New research in the Journal of Physiology has found that certain changes in heart activity, even in the absence of seizures, could be a sign of epilepsy.BackgroundThe autonomic nervous system, which controls bodily functions that we are usually unaware of such as heart rate and breathing, is thought to play an important role in sudden unexpected death in epilepsy (SUDEP), and research efforts are currently exploring the mechanisms of this. Now, scientists at Case Western Reserve University in Ohio have found that, even in the absence of seizures, people with generalised epilepsy have differences in their heart activity compared to ‘normal’.MethodsIn their recent study, the researchers recruited 91 children and adolescents with generalised epilepsy and 25 healthy controls. They then monitored the heart activity of all participants during 30 minutes of light sleep, when their brain activity was normal or ‘interictal’ (between seizures). They were particularly interested in recording the subjects’ heart rates and heart rate variability (the variation in time between heart beats), which corresponds with ‘respiratory sinus arrhythmia’ (altered synchronisation between heart rate and breathing). The team also took blood pressure readings from each participant and added this information to their data set.ResultsFollowing analysis, the researchers found that people with epilepsy had more pronounced changes in synchrony between heart rate and breathing (i.e. respiratory sinus arrhythmia) than controls, but a lower average heart rate (even after accounting for differences in gender, age and height:weight ratio between the groups). This suggests that the branch of the autonomic nervous system called the parasympathetic (or ‘rest and digest’) nervous system was more active in these people. In contrast blood pressure, which is influenced more by the sympathetic (or ‘fight and flight’) branch of the autonomic nervous system, was not significantly different between the groups, suggesting that sympathetic activity was not affected.During the course of the study, the researchers encountered five additional subjects who had initially been assessed as neurologically normal, but who showed pronounced respiratory sinus arrhythmia and lower than average heart rate. These people later developed epilepsy. This is a remarkable finding, and it suggests that an increase in parasympathetic activity may precede the onset of epilepsy in some children.SignificanceThese findings indicate that autonomic activity is imbalanced in childhood generalised epilepsy, and that this imbalance may occur before epilepsy develops. This could have important implications in the future for the diagnosis of epilepsy and the identification of children who are at risk. The specific effects on heart rate and respiration that are highlighted also provide further evidence that this imbalance, if ‘pushed’ to a certain limit, may be a key factor in SUDEP.Note: In light of these results, the authors urge caution in the use of vagal nerve stimulation (VNS) in the treatment of epilepsy, as it increases parasympathetic activity. Although VNS can be effective in some people who are resistant to anti-epileptic drugs, in others it may cause an even slower heart rate and a more pronounced disruption of the synchrony between heart rate and breathing.The team is now seeking more funding in order to carry out their research in adults with epilepsy, and investigate possible new treatments that modulate parasympathetic activity.This study was funded by The Hartwell Foundation.Click here for more news articles.