Closed-loop vagus nerve stimulation. Patient-tailored therapy or undirected treatment?

Abstract

Background: In multi-drug-resistant epilepsy vagus nerve stimulation (VNS) is an efficacious additional treatment to reduce seizure frequency and severity. A recently developed cardiac-based seizure detection (CBSD) algorithm triggers automate stimulation (AutoStim) upon heart rate increases of at least 20%. Yet, long term sensitivity and specificity of the CBSD-algorithm remain unclear. We present a case series of 15 adult patients with epilepsy with AutoStim VNS therapy.

Methods: We reviewed CBSD-settings, operating hours and battery status of the devices. Percentage of AutoStim was assessed in comparison to continuous but intermittent stimulation. If seizure diaries were available, we verified whether a high rate of AutoStim was present during the documented seizures.

Results: We reviewed 15 patients with a mean age of 34 years (±11y). Mean duration since implantation was 47 months (±12 m). Of 1296 (±686) continuous intermittent stimulations per week, 4.8 (±3.9)% were AutoStim. Proportion of AutoStim varied substantially. While 9 patients had a mean of 1.5% (±1.4%), 6 patients had a significantly higher proportion of AutoStim 9.0% (±1.6%). Seizure-frequency was higher in patients with higher AutoStim frequency. Adverse events occurred in none of the patients.

Conclusion: We provide long-term results for sensitivity and specificity of the CBSD algorithm. While sensitivity seems to be high, we presume specificity to be poor. An extremely high number of AutoStim is supposedly false-positive. Yet, treatment was well tolerated by the patients without any adverse events, despite the high number of AutoStim. CBSD is a promising development, yet the algorithm should be revised to provide a better specificity.