Abstracts

Rationale: The field of neuromodulation evolved fastly over the last decade. More recently, a device capable of delivering cardiac-based closed-loop VNS has been available in the market. Two pivotal studies on both sides of the Atlantic showed that the device was able to deliver the expected stimulation paradigm. On the other hand, there is no adequate documentation that closed-loop VNS would be more efficacious than regular VNS in a clinical setting. We report on the interim mid-study analysis of a prospective cohort of patients serving as their own control.  Methods: Ten patients with Lennox-Gastaut syndrome (9 boys) were studied. All patients were implanted with an Aspire VNS generator. Basal seizure frequency was determined in a 3-month pre-implantation period. Patients were allowed to recover for one month and were titrated up to 2.5mA (30 sec 'on'; 5 min 'off', 500usec, 30Hz; autostim feature off) over an additional month. They were followed up every 2 months for six months, after which the Autostim cardiac-based feature was activated using the same parameters (and sensitivity=2; threshold 20%); . The patients were followed up every 2 months for 6 additional months. Results: Age ranged from 4 to 35 years (mean= 13.7 years). EEG showed slow generalized spike and wave discharges, secondary bilateral synchrony and multifocal activity in all patients. All patients had some degree of mental retardation. MRI showed atrophy in 7 patients, bilateral pachygyria in 2 and bilateral periventricular nodular heterotopia in one. Regular open-loop VNS yielded a mean of 58.2% of seizure frequency reduction (range 0-92%). Activation of the Autostim feature led to a mean of 37% of additional seizure frequency reduction (range 0-100%). Under closed-loop stimulation, 1 patient had his seizure frequency worsened and 3 were unaltered. One patient discontinued closed-loop VNS due to worsening of sleep apnea. There was a mean of 59.3% of Autostim activation. Responders got 67% activation of the Autostim feature, while non-responders got 54%. Conclusions: Additional seizure frequency reduction seemed to be related to the amount of additional stimulation cycles. This increased duty cycle also appeared to be related to additional side effects. Four out of 10 patients did not benefit from activation of the Autostim feature.  Funding: No funding