Predicting success of vagus nerve stimulation (VNS) from interictal EEG.

PURPOSE: Vagus nerve stimulation (VNS) has shown to be an effective treatment for drug resistant epilepsy in numerous patients, however, not in all. It is still not possible to predict which patients will profit from VNS. In this pilot study, we explore predictive interictal EEG features for seizure reduction after VNS. METHODS: 19 Patients with medically refractory epilepsy and an implanted VNS system were included. Interictal EEG registrations, recorded before implantation, were retrospectively analysed. A quantative symmetry measure, the pair wise derived brain symmetry index (pdBSI), was tested to predict VNS outcome. Reduction in seizure frequency was used to define the responders. RESULTS: 10 Patients did respond to VNS, of whom 7 patients had a seizure reduction of at least 50% in a follow-up period of 2 years. On average, we find higher pdBSI values for delta, theta, alpha and beta bands for non-responders than for responders. The average pdBSI of the theta and alpha bands could significantly discriminate between responders and non-responders. CONCLUSION: In this study, quantifying EEG symmetry using the pdBSI shows promising results in predicting the reduction of seizure frequency after VNS treatment.

Vagus nerve stimulation for epilepsy activates the vocal folds maximally at therapeutic levels.

PURPOSE: Vagus nerve stimulation (VNS) for medically refractory epilepsy can give hoarseness due to stimulation of the recurrent laryngeal nerve. For a group of VNS-therapy users this side-effect interferes severely with their daily activities. Our goal was to investigate the severity of intra-operative VNS-related vocal fold contraction at different pulse widths and current output parameters. We investigated electromyographic and morphometric alterations on the vocal folds during VNS. METHODS: Vocal fold EMG experiments were conducted intra-operatively during the implantation of a VNS system. During surgery the VNS pulse generator was programmed to stimulate at different pulse durations. At each pulse width the EMG-threshold current was determined by electrical stimulation of the vagus nerve with increasing stimulation currents. Laryngostroboscopic examination was performed after surgery to analyze the effects of spontaneous stimulation on the larynx. RESULTS: The vocal fold EMG and morphodynamic changes in the larynx have been analyzed in eight patients. In all patients left vocal fold EMG-threshold was between 0.25 and 0.50 mA. Pulse duration had little influence on the EMG-threshold level. Vocal fold EMG saturation levels were reached between 0.75 and 1.00 mA. Video stroboscopic monitoring showed that stimulation induced an adductory spasm of either the ipsilateral vocal fold or the vestibular fold, and was present remarkably irrespective of the presence of hoarseness. CONCLUSIONS: VNS causes pronounced effects on the vocal folds even at low stimulation amplitudes. At therapeutic levels even at the lowest stimulation pulse durations, the vocal fold contract, however, this does not necessarily give hoarseness.

Cardiac responses of vagus nerve stimulation: intraoperative bradycardia and subsequent chronic stimulation.

OBJECTIVES: Few adverse events on heart rate have been reported with vagus nerve stimulation (VNS) for refractory epilepsy. We describe three cases with intraoperative bradycardia during device testing. PATIENTS AND METHODS: At our hospital 111 patients have received a VNS system. Intraoperative device testing is performed under ECG-monitoring. We reviewed the patients and their VNS-therapy follow-up outcome who experienced a change in heart rate, during device testing (Lead Test). RESULTS: Three patients with medically refractory epilepsy showed a bradycardia during intraoperative Lead Test. Postoperative the VNS-therapy started under ECG-monitoring. No change in cardiac rhythm occurred. Subsequent chronic stimulation is uneventful. All three have reduced seizure frequency. Two already have had their second implant, without the occurrence of bradycardia. CONCLUSION: In case of intraoperative bradycardia VNS-therapy onset should be done under ECG-monitoring. Subsequent chronic stimulation is safe in respect to heart rate. Bradycardia during intraoperative device testing is no reason to abort the operation.

Vagus nerve stimulation for medically refractory epilepsy: a long-term follow-up study.

INTRODUCTION: Vagus nerve stimulation (VNS) is thought to have a cumulative effect in time on seizure frequency reduction. There also might be other variables than reduction of seizure frequency in order to determine VNS efficacy. In this study we describe the long-term outcome of the first group of vagus nerve stimulation patients with pharmacoresistant epilepsy at the Medisch Spectrum Twente, The Netherlands. METHODS: This long-term descriptive prospective study included 19 patients, 11 males and 8 females, aged 17-46 years with pharmacoresistant epilepsy. They had received 3-16 (mean 9) different anti-epileptic drugs and were not eligible for surgical resection of an epileptic focus. A vagus nerve stimulator was implanted in the period April 1999-October 2001. Follow-up ranges from 2 to 6 years (mean 4 years). Efficacy was measured as the percentage change in seizure rate during 1 year and then after each year follow-up of VNS compared to 5 months baseline before implantation. RESULTS: Mean seizure reduction at 1-6 years was, respectively, 14% (n = 19), 25% (n =1 9), 29% (n = 16), 29% (n = 15), 43% (n = 9) and 50% (n = 7). Because of VNS two patients were able to start living without supervision. One patient died after 2 years of follow-up possibly as a result of SUDEP. Four patients had no apparent reduction in seizure frequency. Two of them had their stimulator removed. The other two patients however had significantly reduced post-ictal periods and seizure time and received a new pulse generator when the battery was depleted. One stimulator was switched off due to adverse effects, even though there was a positive effect on his seizure reduction. In six patients the medication regimen was changed during VNS by adding one anti-epileptic drug, however without significant change in seizure reduction. Adverse effects were hoarseness and coughing during stimulation. One patient had a temporary paralysis of his left vocal cord. CONCLUSION: We think that VNS is an effective treatment for pharmacoresistant epilepsy and its positive effect persists during the years of follow-up. Our results suggest that seizure reduction should not be considered as the only variable of importance to describe the outcome of VNS on epilepsy and it is worthwhile to look at other outcome measures.