Abstracts

Rationale: Vagus nerve stimulation (VNS) is a non-pharmacologic antiepileptic therapy for patients with refractory epilepsy who are not candidates for resective surgery or who have had resective surgery with unsatisfactory results. Although some studies have shown that VNS treatment is safe, well tolerated, and effective in seizure reduction, there are only a few reports concerning an effect of VNS on heart rate or heart rate variability (HRV). Our aim was to investigate the effects of VNS on interictal heart rate variability (HRV) in patients with refractory epilepsy before, after 6, and 12 month implantation of VNS. Methods: Twenty patients (mean age 11.74.2) with refractory epilepsy were evaluated in terms of interictal heart rate variability with 24 hour ECG recordings before, after 6 and 12 months of VNS treatment for each patient. Therefore, we analyzed heart rate, NN intervals, frequency-dependent parameters including total power, low-frequency (LF), high-frequency (HF); time- dependent parameters including SDNN, SDNN index, SDANN, RMMSD, and PNN50; and Triangular index. While RMMSD and PNN50 were used to evaluate parasympathetic effects; LF, HF and LF/HF ratios were investigated to sympathetic effects. Night and daytime HRV were separately investigated for diurnal rhythm. The results were compared to control groups applied recorded 24 hours ECG recording due to different reasons. The patients were also evaluated demographics, clinical and electrographical finding. Statistical analysis was done by paired and independent student T Test. The p < 0.05 was considered statistically significant. Results: We found that increased minimum and maximum HR before the treatment compared to control group (p < 0.05). Heart rate variability was reduced in two times in both 6 and 12 month compared to control group (p < 0.05). Therefore, the nocturnal increase in HRV usually seen in the normal population was absent in patients with refractory epilepsy (p < 0.05). The patients had also narrow NN intervals, suppression in all frequency and time-dependent parameters compared to control groups (p < 0.05). Those differences were also seen between pre and post VNS implantation in both 6 and 12-month treatment (p< 0.05). There was a sympathetic dominancy in LF/HF ratio due to an increment LH levels during daytime period (p < 0.05). Interestingly, in some parameters including daytime LH/HF ratio and total power were seen to get close to their basal rhythm (before the VNS implantation) again. However, those parameters were significantly different from the control groups in 12 month (p< 0.05). There was also significant seizure reduction (almost 50%) after treatment (p < 0.05). No rhythmical or structural defects were seen for all patients. Conclusions: Increased levels of minimum and mean heart rate, narrow NN intervals, suppressed all the frequency and time dependent parameters, and increased LF/HF levels indicated to sympathetic system dominancy during daytime before the treatment. There was a significant improvement all the parameters which were seen as decreased sympathetic tonus due to increased parasympathetic effect after VNS therapy. Even if substantial improvement in those parameters, still diminished levels in patients with 6 or 12-month-VNS treatment compared to healthy group. Interestingly, maximum improvement was seen in the 6 month and then no further improvement was observed. It was suggested that impaired cardiovascular autonomic regulation is associated with the epileptic process itself rather than with recurrent seizures. Funding: We do not have any fundings for this abstract