The four main types of arrhythmia are premature (extra) beats, supraventricular (SU-prah-ven-TRIK-yu-lar) arrhythmias, ventricular arrhythmias, and bradyarrhythmias (bray-de-ah-RITH-me-ahs).
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 heartbeat. Most of the time, premature beats need no treatment, especially in healthy people.
Premature beats that occur in the atria (the heart's upper chambers) are called premature atrial contractions, or PACs. Premature beats that occur in the ventricles (the heart's lower chambers) are called premature ventricular contractions, or PVCs.
In most cases, premature beats happen naturally. However, some heart diseases can cause premature beats. They also can happen because of stress, too much exercise, or too much caffeine or nicotine.
Supraventricular arrhythmias are tachycardias (fast heart rates) that start in the atria or 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.
AF is the most common type of serious arrhythmia. It involves a very fast and irregular contraction of the atria.
In AF, the heart's electrical signals don't begin in the SA node. Instead, they begin in another part of the atria or in the nearby pulmonary veins.
The signals don't travel normally. They may spread throughout the atria in a rapid, disorganized way. 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 what happens during AF. 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.
In AF, electrical signals can travel through the atria at a rate of more than 300 per minute. Some of these abnormal 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 if it causes the ventricles to beat very fast.
In AF, blood can pool in the atria, causing blood clots to form. If a clot breaks off and travels to the brain, it can cause a stroke. Blood-thinning medicines that reduce the risk of stroke are an important part of treatment for people who have AF.
Heart failure occurs if the heart can't pump enough blood to meet the body's needs. AF can lead to heart failure because the ventricles are beating very fast and can't completely fill with blood. Thus, they may not be able to pump enough blood to the lungs and body.
Damage to the heart's electrical system causes AF. The damage most often is the result of other conditions that affect the health of the heart, such as high blood pressure, coronary heart disease, and rheumatic heart disease. Inflammation also is thought to play a role in the development of AF.
Other conditions also can lead to AF, including an overactive thyroid gland (too much thyroid hormone produced) and heavy alcohol use. The risk of AF increases with age.
Sometimes AF and other supraventricular arrhythmias can occur for no obvious reason.
Atrial flutter is similar to AF. However, the heart's electrical signals spread through the atria in a fast and regular—instead of irregular—rhythm. Atrial flutter is much less common than AF, but it has similar symptoms and complications.
PSVT is a very fast heart rate that begins and ends suddenly. PSVT occurs because of 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 physical activity.
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 what happens during 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.
These arrhythmias start in the heart's lower chambers, the ventricles. They can be very dangerous and usually require medical care right away.
Ventricular arrhythmias include ventricular tachycardia and ventricular fibrillation
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 serious arrhythmias, such as v-fib.
V-fib occurs if disorganized electrical signals make the ventricles quiver instead of pump normally. Without the ventricles pumping blood to the body, sudden cardiac arrest and death can occur within a few minutes.
To prevent death, the condition must be treated right away with an electric shock to the heart called defibrillation (de-fib-rih-LA-shun).
V-fib may occur during or after a heart attack or in someone whose heart is already weak because of another condition.
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.
Torsades de pointes (torsades) is a type of v-fib that causes a unique pattern on an EKG (electrocardiogram) test. 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 increased risk for torsades. People who have this condition need to be careful about taking certain antibiotics, heart medicines, and over-the-counter products.
Bradyarrhythmias occur if 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 pass out.
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, serious diseases or other conditions may cause bradyarrhythmias.
Bradyarrhythmias can be caused by:
Children's heart rates normally decrease as they get 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 fast or slow 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.
Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Arrhythmia, visit www.clinicaltrials.gov.
December 9, 2013
Gary H. Gibbons
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