You don’t have to tell your heart to beat or your lungs to breathe, thanks to your autonomic nervous system (ANS). Your brain controls the ANS. So when you have a seizure, other aspects of the body are affected as well.

A seizure is a “brainstorm,” where electrical activity in the brain is disturbed. The changes in brain function can affect the ANS, potentially leading to cardiac arrhythmias. These are abnormal heart rhythms that could potentially prove fatal.

Cardiac arrhythmia can also lead to seizure-like activity, known as convulsive syncope. This isn’t the same as a seizure, but they can sometimes be hard to tell apart.

Keep reading to learn more about the connections between seizures, convulsive syncope, and abnormal heart rhythms.

Convulsive syncope and seizures are two conditions that can cause similar symptoms, most commonly loss of consciousness (passing out). While the two may look similar, they have different causes.

A seizure is due to excessive nervous system activity. Convulsive syncope is due to a lack of oxygen to the brain, often because of an underlying abnormal heart rhythm.

Diagnosing either condition can be difficult because they seem so similar, and it’s hard to identify the exact cause once something has already happened.

Studies found that around 20 to 30 percent of people who experienced syncope episodes were misdiagnosed as having epilepsy. Cardiovascular syncope was the most common misdiagnosed underlying condition.

The 10/20 rule

It can be hard to distinguish between convulsive syncope and a seizure. In both events, the body may jerk uncontrollably. Doctors use medical history and testing to confirm a diagnosis, but there could be an easy way for you to tell them apart.

A 2018 study recommends the 10/20 rule. Fewer than 10 jerks likely means that syncope is occurring. If there are more than 20 jerks, it’s more than likely a seizure.

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Doctors don’t know exactly why seizures can lead to cardiac arrhythmias. There are several possible reasons. These include:

  • over- or under-activating the ANS in the brain
  • increase in activity of the vagus nerve due to changes in the brainstem
  • respiratory failure after a seizure that affects the heart’s ability to pump well

Each of these factors could contribute to cardiac arrhythmia in a person who has undergone a seizure.

In a study of 1.4 million people with epilepsy, about 1 in 4 had a cardiac arrhythmia. The most common arrhythmia was atrial fibrillation (AFib). AFib causes the top part of the heart (the atrium) to fibrillate or quiver before pumping to the bottom part of the heart.

Other arrhythmia types that commonly co-occur with epilepsy include:

Cardiac arrhythmias can cause convulsive syncope, which is a seizure-like episode. Cardiac syncope is often due to structural changes or mechanical issues in the heart.

Most cases of arrhythmia that lead to cardiac syncope involve ventricular tachycardia (v-tach). V-tach is an arrhythmia in which your heart beats very quickly. Sustained v-tach can have very serious complications.

According to a 2016 review, syncope due to v-tach is most common in men older than 35 years. A 2020 case study reports that syncope due to v-tach may resemble tonic-clonic seizure activity.

You may picture a seizure as uncontrolled, shaking movements. But many different seizure types exist. The symptoms depend upon the underlying type.

Examples of different seizure types and their symptoms include:

  • Absence: rapid blinking, staring off into space, unable to capture the person’s attention
  • Focal: twitching, confusion; and changes in sensation, such as taste or smell
  • Tonic-clonic: muscle spasms or jerking, falling to the ground, losing consciousness, significant fatigue after the seizure

If a seizure lasts longer than 5 minutes or a person injures themself while having the seizure, call emergency services and help the person seek emergency medical attention.

What happens to the heart during a seizure?

The heart can respond in a number of different ways during and immediately after a seizure. Different types of seizures affect different parts of the brain. Some can affect the parts of your brain that control your heart rhythm.

In about 80 percent of cases with seizures where the heart is affected, the heart speeds up after a seizure. This heart rhythm is known as sinus tachycardia and can cause heart palpitations.

In other instances, a person can experience heart rate changes that even include systole or the absence of the heart beating entirely.

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Cardiac arrhythmias often don’t have any symptoms. In the case of v-tach, you might feel like your heart is racing. The only way to know for sure is to see your doctor.

Doctors diagnose cardiac arrhythmias by using an electrocardiogram (ECG or EKG). This painless, noninvasive test allows a doctor to measure your heart rhythm.

Sometimes, your doctor may recommend wearing a monitor to check your heart’s rhythm. If you have a seizure, the heart monitor can capture your heart’s rhythm and allow your doctor to determine if there’s an arrhythmia.

Doctors are still learning about seizures and cardiac arrhythmias. In some instances, cardiac arrhythmia can take place before a seizure. Researchers have therefore suggested that arrhythmias can be a precursor or sign that a seizure may be about to occur.

However, it is difficult to say if arrhythmias increase your risk of seizures. To identify the connection, a person would have to wear a heart monitor before, during, and after a seizure. But the timing of seizures is difficult to predict.

If you’re concerned about your risks, talk with your doctor about how to best minimize them.

Your outlook will depend on the type of cardiac arrhythmia you have with your seizure. Very rarely, cardiac arrhythmia can lead to ictal asystole, where the heart can stop. Ictal asystole can be a possible cause of sudden unexpected death in epilepsy or SUDEP.

If a doctor has identified that you have a cardiac arrhythmia after a seizure, they may recommend treatments such as an implantable cardioverter defibrillator (ICD). An ICD can “shock” the heart back into rhythm if an arrhythmia occurs.

The following are some commonly asked questions related to cardiac arrhythmias and seizures.

Can atrial fibrillation cause a seizure?

According to the Centers for Disease Control and Prevention (CDC), atrial fibrillation (AFib) is the most commonly treated cardiac arrhythmia in the United States.

Some case reports indicate that a person can experience atrial fibrillation after a seizure. However, there are no reports that indicate that AFib causes a seizure.

AFib can, however, increase your risk of stroke.

What’s my risk of developing a cardiac arrhythmia if I have epilepsy?

In the study of 1.4 million people with epilepsy, 1 in 4 experienced some type of cardiac arrhythmia, with atrial fibrillation being the most common. Some people may have an arrhythmia without it being related to their epilepsy.

Can seizure medication cause arrhythmia?

Some seizure medications can have side effects known as cardiotoxicity. This means the medications can potentially damage the heart. Examples of known side effects include:

  • pregabalin: increased risk of heart failure
  • oxcarbazepine: induce ventricular fibrillation, a severe and life threatening arrhythmia
  • carbamazepine: increased risk of AV block or bradycardia (slow heart rate)

Although these are potential side effects, they don’t happen to everyone.

Cardiac arrhythmias can occur following a seizure. Sometimes, they may resolve. At other times, the cardiac arrhythmia can cause severe and potentially life threatening effects.

Cardiac arrhythmias can also cause convulsive syncope, which can look like a seizure. The 10/20 rule can help you distinguish between the two. Most arrhythmias don’t cause convulsive syncope, but ventricular tachycardia might.

Talk with your doctor if you have concerns about seizures, convulsive syncope, or cardiac arrhythmia.