Responsive Vagus Nerve Stimulation for Drug Resistant Epilepsy: A Review of New Features and Practical Guidance for Advanced Practice Providers.

Vagus nerve stimulation (VNS) is a safe and effective therapy that has been available for over 20 years for adults and children with drug resistant epilepsy (DRE). Since U.S. Food and Drug Administration approval in 1997, VNS has been implanted in over 100,000 patients including over 30,000 children as an adjunctive therapy in reducing the frequency of seizures in patients 4 years of age and older with focal seizures that are refractory to antiseizure medications. VNS Therapy® has evolved over time and currently offers closed-loop, responsive stimulation as well as advanced features that streamline dosing and patient management. Advanced Practice Providers (APPs) such as nurse practitioners, physician assistants and clinical nurse specialists are integral in a comprehensive healthcare team, and dedicated VNS clinics have formed at comprehensive epilepsy centers across the world that are often managed by APPs. This approach improves access, education, and continuity of care for those with VNS or those considering VNS. Here we provide a review for APPs on the VNS Therapy® system focused on new features, dosing, and troubleshooting strategies with the goal to provide guidance to those managing VNS patients.

Baroreflex activation therapy for the treatment of heart failure with reduced ejection fraction in patients with and without coronary artery disease.

BACKGROUND: In a randomized trial, baroreflex activation therapy (BAT) improved exercise capacity, quality of life and NT-proBNP in patients with heart failure with reduced ejection fraction (HFrEF). In view of different mechanisms underlying HFrEF, we performed a post-hoc subgroup analysis of efficacy and safety of BAT in patients with and without coronary artery disease (CAD). METHODS AND RESULTS: Patients with left ventricular ejection fraction <35% and NYHA Class III were randomized 1:1 to guideline-directed medical and device therapy alone or plus BAT. Patients with a history of CAD, prior myocardial infarction or coronary artery bypass graft were assigned to the CAD group with all others assigned to the no-CAD group. Of 71 BAT treated patients, 52 had CAD and 19 had no CAD. In the control group, 49 of 69 patients had CAD and 20 had no CAD. The system- or procedure-related major adverse neurological or cardiovascular event rate was 3.8% in the CAD group vs. 0% in the no-CAD group (p = 1.0). In the whole cohort, NYHA Class, Minnesota Living with Heart Failure score, 6-minute hall walk distance and NTproBNP were improved in BAT treated patients compared with controls. Statistical analyses revealed no interaction between the presence of CAD and effect of BAT (all p > 0.05). CONCLUSION: No major differences were found in BAT efficacy or safety between patients with and without CAD, indicating that BAT improves exercise capacity, quality of life and NTproBNP in patients with ischemic and non-ischemic cardiomyopathy. CLINICALTRIALS. GOV IDENTIFIER: NCT01471860 and NCT01720160.

Non-clinical and Pre-clinical Testing to Demonstrate Safety of the Barostim Neo Electrode for Activation of Carotid Baroreceptors in Chronic Human Implants.

The Barostim neo™ electrode was developed by CVRx, Inc.to deliver baroreflex activation therapy (BAT)™ to treat hypertension and heart failure. The neo electrode concept was designed to deliver electrical stimulation to the baroreceptors within the carotid sinus bulb, while minimizing invasiveness of the implant procedure. This device is currently CE marked in Europe, and in a Pivotal (akin to Phase III) Trial in the United States. Here we present the in vitro and in vivo safety testing that was completed in order to obtain necessary regulatory approval prior to conducting human studies in Europe, as well as an FDA Investigational Device Exemption (IDE) to conduct a Pivotal Trial in the United States. Stimulated electrodes (10 mA, 500 µs, 100 Hz) were compared to unstimulated electrodes using optical microscopy and several electrochemical techniques over the course of 27 weeks. Electrode dissolution was evaluated by analyzing trace metal content of solutions in which electrodes were stimulated. Lastly, safety testing under Good Laboratory Practice guidelines was conducted in an ovine animal model over a 12 and 24 week time period, with results processed and evaluated by an independent histopathologist. Long-term stimulation testing indicated that the neo electrode with a sputtered iridium oxide coating can be stimulated at maximal levels for the lifetime of the implant without clinically significant dissolution of platinum or iridium, and without increasing the potential at the electrode interface to cause hydrolysis or significant tissue damage. Histological examination of tissue that was adjacent to the neo electrodes indicated no clinically significant signs of increased inflammation and no arterial stenosis as a result of 6 months of continuous stimulation. The work presented here involved rigorous characterization and evaluation testing of the neo electrode, which was used to support its safety for chronic implantation. The testing strategies discussed provide a starting point and proven framework for testing new neuromodulation electrode concepts to support regulatory approval for clinical studies.

Voltage biasing, cyclic voltammetry, & electrical impedance spectroscopy for neural interfaces.

Electrical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measure properties of the electrode-tissue interface without additional invasive procedures, and can be used to monitor electrode performance over the long term. EIS measures electrical impedance at multiple frequencies, and increases in impedance indicate increased glial scar formation around the device, while cyclic voltammetry measures the charge carrying capacity of the electrode, and indicates how charge is transferred at different voltage levels. As implanted electrodes age, EIS and CV data change, and electrode sites that previously recorded spiking neurons often exhibit significantly lower efficacy for neural recording. The application of a brief voltage pulse to implanted electrode arrays, known as rejuvenation, can bring back spiking activity on otherwise silent electrode sites for a period of time. Rejuvenation alters EIS and CV, and can be monitored by these complementary methods. Typically, EIS is measured daily as an indication of the tissue response at the electrode site. If spikes are absent in a channel that previously had spikes, then CV is used to determine the charge carrying capacity of the electrode site, and rejuvenation can be applied to improve the interface efficacy. CV and EIS are then repeated to check the changes at the electrode-tissue interface, and neural recordings are collected. The overall goal of rejuvenation is to extend the functional lifetime of implanted arrays.

Multimodal, longitudinal assessment of intracortical microstimulation.

The fundamental obstacle to neuroprostheses based on penetrating microstimulation is the tissue's response to the device insertion and to the application of the electrical stimulation. Our long-term goal is to develop multichannel microstimulation of central nervous tissue for clinical therapy. The overall objective of this research is to identify the optimal parameters for a chronically implanted microstimulation device. In particular, the work presented here focuses on the effects of repeated stimulation and the reactive tissue response on the efficacy of stimulation-driven behavior. To this end, psychophysical experiments were performed using multichannel cortical implants in the auditory cortex of rats. Further, we investigated the effect of the device-tissue interfacial quality on the psychophysical threshold. Here, we report the effects of cortical depth, days postimplant on the psychophysical threshold of auditory cortical microstimulation, along with correlated impedance spectral changes and post vivo histology. We expect that these data will further enable neuroprosthetic development.

In vivo polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) in rodent cerebral cortex.

Maintaining a reliable neural interface is a well-known challenge with implanted neural prostheses. Here we evaluate a method of forming an integrated neural interface through polymerization of PEDOT in vivo. Polymerization resulted in lower impedance and improved recording quality of local field potentials on implanted electrodes in the rat cerebral cortex. Histological analysis by optical microscopy confirmed successful integration of the PEDOT within tissue surrounding implanted electrodes. This technique offers a unique neural interfacing approach with potential to improve the long-term functionality of neural prostheses.

Evaluation of micro-electrocorticographic electrodes for electrostimulation.

Chronic neural recording and stimulation on the surface of the cortex with macroelectrodes has been shown to be promising for treating a wide range of neurological deficits. To enhance the specificity of these devices, dense arrangements of small area electrodes have been microfabricated for precise recording and control of neural populations. In this study micro-electrocorticographic (microECoG) electrodes were evaluated for electrostimulation. Surface modification with electrodeposited iridium oxide (EIrOx) resulted in lower impedance, higher charge carrying capacity, and lower, more linear voltage excursions during current controlled stimulation.

Poly(3,4-ethylenedioxythiophene) as a Micro-Neural Interface Material for Electrostimulation.

Chronic microstimulation-based devices are being investigated to treat conditions such as blindness, deafness, pain, paralysis, and epilepsy. Small-area electrodes are desired to achieve high selectivity. However, a major trade-off with electrode miniaturization is an increase in impedance and charge density requirements. Thus, the development of novel materials with lower interfacial impedance and enhanced charge storage capacity is essential for the development of micro-neural interface-based neuroprostheses. In this report, we study the use of conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) as a neural interface material for microstimulation of small-area iridium electrodes on silicon-substrate arrays. Characterized by electrochemical impedance spectroscopy, electrodeposition of PEDOT results in lower interfacial impedance at physiologically relevant frequencies, with the 1 kHz impedance magnitude being 23.3 +/- 0.7 kOmega, compared to 113.6 +/- 3.5 kOmega for iridium oxide (IrOx) on 177 mum(2) sites. Further, PEDOT exhibits enhanced charge storage capacity at 75.6 +/- 5.4 mC/cm(2) compared to 28.8 +/- 0.3 mC/cm(2) for IrOx, characterized by cyclic voltammetry (50 mV/s). These improvements at the electrode interface were corroborated by observation of the voltage excursions that result from constant current pulsing. The PEDOT coatings provide both a lower amplitude voltage and a more ohmic representation of the applied current compared to IrOx. During repetitive pulsing, PEDOT-coated electrodes show stable performance and little change in electrical properties, even at relatively high current densities which cause IrOx instability. These findings support the potential of PEDOT coatings as a micro-neural interface material for electrostimulation.