What is atrial fibrillation?
Atrial fibrillation — often shortened to AF — is the most common heart rhythm disorder. Instead of beating in a steady, regular rhythm, the heart's upper chambers quiver or "fibrillate", and the heartbeat becomes irregular and often faster than normal.
More than 500,000 Australians are estimated to live with AF, and the number is growing as the population ages and rates of high blood pressure, obesity and diabetes rise. Around one in three people will develop it at some point in their lives.
AF is not usually life-threatening in itself, but it matters a great deal: it is one of the leading causes of stroke, it can lead to heart failure, and it is frequently missed because it can come and go without obvious symptoms. The good news is that it is very treatable — and that many of the factors that cause it can be changed.
This explainer looks at what happens in the heart during AF, who is most at risk, how it is diagnosed and treated, and what Baker Institute research is doing to improve care.
What happens in the heart during atrial fibrillation?
A healthy heartbeat begins with an electrical signal from the heart's natural pacemaker, which spreads in an orderly way through the two upper chambers (the atria) and then the two lower chambers (the ventricles). This coordinated sequence pumps blood efficiently around the body, usually at 60 to 100 beats a minute at rest.
In AF, that orderly signal is replaced by chaotic electrical activity in the atria. Rather than contracting properly, the atria quiver, and the ventricles receive irregular signals — so the pulse becomes uneven and often rapid. Because the atria are no longer emptying fully, blood can pool inside them, which is how clots can form.
AF is often described by how long it lasts:
- Paroxysmal AF comes and goes, with episodes that stop on their own, usually within a few days.
- Persistent AF lasts longer than a week, or needs treatment to stop it.
- Permanent AF is long-standing AF where a decision has been made not to try to restore a normal rhythm.
For many people, AF starts as occasional episodes and becomes more frequent or continuous over time — one reason early diagnosis and treatment are so important.
What are the symptoms?
Symptoms vary widely. Some people feel every episode; others have no idea their heart is out of rhythm until it is picked up during a check-up or, worse, after a stroke.
Common symptoms include:
- palpitations — a fluttering, racing, pounding or irregular heartbeat
- shortness of breath, particularly with activity
- tiredness or reduced ability to exercise
- dizziness or light-headedness
- chest discomfort.
Because AF can be silent, and because paroxysmal episodes may not be happening when you visit the doctor, it is often under-diagnosed. If you notice an irregular pulse or any of the symptoms above, it is worth having it checked.
If you have chest pain, severe breathlessness or fainting, call 000.
Who is at risk?
Anyone can develop AF, but the risk rises sharply with age — most people diagnosed are over 65. Other factors that increase the risk include:
- High blood pressure — the most common contributor, because it puts strain on the heart and changes the structure of the atria over time.
- Being overweight or obese, and the conditions that travel with it, including type 2 diabetes and obstructive sleep apnoea.
- Alcohol — both heavy drinking and regular moderate drinking are linked to AF, and binge drinking can trigger episodes.
- Existing heart disease, including coronary artery disease, heart valve disease, heart failure and a previous heart attack.
- An overactive thyroid.
- Family history — AF can run in families.
- Smoking and physical inactivity.
Less commonly, AF is seen in people who have done many years of intense endurance exercise. AF can also be triggered by acute illness, surgery or infection, and may settle once the underlying problem is treated.
Many of these risk factors overlap with those for heart disease more broadly, and several of them can be changed — which is why lifestyle now sits alongside medicines and procedures in the treatment of AF.
Why does atrial fibrillation matter?
Stroke
This is the most serious consequence. Blood pooling in the quivering atria can form clots, and if a clot travels to the brain it causes a stroke. People with AF have around five times the stroke risk of those without it, and strokes caused by AF tend to be more severe. Roughly a quarter of all strokes are linked to AF.
Heart failure
A heart that beats irregularly and too fast for long periods cannot pump efficiently. Over time this can weaken the heart muscle and lead to heart failure — and, in turn, heart failure makes AF more likely. In some people, treating the AF allows the heart to recover.
Quality of life
Even without these complications, AF can leave people breathless, tired and anxious, and limit what they can do day to day.
Thinking and memory
Research increasingly links AF to a higher risk of cognitive decline and dementia, even in people who have not had a stroke.
How is it diagnosed?
AF is confirmed with an electrocardiogram (ECG), a simple recording of the heart's electrical activity. Because episodes can come and go, your doctor may also arrange longer monitoring — a portable monitor worn for 24 hours to several days, or, for people with infrequent symptoms, a small device implanted under the skin that records the rhythm for months.
Some smartwatches and personal devices can now detect an irregular rhythm and prompt the wearer to seek advice. These can be useful for flagging possible AF, but a diagnosis still needs to be confirmed by a doctor with an ECG.
Once AF is diagnosed, further tests — such as blood tests and an echocardiogram (heart ultrasound) — help to check for underlying causes and to assess how well the heart is working.
How is atrial fibrillation treated?
Treatment has several aims, and most people will need more than one approach.
Preventing stroke
Because stroke is the main danger, most people with AF are assessed for their stroke risk, and many are prescribed blood-thinning medicines (anticoagulants) to reduce the chance of clots forming. For people who cannot take these medicines long term, a procedure to seal off the pocket in the atrium where clots most often form may be an option.
Controlling the heart rate
Medicines such as beta blockers slow the heart so that, even if the rhythm remains irregular, it is not racing. For some people, particularly those with permanent AF, this is the main treatment.
Restoring a normal rhythm
Where the aim is to get the heart back into a regular rhythm and keep it there, options include anti-arrhythmic medicines; cardioversion, a controlled electrical shock delivered under sedation; and catheter ablation, a procedure in which thin tubes are threaded through a vein to the heart and used to create tiny scars that block the faulty electrical signals. Ablation is increasingly used earlier in the course of AF, and can be particularly effective for people whose heart failure is being driven by their AF.
Treating the causes
Managing blood pressure, losing weight, treating sleep apnoea and reducing alcohol are now recognised as treatments in their own right. In many people, addressing these factors reduces how often AF occurs and how severe it is — and improves the results of other treatments.
The right combination depends on the type of AF, your symptoms, your stroke risk and your other health conditions, and is best worked out with your doctor or cardiologist.
Reducing your risk
Whether you are trying to avoid AF or to keep it under control after a diagnosis, the same steps help:
- Keep your blood pressure in a healthy range and have it checked regularly.
- Limit alcohol. Cutting back — or stopping — is one of the most effective changes people with AF can make.
- Aim for a healthy weight, and if you snore heavily or wake unrefreshed, ask about being tested for sleep apnoea.
- Stay physically active. Regular moderate exercise protects the heart.
- Don't smoke.
- Manage diabetes and cholesterol with your GP.
- Know your pulse. Learning to check for an irregular rhythm, especially over 65, can help catch AF early.
If you are worried about atrial fibrillation, talk to your GP, or call the Baker Specialist Clinics on (03) 8532 1800 about seeing one of our cardiologists.