Mini implantable vagus nerve stimulator hits it big in a study

A miniature externally powered implantable stimulator (MEPS) that is approximately 50 times smaller than conventional VNS devices shows significant potential for vagus nerve stimulation (VNS) based on findings from a compilation of three clinical trials.

“VNS is widely used to treat various neurological and psychiatric conditions, including epilepsy and treatment-resistant depression, as well as to enhance motor rehabilitation following stroke,” the investigators said. While conventional VNS devices have been reliable, emerging indications require intermittent stimulation only, they added.

In this study, the MEPS significantly reduced operative time, successfully delivered 481,995 stimulations during 2,205 hrs of therapy, and was associated with a low incidence of device-related adverse events (AEs). [Neurotherapeutics 2025;22:e00625]

Surgical outcomes, recovery

The mean operative duration was markedly shorter with the MEPS (38.1 min) than the conventional device used for VNS after stroke (75.5 min) and a similar VNS device used to treat epilepsy (94 min).

“The reduced operative time reflects the smaller size and direct placement on the nerve, demonstrating a reduction in surgical burden,” the researchers said. “This streamlined procedure may facilitate quicker patient turnover and reduced use of surgical resources.”

Postoperative pain was managed with over-the-counter NSAIDs or acetaminophen, and ice packs. There were no significant surgical site issues at the postop visit.

“Recovery after MEPS implantation was efficient, enabling most participants to begin therapy soon after their postop visit … [Their] rapid recovery enabled timely commencement of therapy, with no major delays attributable to the surgical procedure itself,” the researchers noted.

Safety

There were no significant perioperative complications during device implantation, save for one case of pneumothorax in a participant who began coughing during anaesthesia recovery.

There was a low incidence of surgery-related AEs, and those deemed possibly surgery-related were unremarkable. Incision-site pain was the most common AE (12 percent). All pain-related AEs resolved before study completion. Standard MRI was also safely performed without the need for device removal.

“While we cannot rule out that the lower AE occurrence was due to the reduced sample size, it is plausible that the reduced surgical time and complexity and small device size gave rise to the improved AE rate,” the researchers noted.

Voice alteration – a known consequence of conventional VNS device implantation – was not an issue with the MEPS. Furthermore, there were no reports of oedema, fluid at implant, bruising, or tremor, which are symptoms tied to conventional devices.

Expands therapeutic applications

The study used data from 49 participants across three MEPS feasibility studies and evaluated three indications: upper limb motor recovery after stroke, spinal cord injury (SCI), and treatment-resistant post-traumatic stress disorder (TRPTSD).

“[W]e have successfully implanted VNS devices in individuals with TRPTSD and cervical SCI, expanding the potential therapeutic applications of VNS beyond its traditional use,” said the researchers. “[Our findings] are particularly encouraging for individuals with SCI or PTSD, where existing treatment options remain limited, and further support the need for continued investigation into the broader clinical applications of VNS.”

“The successful implementation of the MEPS highlights the potential for further advancements in neuromodulation technology,” the investigators said. They called for further research to evaluate the device’s long-term efficacy, safety, and performance in larger and more diverse cohorts.