Does Pulse-triggered VNS Autostimulation Increase VNS Efficacy

Inclusion Criteria: * Subjects, 12 years of age or older, who have a VNS without ECG-triggered auto stimulation implanted, have a positive effect and have a device replacement with model 106 or model 1000 due to low battery capacity,. * Subjects, who have 2 or more seizure per month and not more than 28 days between seizures during the baseline. * Subjects, who are on a stable regiment of antiepileptic drug treatment for at least 3 month prior to enrollment and maintain on this regimen throughout the study. * VNS parameters have not been changed I the last 3 month prior to enrollment. * Subjects which are using an off time of at least 1.8 min. (If the patient is on a duty cycle involving an off-time of 1.1 min. or less, and willing to participate in the study the duty cycle will have to be changed to fulfill the inclusion criteria as follows. The off-time will be changed to 1.8 min. and the on-time accordingly to achieve about the same duty cycle as the patient had before. If the duty cycle is above 30% the parameters will be changed to 60 sec./1.8 min., if the duty cycle is between 30% and 23% the parameters will be change to 30 sec./1,8 min., if the duty cycle is 20% the parameters will be change to 21 sec./1,8 min. and if the duty cycle is 15% the parameters will be change to 14 sec./1,8 min. After at periode of 3 month observation the patient can be included in the study.) * Either the subjects or the legal guardian are able to agree to participate by signing the informed consent form. Exclusion Criteria: * Subjects with rapidly progressive neurodegenerative or rapidly progressing neoplastic disease. * Subjects or legal guardians who are unable to understand the study procedures.