Patterns of hardware related electrode failures in sacral nerve stimulation devices

Abnormal electrical impedance in sacral nerve stimulation devices is a cause of device failure. Currently, there is scant literature evaluating the incidence and management of this problem. We evaluated the presentation, characteristics and management of sacral nerve stimulation devices with abnormal electrical impedance.

A total of 565 patients were permanently implanted with sacral nerve stimulation devices using a tined lead between 2003 and 2011. Devices were interrogated postoperatively and at followup. Abnormal electrical impedance was classified as open circuit--impedance greater than 4,000 Ω or short circuit--impedance less than 50 Ω and/or equivalence of impedance. Details on presentation, characteristics and management were recorded.

Of the 565 patients 72 (12.7%) experienced a total of 86 abnormal electrical impedance events, of which 57 (66.2%) were open circuits and 28 (32.5%) were short circuits. One event (1.1%) was a simultaneous open and short circuit. Short circuits presented earlier than open circuits (median 3.5 months, IQR 2-7.5 vs 15, IQR 5.5-30.5, p <0.0001) and required surgical intervention more often (75.0% vs 54.3%, p = 0.09). Patient specific factors, such as trauma history and change in body mass index class, were not associated with abnormal electrical impedance. No electrode failure patterns could be identified.

Abnormal electrical impedance occurred in approximately 13% of cases permanently implanted in our series. Short circuits presented earlier and often required surgical intervention. Open circuits presented later and may have potentially been secondary to microfractures that accumulate with time at the sacral plate, resulting in later presentation. Almost a third of patients with abnormal electrical impedance associated with clinical inefficacy were treated conservatively, primarily with reprogramming.