vagus_nerve_stimulator

www.psych.med.umich.edu_neuromodulation_i_vnsdevice.jpg see Vagus nerve stimulation.

Vagus nerve stimulators (VNSs) are currently an accepted treatment for drug resistant epilepsy not amenable to ablative surgery. Battery death and lead damage are the main reasons for reoperation in patients with VNSs. In general, any damage to the lead requires revision surgery to remove the helical electrodes from the vagus nerve and replace the electrode array and wire. The electrodes are typically scarred and difficult to remove from the vagus nerve without injury.

Ralston et al., describe 6 patients with VNSs who presented with low lead impedance on diagnostic testing, leading to the intraoperative finding of lead insulation disruption, or who were found incidentally at the time of implantable pulse generator battery replacement to have a tear in the outer insulation of the electrode wire. Instead of replacement, the wire insulation was repaired and reinforced in situ, leading to normal impedance testing. All 6 devices remained functional over a follow-up period of up to 87 months, with 2 of the 6 patients having a relatively shorter follow-up of only 12 months. This technique, applicable in a subset of patients with VNSs requiring lead exploration, obviates the need for lead replacement with its attendant risks 1).


Although implanted metallic devices constitute a relative contraindication to magnetic resonance imaging (MRI) scanning, the safety of brain imaging in a patient with a vagus nerve stimulator (VNS) is classified as “conditional,” provided that specific manufacturer guidelines are followed when a transmit and receive head coil is used at 1.5 or 3.0 Tesla.

From September 2009 until November 2011, 101 scans were requested in 73 patients with the VNS in The Netherlands. Patients were scanned according to the manufacturer's guidelines. No patient reported any side effect, discomfort, or pain during or after the MRI scan. In one patient, a lead break was detected based on device diagnostics after the MRI-scan. However, because no system diagnostics had been performed prior to MR scanning in this patient, it is unclear whether MR scanning was responsible for the lead break. The indication for most scans was epilepsy related. Twenty-six scans (26%) were part of a (new) presurgical evaluation and could probably better have been performed prior to VNS implantation. Performing brain MRI scans in patients with an implanted VNS is safe when a modified MRI protocol is followed 2).


1)
Ralston A, Ogden P, Kohrman MH, Frim DM. In situ repair of vagus nerve stimulator lead damage: technical note. J Neurosurg Pediatr. 2016 Dec;25(6):679-682. PubMed PMID: 27611900.
2)
de Jonge JC, Melis GI, Gebbink TA, de Kort GA, Leijten FS. Safety of a dedicated brain MRI protocol in patients with a vagus nerve stimulator.Epilepsia. 2014 Sep 19. doi: 10.1111/epi.12774. [Epub ahead of print] PubMed PMID: 25244102.
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