Introduction
- Vagal Nerve Stimulation (VNS) is a neuromodulatory therapy approved for the treatment of drug-resistant epilepsy (DRE), particularly in patients who are not candidates for resective surgery.
- Initially approved by the FDA in 1997 for adults, VNS was later approved for use in children ≥4 years of age with refractory focal epilepsy.
- Used adjunctively, VNS does not typically achieve seizure freedom but can significantly reduce seizure frequency and improve quality of life.
Anatomy and Physiology of the Vagus Nerve
- The vagus nerve (cranial nerve X) contains approximately 80% afferent fibers and 20% efferent fibers.
- Afferent fibers project to the nucleus tractus solitarius (NTS) in the medulla, which then communicates with various brain regions including the:
- Locus coeruleus (noradrenergic system)
- Dorsal raphe nucleus (serotonergic system) <liAmygdala, hypothalamus, thalamus, hippocampus
Mechanism of Action
- The precise mechanism remains incompletely understood.
- Proposed mechanisms include:
- Modulation of neurotransmitter release (norepinephrine, serotonin, GABA)
- Desynchronization of abnormal epileptic networks
- Activation of thalamocortical pathways with alteration in cortical excitability
- Neuroplasticity and long-term synaptic modulation
Indications for VNS in Paediatric Epilepsy
- Refractory focal epilepsy not amenable to resective surgery
- Generalized epilepsy syndromes (off-label), including Lennox-Gastaut syndrome (LGS), Dravet syndrome, Tuberous Sclerosis Complex
- Patients with:
- Multifocal epilepsy
- Epileptic encephalopathies
- Inconclusive localization studies
- Contraindications to surgery
VNS Implantation Procedure
- Performed under general anesthesia; involves implantation of:
- Pulse generator in the left chest wall
- Lead wires coiled around the left vagus nerve in the carotid sheath
Stimulation Parameters
- Initial stimulation: after wound healing, typically 2 weeks post-implantation
- Common parameters:
- Output current: 0.25–3.5 mA
- Pulse width: 250–500 μs
- Frequency: 20–30 Hz
- On time: 30 sec; Off time: 5 min
Clinical Efficacy
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