Vagus nerve stimulation and heart rate – the influence of vagus nerve stimulation output current on heart rate

Aims: Vagus nerve stimulation (VNS) meanwhile is an accepted therapy in patients with refractory epilepsy. Side effects are rare, and bradycardia during lead test at implantation is only reported in adults.

The aim of the study was to correlate heart rate changes to the VNS output current during stimulation period in comparison to the off-time interval in epilepsy patients during chronic VNS-Therapy.

Methods: The study group consisted of 12 children after VNS device implantation. The main group was subdivided into 3 groups containing of 4 patients each. (Group 1: 1 mA output current; Group 2: 1.75 mA output current; Group 3: 2.5 mA output current). heart rate was documented during EEG recording 30s before and 30s during VNS stimulation. Each recording was repeated 3 times and mean values were calculated. The difference of heart rates during VNS on- and off-time was calculated.

Results: Group 1 and 2 showed a decrease of heart rate during VNS of 2.2%, resp. 1.3%. Surprisingly an increase of heart rate (+4.3%) during VNS was found in group 3.

Conclusion: This study among pediatric epilepsy patients showed an acceleration of the heart rate during VNS with high output current (2.5mA), whereas at low current (1 mA and 1.75 mA) the heart rate decreases. This effect is not expected for regular negative chronotrop vagal nerve stimulation. The increase of heart rate might be induced by an inconscious, vegetative pain reaction due to a non verbalized pain reaction during stimulation period.