Current understanding of seizure alarms
[Part 2: Questions; Hjalgrim H]
Unfortunately, we don’t know the exact mechanism behind SUDEP; most likely several interacting factors have to be activated at the same time, in order to lead to SUDEP.
Because of the uncertainty of the exact causes, it is difficult to decide what to measure. Should we measure alterations in heart rhythm, provided it changes before and during a seizure? Or, should we measure respiration? Some studies have shown affected breathing in relation to seizures. Not all persons with epilepsy show the same physiological reactions and, unfortunately, even appropriately administered resuscitation efforts are sometimes in vain.
Ongoing research in seizure detection devices focuses highly on the quality and reliability of the devices. On one hand they have to have a high sensitivity; they have to react immediately to as many seizures or physiological alterations, such as heart rate or respiration, as possible. On the other hand they also need to have a very high specificity; they must only react to alterations related to epileptic seizures. Today no device has a100% sensitivity, which means that not all seizures are detected, and no device has a 100% specificity, which means that not only seizures are detected; the alarm also reacts to non-epileptic occurrences. Both of these issues give rise to worry in patients, caregivers and relatives.
The devices being developed and validated today can be split into two groups; devices for use in hospital settings and devices for use in patients’ homes. For use outside hospital settings the devices have to be evaluated for user-friendliness, ease of operation, comfort, and appearance. In hospital settings these features are not the most important factors to consider.
For hospital settings, ongoing intracranial and extracranial EEG monitoring is possible with high sensitivity and specificity, but this is not applicable to everyday life outside of hospitals. Research in seizure alarms, be they for warning before, during or after seizures, focuses on the possible relevant features affecting risk of SUDEP.
Central nervous system:
Recognizing epileptic activity
Challenge: wearable EEG devices aren’t relevant for long term monitoring. Currently an implantable device is under development; it is supposed to register epileptic activity and to give a deep brain electric stimulation when needed thus preventing continuation of the seizure.
Monitoring apnea in relation to seizures
Challenge: high rate of false alarms and poor sensitivity.
Monitoring desaturation caused by apnea
Challenge: desaturation is delayed in relation to seizure onset. A device is under development.
Monitoring heart rhythm. If a person with epilepsy is known to have cardiac arrest or severe abnormal rhythm/frequency during or after seizures a permanent cardiac pacemaker or an implantable defibrillator would be advisable. This device operates on its own and doesn’t collect data.
Recognizing motor activity in relation to seizures. So far several attempts have been made to develop devices to detect abnormal movements. Most of the devices have an unsatisfactory sensitivity and specificity, giving rise to more anxiety than security. The devices have been developed to be used either in the bed, where only seizures occurring in bed can be detected, or to be worn by the person. The devices worn on the body focus on movements or muscle tone. They are not yet fully tested but they are showing promising results. Devices monitoring acceleration seem to have a relevant sensitivity and specificity, but they only are efficient for seizures with clonic movements of the limbs.
Ultimately, the best protection against SUDEP that we have today is early recognition of seizures and intervention, even though this is not always enough. Management of the epilepsy, aimed at reducing the number of seizures through medication, diet, or VNS, surgery, and recognition of medically intractable epilepsy with referral to specialized epilepsy centers helps to reduce risk of SUDEP.
Medical Director, Danish Epilepsy Hospital
Associated Professor, Institute of Regional Health Research, University of Southern Denmark, Denmark
How to cite:
Hjalgrim H. Current understanding of seizure alarms. In: Hanna J, Panelli R, Jeffs T, Chapman D, editors. Continuing the global conversation [online]. SUDEP Action, SUDEP Aware & Epilepsy Australia; 2014 [retrieved day/month/year]. Available from: www.sudepglobalconversation.com.