NEW YORK (Reuters Health) Jan 18 - Sacral nerve stimulators (SNS) are plagued with electrode problems, it appears from a recent study.
Abnormal electrical impedance occurs in about one of eight patients permanently implanted with them, according to researchers from the Cleveland Clinic in Ohio.
The devices are used to treat refractory urgency, frequency, urge urinary incontinence, and urinary retention - but damaged hardware, such as lead failures with abnormal impedance or with the equalization of impedance values across multiple electrodes, are common in patients undergoing surgical revision, the researchers said in a report online January 10 in The Journal of Urology.
Dr. Raymond R. Rackley and colleagues investigated electrode failures presenting with abnormal electrical impedance in 565 patients permanently implanted with Medtronic's Interstim SNS devices.
Seventy-two patients (12.7%) had abnormal electrical impedance. These patients accounted for 37.8% of 111 revisions, 7.1% of 56 explantations, and 5.5% of 18 explantations after at least one revision.
Electrode failures included open circuits in 48 patients, short circuits in 19 patients, short and open circuits at different times in four patients, and simultaneous short and open circuit failures in one patient.
Open circuits occurred with similar frequency in Interstim I (9.5%) and Interstim II (8.9%) devices, but short circuits were much more common in Interstim I (8.7% vs 0.6%).
Reprogramming alone was adequate for 16% (4/25) of the short circuits and 39.2% (20/51) of the open circuits that presented with clinical inefficacy, and surgical intervention was required more often with short circuits than with open circuits (75% vs 54.3%).
Patient-reported trauma preceded 21.0% of open circuit events and 17.8% of short circuit events.
A single electrode was responsible for half the open circuits, but all short circuits involved multiple electrodes.
"To our knowledge, this study represents the first description of the characteristics and relevance of abnormal SNS electrical impedance," the researchers say. "Additional studies focused on interventions aimed at decreasing rates of electrode failure are warranted."
"Overall," they conclude, "SNS continues to be a safe, effective, and reliable treatment for refractory lower urinary tract dysfunction."
Dr. Rackley did not respond to a request for comments on this report.
SOURCE: http://bit.ly/XjUZx1J Urol 2013.