Types of Arrhythmia

The four main types of arrhythmia are premature (extra) beats, supraventricular arrhythmias, ventricular arrhythmias, and bradyarrhythmias (bray-de-ah-RITH-me-ahs).

Premature (Extra) Beats

Premature beats are the most common type of arrhythmia. They're harmless most of the time and often don't cause any symptoms.

When symptoms do occur, they usually feel like fluttering in the chest or a feeling of a skipped beat. Most of the time, premature beats need no treatment, especially in healthy people.

Premature beats that occur in the atria are called premature atrial contractions, or PACs. Premature beats that occur in the ventricles are called premature ventricular contractions, or PVCs.

In most cases, premature beats occur naturally, not due to any heart disease. But certain heart diseases can cause premature beats. They also can happen because of stress, too much exercise, or too much caffeine or nicotine.

Supraventricular Arrhythmias

Supraventricular arrhythmias are tachycardias (fast heart rates) that start in the atria or the atrioventricular (AV) node. The AV node is a group of cells located between the atria and the ventricles.

Types of supraventricular arrhythmias include atrial fibrillation (AF), atrial flutter, paroxysmal supraventricular tachycardia (PSVT), and Wolff-Parkinson-White (WPW) syndrome.

Atrial Fibrillation

AF is the most common type of serious arrhythmia. It's a very fast and irregular contraction of the atria.

In AF, the heart's electrical signal doesn't begin in the SA node. Instead, the signal begins in another part of the atria or in the nearby pulmonary veins and is conducted abnormally.

When this happens, the electrical signal doesn't travel through the normal pathways in the atria. Instead, it spreads throughout the atria in a fast and disorganized manner.

This causes the walls of the atria to quiver very fast (fibrillate) instead of beating normally. As a result, the atria aren't able to pump blood into the ventricles the way they should.

The animation below shows atrial fibrillation. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.

The animation shows how the heart's electrical signal starts in a place in the right atrium other than the sinoatrial node, causing the atria to beat very fast and irregularly.

In AF, electrical signals can travel through the atria at a rate of more than 300 per minute. Some of these abnormal electrical signals can travel to the ventricles, causing them to beat too fast and with an irregular rhythm. AF usually isn't life threatening, but it can be dangerous when it causes the ventricles to beat very fast.

The two most serious complications of chronic (long-term) AF are stroke and heart failure. Stroke can happen if a blood clot travels to an artery in the brain, blocking off blood flow.

In AF, blood clots can form because some of the blood "pools" in the fibrillating atria instead of flowing into the ventricles. If a piece of a blood clot in the left atrium breaks off, it can travel to the brain, causing a stroke. People who have AF often are treated with blood-thinning medicines to lower their risk for blood clots.

Heart failure is when the heart can't pump enough blood to meet the body's needs. AF can cause heart failure if the ventricles beat too fast and don't have enough time to fill with blood to pump out to the body. Heart failure causes fatigue (tiredness), leg swelling, and shortness of breath.

AF and other supraventricular arrhythmias can occur for no apparent reason. But most of the time, an underlying condition that damages the heart muscle and its ability to conduct electrical impulses causes AF. These conditions include high blood pressure, coronary heart disease (also called coronary artery disease), heart failure, and rheumatic heart disease.

Other conditions also can lead to AF, including an overactive thyroid gland (too much thyroid hormone produced) and heavy alcohol use. AF also becomes more common as people get older.

Atrial Flutter

Atrial flutter is similar to AF, but instead of the electrical signals spreading through the atria in a fast and irregular rhythm, they travel in a fast and regular rhythm.

Atrial flutter is much less common than AF, but it has similar symptoms and complications.

Paroxysmal Supraventricular Tachycardia

PSVT is a very fast heart rate that begins and ends suddenly. PSVT occurs due to problems with the electrical connection between the atria and the ventricles.

In PSVT, electrical signals that begin in the atria and travel to the ventricles can reenter the atria, causing extra heartbeats. This type of arrhythmia usually isn't dangerous and tends to occur in young people. It can happen during vigorous exercise.

A special type of PSVT is called Wolff-Parkinson-White syndrome. WPW syndrome is a condition in which the heart's electrical signals travel along an extra pathway from the atria to the ventricles.

This extra pathway disrupts the timing of the heart's electrical signals and can cause the ventricles to beat very fast. This type of arrhythmia can be life threatening.

The animation below shows Wolff-Parkinson-White syndrome. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.

The animation shows how an extra, abnormal electrical pathway in the heart disrupts the normal timing of the heart's electrical signal, causing the atria and ventricles to beat too fast.

Ventricular Arrhythmias

These arrhythmias start in the ventricles. They can be very dangerous and usually need medical attention right away.

Ventricular arrhythmias include ventricular tachycardia and ventricular fibrillation (v-fib). Coronary heart disease, heart attack, weakened heart muscle, and other problems can cause ventricular arrhythmias.

Ventricular Tachycardia

Ventricular tachycardia is a fast, regular beating of the ventricles that may last for only a few seconds or for much longer.

A few beats of ventricular tachycardia often don't cause problems. However, episodes that last for more than a few seconds can be dangerous. Ventricular tachycardia can turn into other, more dangerous arrhythmias, such as v-fib.

Ventricular Fibrillation

V-fib occurs when disorganized electrical signals make the ventricles quiver instead of pump normally. Without the ventricles pumping blood out to the body, you'll lose consciousness within seconds and die within minutes if not treated.

To prevent death, the condition must be treated right away with an electric shock to the heart called defibrillation (de-fib-ri-LA-shun).

V-fib may happen during or after a heart attack or in someone whose heart is already weak because of another condition. Health experts think that most of the sudden cardiac deaths that occur every year (about 335,000) are due to v-fib.

The animation below shows ventricular fibrillation. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.

The animation shows how disorganized electrical signals in the heart's ventricles can cause them to pump abnormally and quiver.

Torsades de pointes (torsades) is a type of v-fib that causes a unique pattern on an EKG (electrocardiogram). Certain medicines or imbalanced amounts of potassium, calcium, or magnesium in the bloodstream can cause this condition.

People who have long QT syndrome are at higher risk for torsades. People who have this condition need to be careful about taking certain antibiotics, heart medicines, and over-the-counter medicines.

Bradyarrhythmias

Bradyarrhythmias are arrhythmias in which the heart rate is slower than normal. If the heart rate is too slow, not enough blood reaches the brain. This can cause you to lose consciousness.

In adults, a heart rate slower than 60 beats per minute is considered a bradyarrhythmia. Some people normally have slow heart rates, especially people who are very physically fit. For them, a heartbeat slower than 60 beats per minute isn't dangerous and doesn't cause symptoms. But in other people, bradyarrhythmia can be due to a serious disease or other condition.

Bradyarrhythmias can be caused by:

• Heart attack
• Conditions that harm or change the heart's electrical activity, such as an underactive thyroid gland or aging
• An imbalance of chemicals or other substances, such as potassium, in the blood
• Some medicines, such as beta blockers

Bradyarrhythmias also can happen as a result of severe bundle branch block. Bundle branch block is a condition in which an electrical signal traveling down either or both of the bundle branches is delayed or blocked.

When this happens, the ventricles don't contract at exactly the same time, as they should. As a result, the heart has to work harder to pump blood to the body. The cause of bundle branch block often is an existing heart condition.

Arrhythmias in Children

A child's heart rate normally decreases as he or she gets older. A newborn's heart beats between 95 to 160 times a minute. A 1-year-old's heart beats between 90 to 150 times a minute, and a 6- to 8-year-old's heart beats between 60 to 110 times a minute.

A baby or child's heart can beat faster or slower than normal for many reasons. Like adults, when children are active, their hearts will beat faster. When they're sleeping, their hearts will beat slower. Their heart rates can speed up and slow down as they breathe in and out. All of these changes are normal.

Some children are born with heart defects that cause arrhythmias. In other children, arrhythmias can develop later in childhood. Doctors use the same tests to diagnose arrhythmias in children and adults.

Treatments for children who have arrhythmias include medicines, defibrillation (electric shock), surgically implanted devices that control the heartbeat, and other procedures that fix abnormal electrical signals in the heart.