Stimulation parameters after vagus nerve stimulator replacement

Objectives.  This study aims to assess tolerability and efficacy of stimulation parameters after vagus nerve stimulator (VNS) pulse generator replacement. Materials and Methods.  We carried out an observational, retrospective study, reviewing our experience with VNS generator replacements in 28 epilepsy patients. Results.  Seven patients had actual end of battery life (EOBL) (with symptoms), and 21 patients had asymptomatic projected EOBL. When we reprogrammed stimulation parameters postoperatively, 17 of the 28 patients could not tolerate the preoperative baseline current settings, even one year later. There were no differences in pre- vs. postoperative seizure rates between patients who did or did not return to baseline settings. Failure to return to baseline current was not related to previous VNS duration, same- vs. different-battery generator replacements, or antiepileptic medication changes. Conclusions.  After VNS generator replacement, patients' common inability to tolerate preoperative current settings does not lead to more seizures. A chronic modification of the vagus nerve system's sensitivity to stimulation changes may be hypothesized.