Cardiac vagal tests and vagus nerve stimulation in epilepsy

Vagus nerve stimulation (VNS) is currently widely used for the treatment of intractable epilepsy. The device is implanted to stimulate the left vagal nerve, since stimulation on this side is less likely to cause cardiac effects. Severe adverse reactions associated with VNS appear to be rare [11]. Aspiration [2], worsened sleep apnea syndrome [7], psychotic reaction with a forced normalization [5] and cardiac standstill [12] have been reported. The mortality and sudden unexplained death in the cohort of patients under VNS are similar to those suffering from severe epilepsy [1]. Clinical relevant cardiac effects were not observed throughout the study of RR variability in patients treated with VNS [4]. However, some authors suggest that VNS has complex effects on instantaneous heart rate and heart variability and point to the need for more comprehensive studies [3]. In this paper, the direct and the long-term effect of the VNS on cardiac function were studied by using cardiac parasympathetic tests.