Abstracts

Rationale: Patients with Vagal Nerve Stimulators(VNS) may require turning off the device temporarily for a variety of reasons. It has become commonplace to turn of the VNS for several hours in order to perform head MRIs.The Wake Forest Comprehensive Epilepsy Center(WFCEC) has a high yield protocol for obtaining Magnetoencephalography (MEG) in patient with a VNS implant, but patient must have their VNS turned off for several days prior to the MEG. Some patients elect to have their device turned off due to inefficacy or intolerability, but then choose to have it turned back on, even months later. After turning the device back on following a period of time with no duty cycle stimulation, there are sometimes observed changes in tolerability or seizure pattern, or both. We sought to characterize any association between these observations and the situation or the duration of duty cycle interruption.Methods: We reviewed all cases of active VNS implants followed in the epilepsy clinic at WFCEC. Patients who had a programmed total interruption in their duty cycle were identified and the reason for this programming change was noted. We reviewed patients who had an interruption of <24hours, those with an interruption of 24-96 hours, and those with an interruption >96 hours. We also reviewed cases that were found to have a depleted battery of unclear duration. Charts were reviewed to identify if any new complaints of VNS that emerged after function of the device was re-established. Seizure frequency was also compared to that preceding interruption of VNS function.Results: There were 48 patients with a total interruption of duty cycle. All those turned off for less than 24 hours were due to MRI imaging. 12 patients were turned off for 72-96 hours for MEG imaging. There were 2 patients who chose to have the device turned off only to have it turned back on at >96 hours. The most commonly reported complaint following turning VNS back on was worse tolerability compared to baseline, and this was a more frequent problem in patients who had their VNS turned off for longer periods of time. The majority resumed a duty cycle at lower settings than were previously tolerated. A few patients had less efficacy compared to baseline, and required additional adjustments of the VNS after the interruption.Conclusions: We conclude that, although unusual, an altered response to VNS may be seen after interruptions in duty cycle. MRI and MEG testing does not require prolonged interruptions in VNS function, and so appears to have less potential for altered tolerability or response after the device is turned back on. Careful consideration must be given to the decision to interrupt the duty cycle for longer period of time, and may warrant replacement of battery rather than allowing depletion.