Atrial fibrillation
Atrial fibrillation (AF) is a common type of heart rhythm disorder (arrhythmia). Normally, your heart beats at a rate of 60 to 100 beats per minute, and all of the heart chambers beat in unison. If you have AF, the electrical signals that control your heartbeat are abnormal. These signals cause the upper chambers of your heart (the atria) to beat chaotically and very quickly. In fact, the atria beat so quickly that the lower heart chambers (the ventricles) can’t quite keep up, and your heart doesn’t beat in the usual, co-ordinated manner. This results in an irregular and rapid heart rate, often ranging from 100 to 160 beats per minute.
People with AF have a higher risk of stroke — the risk ranges from less than 1 per cent per year to about 12 per cent per year, depending on your age and other medical conditions. People with AF are also at risk of developing heart failure.
Atrial fibrillation can be ‘paroxysmal’, which means that it occurs in recurrent bouts that usually last less than 48 hours; or chronic (ongoing). It is also possible to have an acute, one-off episode of AF, which may be the result of a particular transient problem such as alcohol intoxication.
How does AF cause stroke?
Because the atria are contracting quickly and abnormally, they don’t pump blood through the heart properly. Blood can then pool in the heart and a blood clot may form. If the clot breaks loose and leaves the heart, it can travel via your blood vessels to other organs in your body. If a clot lodges in a blood vessel that supplies your brain and cuts off the blood supply, it causes a stroke.
Who is affected by atrial fibrillation?
Your risk of having AF increases as you get older — AF affects 5 per cent of people older than 65 years and 10 per cent of people older than 75 years. People who have heart disease or problems with their heart valves are more likely to be affected than those who don’t have these problems. Long-standing high blood pressure, chronic lung disease or an overactive thyroid gland can also put you at a higher risk of AF. It is possible for otherwise healthy people to have AF — in fact, up to one-third of people with AF have no obvious underlying cause, a condition known as lone atrial fibrillation.
How is AF diagnosed?
You may experience palpitations (an awareness of your heart beating or pounding in your chest) if you have AF. Other symptoms include chest pain, dizziness, light-headedness, shortness of breath and fatigue. Some people have no symptoms at all, and AF is only detected after a doctor (or another health care worker) notices that your pulse is irregular.
Your doctor can diagnose AF using a simple, painless test called an electrocardiogram (ECG). When you have an ECG, small patches connected to wires (electrodes) are placed on your chest to measure the electrical impulses given off by your heart. These electrical impulses are recorded on a piece of paper called an ECG strip. The abnormal pattern of electrical impulses seen in people with AF is easily detected by the ECG.
However, if you have paroxysmal AF, your heartbeat may be normal at the time the ECG is recorded. To detect paroxysmal AF, you may need to have a Holter monitor test arranged. A Holter monitor (a portable device that you wear under your clothes) continuously records your heart's electrical impulses for at least 24 hours.
What treatments are available?
Your doctor may prescribe medicine to try to restore the normal, regular rhythm of your heart. Medicine that simply slows your heart rate is also effective. It is likely you will also need to take medicine to prevent your blood from clotting (for example, aspirin or warfarin), to reduce your risk of stroke.
Sometimes, the recommended treatment is to use electrical stimulation to convert your heart into a normal rhythm. This procedure is called electrical cardioversion and is performed while you are under a general anaesthetic.
People with AF that has not been effectively treated with medicines or electrical cardioversion may require a more invasive treatment. For example, a pacemaker (a medical device that helps regulate the heartbeat) may need to be inserted. Pacemakers are placed just under the skin near your collarbone, and a wire connects the pacemaker to your heart.
Sometimes, radiofrequency catheter ablation is used. In this procedure, a catheter (a long, thin tube) is introduced through the femoral vein in your groin and threaded all the way to the heart, where radiofrequency energy is used to damage the small portion of tissue responsible for the abnormal electrical signals.
Rarely, open heart surgery is required.
Last Reviewed: 19 March 2007
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