Abstracts

Rationale: 2012 updated labeling for the use of MRI in patients treated with VNS includes a precautionary statement not to perform MRI when the generator has been explanted, but all or part of the lead remains. Potential tissue damage has been a concern due to the risk for radio-frequency heating of the lead, a property which is a function of the lead length, Tesla of the MRI, and whether a head or body coil system is used. Prior to this advisory statement, patients who had disconnected or nonfunctioning VNS devices but retained partial or full length leads could have had subsequent MRIs. We retrospectively reviewed our cases of MRIs after VNS explants, or end of battery function in order to determine whether our clinical experience is concordant with the postulated risk. Methods: We reviewed all cases of VNS patients followed at WFBH who had any known or possible disconnection of lead from the VNS battery. This included patients in whom the battery was explanted and the lead remained (isolated), those who had original lead problems and the lead was cut and new lead and battery were implanted(partial), and those who had an intact lead and battery, but the battery was nonfunctional, thus lead integrity was untestable, and thus potentially disrupted (dead battery).We identified patients within this population who had any MRI and reviewed by strength of magnet, type of coil and anatomic site of imaging. Charts were reviewed for evidence of adverse effects of MRIs. Results: We identified a total of 22 VNS patients with lead-device disconnections, twelve of whom had MRIs (which would have been prohibited by current labeling change). Of these, 5 patients had surgically disconnected VNS leads. Of these, 2 had MRIs since explant. An additional 7 patients had expired VNS batteries which were not replaced prior to an MRI being done. Four of these patients underwent subsequent MRIs. Nine patients had the VNS turned off, and 6 had subsequent MRIs. All patients underwent 1.0 or 1.5 T head coil studies, predominantly of the brain for further evaluation of medically refractory epilepsy. Several patients had multiple MRIs. There were no reports of any complaints or complications following the MRIs. Conclusions: The current change in labeling of VNS safety in MRI poses practical problems, especially for medical centers that serve as tertiary referral centers for medically refractory epilepsy management. Patients who had previously failed VNS therapy may have the device explanted or the device may simply run down. In these instances, the current labeling change may prohibit some centers from performing MRIs of any type, including those needed for anatomic localization for epilepsy surgery. Evidence from our cases indicates that MRIs can be performed in patients with disconnected VNS leads. We conclude that further definition of specific circumstances in which MRIs are safer need to be excluded from this restriction.