While some arrhythmias are mild and may not cause complications, others can potentially lead to loss of life. These life threatening heart rhythm disturbances are known as malignant arrhythmias.

An arrhythmia is a disturbance in your heart’s electrical system — a system that normally keeps your heart beating in a steady, consistent rhythm.

There are different types of arrhythmias. They can originate in your heart’s upper chambers (atria) or lower chambers (ventricles) and can cause your heart to beat too quickly (tachycardia), too slowly (bradycardia), or in an irregular or chaotic manner (fibrillation).

Some types of arrhythmias are barely noticeable and have a low risk of complications. Others can be much more serious, potentially life threatening. These are known as malignant arrhythmias.

This article will take a closer look at what causes malignant arrhythmias and how they can be treated.

Malignant arrhythmias are heart rhythm disturbances that can cause a life threatening emergency such as sudden cardiac arrest.

They are most often caused by an arrhythmia that originates in the heart’s ventricles (lower chambers). Examples of these are ventricular fibrillation (V-Fib) and ventricular tachycardia (v-tach or VT).

Ventricular fibrillation can cause the ventricles of the heart to quiver uncontrollably instead of contracting in a regular pattern. When this happens, the heart can suddenly stop pumping, preventing blood from flowing to the brain and other organs. This is known as cardiac arrest.

Ventricular tachycardia is an arrhythmia that’s caused by irregular electrical signals in the lower chambers of the heart, causing the heart to beat at more than 100 beats per minute. These episodes may be brief, only lasting a few seconds. But, if this rapid type of heartbeat lasts for more than 30 seconds, it can be life threatening and lead to cardiac arrest.

An arrhythmia that originates in the heart’s atria, known as atrial fibrillation (A-Fib) can also be serious, especially if left untreated. One of the most serious complications of untreated atrial fibrillation is a stroke.

Atrial fibrillation is the most common type of arrhythmia, affecting about 1–2% of the U.S. population. Ventricular arrhythmias are much less common, with some estimates putting the prevalence at around 48 out of every 100,000 people.

It’s not always clear why a malignant arrhythmia develops, but it seems to be more common in people who have underlying structural heart disease.

It can also be triggered when someone has a heart attack, causing their heart to become electrically unstable. This can increase the risk of a life threatening arrhythmia.

Other causes may include:

Other, less common conditions may also raise your risk of a malignant arrhythmia.

For example, 2017 research of people with takotsubo syndrome (sometimes called “broken heart syndrome”), suggests that about 11.4% of people with the condition also had a life threatening arrhythmia.

A 2020 study suggests that people hospitalized with COVID-19 who died as a result of the virus were more likely to have a malignant arrhythmia compared with those who survived.

However, researchers also noted that the cause of death in most of those cases was usually due to “systemic illness” rather than as a direct result of problems with heart function.

The use of certain recreational drugs may also trigger ventricular arrhythmias.

Treatment for a malignant arrhythmia has two stages. The first stage is focused on stopping the arrhythmia and restoring a pulse and blood pressure. This involves cardiopulmonary resuscitation (CPR) or an automated external defibrillator (AED) that delivers electrical impulses to the heart.

The second stage involves treatments to help prevent a recurrence of a malignant arrhythmia in the future. This may include:

  • Medications: Medications such as antiarrhythmic drugs can help restore a normal heart rhythm. But sometimes these drugs can worsen an arrhythmia or trigger a new one, so their use needs to be carefully considered. Beta-blockers, which help the heart work with less effort, may be helpful in some cases.
  • Implantable cardioverter defibrillator (ICD): This small device, which is implanted in the chest, monitors a person’s heart rhythm and, when necessary, sends out shocks to stabilize the rhythm of the heart.
  • Catheter ablation: With this minimally invasive procedure, a catheter (a thin, flexible tube) is inserted into the femoral vein in the groin and threaded to the heart, where it destroys a cluster of cells that are affected by the arrhythmia.
  • Left cardiac sympathetic denervation: This rare procedure helps slow down the left side of the heart. It’s used in people with uncontrolled V-Fib due to a genetic cause.

Heart arrhythmias occur when the electrical system that coordinates how the heart pumps is interrupted, causing the heart to beat too fast, too slow, or in an erratic way.

Some types of arrhythmias can be mild and don’t cause any complications. Others can potentially lead to loss of life or cardiac arrest. These are known as malignant arrhythmias. They require immediate life-saving measures such as CPR or defibrillation to restore a pulse and blood pressure.

If you’ve been diagnosed with a life threatening arrhythmia, work closely with an electrophysiologist (a cardiologist specializing in rhythm disturbances) to learn the signs of disease progression and how to best manage your condition for the long term.