Sudden Unexpected Death in Epilepsy (SUDEP) is a terrible tragedy, often made worse by the unexplained nature of the loss.  Although the exact cause of SUDEP is not known, researchers are making great strides to understand what may contribute to sudden death in people with epilepsy.  It is most likely that SUDEP occurs for different reasons in different people. Often, but not always, there is evidence of a seizure, particularly a generalized tonic-clonic seizure (GTCS), occurring prior to death.  Studies examining the causes of SUDEP have focused on three main areas:

Electrical shutdown of the brain (CES) 

After a seizure, it can be quite common to see a flattening of the brain waves known as post-ictal generalized EEG suppression or PGES. This pattern has been identified in the EEG recordings of people who have died of SUDEP during EEG monitoring. 

Careful examination of the EEG records showed that in these cases, the EEG flattening did not recover and was followed by death. In one study, people who had died of SUDEP had longer periods of PGES after seizures than living patients with epilepsy, though another study could not confirm this finding. These findings suggest that SUDEP might result from a severe electrical shutdown of the brain, which leads to failure of heart and breathing functions.

Changes in heart function

There are several ways in which changes in heart function may contribute to SUDEP.

Seizures are known to affect heart rhythms. Usually a person's heart rate increases during a seizure. One study found that a greater degree of heart rate increase with a seizure was associated with a greater risk of SUDEP. Less often, the heart rate can slow down too much during or after a seizure.  Irregular heart rhythms or even periods without a heart beat can also occur. Some individuals with abnormal heart rhythms recorded during seizures have had pacemakers implanted to protect against future heart rhythm problems.   

Severe seizures may also cause Takotsubo Syndrome, a condition in which the heart muscle does not function properly after a severe stress.   About 8 % of people with Takotsubo Syndrome die from heart failure, shock, irregular heart rhythms, blood clots or sudden death.  Long-term changes in the structure of the heart have also been described in some people with epilepsy but how this relates to SUDEP is not known.

Genetic conditions are well known to cause sudden unexpected death in young people. Long QT syndrome is an inherited condition that affects the heart and can cause sudden death. Changes (called mutations) in a number of different genes controlling the electrical activity of heart cells have been described in Long QT Syndrome. Since similar gene mutations can also affect the electrical activity of brain cells, researchers are looking at whether these disorders could make people more likely to have seizures and sudden death.  Studies in animals have found changes in several such genes.  Researchers are now trying to see how this relates to people with epilepsy.

Changes in breathing

Problems with breathing are commonly seen with seizures and are frequently reported in relation to SUDEP and near-SUDEP. 

During seizures, people may stop breathing, either due to problems with the brain’s control of breathing or a blockage of the airways. Sometimes seizures can cause increased secretions or fluid in the airways or lungs that may interfere with breathing. Spasms of the larynx (also known as the “voice box”) and suffocation have also been described in cases of near-SUDEP and SUDEP. 

About 1/3 of people with uncontrolled partial epilepsy have low oxygen levels and high carbon dioxide levels in the blood associated with some seizures.  These abnormalities can contribute to changes in heart rhythms and blood pressure.  If severe enough, they can affect brain function, leading to sleepiness, seizures, coma and death.

SUDEP has often been compared to Sudden Infant Death Syndrome (SIDS). In both cases the deaths occur more frequently in sleep and a cause of death is not found on autopsy. Scientists have found that some infants who died of SIDS had an abnormality of the brainstem, a part of the brain that is critical for the control of breathing and heart function. A similar problem has been identified in a mouse model of epilepsy in which the mice often stop breathing and die after seizures. This suggests that brainstem problems may play a role in some cases SUDEP.


It seems likely that the changes we see in brain, heart and lung functions during seizures are contributing to SUDEP. The brain controls the functions of the heart and the lungs. The effects of a seizure on the brain can in turn affect heart and lung function. Abnormal heart rhythms are more likely to occur if breathing is abnormal and the lungs, like the rest of the body, rely on the heart for their blood supply. Abnormal heart function can reduce blood flow to the brain, while brain function can also be affected by low oxygen and high carbon dioxide in the blood.

Understanding how SUDEP occurs is an important step in reducing risk. Studies in high risk epilepsy monitoring units have shown that actions taken by nurses and medical staff at the time of a seizure may shorten the length of a seizure and improve EEG flattening, breathing and heart function. These actions included turning the patient to the side, suctioning the mouth, giving oxygen and quickly performing CPR when needed. While a role for the routine use of suction devices and oxygen in the home environment has not been established, simple first aid steps like stimulation (to help arouse someone after a seizure) and adjusting the person’s position to keep their airway open after a seizure may help. 

SUDEP more frequently occurs in bed and victims are often found face down. One community-based study showed that SUDEP risk was lowered when listening devices (such as baby monitors) were used or the person with epilepsy shared their bedroom with someone who could help if a seizure occurred.

While researchers continue to explore the factors that contribute to SUDEP, it is important to remember that there are ways to reduce the risk of death in people with epilepsy.

  • Working to have as few seizures as possible, particularly reducing the number of GTCS, is the most important way to lessen the risk of SUDEP. 
  • Important actions people can take include: taking prescribed seizure medications consistently, identifying and avoiding seizure triggers, keeping regular appointments with your doctors and considering other epilepsy treatments, such as surgery, when medications are not working to control seizures.


Authored By: 
Lisa M. Bateman, MD, FRCPC
Elizabeth J. Donner MD, FRCPC
Authored Date: 
Reviewed By: 
Daniel Friedman MD
Tuesday, November 12, 2019