The heart is a hollow muscle that is about the size of an adult fist, and is found to the left of the breastbone. The heart is the most important organ in our body, as it is a complex pump, responsible for circulating blood, oxygen and nutrients around the body. It pumps blood around your body and beats approximately 70 times a minute.
The heart has two upper chambers (the left and right atrium, together called the atria) and two lower chambers (the left and right ventricles). Atrial fibrillation occurs when the electrical impulses in the atria become disorganised, overriding the heart's normal rate and rhythm. This causes the atria to contract in an irregular manner or 'fibrillate'. The heartbeat is irregular or feels uneven.
The atria and ventricles have walls of virtually pure muscle, and when the heart "beats" it is the sudden tightening of this muscle so that the chambers become smaller and the blood inside them is squeezed out. The control of the heartbeat starts with a small clump of muscle cells in the right atrium, called the sinoatrial node. This acts as the heart's natural pacemaker by transporting electrical impulses to the atrioventricular node, which is located between the atria and ventricles.
Atrial fibrillation occurs when the atrioventricular node receives more impulses than it can conduct and causes irregular squeezing of the ventricles. This then causes a highly irregular pulse rate in people with atrial fibrillation. The most obvious symptom of atrial fibrillation is a fast and irregular heartbeat rate, usually over 140 beats per minute.
People with atrial fibrillation may also experience dizziness, palpitations, breathlessness, or chest pains on physical exertion. However, some people with atrial fibrillation have no symptoms at all.
Because of the way the heart is beating in atrial fibrillation, the heart's efficiency and performance is reduced. This can result in angina, low blood pressure, disorders of the heart muscle, and heart failure.
The most common causes of atrial fibrillation are high blood pressure, coronary artery disease, mitral valve disease (disease of the heart valve), cardiomyopathy (wasting of the heart muscle), pericarditis (inflammation of the bag surrounding the heart), hyperthyroidism (overactive thyroid gland),excessive alcohol intake, and drinking lots of caffeine.
Atrial fibrillation becomes more common with increasing age. It is uncommon in younger people unless they have an underlying heart condition. In some cases of atrial fibrillation there is no known cause.
Atrial fibrillation can lead to a blood clot forming in your heart. This is because your blood is not able to flow properly through your heart. If a clot forms, it can travel to your brain and cause a stroke. Because of this, people with atrial fibrillation are five times more likely to have a stroke than people without the condition. If you have atrial fibrillation, you may need anticoagulant medicine (such as aspirin or warfarin) to prevent a clot forming.
If there is an underlying cause for your atrial fibrillation, such as overactive thyroid, this will be treated. If you have atrial fibrillation which has come on quite suddenly, your treatment will be aimed at restoring your normal heart rhythm with either medicine or an electrical current (this is called cardioversion).
If your atrial fibrillation is a permanent problem or comes and goes on its own, you may be offered tablets to try and maintain a normal rhythm, or an ablation - a procedure which can cure atrial fibrillation. However you may not need any treatment at all if your atrial fibrillation is not bothering you.
Whichever type of atrial fibrillation you have, you will probably be offered medicines to reduce your risk of getting a blood clot. There are a number of different types of medicine that can help control atrial fibrillation, including beta-blockers, calcium channel blockers, anti-arrhythmic drugs and a drug called digoxin. They all work in different ways to control your heart rate or restore a normal rhythm.