We have found that the risk of SUDEP in our population of people with drug-resistant epilepsy is very high, and for those that we are assessing for epilepsy surgery (the most refractory patients), the risk is more than 1per cent per year.
We have taken advantage of the close monitoring of patients with poorly controlled epilepsy who are undergoing assessment for epilepsy surgery on the video-EEG unit to detect potential risk factors for SUDEP. We are particularly interested in what happens to the electrical activity of the heart during seizures. We have found that during and after tonic-clonic seizures (convulsions), there are changes in the variability of the heart rate, and in the electrical activity of the heart that have been shown to predispose to sudden death in heart disease.
We could find no differences in the reaction of the heart to tonic-clonic seizures in those that later die from SUDEP and those that do not. Less severe seizures (complex partial and simple partial seizures) did not affect the heart to nearly the same degree, but we, nevertheless, still observed abnormal electrical activity of the heart in some milder seizures. Importantly, we found that having major seizures (tonic-clonic seizures) strongly correlated with the risk of SUDEP.
The messages from these studies are: 1) The reaction of the heart to tonic-clonic seizures is much greater than to less severe seizures. 2) The sort of “reaction” that we saw is known to increase the risk of death in other conditions such as heart disease. 3) The risk of SUDEP seems to relate to the frequency of all seizures, but especially tonic-clonic seizures. 4) There is nothing particularly different between those that die from SUDEP and those that do not other than the severity of the epilepsy.
We are now setting out to determine how tonic-clonic seizures are affecting the heart, and to identify those people who are at particularly high risk of SUDEP in order to determine ways of preventing these deaths.
Professor Matthew Walker
UCL Institute of Neurology
London WC1N 3BG