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About atrial fibrillation

Atrial fibrillation (AF)

About atrial fibrillation

AF is the most common cardiac arrhythmia and is characterised by an irregular, often very fast, heart rate. 

What is normal (sinus) rhythm?

The heart is divided into four chambers: two at the top, called the atria, and two at the bottom, called the ventricles. The heart normally beats regularly and in a coordinated manner (first the atria followed by the ventricles with every heartbeat). At rest the heart rate is usually between 60 and 100 bpm (beats per minute). This is called normal sinus rhythm.

The heart beat needs an electrical conduction system, rather like electrical wiring. This is made up of cells in the heart that send electrical messages or impulses to the heart muscle. These electrical impulses stimulate the heart to contract.

In a normal heart, the electrical impulse starts from our natural pacemaker, the sinoatrial node (SA node), which is located at the top of the right atrium. This electrical impulse then spreads very quickly throughout the right and left atria, making them contract. It then goes through a gateway from the atria to the ventricles called the atrioventricular node (AV node). Once it is past the AV node, the electrical impulse speeds its way into the ventricles making them contract and push the blood out of the heart.

The AV node is situated at the lower right atrium, and acts as an electrical junction between the atria and ventricles. During normal sinus rhythm, the AV node's main function is to delay the speed at which the electrical impulse travels between the atria and the ventricles. This means the heart pumps blood more efficiently.

What is atrial fibrillation?

Atrial fibrillation (AF) is an abnormal heart rhythm, where the heart beats irregularly and often fast. It is the most common heart rhythm disorder in the UK.

AF can occur at any age but is most common in people aged over 65 years old. In the over 80s, it can affect 7-10 per cent of people. The top chambers of the heart (atria) have abnormal, disorganised electrical activity. This overrides the sinus node, causing the atria to beat rapidly (more than 300 times a minute) and irregularly (known as fibrillating or fibrillation). At this rate the atria can not pump blood efficiently. 

The AV node has a very important protective mechanism; it is able to stop many of these electrical impulses being transmitted from the atria to the ventricles, preventing the ventricles from beating at the same rate as the atria. The rate of the ventricles in AF depends on the AV node and can range from slow to very fast. 


The protective function of the AV node means AF is a non-life threatening arrhythmia. However, it can still cause the heart function to become impaired and, regardless of how slow or fast the heart is beating, can increase the risk of stroke.

What are the causes of AF?

The cause of AF is still not fully understood. AF is more likely to occur with increasing age and there are several ill-health factors that can contribute to AF developing:

  • ischaemic heart disease
  • mitral valve disease
  • hypertension
  • heart failure
  • obesity
  • sleep apnoea
  • congenital heart disease

Other factors include:

  • hyperthyroidism / hypothyroidism
  • respiratory disease / pneumonia / chest infections
  • pulmonary embolism (PE)
  • alcohol / drugs
  • carbon monoxide poisoning

There may be no apparent reason for developing AF; this is when it is called "lone" AF.

What are the symptoms of AF?

Some people might not experience any symptoms associated with their AF; however, if they do, the most commonly reported are:

  • palpitations
  • breathlessness
  • tiredness / lethargy
  • reduced exercise capacity
  • chest discomfort
  • dizziness

Is there more than one type of AF?

There are three types of AF, based on both frequency and duration of AF episodes:

  • Paroxysmal AF intermittent episodes that return to normal rhythm within seven days.
  • Persistent AF  Episodes that persist for more than seven days and may stop with treatment or sometimes on their own. If it continues for more than 12 months, it is known as long-standing persistent AF.
  • Permanent AF AF that does not terminate with treatment or it has been decided that accepting AF is the best option for you.

Atrial tachycardia

Atrial tachycardia (AT) is an abnormal heart rhythm, but unlike AF is more regular and organised. AT also comes from the top chambers (atria) of the heart, from either the right side, left side or both. AT is usually seen in patients that have undergone heart surgery, have congenital heart defects or have undergone previous ablation procedures.


Some people may experience symptoms such as a fast heartbeat, which may feel regular in nature but can also feel irregular. Other symptoms experienced may be similar to AF, such as breathlessness, dizziness and tiredness. 



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