Originating in the Atria
Premature (Extra) Beats
Premature beats are the most common type of heart 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 otherwise 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.
Atrial Fibrillation (A Fib)
A fib is the most common type of serious arrhythmia. A fib is a very fast and irregular rhythm originating in the atria. A fib occurs when the heart’s electrical signal begins in a different part of the atrium other than where it is supposed to begin, the sinoatrial (SA) node, which is known as the pacemaker of the heart.
When this happens, the electrical signal does not 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 are not able to adequately fill with blood or pump blood in sufficient amounts.
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 occurs when the heart cannot pump enough blood to meet the needs of the body. AF can cause heart failure when the ventricles beat too fast and do not 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 (originating above the ventricles) arrhythmias can occur for no apparent reason. Most of the time, however, supraventricular arrhythmias are caused by an underlying condition that interferes with the heart’s 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. The atria contract at 300 beats per minute. The lower chambers (the ventricles) contract at multiples of this (150, 100, or 75 beats per minute). The usual rate is 150 beats per minute.
Paroxysmal Supraventricular Tachycardia (PSVT)
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 younger people, often during vigorous exercise.
A special type of PSVT is 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.
Ventricular Arrhythmia (Originating in the Ventricles)
Ventricular arrhythmias start in the electrical pathways of the ventricles. They can be very dangerous and usually require 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 a few seconds can be dangerous. Ventricular tachycardia can turn into other, more dangerous arrhythmias, such as v-fib.
Ventricular Fibrillation (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 may lose consciousness within seconds and may die within minutes if not treated. To prevent death, v-fib requires immediate treatment with defibrillation, which is 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.
Premature Ventricular Complexes (PVC)
An electrical signal from the ventricles causes an early heart beat that generally goes unnoticed. The heart then seems to pause until the next beat of the ventricle occurs in a regular fashion.
Torsades de Pointes
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 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 does not cause symptoms. However, in other people, bradyarrhythmia can be due to a serious health 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 occur due to a condition known as ‘severe bundle branch block.’ Bundle branch block is a condition in which the electrical signal traveling along either or both of the electrical pathways between the ventricles, called bundle branches, is delayed or blocked. When this happens, the ventricles do not 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.
Like adults, when children are active their hearts beat faster and slower when they are asleep. 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 as 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 electrical signals in the heart.
This is the name for changes in the heart rate that occur during breathing. Sinus arrhythmia is common in children and often found in adults. This is normal.
The sinus node sends out electrical signals faster than usual, speeding up the heart rate. Causes include exercise, fever, excitement, certain medications, dehydration and an overly active thyroid gland.
Sick sinus syndrome
The sinus node does not fire signals properly, so the heart rate slows down. Sometimes the rate changes back and forth between a slow (bradycardia) and fast (tachycardia) rate.
Portions of this information were provided by the National Heart Lung Blood Institute.