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Publication Date: 2016-May-13
Document File: 4 page(s) / 503K

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Electrode DC Blocking Capacitor Failure Detection

     Implantable neurostimulation devices have been used for the past 10+ years to treat acute or chronic neurological conditions. Deep brain stimulation ("DBS"), the mild electrical stimulation of sub-cortical structures, belongs to this category of implantable devices and has been shown to be therapeutically effective for Parkinson's disease, Dystonia, and Tremor. New applications of DBS in the domain of psychiatric disorders (Obsessive Compulsive Disorder, Depression) are being researched and show promising results. In some current commercially available systems, the 1.27 mm diameter, 10-50 cm long probes are connected to the Implantable Pulse Generator ("IPG") using a 3.8 mm-diameter, 4 screw-contacts connector by means of 110 mm long, and 2.8 mm diameter connector cables. The IPG may be implanted in the torso region of a patient and coupled to the probe (or lead) via lead extensions that extend from the torso to a burr hole in the patient's skull through which the probe is placed to contact cortical or sub-cortical tissue. The proximal end of the probe has 4 concentric contacts that fit into the 4-contacts connector of the IPB, and the body of the probe is cylindrical through its end. As a consequence, the probe can pass easily through the microdrive assembly that guides the flexible probe and the stiff guiding wire into the brain tissue to the desired target.

     Future systems may be designed with more, smaller electrodes that may not encircle the full circumference of the lead body in order to better control the delivery of electrical stimulation. Such electrodes, sometimes referred to as "segmented electrodes", may have a smaller area than electrodes that encircle the full lead body and may direct stimulation in a more focused direction. Better control of the stimulation may reduce the side effects caused by stimulation, which may result in about 30% of the patients.

     Leakage current requirements are very stringent (<1μA) in the applicable Active Implantable Medical Device ("AIMD") standards (e.g., EN-45502-1 [2010]), especially when connection to a small area electrodes, such as segmented electrodes, is involved (<100nA), as is the case in with a commercially available system. Therefore, control of these leakage currents is of prime importance both in normal operation and under single failure conditions of the implant.

     When the IPG is in stimulation mode, several techniques (e.g., biphasic stimulation pulses, grounding, active charge balancing, etc.) can be applied to guarantee that the net charge injection, and thus the DC current, on the stimulation lines, and therefore on the lead electrodes, is zero. However, it is difficult to impossible to guarantee this under single failure conditions. As such, it is industry practice to apply DC blocking capacitors (not part of the pulse generator electronics) to ensure that if the electronics fails, no DC current can arise on output line...