has steadily grown as an option for treating refractory epilepsy. Unfortunately, considerable variability remains in the success of VNS in patients. Therefore, it is necessary to identify which characteristics increase or decrease the likelihood of successful VNS treatments to mitigate potential complications by performing unnecessary procedures. We examine available literature to determine the known predictors and characteristics of patients in relation to VNS performance.

Methods: PubMed was queried for articles pertaining to vagus nerve stimulation and predictive variables. Articles included in the review met the following inclusion criteria: clinical data on human subjects in English, articles reporting treatment of seizure disorder with VNS, data that was supported with multivariate analysis. No limit was placed on publication date.

Results: Younger age at implantation, later onset of epilepsy, and generalized over partial seizures were most strongly supported as predictive of successful therapy. Other potential positive predictors supported by smaller data sets include: lower seizure frequency, duration of epilepsy prior to implantation, unilateral IED or absence of bilateral IED, focal epilepsy, presence of temporal discharges, cortical dysgenesis, Lennox-Gastaut syndrome, post-traumatic epilepsy, and tuberous sclerosis. There are conflicting results regarding the prognostic value of pairwise derived brain symmetry index and the presence of MRI lesions. Indices of heart rate variability are a new and potentially useful predictor of response.

Conclusions: VNS remains a safe and efficacious method of treating refractory epilepsy. However, as the response is highly variable, there is a need for better understanding of its mechanisms and predictive variables to reduce unnecessary procedures. Though there are many potential VNS predictors, additional corroborative data is needed before these may guide decision making. Thus far, younger age of implantation, later onset of epilepsy, and generalized seizures are the factors most strongly associated with successful VNS therapy.

Patient Care: Our research identifies potential factors that may be instructive when considering VNS treatment for refractory epilepsy and highlights the need for further study in this area.

Learning Objectives: By the conclusion of this session, participants should understand: 1) VNS can be a safe and efficacious treatment for refractory epilepsy but the response is highly variable, 2) the current state of the research on predictors of response to VNS for refractory epilepsy, and 3) there is conflicting or insufficient data about many potential predictors of response to VNS

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