What is atrial fibrillation?

What atrial fibrillation actually is

A normal heartbeat is an electrical wave that travels in an orderly pattern from the top of the heart to the bottom. In AF, that orderly wave is replaced by chaos in the heart's two upper chambers — the atria.

Instead of contracting cleanly, the atria quiver — hundreds of disorganised electrical signals firing at once. Only some of those signals make it through to the lower chambers (the ventricles), and they arrive at irregular intervals. The result is an irregular, often fast pulse.

A normal resting heart rate sits between 60 and 100 beats per minute. In uncontrolled AF, the heart rate can climb to 120, 150, even 175 beats per minute at rest. When medications keep the rate around or below 100, doctors call this rate-controlled AF — the rhythm is still irregular, but the heart isn't being overworked.

Symptoms (and why some people feel nothing)

AF presents very differently from one person to the next. Some people are aware of every irregular beat. Others have no symptoms at all and only discover they're in AF when a smartwatch alerts them, a GP checks their pulse, or — in the worst case — they have a stroke.

Common symptoms

• Palpitations — an awareness of the heart racing, fluttering, or beating irregularly
• Shortness of breath, particularly on exertion
• Fatigue and reduced exercise capacity
• Light-headedness or dizziness
• Chest discomfort (less common, and warrants prompt assessment)
• Increased need to pass urine during an episode

Silent AF — the case for paying attention

Up to a third of people with AF have no symptoms whatsoever. This is called silent or subclinical AF, and it's a particular concern because the stroke risk is the same — but without symptoms, there's nothing prompting the person to see a doctor.

What causes AF and who's at risk

AF rarely has a single cause. It usually emerges from a combination of factors that stress and remodel the upper chambers of the heart over years.

The major risk factors

Other contributors include chronic kidney disease, lung diseases such as COPD, and recent major surgery or serious infection. In some people — particularly younger ones — no clear risk factor is found. This is called lone AF.

The three types of AF

AF is grouped by how long episodes last and whether the rhythm returns to normal on its own. The category matters because it guides treatment decisions.

Why AF matters: stroke and heart failure

AF itself rarely causes sudden harm. The reason cardiologists take it seriously is what it can lead to.

Stroke

When the atria quiver instead of contracting, blood pools and can form clots — most often in a small pouch called the left atrial appendage. If a clot breaks free, it travels through the bloodstream and can lodge in a brain artery, causing a stroke. People with untreated AF are roughly five times more likely to have a stroke than people without AF, and AF-related strokes tend to be larger and more disabling than other strokes.

This is why blood-thinning medication (anticoagulation) is central to AF management. Your doctor will use a stroke-risk score to decide whether anticoagulation is appropriate — for most people over 65, and for many younger people with risk factors, the answer is yes.

Heart failure

When the heart races for long periods, the heart muscle gradually weakens — a condition called tachycardia-induced cardiomyopathy. The reassuring part: it's usually reversible once the heart rate is controlled. Even in patients with established heart failure, restoring normal rhythm (where possible) can substantially improve symptoms and outcomes.

How AF is diagnosed

AF is diagnosed by recording the heart's electrical activity during an episode. The standard test is an ECG (electrocardiogram) — a short, painless recording with stickers placed on the chest, arms, and legs.

If you have symptoms but the ECG is normal

This is common — episodes are intermittent and may not coincide with the test. Options to capture an episode include:

• Holter monitor — a small recorder worn for 24 hours to 14 days
• Event monitor or loop recorder — worn for longer periods, activated when symptoms occur
• Implantable loop recorder — a small device placed under the skin that records continuously for up to three years
• Smartwatch ECG — increasingly accepted as a screening tool, with confirmation by a 12-lead ECG

Tests done alongside the ECG

Once AF is confirmed, most patients have:

• An echocardiogram to look at heart structure, valve function, and pumping strength
• Blood tests including thyroid function, kidney function, and electrolytes
• An assessment of stroke and bleeding risk
• Sleep history and, where appropriate, a referral for sleep study

How AF is treated

Modern AF care follows three pillars — often referred to as the ABC pathway. Each pillar matters; none replaces the others.

A — Anticoagulation (preventing stroke)

For most patients with AF, a blood thinner is the single most important treatment. The choice today is between:

• Direct oral anticoagulants (DOACs) — apixaban, rivaroxaban, dabigatran, edoxaban. Preferred for most patients. No INR monitoring, fewer food and drug interactions, and lower bleeding risk than warfarin.
• Warfarin — still used in specific situations such as mechanical heart valves or moderate-to-severe mitral stenosis. Requires regular INR blood tests.

Aspirin is not effective for stroke prevention in AF and is no longer recommended for this purpose.

B — Better symptom control (rate or rhythm)

The aim here is to make you feel well. Two strategies, often used in combination:

• Rate control — medications such as beta blockers or calcium channel blockers slow the heart rate so the irregular rhythm doesn't make you breathless or tired.
• Rhythm control — restoring and maintaining normal sinus rhythm. Options include:
  • Electrical cardioversion — a brief, controlled shock under sedation that resets the rhythm
  • Antiarrhythmic medications — such as flecainide, sotalol, or amiodarone
  • Catheter ablation — a procedure that uses heat or cold energy to isolate the electrical triggers in the upper chambers, typically around the pulmonary veins

Recent evidence has shifted practice: in selected patients with symptomatic paroxysmal AF, catheter ablation is now considered a reasonable first-line option rather than a last resort, with better symptom control and fewer recurrences than medication alone.

C — Comorbidities and risk factors

This pillar is sometimes overlooked, but the evidence is now compelling: treating the conditions that drive AF can halve the frequency of episodes and improve the success of every other treatment.

• Sustained weight loss (in patients with overweight or obesity)
• Treating obstructive sleep apnoea
• Tight blood pressure control
• Reducing or eliminating alcohol
• Regular moderate exercise (extreme endurance exercise can paradoxically increase risk)
• Good control of diabetes and thyroid function

Living with AF

An AF diagnosis is unsettling, but the long-term outlook for well-managed AF is generally good. Most people continue to work, travel, and exercise without major restrictions.

Exercise

Regular moderate exercise is encouraged — it actually reduces AF burden. Walking, swimming, cycling, and structured gym programs are all appropriate. Very high-intensity endurance exercise (marathons, long-distance cycling) is one of the few activities that may slightly increase AF risk in some people.

Travel and flying

AF on its own is not a contraindication to flying. Keep your medication with you in hand luggage and stay well hydrated.

Alcohol and caffeine

Alcohol is a clear trigger. Even one or two drinks can provoke episodes in some patients, and reducing alcohol meaningfully reduces AF burden. Caffeine is much less commonly a trigger — most patients tolerate normal coffee intake without problems.

Mental load

Living with an unpredictable rhythm is genuinely stressful, and anxiety and AF often feed each other. If you find the diagnosis is affecting your mood or sleep, raise it with your GP or cardiologist — it's a normal part of the picture and there's help available.

When to seek urgent help

Most AF episodes are not emergencies. But certain symptoms — whether or not you already have an AF diagnosis — need immediate medical attention.

For sustained palpitations that don't settle within an hour, persistent racing heart, or new symptoms that are different from your usual AF, contact your GP or cardiologist promptly — same-day assessment is usually appropriate.

Frequently asked questions