Abstracts

RATIONALE: Left vagus nerve stimulation (VNS) has been used over the last years in the treatment of refractory epilepsy. The physiological mechanism involved in the antiepileptic effect is still unknown, as are the causes for the lack of response in many patients. Presumably, an increased parasympathetic tone should be involved in the VNS mediated antiepileptic effect. This paper reports on the autonomic effects findings of VNS in men.
METHODS: Three adult epileptic patients submitted to VNS were studied. Patient 1 had bilateral perisylvian polimicrogyria and daily complex partial seizures. EEG showed interictal bilateral independent centro-temporal spikes and non-localizing seizure-onset. He was submitted to VNS as primary treatment and got 90% of seizure[scquote]s frequency reduction. Patient 2 had multiform secondary generalized seizures (Lennox-like syndrome) and has been previously submitted to maximized callosal section. A 40% reduction in seizure[scquote]s frequency was noted after surgery. After VNS, she got additional 85% of generalized seizure[scquote]s reduction. Patient 3 had refractory versive seizures and had been previously submitted to left frontal lobe resection. An 85% reduction of seizure[scquote]s frequency was noted after surgery. VNS showed no antiepileptic effect in this patient. All patients were stimulated with 2mA, 100 Hz and 0,5 ms pulses for 30 seconds, every 5 minutes. All patients were submitted to 24-hours continuous EKG monitoring (Holter) and tilt table test (TTT) with the stimulator turned on or off. The heart rate variability (HRV) was studied during the Holter using SDNN (standard-deviation of RR interval) and pNN[gt]50 (percent of RR intervals [gt]50 ms) indexes. HRV was studied during the TTT by power spectral analysis obtained over the last 5 minutes of a 20 minutes resting baseline and over the first 5 minutes after passive postural stress.
RESULTS: Patients 1 and 2 disclosed an increased parasympathetic tone after VNS. Patient 3 showed no autonomic response to VNS. Stimulator off SDNN values (ms) were 63, 88 and 144 for patients 1, 2 and 3, respectively. SDNN values were 89, 97 and 114 for patients 1,2 and 3, respectively, after the stimulator was turned on; pNN[gt]50 values (%) were 1.03, 0.56 and 6.34 with the stimulator turned off and 11.29, 0.59 and 4.10 with the device turned on, for patients 1,2 and 3, respectively. The sympathetic/parasympathetic ratio (S/P) calculated with the stimulator off during TTT was 0.98, 1.33 and 1.38 in the resting state, and 1.96, 1.48 and 1.59 after table inclination, for patients 1, 2 and 3, respectively. After the stimulator was turned on, S/P was 1.59, 1.72 and 3.74 during the resting state and 0.85, 0.70 and 3.21 after table inclination, for patients 1, 2 and 3, respectively.
CONCLUSIONS: Discussion: Despite including a small sample, this report suggests that VNS was effective only in patients in whom an actual increase in parasympathetic tone could be documented during Holter and TTT studies. The evaluation of autonomic changes in cardiovascular system induced (or not) by VNS might be an indicator of outcome in relation to seizures in these patients.
[Supported by: Sao Paulo Secretary of Health]