Abstracts

To study, in patients on unchanged antiepileptic drugs (AEDs): 1) seizure rate changes after 3 and 12 months of vagus nerve stimulation (VNS); and 2) effects of VNS parameters on seizure rates. In most previous large, long-term studies, modifications of the patients[apos] concomitant AED regimens were allowed.
We located in the VNS treatment outcome registry 269 patients treated for 1 year with VNS who had no change in AEDs or AED doses. Seizure rate changes relative to baseline were calculated at 3 and 12 months follow-up on VNS. We analyzed and compared: 1) three vs. 12 months seizure rate changes; 2) effects of changing duty cycle between 3 and 12 months ([quot]rapid[quot] vs. [quot]standard[quot] cycling); and 3) effects of stimulation parameters (output current and duty cycle) at 12 months.
Seizure rate reductions improved between 3 months (median=45%) and 12 months (median=58%)(p[lt]0.0001, Wilcoxon sign-rank test). There were no differences in outcomes between patients who stayed on standard cycling for all 12 months, stayed on rapid cycling for all 12 months, or changed from standard to rapid cycling between months 3 and 12. There was no relationship between stimulation parameters at 12 months follow-up and seizure rate changes.
This study was an analysis of treatment outcomes from clinical practice, not a prospective randomized clinical trial. None-the-less, our results suggest: 1) seizure rates decline with increasing duration of VNS therapy, 2) this seizure rate decline can occur without changes in AEDs, 3) this decline may not be due to sequential changes in stimulation parameters, and 4) similar degrees of long-term seizure rate reduction may be seen on various VNS stimulation settings.
[Supported by: Cyberonics]