Abstracts

Rationale: Neuromodulation devices such as Vagus Nerve Stimulation Therapy (VNS Therapy®) play an expanding foundational role in treating patients with drug-resistant epilepsy. In addition to device labeling and diagnostics, tracking device reliability assists in understanding when to increase patient follow-up for impending end of service for generator batteries or wearing of the lead. As such, device reliability and longevity of both the implantable pulse generator and lead components are important to patients, physicians and payors. Methods: In order to track device reliability and longevity, all device-related complaints from US patients implanted with VNS Therapy for epilepsy with a known social security number are assessed. This subset of US patients provides the most complete dataset of nearly 100,000 initial and replacement registered devices. All device-related complaints are investigated as potential failures and all returned explanted products are analyzed for specific component failures. Survival curves for device performance are calculated for both generators and leads using the actuarial method beginning on the date of implant and ending on the first occurrence of normal battery depletion, a device failure, or a censored event (e.g. device explant or the last follow-up date of April 30, 2014). For generators, battery longevity curves are assessed using last known programmed settings in groups of "Low", "Medium" and "High" that represent typical device settings while incorporating the known under-reporting rate based on long-term follow-up. Results: In the US, VNS Therapy implantables have accumulated 440,000 patient years of experience. Over sixteen years of follow-up data are available on the earliest lead Model 300, with a cumulative survival of 87.7% at 10 years (Figure 1). Design improvements of currently distributed models have reduced the annual failure rate by 55% (PerreniaFLEX^® 304) to 63% (PerreniaDURA^® 303). The primary determinant of longevity for generators is the programmed settings, and device failures are a relatively rare occurrence given by a reliability rating of 99.6% at 5 years post-implant for Pulse^TM Model 102/102R generators (Figure 2). The expected longevity curves vary by generator model as device improvements have led to smaller batteries (Demipulse^® 103/104) and improved longevity (AspireHC^® 105). Conclusions: This analysis demonstrates the reliability of implantable leads and generators for VNS Therapy. Differences by device model highlight design improvements made over time based on feedback from patients and physicians along with improvements in technology. The high reliability, with improvements in subsequent generations of the devices, minimizes the loss of therapy or the need for additional surgical procedures. The reliability data and battery longevity analyses summarize the expected performance of VNS Therapy using post-market experience and may assist physicians in the treatment of their patients with drug-resistant epilepsy by informing decisions regarding frequency of follow-up evaluations.