Hödl S, Olbert E, Mahringer C, et al. - Since 1997, vagus nerve stimulation (VNS) has been a well-known and efficacious treatment for patients with drug-resistant epilepsy (DRE), but research continues on predicting therapeutic response prior to implantation, so experts explored whether pre-ictal heart rate variability (HRV), an event-related parameter, is correlated with response to VNS therapy. They assessed 104 seizures from 22 patients. A significant decrease in pre-ictal HRV (time-domain/non-linear variables) characterized VNS non-responders, indicating a sudden autonomic imbalance possibly caused by an impaired central autonomic function that makes it impossible to respond to VNS at the same time. No changes in HRV parameters were found in VNS responders