Atrial Fibrillation


The heart has four chambers - two atria and two ventricles. The walls of these chambers are mainly made of special heart muscle. The chambers have to squeeze (contract) in the correct order for the heart to pump blood correctly with each heartbeat.

Cross-section diagram of the heart describing a heartbeat

The sequence of each normal heartbeat is as follows:

  • The electrical impulse gets to the atrioventricular (AV) node at the lower right atrium. This acts like a junction box and the impulse is delayed slightly. Most of the tissue between the atria and ventricles does not conduct the impulse. However, a thin band of conducting fibres called the AV bundle acts like wires and carries the impulse from the AV node to the ventricles.
  • The AV bundle splits into two - a right and a left branch. These then split into the Purkinje's system (many tiny fibres) which conducts the electrical impulse throughout the ventricles. This makes the ventricles contract and pump blood through one-way valves into large arteries:

If you have AF:

  • The force of each heartbeat can vary in intensity.

What happens is that the normal controlling timer in the heart is overridden by many random electrical impulses that fire off from the heart muscle in the atria. The atria then fibrillate. This means that the atria only partially squeeze (contract) - but very rapidly (up to 400 times per minute). Only some of these impulses pass through to the ventricles in a haphazard way. Therefore, the ventricles contract anywhere between 50 and 180 times a minute but usually between 140 and 180 times a minute. However, the ventricles contract in an irregular way and with varying force.

Therefore, if you have AF and feel your pulse, you may count up to 180 beats per minute. Also, the force of each beat can vary and the pulse feels erratic.

Describing AF

AF is commonly divided into the following types:

  • Paroxysmal AF. The word paroxysmal means repeated (recurring) sudden episodes of symptoms. If you have paroxysmal AF it means that you have episodes of AF that come and go. Each episode comes on suddenly but will stop without treatment within seven days (usually within two days). Each episode stops just as suddenly as it starts and the heartbeat goes back to a normal rate and rhythm. The period of time between each episode (each paroxysm) can vary greatly from case to case. Although paroxysmal AF means that it will stop on its own, some people with paroxysmal AF take treatment as soon as the AF develops, to stop it as quickly as possible after it starts.

It is common but mainly occurs in older people. Nearly 50,000 cases are diagnosed each year in the UK. It becomes more common with increasing age. About 1 in 200 people aged 50-60 years have AF. This rises to around 1 in 10 people aged over 80 years. It is uncommon in younger people unless they have certain heart conditions.

Causes of AF include the following:


  • A 'thumping' heart (palpitations). This means that you become aware of your heart. You may feel it beating in a fast and irregular way.
  • Dizziness.
  • Chest pains (angina) may develop. The pains tend to occur when you exert yourself but they may also occur even when you are resting.
  • Breathlessness is often the first symptom that develops. It may occur all the time but you may become breathless just when you exert yourself, such as when you walk up stairs.





A clot can travel in the blood vessels until it becomes stuck in a smaller blood vessel in the brain (or sometimes in another part of the body). Part of the blood supply to the brain may then be cut off, which causes a stroke.


Other complications

Less common complications of AF include the following:

Treatments that may be considered include:

  • Anticoagulation treatment which aims to prevent a stroke.
  • Other treatments in certain circumstances.

Each of these is now discussed further.

Rate control treatment

If your heart rate is brought down to normal, your heart becomes efficient again and your symptoms usually improve. Your pulse may still feel irregular but not fast.

Several medicines can slow the heart rate down. They include beta-blocker medicines (such as atenolol and propranolol), calcium-channel blocker medicines (such as diltiazem and verapamil) and digoxin. These medicines work by interfering with the electrical impulses of the heart. The medicine chosen may depend on factors such as other heart problems that you may have.



Rhythm control treatment


One method of cardioversion is to give your heart an electric shock. Another method is to use a medicine that may convert the heart rhythm back to a regular beat. One medicine used for rhythm control is amiodarone. Both of these methods have only limited success. For example, after cardioversion, within a year, in about half of cases, the heart has reverted back to AF.


  • If your AF developed recently.
  • If you are younger than 65 years. (Age is no bar to cardioversion but it is less likely to be an option the older you become.)
  • If you have no other heart abnormality (lone AF, as described earlier).



A newer technique to restore the heart rhythm is called catheter ablation. In this procedure a long, thin wire (catheter) is passed into the chambers of the heart via a large blood vessel in a leg. The tip of the catheter can destroy tiny sections of heart tissue that may be the source or trigger of the abnormal electrical impulses. This treatment is only suitable in certain cases and is not a routine treatment. It does not always work and there is a small risk of serious complications. Your doctor will discuss with you in more detail if you are suitable to have rhythm control treatment and which method of cardioversion would be best for you.


All people with AF (except those with the lowest risk of having a stroke) should be offered anticoagulation treatment. Anticoagulation means that you take a medicine to reduce the chance of forming a blood clot and having a stroke. Some people call anticoagulation 'thinning the blood' although the blood is not actually made any thinner. The most commonly used anticoagulant medicine has been warfarin, although others have recently been developed. They work by interfering with certain chemicals in the blood to prevent blood clots forming so easily.



If you take warfarin you will need regular blood tests (INR tests) to check how quickly your blood clots. Blood tests may be needed quite often at first but should become less often quite quickly. The aim is to get the dose of warfarin just right so your blood does not clot as easily as normal but not so much as to cause bleeding problems. Dabigatran and rivaroxaban do not need regular blood tests. If you have had trouble getting your INR level just right, your doctor may suggest one of these medicines as an alternative to warfarin.

See separate leaflet called Preventing Stroke When You Have Atrial Fibrillation for more details.

  • Compare the options  

Aspirin is another medicine that helps to prevent blood clots forming and was used extensively in the past. It is now known that it is not as effective as warfarin but is just as likely to cause problems. Aspirin is therefore no longer recommended.

Other treatments

Other treatments may be advised, depending on the need to treat any underlying problems such as chest pains (angina), heart valve problems, high blood pressure (hypertension), and overactive thyroid (hyperthyroidism).

Now read about Atrial Fibrillation

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Original Author:
Dr Tim Kenny
Current Version:
Dr Colin Tidy
Peer Reviewer:
Dr Hannah Gronow
Document ID:
4198 (v45)
Last Checked:
21 October 2016
Next Review:
21 October 2019
The Information Standard - certified member



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