Understanding a normal heartbeat

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 contract (squeeze) in the correct order for the heart to pump blood correctly with each heartbeat.

• The sinoatrial (SA) node in the right atrium is a tiny inbuilt 'timer'. It fires off an electrical impulse at regular intervals. (About 60-80 per minute when you rest, and faster when you exercise. This controls the heart rate.) Each impulse spreads across both atria. This causes them to contract and pump blood through one-way valves into the ventricles.
  
  
• 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 atrioventricular (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 left branch. These then split into many tiny fibres (Purkinje's system) which conducts the electrical impulse throughout the ventricles. This makes the ventricles contract and pump blood through one-way valves into large arteries:
  • The artery going from the right ventricle (pulmonary artery) takes blood to the lungs.
  • The artery going from the left ventricle (aorta) takes blood to the rest of the body.
• The heart then rests for a short time (diastole). Blood coming back to the heart from the large veins fills the atria during diastole.
  • The veins coming into the left atria bring blood from the lungs (full of oxygen).
  • The veins coming into the right atria bring blood from the body (needing oxygen).

What is atrial fibrillation?

If you have atrial fibrillation (AF) then:

• Your heart rate is usually a lot faster than normal.
• Your heartbeat is irregular. That is, an abnormal heart rhythm (an arrhythmia).
• 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 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.

Classification of AF

AF is commonly classified in the following way:

• Paroxysmal AF. The word paroxysmal means '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.
• Persistent AF. This means AF that lasts longer than seven days and is unlikely to revert back to normal without treatment. However, the heartbeat can be reverted back to a normal rhythm with cardioversion treatment (see later). Persistent AF tends to be recurrent so it may come back again at some point after successful cardioversion treatment.
• Permanent AF. This means that the AF is present long-term and the heartbeat has not been reverted back to a normal rhythm. This may be because cardioversion treatment was tried and was not successful, or because cardioversion has not been tried. People with permanent AF are treated to bring their heart rate back down to normal, but the rhythm remains irregular (see below). Permanent AF is sometimes called established AF.

Most people with AF have permanent AF.

How common is atrial fibrillation?

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 have AF. This rises to around 1 in 10 people aged over 80 years.

It is uncommon in younger people unless you have certain heart conditions.

What causes atrial fibrillation?

Causes of AF include the following:

• High blood pressure is the most common cause. (High blood pressure puts a strain on the heart muscle.)
• AF is a common complication of various heart conditions. For example, AF is a complication of ischaemic heart disease. This is the condition that causes angina and heart attacks and is common in older people. Various other heart problems may also trigger AF to develop. For example, AF occurs in some people with heart valve problems, cardiomyopathy and pericardial disease.
• Other conditions and situations that may trigger AF to develop include: an overactive thyroid gland (hyperthyroidism); pneumonia; pulmonary embolus; obesity; lung cancer; drinking a lot of alcohol; drinking a lot of caffeine (tea, coffee, etc).
• In about 1 in 9 cases of AF there is no apparent cause. The heart is otherwise fine and there are no other diseases to account for it. This is called lone AF.

What are the symptoms of atrial fibrillation?

Symptoms often develop quickly, soon after the AF develops. Possible symptoms include:

• Palpitations. This means that you become aware of your heart. You may feel it beating in a fast and irregular way.
• Dizziness.
• Angina (chest pains) may develop. In particular, the pains tend to occur when you exert yourself, but they may 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.

The reason why breathlessness, dizziness and angina may develop is because when the heart beats too fast, it becomes less efficient. Small amounts of blood pumped faster by the heart are not as good as larger amounts that are pumped at the slower normal rate. This can lead to a pooling of blood in the veins of the lungs and a reduced output of blood from the heart which can lead to these symptoms.

However, many people with AF have no symptoms, particularly if their heart rate is not very fast. The AF may then be diagnosed by chance when a doctor or nurse feels your pulse.

Are any tests needed?

• A heart tracing called an electrocardiogram (ECG) can usually confirm the diagnosis. This test can also rule out other causes of an erratic or fast heart rate. Sometimes a 24-hour ECG is taken if you have paroxysmal AF and a resting ECG does not show AF.
• Other tests such as blood tests and an echocardiogram (ultrasound scan of the heart) are often advised. These tests look for an underlying cause of AF such as a heart problem or an overactive thyroid gland.
• Often an underlying cause is already known about. For example, you may already have angina. You may not need any further tests if AF develops as a complication.

What are the possible complications of atrial fibrillation?

An increased risk of having a stroke (or other blood clot problem)

The main complication of AF is an increased risk of having a stroke. AF causes turbulent blood flow in the heart chambers. This sometimes leads to a small blood clot forming in a heart chamber.

A clot can travel in the blood vessels until it gets 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.

The risk of developing a blood clot and having a stroke varies, depending on various factors. The level of risk is divided into three categories: high, medium and low risk.

• High risk means that, without treatment, you have about a 6-12 in 100 chance (sometimes higher) of having a stroke in the next year. People in the high risk group include those:
  • who have already had a stroke or known blood clot, or
  • are aged 75 years or older who also have one of the following risk factors: high blood pressure, diabetes or a cardiovascular disease (such as angina, heart attack, peripheral vascular disease), or
  • who have a heart valve problem, or
  • who have heart failure or poor heart function shown on a heart scan (echocardiogram).
• Moderate risk means that you have about a 3-5 in 100 chance of having a stroke in the next year. People in the moderate risk group include those:
  • aged 65 years or older (with no high risk factors), or
  • who are of any age (up to age 75 when the risk is high) but who also have one of the following risk factors: high blood pressure, diabetes or a cardiovascular disease (such as angina, heart attack, peripheral vascular disease).
• Low risk means that you have about a 1-2 in 100 chance or less of having a stroke in the next year. People in the low risk group are all people with AF aged less than 65 and who do not have any risk factors that put them in the high or moderate risk category.

Other complications

Less common complications of AF include the following:

• Heart failure develops in some cases. See separate leaflet called 'Heart Failure'.
• Cardiomyopathy. There are various causes of cardiomyopathy and AF with a fast heart rate is an uncommon cause. Cardiomyopathy means 'weakness of the heart muscle'. The reason why cardiomyopathy should develop in some people with AF is not clear.
• Angina pains may get worse if you have angina.

What are the treatment options for atrial fibrillation?

Treatments that may be considered include:

• Rate control. This means bringing the heart rate back down to normal. This is done for all people with AF who have fast heart rate (that is, most cases).
• Rhythm control. This means converting the irregular rhythm back to a normal regular rhythm. This is only possible in some cases.
• Anticoagulation treatment which aims to prevent a stroke.
• Other treatments in certain circumstances.

Each of these are 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 drugs can slow the heart rate down. They include betablocker drugs (such as atenolol, metoprolol and propranolol), diltiazem, verapamil and digoxin. These drugs work by interfering with the electrical impulses of the heart. The drug chosen may depend on factors such as other heart problems that you may have.

In untreated AF, the heart rate may be as fast as 180 beats per minute, although it is more commonly between 120 and 160 beats per minute. The aim of medication is to bring the heart rate back down to normal (ideally, to less than 90 beats per minute when resting).

Treatment is usually successful, but the dose needed can vary from case to case. Also, in some cases a combination of drugs may be needed if the heart rate is not brought down low enough with a single drug.

Rhythm control treatment

Rhythm control means reverting the erratic heartbeat back to a normal regular rhythm. This is called cardioversion.

One method of cardioversion is to give your heart an electric shock. Another method is to use drugs that may convert the heart rhythm back to a regular beat. 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.

Cardioversion is more likely to be considered in certain situations, for example:

• If your AF developed recently.
• If you are younger than 65. (Age is no bar to cardioversion, but it is less likely to an option the older you become.)
• If an underlying cause of the AF has been successfully treated (and so AF is unlikely to come back again once the normal heart rhythm has been restored).
• If you have no other heart abnormality. (That is, if you have lone AF described earlier.)
• If you have acute heart failure or unstable angina which is being made worse by the irregular heartbeat of AF.

Cardioversion is usually not an option in certain situations. For example:

• If you have certain heart diseases that include a structural problem to the heart. For example, certain valve problems such as mitral stenosis.
• If you have had AF for a long time (usually more than 12 months).
• If you have had several previous attempts at cardioversion which have not worked, or only worked for a short time before the heart reverted back to AF.

A newer technique to restore the heart rhythm is called catheter ablation. In this procedure a catheter (a long thin wire) 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.

Anticoagulation - usually with warfarin

Anticoagulation means that you take a drug to reduce the chance of forming a blood clot. Therefore, anticoagulation helps to prevent a stroke from occurring. Some people call anticoagulation 'thinning the blood' although the blood is not actually made any thinner. The most commonly used anticoagulant drug is called warfarin. Warfarin interferes with certain chemicals in the blood to prevent blood clots forming so easily.

Overall, warfarin reduces the risk of stroke by nearly two-thirds. In other words, warfarin treatment can prevent about 6 in 10 strokes that would have occurred in people with AF. The greatest benefit is seen in those people who are in the high risk category of having a stroke (described above).

As with all treatments, there is a small risk if you take warfarin. The main risk is that a bleeding problem may develop as the blood will not clot so well. For example, some people develop a serious bleeding ulcer in the gut. Warfarin can also interact with many different medications.

Most people with AF who have a high or medium risk of having a stroke are advised to take warfarin. However, some people with a moderate risk may be treated with aspirin rather than warfarin (see below), particularly if the risks of taking warfarin are higher than average.

People with a low risk of having a stroke are not usually advised to take warfarin. This is because the benefit does not usually outweigh the risk of serious bleeding problems with taking warfarin. In short, the decision to take warfarin is a joint decision between you and your doctor. It involves weighing up the risk of having a stroke against the small risk of a complication from taking warfarin.

If you take warfarin you will need regular blood tests (called INR tests) to check on 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.

Aspirin is another drug that helps to prevent blood clots forming. It is not as effective as warfarin, but is less likely to cause problems. It is usually advised if you only have a low risk of stroke or if you cannot take warfarin.

Alternatives to warfarin
New anticoagulants are being developed and produced which appear to be as effective as warfarin with fewer side-effects. These are likely to be used in the future.

Other treatments

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

Further help and information

British Heart Foundation

Greater London House, 180 Hampstead Road, London, NW1 7AW
Tel (Heart Help Line): 0300 330 3311 Web: www.bhf.org.uk

Atrial Fibrillation Association

PO Box 1219, Chew Magna, Bristol BS40 8WB
Tel: 01789 451837 Web: www.afa.org.uk
This is an international charity which provides information, support and access to established, new or innovative treatments for atrial fibrillation.

Anticoagulation Europe

PO Box 405, Bromley, Kent, BR2 9WP
Tel: 020 8289 6875 Web: www.anticoagulationeurope.org
A charity providing information and advice to people on oral anticoagulation treatment.

References

• Atrial fibrillation, Prodigy (August 2009)
• Atrial Fibrillation: The management of atrial fibrillation, NICE Clinical Guideline (Jun 2006)
• Lafuente-Lafuente C, Mahe I, Extramiana F; Management of atrial fibrillation. BMJ. 2009 Dec 23;339:b5216. doi: 10.1136/bmj.b5216.
• Mant J, Hobbs FD, Fletcher K, et al; Warfarin versus aspirin for stroke prevention in an elderly community population with atrial fibrillation (the Birmingham Atrial Fibrillation Treatment of the Aged Study, BAFTA): a randomised controlled trial. Lancet. 2007 Aug 11;370(9586):493-503. [abstract]
• Lubitz SA, Fischer A, Fuster V; Catheter ablation for atrial fibrillation. BMJ. 2008 Apr 12;336(7648):819-26.
• Connolly SJ, Ezekowitz MD, Yusuf S, et al; Dabigatran versus warfarin in patients with atrial fibrillation. N Engl J Med. 2009 Sep 17;361(12):1139-51. Epub 2009 Aug 30. [abstract]
• Anticoagulation - oral, Prodigy (March 2009)