Seizure improvement following vagus nerve stimulator (VNS) battery change with cardiac-based seizure detection automatic stimulation (AutoStim): early experience in a regional paediatric unit

Vagus Nerve Stimulation Therapy in Epilepsy: An Overview of Technical and Surgical Method, Patient Selection, and Treatment Outcomes

Epilepsy affects over 65 million people worldwide. One-third of people with epilepsy do not respond to medication and may benefit from surgery. Vagus nerve stimulation (VNS) is the first neuromodulation therapy for the treatment of drug-resistant epilepsy. This method is used in combination with anti-seizure medications in adults and in the pediatric population. VNS has also been demonstrated to have benefits for some epilepsy comorbidities, such as depression, and can be used in combination with other neuromodulation therapies in epilepsy. The authors present an overview of VNS physiology, patient selection, surgery and risks, neuromodulation therapy, and application to epilepsy comorbidities.

Replacement of traditional vagus nerve stimulation with cardiac-based device and seizure reduction: A systematic review and meta-analysis

INTRODUCTION

For patients with drug-resistant epilepsy (DRE) who are not suitable for surgical resection, neuromodulation with vagus nerve stimulation (VNS) is an established approach. However, there is limited evidence of seizure reduction when replacing traditional VNS (tVNS) device with a cardiac-based one (cbVNS). This meta-analysis compares the seizure reduction achieved by replacing tVNS with cbVNS in a population with DRE.

METHODS

We systematically searched PubMed, Embase, and Cochrane Central following PRISMA guidelines. The main outcomes were number of patients experiencing a ≥ 50 % and ≥80 % reduction in seizures, as defined by the McHugh scale. Additionally, we assessed the number of patients achieving freedom from seizures.

RESULTS

We included 178 patients with DRE from 7 studies who were initially treated with tVNS and subsequently had it replaced by cbVNS. The follow-up for cbVNS ranged from 6 to 37.5 months. There was a statistically significant reduction in seizure frequency with the replacement of tVNS by cbVNS, using a ≥ 50 % (OR 1.79; 95 % CI 1.07 to 2.97; I²=0 %; p = 0.03) and a ≥ 80 % (OR 2.06; 95 % CI 1.17 to 3.62; I²=0 %; p = 0.01) reduction threshold. Nineteen (13 %) participants achieved freedom from seizures after switching to cbVNS. There was no difference in the rate of freedom from seizures between groups (OR 1.85; 95 % CI 0.81 to 4.21; I²=0 %; p = 0.14).

CONCLUSION

In patients with DRE undergoing battery replacement, cbVNS might be associated with seizure reduction (≥50 % and ≥80 % threshold) after switching from tVNS. Randomised controlled trials are necessary to validate these findings.

Neuromodulation in Children with Drug-Resistant Epilepsy

The introduction of neuromodulation was a revolutionary advancement in the antiseizure armamentarium for refractory epilepsy. The basic principle of neuromodulation is to deliver an electrical stimulation to the desired neuronal site to modify the neuronal functions not only at the site of delivery but also at distant sites by complex neuronal processes like disrupting the neuronal circuitry and amplifying the functions of marginally functional neurons. The modality is considered open-loop when electrical stimulation is provided at a set time interval or closed-loop when delivered in response to an incipient seizure. Neuromodulation in individuals older than 18 years with epilepsy has proven efficacious and safe. The use of neuromodulation is extended off-label to pediatric patients with epilepsy and the results are promising. Vagus nerve stimulation (VNS), responsive neurostimulation (RNS), and deep brain stimulation (DBS) are Food and Drug Administration-approved therapeutic techniques. The VNS provides retrograde signaling to the central nervous system, whereas DBS and RNS are more target specific in the central nervous system. While DBS is open-loop and approved for stimulation of the anterior nucleus of the thalamus, the RNS is closed-loop and can stimulate any cortical or subcortical structure. We will review different modalities and their clinical efficacy in individuals with epilepsy, with a focus on pediatric patients.

Neuromodulation in drug-resistant epilepsy: A review of current knowledge

Nearly 1% of the global population suffers from epilepsy. Drug-resistant epilepsy (DRE) affects one-third of epileptic patients who are unable to treat their condition with existing drugs. For the treatment of DRE, neuromodulation offers a lot of potential. The background, mechanism, indication, application, efficacy, and safety of each technique are briefly described in this narrative review, with an emphasis on three approved neuromodulation therapies: vagus nerve stimulation (VNS), deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS), and closed-loop responsive neurostimulation (RNS). Neuromodulatory approaches involving direct or induced electrical currents have been developed to lessen seizure frequency and duration in patients with DRE since the notion of electrical stimulation as a therapy for neurologic diseases originated in the early nineteenth century. Although few people have attained total seizure independence for more than 12 months using these treatments, more than half have benefitted from a 50% drop in seizure frequency over time. Although promising outcomes in adults and children with DRE have been achieved, challenges such as heterogeneity among epilepsy types and etiologies, optimization of stimulation parameters, a lack of biomarkers to predict response to neuromodulation therapies, high-level evidence to aid decision-making, and direct comparisons between neuromodulatory approaches remain. To solve these existing gaps, authorize new kinds of neuromodulation, and develop personalized closed-loop treatments, further research is needed. Finally, both invasive and non-invasive neuromodulation seems to be safe. Implantation-related adverse events for invasive stimulation primarily include infection and pain at the implant site. Intracranial hemorrhage is a frequent adverse event for DBS and RNS. Other stimulation-specific side-effects are mild with non-invasive stimulation.

Evaluating vagus nerve stimulation treatment with heart rate monitoring in pediatric patients with intractable epilepsy

PURPOSE

Vagus nerve stimulators (VNS) have emerged as an effective treatment modality for pediatric patients suffering from intractable, drug-resistant epilepsy. Newer devices, AspireSR™ Model 106 and the SenTiva™ Model 1000 (VNS TherapyⓇ, LivaNova™), contain an "auto-stimulation" feature that detects ictal tachycardia and transmits pulsations to attenuate seizures. However, the exact benefits of auto-stimulation compared to its risks still merit further exploration. This study evaluates the utility of these specific devices in a heterogeneous population of pediatric and young adult patients with intractable epilepsy.

METHODS

This is a retrospective chart review of 55 patients who underwent either VNS insertion with or without an auto-stimulation-enabled VNS device at a single level four epilepsy center. Seizure frequency, seizure subtype, side effects, and change in anti-seizure medication load both before and after VNS implantations were collected from patient self-reporting at the time of VNS insertion and 12 months following implantation. Information regarding output current, auto-stimulation current, duty cycling, and auto-stimulation threshold of the device was obtained from documented VNS interrogation for patients with auto-stimulation-enabled VNS devices.

RESULTS

Patients with auto-stimulation-enabled VNS devices had a mean 56.0% (SD = 0.414) seizure frequency reduction 12 months post-VNS insertion, while patients without auto-stimulation-enabled VNS devices had a mean 41.6% (SD = 0.456) seizure frequency reduction during the same interval. The mean seizure frequency reduction 12 months post-VNS insertion for patients with a SenTiva™ 1000 model was 66.0% (SD = 0.426). For patients with auto-stimulation-enabled VNS devices, post-treatment seizure reduction was significantly correlated with daily auto-stimulation activation (R = 0.432, p = 0.025).

CONCLUSION

This study supports the clinical safety and utility of auto-stimulation-enabled VNS models, specifically the SenTiva™ 1000, in treating pediatric patients with intractable epilepsy of various subtypes and etiologies. Further research is needed to evaluate the sustained impact of auto-stimulation on long-term outcomes (≥ 2 years follow-up post-VNS).

Evolution of the Vagus Nerve Stimulation (VNS) Therapy System Technology for Drug-Resistant Epilepsy

The vagus nerve stimulation (VNS) Therapy® System is the first FDA-approved medical device therapy for the treatment of drug-resistant epilepsy. Over the past two decades, the technology has evolved through multiple iterations resulting in software-related updates and implantable lead and generator hardware improvements. Healthcare providers today commonly encounter a range of single- and dual-pin generators (models 100, 101, 102, 102R, 103, 104, 105, 106, 1000) and related programming systems (models 250, 3000), all of which have their own subtle, but practical differences. It can therefore be a daunting task to go through the manuals of these implant models for comparison, some of which are not readily available. In this review, we highlight the technological evolution of the VNS Therapy System with respect to device approval milestones and provide a comparison of conventional open-loop vs. the latest closed-loop generator models. Battery longevity projections and an in-depth examination of stimulation mode interactions are also presented to further differentiate amongst generator models.

Vagus nerve stimulation therapy in people with drug-resistant epilepsy (CORE-VNS): rationale and design of a real-world post-market comprehensive outcomes registry

Introduction

The Vagus Nerve Stimulation Therapy System (VNS Therapy) is an adjunctive neuromodulatory therapy that can be efficacious in reducing the frequency and severity of seizures in people with drug-resistant epilepsy (DRE). CORE-VNS aims to examine the long-term safety and clinical outcomes of VNS in people with DRE.

Methods and analysis

The CORE-VNS study is an international, multicentre, prospective, observational, all-comers, post-market registry. People with DRE receiving VNS Therapy for the first time as well as people being reimplanted with VNS Therapy are eligible. Participants have a baseline visit (prior to device implant). They will be followed for a minimum of 36 months and a maximum of 60 months after implant. Analysis endpoints include seizure frequency (average number of events per month), seizure severity (individual-rated categorical outcome including very mild, mild, moderate, severe or very severe) as well as non-seizure outcomes such as adverse events, use of antiseizure medications, use of other non-pharmacological therapies, quality of life, validated measures of quality of sleep (Pittsburgh Sleep Quality Index or Children’s Sleep Habit Questionnaire) and healthcare resource utilisation. While the CORE-VNS registry was not expressly designed to test hypotheses, subgroup analyses and exploratory analysis that require hypothesis testing will be conducted across propensity score matched treatment groups, where possible based on sampling.

Ethics and dissemination

The CORE-VNS registry has already enrolled 823 participants from 61 centres across 15 countries. Once complete, CORE-VNS will represent one of the largest real-world clinical data sets to allow a more comprehensive understanding of the management of DRE with adjunctive VNS. Manuscripts derived from this database will shed important new light on the characteristics of people receiving VNS Therapy; the practical use of VNS across different countries, and factors influencing long-term response.

Trail registration number

NCT03529045.

Comparison of traditional and closed loop vagus nerve stimulation for treatment of pediatric drug-resistant epilepsy: A propensity-matched retrospective cohort study

OBJECTIVE

For epilepsy patients with drug-resistant, unresectable epilepsy, vagus nerve stimulation (VNS) is an option for seizure control. Approximately 40-70% of patients will achieve ≥50% seizure reduction with VNS. New closed loop VNS models detect ictal tachycardia and responsively stimulate the vagus nerve. The effectiveness of closed loop VNS compared to traditional VNS for pediatric epilepsy is unknown.

METHODS

An 11-year retrospective electronic medical record review at Children's Hospital of Pittsburgh was performed. Patients with drug-resistant epilepsy who underwent VNS implantation were included. Patients were divided into groups based on VNS model: traditional versus closed loop. Those who transitioned from traditional to closed loop VNS were excluded. Given potential for selection bias, propensity scores matching was utilized to compare traditional to closed loop VNS patients. Patients with focal versus generalized epilepsy were also separately analyzed. The primary outcome was "VNS response", defined as at least 50% seizure frequency reduction from baseline.

RESULTS

A total of 320 patients were included in this sample. The percentage of matched patients (total n = 220: n = 179 traditional VNS, n = 41 closed loop VNS) who responded to VNS after one year of therapy was 43% for traditional VNS and 39% for closed loop VNS (p = 0.64). After two years of therapy, a higher proportion of closed loop VNS patients than traditional VNS patients responded to VNS among all subgroups, though no differences were statistically significant (p>0.05). Notably, for those with generalized epilepsy, 73% of closed loop patients responded to VNS compared to only 46% of traditional patients (p = 0.10). After two years of VNS therapy, patients were taking approximately the same quantity of antiseizure medications as baseline (change of +0.074 +/- 0.90 ) with no difference between VNS models (p = 0.87).

SIGNIFICANCE

Among pediatric patients with drug-resistant epilepsy, closed loop VNS trends towards a higher rate of VNS response after two years of treatment, especially among generalized epilepsy patients. Neither model of VNS allows patients to reduce antiseizure medication quantity after two years.

Neuromodulation for Refractory Epilepsy

Three neuromodulation therapies, all using implanted device and electrodes, have been approved to treat adults with drug-resistant focal epilepsy, namely, the vagus nerve stimulation in 1995, deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS) in 2018 (2010 in Europe), and responsive neurostimulation (RNS) in 2014. Indications for VNS have more recently extended to children down to age of 4. Limited or anecdotal data are available in other epilepsy syndromes and refractory/super-refractory status epilepticus. Overall, neuromodulation therapies are palliative, with only a minority of patients achieving long-term seizure freedom, justifying favoring such treatments in patients who are not good candidates for curative epilepsy surgery. About half of patients implanted with VNS, ANT-DBS, and RNS have 50% or greater reduction in seizures, with long-term data suggesting increased efficacy over time. Besides their impact on seizure frequency, neuromodulation therapies are associated with various benefits and drawbacks in comparison to antiseizure drugs. Yet, we lack high-level evidence to best position each neuromodulation therapy in the treatment pathways of persons with difficult-to-treat epilepsy.

Neuromodulation in Intractable Epilepsy Through Responsive Vagal Nerve Stimulation: A Three-Year Retrospective Study at the University of Texas Medical Branch, Galveston

Background: Vagus nerve stimulation (VNS) functions through neuromodulatory mechanisms to provide quality of life improvements to those with drug-resistant epilepsy. Responsive VNS (rVNS) generators are designed to further reduce seizure burden by detecting ictal tachycardia and aborting seizures soon after their onset. 

Methods: Electronic medical records were accessed from January 2015 to December 2018 to identify patients with epilepsy managed with rVNS generators. Data were collected on seizure burden before and after rVNS implantation. Seizure burden was compared using t-tests, and monthly seizure reductions were gauged with the McHugh scale. Twenty-seven individuals met inclusion criteria; 10 were eliminated due to prior VNS implantation or undocumented seizure frequencies.

Results: The average seizure burden prior to rVNS implantation was 24.78 seizures/month. Following generator placement, the mean seizure frequencies at three months, six months, 12 months, and 18 months were 6.81, 16.57, 5.65, and 5.78 seizures/month, respectively. However, despite documented reductions in the average monthly seizure frequency, we found no statistically significant differences in seizure frequency relative to baseline.

Conclusion: While many participants showed individual reductions in seizure burden, this study was unable to definitively conclude that rVNS therapy leads to statistically significant reduction in seizure burden.

Neuromodulation in epilepsy: state-of-the-art approved therapies

Three neuromodulation therapies have been appropriately tested and approved in refractory focal epilepsies: vagus nerve stimulation (VNS), deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS), and closed-loop responsive neurostimulation of the epileptogenic zone or zones. These therapies are primarily palliative. Only a few individuals have achieved complete freedom from seizures for more than 12 months with these therapies, whereas more than half have benefited from long-term reduction in seizure frequency of more than 50%. Implantation-related adverse events primarily include infection and pain at the implant site. Intracranial haemorrhage is a frequent adverse event for ANT-DBS and responsive neurostimulation. Other stimulation-specific side-effects are observed with VNS and ANT-DBS. Biomarkers to predict response to neuromodulation therapies are not available, and high-level evidence to aid decision making about when and for whom these therapies should be preferred over other antiepileptic treatments is scant. Future studies are thus needed to address these shortfalls in knowledge, approve other forms of neuromodulation, and develop personalised closed-loop therapies with embedded machine learning. Until then, neuromodulation could be considered for individuals with intractable seizures, ideally after the possibility of curative surgical treatment has been carefully assessed and ruled out or judged less appropriate.

Advances in Epilepsy Surgery

BACKGROUND

A large number of patients have epilepsy that is intractable and adversely affects a child's lifelong experience with addition societal burden that is disabling and expensive. The last two decades have seen a major explosion of new antiseizure medication options. Despite these advances, children with epilepsy continue to have intractable seizures. An option that has been long available but little used is epilepsy surgery to control intractable epilepsy.

METHODS

This article is a review of the literature as well as published opinions.

RESULTS

Epilepsy surgery in pediatrics is an underused modality to effectively treat children with epilepsy. Adverse effects of medication should be weighed against risks of surgery as well as risks of nonefficacy.

CONCLUSIONS

We discuss an approach to selecting the appropriate pediatric patient for consideration, a detailed evaluation including necessary evaluation, and the creation of an algorithm to approach patients with both generalized and focal epilepsy. We then discuss surgical options available including outcome data. New modalities are also addressed including high-frequency ultrasound and co-registration techniques including magnetic resonance imaging-guided laser therapy.