Objective: The objective was to characterize the possible effects that directional leads impedances have on Deep Brain Stimulation (DBS) therapy.

Background: DBS of the subthalamic nucleus (STN) has proven to be effective into treating some motor symptoms in Parkinson’s Disease patients by activating neural tissue that renders therapeutic benefits while avoiding the activation of tissue that provokes side effects. The activation of tissue is defined by the amount of current applied to it, which in turn could depend on the impedance of the tissue-contact interface. Recently, directional leads have been introduced into DBS systems in order to have more selective stimulation of therapeutically relevant areas. However, the stimulation accuracy, precision and stability for these directional leads might be compromised by differences or changes on individual tissue-contact interface impedances.

Methods: DIRECT-DBS is a prospective, randomized, multi-center, double-blind study with a crossover design, for which 12 subjects have been enrolled and implanted for STN DBS with bilateral directional leads (Vercise Cartesia, Boston Scientific) connected to a pulse generator. Within the framework of the study, impedance and stimulation settings data will be collected at different time points for analysis.

Results: The collected data so far shows significant differences between ring and segmented contacts’ impedances. The data also shows substantial impedance changes through time for ring and especially the segmented contacts (5.7% and 11.4% average impedance change, respectively). By calculating the equivalent current delivered by single source voltage (and current DBS systems) under these impedance changes conditions, it was found that these systems are unable to deliver the same current distribution for the desired stimulation setting when multiple contacts are needed for effective stimulation. In addition, these systems are unable to constantly deliver the desired current as opposed to DBS systems using multiple independent current sources.

Conclusions: The results suggest that in order to leverage the advantages of directional leads for an effective DBS therapy, it is fundamental to use them in combination with multiple independent current sources systems to allow for accurate, precise and stable current delivery. The clinical relevance of these findings has to be further investigated.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/directional-lead-impedances-and-their-possible-effects-on-deep-brain-stimulation/