Atrial fibrillation Dr Rob Hicks Atrial fibrillation is the most common cause of the heart beating irregularly. Such palpitations feel unpleasant and can also signify other health problems.

In this article

What causes it? What are the symptoms?

Who's affected? How is it diagnosed?

What's the treatment?

When electrical impulses travel along pathways to the heart muscle, they trigger the muscle to contract or beat. While this system is working properly, the heart beats regularly and without a problem.

But if something damages or interferes with the transmission of these electrical impulses, the heart may beat faster and irregularly, called fibrillation. As a consequence, the heart doesn't work as effectively as it should.

When the large chambers of the heart that are responsible for pumping blood around the body, known as the ventricles, go into a state of fibrillation, the effect is catastrophic and likely to prove rapidly fatal as they lose their pumping action and oxygen is no longer delivered to the brain.

More commonly it’s the smaller and less crucial upper chambers of the heart, known as the atria, which go into fibrillation. Although this isn’t directly fatal, it can mean the blood may clot within the chamber, causing parts of the clot to break off and travel up to the brain causing a stroke. A person with atrial fibrillation is six times more likely to have a stroke, and twice as likely to die as someone with a normal heart rhythm.

In recent years it has become clear that atrial fibrillation develops when tiny waves of electrical current travel randomly around, in and out of the atria, usually from an initial trigger in the pulmonary veins (the veins which brings oxygenated blood to the heart from the lungs). Many factors make this process more likely to occur, including:

• Cardiovascular causes, such as coronary artery disease and heart attack, high blood pressure (hypertension), disease of the heart valves, damage to the muscle of the heart, inflammation of the tissues of the heart and heart surgery
• Overactive thyroid gland (hyperthyroidism)
• Diabetes
• Certain drugs and medicines
• Excess alcohol (sometimes known as “holiday heart” syndrome)
• Low potassium, magnesium, or calcium levels in the body
• Following surgery of any kind
• Hypothermia (low body temperature)
• Respiratory causes, such as pneumonia, lung cancer or pulmonary embolus

Quite often – in as many as one in nine cases – there's no disease present to account for the atrial fibrillation. This is especially so in younger people, under 60 years of age, and is sometimes called lone AF.

People with atrial fibrillation (often called simply AF) may feel their heart is racing or thumping in their chest. People often describe this sensation as palpitations. Many people also feel faint or light-headed, but many are completely unaware that their heart isn’t behaving as it should, especially if the heart isn’t beating very fast.

Symptoms are more likely to develop when the heart is in what is known as fast AF with a rate of over 100 (although most people cope, and doctor’s are only usually concerned when the rate is over about 120 or more).

When blood doesn't pass through the heart as effectively as it should, other symptoms may occur. People may feel short of breath, especially when lying down flat, their ankles may become swollen and they may feel unusually tired for a great deal of the time.

Each year in the UK more than 46,000 people are newly diagnosed with atrial fibrillation. It’s slightly more common in men than women and is more likely to develop as people get older (the risk doubles with each decade after the age of 50).

The diagnosis of atrial fibrillation is confirmed with an electrocardiogram (ECG), which will show the heart's irregular electrical pattern. Blood tests are used to exclude causes such as an overactive thyroid gland.

When someone gets only occasional attacks (known as paroxysmal AF), it may be necessary to record the electrical activity of the heart over a period of 24 hours. This is a 24-hour ECG.

Other tests, such as a chest x-ray and an echocardiogram, are usually performed to help establish the cause of the atrial fibrillation.

Having atrial fibrillation increases the risk of stroke, so although some people may not be troubled by their palpitations, it's still important to find the cause and provide appropriate treatment.

The goals of treatment are:

• To restore a regular heart rhythm using an electrical current - electrocardioversion - to shock the heart back into normal rhythm. But the longer atrial fibrillation has been going on (especially after three months), the less successful this is likely to be, because the heart adapts to its new rhythm. Certain medicines can also be used to induce the heart to switch back to a regular rhythm, especially when AF has only been present for a few days.
• To control the heart rate with medication, for example, digoxin.
• To prevent clots forming and causing strokes, by giving blood-thinning medication.

When atrial fibrillation persists, another ioption is to destroy the abnormal electrical pathways using a technique called radiofrequency catheter ablation (or similar techniques). This works in about 60 per cent of people but atrial fibrillation eventually returns in up to half.

More invasive surgical treatments are being developed and may provide a more permanent cure.

Another option when drug treatments have no effect is to put in a cardiac pacemaker to control the atria.

Atrial fibrillation may be a result of other heart problems, such as coronary artery disease, which may need treatment. When it's because of an overactive thyroid gland, treating the thyroid dysfunction will usually resolve the atrial fibrillation.

This article was last medically reviewed by Dr Trisha Macnair in April 2008.