TP3-3 Why do some patients fail to respond to VNS? – a retrospective analysis of cardiac based seizure detection (CBSD) therapy

Objectives To identify predictors of poor response to cardiac based seizure detection (CBSD) VNS therapy. Design Data was collected retrospectively for patients with epilepsy who had VNS Aspire SR implanted between June 2014 and June 2017. 51 patients who reached a therapeutic level of stimulation were included. We compared those who achieved significant seizure reduction (at least 50%) with the remainder to identify potential factors predicting response. Subjects 51 patients achieving therapeutic stimulation (1.5mA) with the VNS Aspire SR. Methods We reviewed patients’ electronic records over the period between June 2014 and June 2018. Results 32 (63%) patients achieved significant seizure reduction. The following factors applied equally to both responders and non-responders: patient age, duration of epilepsy prior to VNS insertion, seizure type, the presence of a causative structural abnormality and the presence of a carer. Co-existing learning disability and/or non-epileptic attacks were commoner among poor responders. Polytherapy (3 or more AEDs) and non-compliance with medical treatment were also commoner among the poor responders; none of these factors was statistically significant. Conclusions Factors potentially predicting response to resective surgery (including patients’ age and duration of epilepsy) do not necessarily predict response to VNS therapy. The presence of a learning disability and the extent of seizure refractoriness may influence response to VNS therapy; a larger study is needed to assess their significance.