Atrial fibrillation is a heart condition that causes episodes of irregular and often abnormally fast heart rate.
A normal heart rate should be between 60 and 100 beats a minute at rest. You can measure your heart rate by feeling the pulse in your wrist or neck. In atrial fibrillation, the heart rate may be over 140 beats a minute.
There are three main types of atrial fibrillation:
- Paroxysmal atrial fibrillation. This comes and goes and usually stops within 48 hours without any treatment.
- Persistent atrial fibrillation. This lasts for longer than seven days (or less when it is treated).
- Longstanding persistent atrial fibrillation. This usually lasts for longer than a year.
When the heart beats normally, its muscular walls contract (tighten and squeeze) to force blood out and around the body. They then relax, so the heart can fill with blood again (see box, left). This process is repeated every time the heart beats.
In atrial fibrillation, the upper chambers of the heart (atria) contract randomly and sometimes so fast that the heart muscle cannot relax properly between contractions.
This may lead to a number of problems, including dizziness and shortness of breath. You may also be aware of a fast and irregular heartbeat (palpitations) and feel very tired (see Symptoms).
Some people with atrial fibrillation have no symptoms and are completely unaware that their heart rate is not regular.
Why it happens
Atrial fibrillation occurs when abnormal electrical impulses suddenly start firing in the atria. These impulses override the heart's natural pacemaker, which can no longer control the rhythm of the heart. This causes you to have a highly irregular pulse rate.
The cause is not fully understood, but it tends to occur in certain groups of people (see below) and may be triggered by certain situations, such as drinking excessive amounts of alcohol or smoking (see Causes).
Who is affected?
Atrial fibrillation can affect adults of any age, but affects men more than women and becomes more common the older you get. It affects about 10% of people over 75.
Atrial fibrillation is more likely to occur in people with other conditions, such as high blood pressure or atherosclerosis (see Causes for a full list of conditions).
It is not common in younger people unless they have a heart condition.
Atrial fibrillation is generally not life threatening, but it can be uncomfortable and often needs treating.
Treatment may involve medication to control heart rate and/or rhythm, and medication to prevent stroke (see Treatmentf or a full list of treatment options).
A healthy lifestyle, regular blood pressure checks and treatment for raised blood pressure can reduce the chances of developing the heart problems that cause atrial fibrillation.
How the heart works
The heart has two upper chambers (left and right atria) and two lower chambers (left and right ventricles).
The atria and ventricles have walls of muscle. A heartbeat happens when this muscle suddenly contracts (tightens). The chambers become smaller and the blood inside them is squeezed out.
The sinoatrial node is a small clump of cells in the right atrium which is involved in controlling the heartbeat. It acts as the heart's natural pacemaker by sending out electrical impulses through the heart to another clump of cells called the atrioventricular node, found between the atria and ventricles.
The atrioventricular node determines the rate at which these electrical impulses are transmitted, and therefore the rate at which the ventricles contract. It is the contraction of the left ventricle that produces the pulse rate.
Some people with atrial fibrillation have no symptoms and it is only discovered during routine tests or investigations for another condition.
The most obvious symptom of atrial fibrillation is a fast and irregular heartbeat, usually over 140 beats a minute. You can determine your heart rate by feeling the pulse in your wrist or neck.
You may also experience:
- dizziness, or
- chest pain (angina).
The way the heart beats in atrial fibrillation reduces the heart's efficiency and performance. This can result in low blood pressure and heart failure.
If you notice a sudden change in your heartbeat and have chest pain, see your doctor immediately.
The exact cause of atrial fibrillation is unknown, but it becomes more common with age and affects certain groups of people more than others.
Those at risk
Atrial fibrillation is common in people with other heart conditions, such as:
- high blood pressure,
- heart valve disease,
- congenital heart disease (heart disease at birth)
- cardiomyopathy (wasting of the heart muscle), and
- pericarditis (inflammation of the lining surrounding the heart).
It is also associated with other medical conditions:
- hyperthyroidism (overactive thyroid gland),
- chronic obstructive pulmonary disease,
- lung cancer,
- pulmonary embolism (a blockage in a vessel in your lungs), and
- carbon monoxide poisoning.
Certain situations can trigger an episode of atrial fibrillation, including:
- drinking excessive amounts of alcohol (particularly binge drinking),
- being overweight,
- drinking lots of caffeine, such as tea, coffee or energy drinks,
- taking illegal drugs (particularly amphetamines or cocaine), and
If you notice a sudden change in your heartbeat and you have chest pain, see your GP straight away.
Feeling your pulse can give a strong indication of whether you have atrial fibrillation, but a complete diagnosis requires a full medical investigation.
If your GP thinks you have atrial fibrillation after assessing your symptoms, they may ask you to have an electrocardiogram and refer you to a cardiologist (heart specialist).
An electrocardiogram (ECG) is a test that records the rhythm and electrical activity of your heart.
Small stickers, called electrodes, are attached to your arms, legs and chest and connected by wires to an ECG machine.
Every time your heart beats, it produces tiny electrical signals. An ECG machine traces these signals on paper. During atrial fibrillation, your heart rate is irregular and may be over 140 beats a minute.
An ECG is usually carried out in a hospital or GP surgery. It takes about five minutes and is painless.
If you have the test during an attack of atrial fibrillation, the ECG will record your abnormal heart rate and a diagnosis of atrial fibrillation can be confirmed (and other conditions ruled out).
However, it may be difficult to capture an attack, so your GP may ask you to wear a small, portable electrocardiogram recorder that will either trace your heart rate continuously over 24 hours, or when you switch it on (at the start of an attack).
An echocardiogram is an ultrasound scan of the heart. It can help identify any other heart problems and assess the structure and function of the heart and valves.
A chest X-ray will identify any lung problems that may have caused the atrial fibrillation.
Blood tests can also be useful in the diagnosis. They may show anaemia, which may be complicating the situation, problems with kidney function or hyperthyroidism (overactive thyroid gland).
The treatment of atrial fibrillation varies from person to person and depends on:
- the type of atrial fibrillation,
- treatment of any underlying cause,
- age, and
- overall health.
Some people may be treated by their GP, whereas others may be referred to a cardiologist (heart specialist).
The first step is to try to find out the cause of the atrial fibrillation. If a cause is found, you may just need treatment for this.
For example, medication to correct hyperthyroidism (an overactive thyroid gland) may cure atrial fibrillation.
If no underlying cause can be found, the treatment options are:
- medicines to control atrial fibrillation,
- medicines to reduce the risk of stroke,
- cardioversion (electric shock treatment),
- ablation, or
- having a pacemaker fitted.
Medicines to control atrial fibrillation
Medicines called anti-arrhythmics can control atrial fibrillation by:
- restoring a normal heart rhythm, and/or
- controlling the rate at which the heart beats.
The choice of anti-arrhythmic medicine depends on the type of atrial fibrillation, any other medical conditions, side effects of the medicine chosen and how well the atrial fibrillation responds.
Some people with atrial fibrillation may need more than one anti-arrhythmic medicine to control it.
Restoring a normal heart rhythm
A variety of drugs are available to restore normal heart rhythm. These include:
- flecainide (and other similar drugs),
- beta-blockers (particularly sotalol), and
New drugs are in development that may restore normal heart rhythm, but they are not widely available yet. If a particular drug does not work or the side effects are troublesome, another may be tried.
Controlling the rate of the heartbeat
The aim is to reduce the resting heart rate to under 90 beats a minute, although in some people the target is under 110 beats a minute.
A beta-blocker (such as bisoprolol or atenolol) or a calcium channel blocker (such as verapamil or diltiazem) will be prescribed.
A medicine called digoxin may be added to help further control the heart rate. In some cases, amiodarone may be tried.
As with any medicine, anti-arrhythmics can cause side effects. Read the patient information leaflet that comes with the medicine for more details.
The most common side effects of anti-arrhythmics are:
- Beta-blockers: tiredness, coldness of hands and feet, low blood pressure, nightmares and impotence.
- Flecainide: nausea, vomiting and heart rhythm disorders.
- Amiodarone: sensitivity to sunlight (high-protection sunscreen must be worn or skin covered up), lung problems, changes to liver function or thyroid function (regular blood tests can check for this) and deposits in the eye (these go away when treatment is stopped).
- Verapamil: constipation, low blood pressure, ankle swelling and heart failure.
Medicines to reduce the risk of stroke
The way the heart beats in atrial fibrillation means that there is a risk of blood clots forming in the heart chambers. If these get into the bloodstream, they can cause a stroke (see Complications).
Your doctor will assess your risk to minimise your chance of a stroke. They will consider your age and whether you have a history of any of the following:
- stroke or blood clots,
- heart valve problems,
- heart failure,
- high blood pressure,
- diabetes, or
- heart disease.
You will be classed as having a high, moderate or low risk of stroke and will be given medication according to your risk.
Depending on your level of risk, you may be prescribed warfarin or aspirin.
People with atrial fibrillation who have a high or moderate risk of stroke are usually prescribed warfarin, unless there is a reason they cannot take it.
Warfarin is an anticoagulant, which means it stops the blood from clotting. There is an increased risk of bleeding in people who take warfarin, but this small risk is usually outweighed by the benefits of preventing a stroke.
It is very important to take warfarin as directed by the doctor. People on warfarin need to have regular blood tests and, following these, their dose may be changed.
Lots of medicines can interact with warfarin and cause serious problems, so check that any new medicines are safe to take with warfarin.
Drinking more than moderate amounts of alcohol or drinking cranberry juice can also affect your warfarin and is not recommended.
People with atrial fibrillation who have a low risk of stroke are likely to be given a low dose of aspirin to take every day instead of warfarin.
People who are unable to take warfarin may also be given aspirin instead.
Cardioversion may be tried in some people with atrial fibrillation. The heart is given a controlled electric shock to try to restore a normal rhythm.
The procedure normally takes place in hospital, where the heart is carefully monitored.
In people who have had atrial fibrillation for more than two days, cardioversion is associated with an increased risk of clot formation. If this is the case, warfarin is given for three to four weeks before cardioversion and for at least four weeks afterwards to minimise the chance of having a stroke.
If the cardioversion is successful, warfarin may be stopped. However, some people may need to continue with warfarin after cardioversion if there is a high chance of their atrial fibrillation returning and they have a moderate to high risk of stroke (see above).
Catheter ablation is a procedure that very carefully destroys the diseased area of your heart and interrupts abnormal electrical circuits. It is an option if medication has not been effective or tolerated.Catheters (thin, soft wires) are guided through one of your veins into your heart, where they record electrical activity. When the source of the abnormality is found, an energy source (such as high-frequency radiowaves that generate heat) is transmitted through one of the catheters to destroy the tissue. This can be quite a long procedure and commonly takes two to three hours, so it may be done under general anaesthetic (where you are put to sleep).
Having a pacemaker fitted
A pacemaker is a small, battery-operated device that is implanted in your chest (just below your collarbone). It is usually used to prevent your heart rate going too slowly, but in atrial fibrillation, it may help your heart beat regularly.
Having a pacemaker fitted is usually a minor surgical procedure performed under a local anaesthetic (the area is numbed).
This treatment may be used when medicines are not effective or are unsuitable.
For more information, go to Health A-Z: pacemaker implantation.
When the atria (upper chambers of the heart) are not pumping efficiently, as in atrial fibrillation, there is a risk of blood clots forming.
These blood clots may move into the ventricles (lower chambers of the heart) and get pumped into the lungs or the general blood circulation.
Clots in the general circulation can block arteries in the brain, causing a stroke.
The risk of stroke in people with atrial fibrillation is about double that of the general population. However, the risk depends on a number of factors, including age and whether you have high blood pressure, heart failure, diabetes and a previous history of embolism (blood clots).
If your atrial fibrillation is persistent, it may start to weaken your heart. In extreme cases, it can lead to heart failure (where your heart cannot pump blood around your body efficiently).