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.
What happens
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).
How common is it?
Atrial fibrillation is the most common heart rhythm disturbance and affects up to 500,000 people in the UK.
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.
Outlook
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 Treatment for 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.
