A seizure is a transient disturbance of brain function caused by abnormal neuronal activity. Cardiac arrest is the sudden cessation of the heart’s electrical and mechanical activity, leading to the abrupt loss of heart function, breathing, and consciousness. Although these events originate in different systems, a rare connection exists. Seizure activity can disrupt the body’s control systems, potentially precipitating a life-threatening heart rhythm abnormality that results in cardiac arrest.
How Seizures Impact Heart Rhythm
The brain and heart are linked by the autonomic nervous system (ANS), which regulates involuntary functions like heart rate and breathing. Seizures, particularly widespread ones, can acutely disrupt this balance. The electrical activity often spreads to ANS-controlling areas, such as the limbic system and the brainstem.
This intense neural firing can trigger a massive release of catecholamines, stress hormones like adrenaline. This chemical surge typically causes a rapid heart rate, known as tachycardia, seen in up to 80% of seizures. This sympathetic overstimulation strains the heart and can, rarely, trigger dangerous ventricular arrhythmias leading to cardiac arrest.
A seizure can also cause a sudden, severe drop in heart rate called bradycardia, or even asystole (complete absence of electrical activity). This results from excessive activation of the parasympathetic (vagal) nervous system, which slows the heart. If this severe slowing, known as ictal asystole, lasts too long, it causes a transient loss of consciousness.
Serious cardiac events more commonly occur immediately after the seizure, in the postictal period. This state involves profound cardiorespiratory depression, where heart rate and blood oxygen levels drop significantly because the brain’s control over these functions is temporarily suppressed. This failure to recover is a primary mechanism that can lead to death.
Understanding Sudden Unexpected Death in Epilepsy (SUDEP)
The most severe manifestation of the seizure-cardiac link is Sudden Unexpected Death in Epilepsy (SUDEP). This term is used for the death of a person with epilepsy that is not caused by trauma, drowning, or status epilepticus, and where an autopsy fails to find another cause of death. SUDEP is the leading cause of epilepsy-related mortality, affecting about one in 1,000 adults with epilepsy annually.
The cause of SUDEP is attributed to a combination of respiratory failure and cardiac dysfunction. Following a generalized seizure, a person often experiences a prolonged pause in breathing, called apnea, which causes blood oxygen levels to plummet. This respiratory failure is theorized to be the most common pathway.
The heart is simultaneously affected by life-threatening arrhythmias, such as post-seizure bradycardia or asystole. The profound oxygen deprivation from apnea, combined with autonomic nervous system instability, causes the heart to fail to recover its normal rhythm. This catastrophic cardiopulmonary failure is considered the “final common pathway” for SUDEP.
SUDEP is diagnosed post-mortem when a thorough examination, including toxicology and histology, does not reveal an alternative cause of death. Because it is often unwitnessed, especially when it occurs during sleep, the exact sequence of events—whether the heart stopped first or the breathing stopped first—is frequently unknown.
Identifying High-Risk Factors
While all individuals with epilepsy face some risk of SUDEP, it is highly concentrated in certain groups. The most important identified risk factor is the occurrence of generalized tonic-clonic seizures (GTCS). Individuals who experience frequent or uncontrolled GTCS are at a significantly higher risk compared to those with other seizure types.
The frequency of GTCS is directly correlated with risk. Seizures that occur during sleep, known as nocturnal seizures, also pose a higher risk because they are less likely to be witnessed or interrupted.
Other Contributing Factors
- Having epilepsy for many years.
- An early age of seizure onset.
- Not taking anti-seizure medication as prescribed.
- Specific genetic syndromes affecting the brain and heart’s electrical channels.
- Drug-resistant epilepsy that cannot be controlled with medication.
This concentration of risk factors necessitates aggressive seizure control and proactive monitoring in vulnerable patient populations.
Strategies for Risk Reduction and Monitoring
The most effective strategy for reducing the risk of seizure-related cardiac complications and SUDEP is achieving optimal seizure control. This starts with strict and consistent adherence to anti-seizure medication (ASM) regimens as prescribed. Missing doses significantly increases seizure frequency and risk.
For patients with nocturnal seizures, nighttime supervision is a major preventative measure. This can involve sharing a bedroom with a caregiver or utilizing monitoring devices that alert a third party to a seizure event. These devices include wearable monitors that detect movement or heart rate changes, as well as specialized bed sensors that track breathing or body motion.
Routine cardiac assessments are increasingly recommended for high-risk individuals. This may involve periodic electrocardiograms (ECGs) to check for underlying heart rhythm abnormalities, such as a prolonged QT interval, which can be an independent risk factor for sudden cardiac death. Addressing other lifestyle factors, such as optimizing sleep hygiene and avoiding excessive alcohol, also contributes to overall risk reduction.
If a seizure is witnessed, a caregiver can intervene immediately, such as repositioning the person to ensure an open airway. The combination of optimal seizure control, consistent medication use, and proactive nocturnal monitoring represents the current standard of care. Ongoing communication with a healthcare team is necessary to personalize a comprehensive risk management plan.