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There are four main types of arrhythmia: premature (extra) beats, supraventricular arrhythmias, ventricular arrhythmias, and bradyarrhythmias.
Premature (Extra) Beats
Premature beats are the most common type of arrhythmia. They are harmless most of the time and often don’t cause any symptoms. When symptoms do occur, they usually feel like a fluttering in the chest or a sensation 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 are tachycardias (fast heart rates) that start in the atria or the atrioventricular node (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’s a very fast and irregular contraction of the atria. AF occurs when the heart’s electrical signal begins in a different part of the atrium than the sinoatrial (SA) node or when the signal is conducted abnormally. When this happens, the electrical signal doesn’t travel through the normal pathways in the atria, but instead may spread 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.
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 is not usually life threatening, although 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 when a blood clot travels to an artery in the brain, blocking off blood flow. In AF, blood clots can form in the atria 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 with AF are often treated with blood-thinning medicines to reduce the chances of developing blood clots.
Heart failure is when the heart can’t pump enough blood to meet the needs of the body. AF can cause heart failure when the ventricles beat too fast and don’t have enough time to fill with blood to pump out to the body. Heart failure causes tiredness, leg swelling, and shortness of breath.
AF and other supraventricular arrhythmias can occur for no apparent reason. Most of the time, however, they are caused by an underlying condition that damages the heart muscle and its ability to conduct electrical impulses. These conditions include high blood pressure (hypertension), coronary artery disease, heart failure, or rheumatic heart disease.
Other conditions also can lead to AF, including overactive thyroid gland (too much thyroid hormone produced) and heavy alcohol use. AF also becomes more common as people get older.
Atrial flutter is similar to atrial fibrillation, 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 atrial fibrillation, but 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 is not usually 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.
These are arrhythmias that start in the ventricles. They can be very dangerous and usually need immediate medical attention. Ventricular arrhythmias include ventricular tachycardia and ventricular fibrillation (v-fib). Coronary artery disease, heart attack, weakened heart muscle, and other problems can cause ventricular arrhythmias.
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, but ventricular tachycardia episodes that last for more than just a few seconds can be dangerous. Ventricular tachycardia can turn into other, more dangerous arrhythmias, such as v-fib.
V-fib occurs when disorganized electrical signals make the ventricles quiver instead of pump normally. Without the ventricles pumping blood out to the body, a person will lose consciousness within seconds and will die within minutes if not treated. To prevent death, the condition must be treated immediately with defibrillation, an electric shock to the heart. V-fib may happen during or after a heart attack, or in a heart that 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.
Torsades de pointes (torsades) is a specific form of v-fib with a unique pattern on an EKG (electrocardiogram). Certain medicines and imbalanced amounts of potassium, calcium, or magnesium in the bloodstream can cause this condition. People with a particular finding on an EKG test, called prolonged QT interval, are at increased risk of developing torsades. People with prolonged QT interval need to be careful about taking certain antibiotics, heart medicines, and over-the-counter medicines.
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, and the person can 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 is not 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 system (such as underactive thyroid gland or aging), an imbalance of chemicals or other substances (such as potassium) in the blood, or even 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 the 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, and the heart has to work harder to pump blood to the body. The cause of bundle branch block is often an existing heart condition.
Arrhythmias in Children
Normally, a child’s heart beats between 70 and 100 times a minute. A newborn’s heart beats about 140 times a minute. A baby or child’s heart can beat faster or slower than normal for many reasons. As is true for adults, when children are active, their hearts will beat faster. When they are sleeping, their heart will beats 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 do the same kinds of tests in children and adults to diagnose arrhythmias.
Treatments for children with arrhythmias include medicines, electric shock (defibrillation), surgically implanted devices that control the heartbeat, and other procedures that fix distorted electrical signals in the heart.