An arrhythmia is a problem with the rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm. A heartbeat that is too fast is called tachycardia. A heartbeat that is too slow is called bradycardia.
Most arrhythmias are harmless, but some can be serious or even life-threatening. When the heart rate is too fast, too slow, or irregular, the heart may not be able to pump enough blood to the body. Lack of blood flow can damage the brain, heart, and other organs.
Understanding the Heart’s Electrical System
To understand arrhythmias, it helps to understand the heart’s internal electrical system. The heart’s electrical system controls the rate and rhythm of the heartbeat.
With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As the signal travels, it causes the heart to contract and pump blood. The process repeats with each new heartbeat.
A problem with any part of this process can cause an arrhythmia. For example, in atrial fibrillation, a common type of arrhythmia, electrical signals travel through the atria in a fast and disorganized way. This causes the atria to quiver instead of contract.
There are many types of arrhythmia. Most arrhythmias are harmless, but some are not. The outlook for a person who has an arrhythmia depends on the type and severity of the arrhythmia.
Even serious arrhythmias often can be successfully treated. Most people who have arrhythmias are able to live normal, healthy lives.
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 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.
AF is the most common type of serious arrhythmia. It’s a very fast and irregular contraction of the atria.
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 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.
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 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.
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.
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.
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 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.