- Department of Neurosurgery, University of Kansas Medical Center, Kansas City, KS, USA
- Department of Neurology, University of Kansas Medical Center, Kansas City, KS, USA
- Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS, USA
Jules M. Nazzaro
Department of Neurology, University of Kansas Medical Center, Kansas City, KS, USA
DOI:10.4103/2152-7806.85473Copyright: © 2011 Nazzaro JM. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Nazzaro JM, Lyons KE, Pahwa R, Ridings LW. The importance of testing deep brain stimulation lead impedances before final lead implantation. Surg Neurol Int 27-Sep-2011;2:131
How to cite this URL: Nazzaro JM, Lyons KE, Pahwa R, Ridings LW. The importance of testing deep brain stimulation lead impedances before final lead implantation. Surg Neurol Int 27-Sep-2011;2:131. Available from: http://sni.wpengine.com/surgicalint_articles/the-importance-of-testing-deep-brain-stimulation-lead-impedances-before-final-lead-implantation/
Background:In the setting of a deep brain stimulation (DBS) lead with defective electrical circuitry, potential patient morbidity and additional surgery may be avoided if impedance testing of the brain lead is performed prior to final lead implantation. In the present report, detection of a short circuit upon lead placement and prior to lead anchoring was detected utilizing recently released DBS hardware and software (Medtronic, Minneapolis, MN). This report suggests that neurosurgeons need to be aware and consider the use of the newly available DBS testing equipment.
Methods:During the first DBS lead placement in a 69-year-old man with advanced idiopathic Parkinson's disease undergoing bilateral subthalamic nucleus DBS over staged procedures, test stimulation and lead impedance testing were accomplished prior to lead anchoring. An external neurostimulator (ENS) was affixed to an updated clinician programmer and connected to the DBS lead with a screening cable specific for the ENS and DBS.
Results:Impedance testing demonstrated a short circuit involving the 1 and 3 lead-electrode bipolar combination in a visually intact lead. The lead was replaced, repeat impedance testing and test stimulation were completed and the intact lead was secured. Subsequent DBS surgeries were completed uneventfully. The lead abnormality was verified by the manufacturer.
Conclusions:This case highlights a new method to test DBS lead circuitry at the time of placement. The method may also be employed to directly test lead integrity when localizing a DBS system short or open circuit of unclear etiology. Our case suggests that the method is valuable and should be utilized.
Keywords: Complication avoidance, deep brain stimulation, external neurostimulator, impedance testing, intraoperative test stimulation
Until recently, it has not been possible to test the impedances and thus the integrity of a deep brain stimulation (DBS) lead until the lead was connected via extension wire to an implanted DBS pulse generator (IPG). DBS system implantations are often staged, with implantation and connection of the extension wire and IPG to the brain lead completed at a later date following lead implantation. Should a short or open circuit be detected upon extension wire and IPG implantation, the specific DBS hardware causing the abnormal readings often can only be isolated via trial and error, which usually entails directly checking the extension wire connections to the IPG and then the lead. This may result in extension wire replacement and if this fails, ultimately lead replacement. Further, if a short or open circuit is localized to the lead, it is generally assumed that the lead was damaged during surgery.
Recently, hardware and software for measuring DBS lead impedances was released allowing the ability to check the integrity of a brain lead at the time of lead placement, prior to and independent of IPG implantation. In the present case, we report the detection of a short circuit involving a DBS lead at the time of lead implantation with the stereotactic frame in place, prior to final lead anchoring. Prior to testing the lead impedances, abnormality involving the lead was not suspected. This case highlights the availability and importance of testing lead circuitry at the time of lead placement and suggests that such testing should initially be performed prior to separating the lead and associated guide tube from the stereotactic apparatus. The method can be repeated following securing the lead if questions regarding lead integrity arise during lead anchoring or subsequently. The lead could also be checked prior to starting surgery.
The patient was a 69-year-old male with a 15-year history of idiopathic Parkinson's disease undergoing bilateral subthalamic nucleus (STN) DBS and satisfying inclusion and exclusion criteria for the surgery.[
Test stimulation followed by a check of lead-electrode impedances was accomplished using a clinician programmer (model 8840, Medtronic) and the recently available DBS external neurostimulator (ENS) (model 37022, Medtronic) affixed to the programming head of the clinician programmer [
Front (left) and back (right) views of clinician programmer (model 8840, Medtronic, Minneapolis, MN) with external neurostimulator (model 37022, Medtronic) attached to the back of the programmer. The programmer has been updated (model 8870 version AAO Application Card, Medtronic). Also shown is the deep brain stimulation specific external neurostimulator twist-lock screening cable (model 3550-68, Medtronic) which connects the external neurostimulator to a deep brain stimulation lead. In addition to intraoperative test stimulation using the programmer, the system makes possible check of impedances specific to the deep brain stimulation lead and thus the integrity of the lead. Deep brain stimulation specific external neurostimulator screening cable with alligator clips (not shown) rather than twist-lock may be used.
Upon impedance testing at 0.7 V, readings consistent with a short circuit (<50 Ω) involving the number 1 and number 3 lead-electrode bipolar combination were encountered. Impedances involving the other lead-electrode bipolar combinations were within normal limits. The impedance testing was repeated at 1.5 V and again readings consistent with a short circuit involving bipolar stimulation of the lead-electrode 1 and 3 combination were encountered. Repeat testing at 3 V gave the same results. The lead was removed and the guide tube with guide stylet in place was advanced the distance that it had earlier been retracted following which a new lead was placed. Impedance testing of the new lead at 0.7 V, 1.5 V, and 3.0 V demonstrated all impedances of the new lead to be within normal limits. Test stimulation using electrodes 0 and 3 of the new DBS lead again demonstrated beneficial effects within clinical desirable stimulation range and without side effects upon testing to 6 V. The lead was secured and remaining planned staged procedures to accomplish bilateral STN DBS were accomplished without incident.
After completion of the case involving the lead in question, the removed lead was tested using 0.9% saline bath to submerge the lead-electrodes and using the clinician programmer, ENS, and twist-lock cable used as during the surgery together with short lead stylet, the latter packaged with DBS leads and also the new connection cables. Upon bench testing, a short circuit (< 50 Ω) involving the lead- electrode 1 and 3 bipolar combination was again encountered at all test voltages (0.7 V, 1.5 V, and 3.0 V). A defect or breakage either in the outer polyurethane coating, conductor wires, proximal connector, or stimulating electrodes comprising the lead was not appreciated to visual inspection with 2.5 × loupe magnification. The lead was returned to the manufacturer for analysis. The manufacturer reported, “… A low impedance measurement was observed on electrode pairs 1 and 3 (<50 Ω), indicating a short circuit. Visual analysis noted that the distal end of the lead was stretched and the outer insulation of the lead was broken between the electrode sleeves. Analysis confirmed an electrical short circuit at the proximal end of the lead, near the #1 connector sleeve.”
Until very recently, intraoperative clinical test stimulation required using model 3625 Test Stimulator (Medtronic) connected to the DBS lead via alligator clip- or twist-lock screening cable provided with the DBS lead. However, testing of DBS lead impedances was not possible at the time of test stimulation using the 3625 stimulator. The only way to ensure the integrity of a DBS lead was after the lead had been connected to an IPG by way of telemetry using the clinician programmer (model 8840, Medtronic). However, the IPG needed to be located within body soft tissues. If during impedance testing the lead is connected to an externalized IPG, impedance readings of open circuits for both monopolar and bipolar parameters are obtained for all lead-electrodes.
In staged procedures, implantation of the IPG together with the extension wire and connection to the already implanted lead occurs as a separate operation most usually one to two weeks after lead implantation, possibly longer. Discovery of a lead circuitry problem in such a setting requires, dependent on surgical method, one if not more additional surgeries for lead replacement. Even in a surgery in which lead, extension wire, and IPG are planned as a single procedure, discovery of a lead circuitry problem upon connection to the IPG would complicate the procedure and in many instances would also require separate surgery to correct the hardware problem.
Recently released hardware and software makes possible the intraoperative testing of impedances of DBS leads (3387 and 3389) at time of lead placement and independent of IPG implantation. The 8870AAO Application Card is loaded to the 8840 clinician programmer making possible communication between the programmer and the 37022 ENS. For intraoperative testing, the ENS is attached to the programmer within a slot in the programmer head, which in turn is connected to the lead via alligator clip (model 3550-67, Medtronic) or twist-lock screening cable (model 3550-68, Medtronic) specific for the ENS and DBS. As specified by the manufacturer, orientation of the ENS in relation to the programmer should be as depicted in
In the present report, a defective lead was detected following insertion into brain though prior to removal of the lead's straight stylet and while the guide cannula was in place within the stereotactic frame. Until very recently, localization of such a problem to the lead was possible only by inference and following elimination of possible problems elsewhere in a complete DBS system. Etiology of why the lead was defective in our case is not clear and a lead problem was not suspected until impedance test results were obtained. The lead was handled only by the lead surgeon (JMN). The defects referable to the lead upon the DBS manufacturer's analysis are very unlikely to be secondary to over tightening of the FHC lead holder screw as this is not permitted by the FHC hardware design. In addition, our lead holder was not part of a recent FDA recall (Z-0311-2011) specific to this problem of lead damage related to the lead holder, and the locations of the lead defects do not correlate with the FHC securing screw location in reference to the lead.
While we tested the lead following test stimulation, a DBS lead may be tested prior to brain insertion by submerging the lead-electrodes in 0.9% saline and using the ENS and twist-lock screening cable together with an updated (8870AAO Application Card) 8840 clinician programmer. However, this may increase the risk of infection and currently is not our standard method. The lead may also be tested following insertion within brain and after removal of the straight (long) stylet from within the lead with proper use of the DBS ENS alligator clip or twist-lock screening cables, depending on surgeon preference. The later method may prove useful if there is question of lead integrity after securing the lead to the skull or should plain radiographs[
Recently released hardware and software make it possible to check DBS lead electrical integrity at the time of lead placement. It may also be employed when attempting to isolate the hardware responsible for a new short or open circuit in an already implanted and otherwise intact DBS system. Our case suggests that the method is valuable and should be considered as it may reduce additional surgeries related to a faulty lead.
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