Introduction: Deep brain stimulation (DBS) entails focal electrical stimulation optimized for each patient. Though electrode impedance substantially affects the electrical current delivery to target tissues, long-term variation in impedance has received little attention in the existing literature. Our objective was to assess the relationship between electrode impedance and time in a large DBS patient population and characterize the relationship between contact activity and impedance.
Methods: We collected retrospective impedance and programming data from 128 electrodes in 84 patients with Parkinson’s disease, essential tremor, or dystonia. Effects of time, contact activity, diagnosis, anatomical target, electrode model, contact laterality, contact number, and stimulation voltage on impedance were assessed. We also examined impedance changes following contact activation and deactivation.
Results: Impedance was found to decrease by 73 ohms/year (P < .001), with 72% of contacts following a downward trend. Impedance was on average 163 ohms lower in active contacts (P < .001). Activation of a contact was associated with a more rapid decline in impedance (121 ohms lower at the follow-up visit relative to a contact left off, P < .001) and inactivation was associated with a less rapid decline in impedance (81 ohms higher, P = .016). Higher stimulation voltages were associated with lower impedance values (P < .001). Contact number and electrode model were also significant predictors of impedance.
Conclusions: Impedance decreases gradually over years following implantation in a stimulation-dependent manner. These trends have implications for long-term programming and for the development of a closed-loop DBS device.
Patient Care: Understanding long-term trends in impedance will facilitate more informed DBS device programming, as well as the development of more advanced DBS systems that provide optimal stimulation throughout the device lifetime. These latter devices may include a closed-loop DBS system that mitigates the need for reprogramming.
Learning Objectives: By the conclusion of this session, participants should understand:
1) The importance of impedance in the therapeutic efficacy of deep brain stimulation
2) Factors, such as time and contact activity, that influence impedance
3) The ramifications of long-term changes in impedance