Objective: To document any differences in impedance assessments across neurostimulator models during device exchanges.

Background: The Activa PC parameters, with which impedance is measured are 14 pulses delivered at 100Hz of 80µs pulse duration, at (0.7V, 1.5v or 3.0V) amplitudes. The Percept^tm parameters at either automatic amplitude increases, or at a fixed 1.0mA. We investigated whether the different device measurements would register a systematic impedance difference.

Method: We analyzed the impedances across 23 device exchanges. 13 of the device exchanges were from Activa PC to Activa PC, while 10 were from Activa PC to Percept^tm. We employed mixed repeated measures within and between general linear models to analyze the impedances from the depleted device immediately prior to the exchange to the newly implanted device immediately prior to closure.

Results: Bipolar impedances were greater than monopolar impedances, and within the bipolar impedances, increased spacing was associated with increased impedance. These are standard differences and occurred, regardless of device model and regardless of depleted or new device. Further, these statistical differences were not altered across device exchanges. However, impedances consistently exhibited decreases going from Activa PC to Activa PC (mean decrease: -124.04 Ohms, sem: 9.23); whereas impedances consistently exhibited increases upon going from an Activa PC to the Percept^tm (mean increase 81.62 Ohms, sem: 14.80). The direction and degree of impedance difference across the different devices going from a depleted device to a new device was statistically significant (F_(1,436)=154.18; p<0.0005).

Conclusion: The Percept^tm is a constant current device and the impedance test uses different circuitry and parameters than its predecessor the Activa PC and appears to result in a different assessment when compared within subject across device exchanges. Whether one device is more accurate than the other, will require bench tests across known values, as we have performed before. Further, all Activa PC to PC exchanges were based on an initial device exchange, whereas more than half of the Activa PC to Percept^tm exchanges involved multiple previous exchanges. Whether the number of exchanges plays a role in the impedance change across models remains to be explored.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/comparison-of-activa-pc-to-percepttm-impedance-assessment-across-device-exchanges/