Vagal nerve stimulation technique: enhancing its efficacy and acceptability by augmentation with auto activation and deactivation mode of operation

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Abstract

The purpose of this article is to search for an additional modus operandi to improve the functioning of currently deployed vagal nerve stimulation (VNS) technique that is being used as an adjunctive therapy for intractable epilepsy, mainly complex partial seizures (partial onset with secondary generalization). The efficacy and success of current VNS technique is variable and limited, which can be attributed (to a considerable extent) to its present modi operandi. The mechanism of anti-epileptic action of VNS that has been hypothesized in the article is found to conform to observations and results in a large number of studies including those on VNS itself. Based on this mechanism in controlling seizures, the author proposes an additional mode of operation of the VNS device, (an auto activation and deactivation mode), designed to work on a feedback mechanism, which would deliver VNS as and when the brain requires it to abort/arrest the impending focal attack and/or its generalization, thus eliminating the limitations associated with the current VNS device. This mode should enhance its acceptability, efficacy and success.

Introduction

Vagus nerve stimulation (VNS) is emerging as a useful technique in managing seizure activity in patients with intractable epilepsy. The VNS device has been approved by the US Food and Drug Administration (FDA) as an adjunctive therapy to disrupt or prevent seizures in patients above 12 years of age with partial onset seizures with secondary generalization that are medically refractory. The efficacy and the safety of VNS treatment have been reported in several studies. Certain limited trials have demonstrated the efficacy and safety of this technique for younger patients as well. The exact mechanism by which VNS suppresses seizure activity remains to be elucidated. However, much progress regarding its functioning has been made through neurophysiological and neurochemical studies in animals and human patients fitted with VNS device.

The pulse generator of the VNS device is programmed usually to generate a stimulus every 5 min for 30-s duration throughout the day. However, the settings and the timings of the VNS device may have to be periodically adjusted to control the seizure activity in patients. In addition patients are given a hand-held magnet to activate the VNS device at the onset of an aura or focal attack in an effort to abort an impending seizure or its generalization. These modes of VNS operation however could allow a seizure and/or its generalization to escape from getting aborted every now and then.

In order to further increase the efficacy of VNS, an augmentation of the device that causes it to get activated and deactivated by the electrical activity generated in the brain itself at the onset and suppression of a seizure, respectively, is proposed here. The utility of this technique along with the relevant hypotheses of the VNS mechanism in controlling seizure activity in epileptic patients are also discussed.

Section snippets

Hypotheses for mechanism of VNS action

In order to understand the significance and rationale behind the proposal for augmentation of the VNS technique to be presented in this paper, it is important first to discuss some of the neuroanatomic and neurophysiologic concepts behind the mechanism of VNS action.

Limitations of present modes of VNS activation

At present there are two modes of activation of the VNS device available, one is the manual hand-held magnetic gadget and the other is a programmed activation of the VNS. However both have limitations based on the nature of seizures in the epileptic patients, which limit the efficacy of VNS. As in case of manual activation it is possible that the patient may fail to activate the VNS device in the event of experiencing an aura or at the onset of a focal attack due to impaired consciousness. Also

Proposed augmentation of VNS device

Based on the hypothesized mechanism of VNS action, I propose to augment the VNS device with auto activation and deactivation mode to further increase its efficacy and safety. The idea is to activate and deactivate the VNS device automatically by the electrical activity that develops in the brain itself at the onset and suppression of seizure activity, respectively.

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