Atrial Fibrillation: Causes, Risks and Treatment

Atrial fibrillation (AF or AFib) is the most common sustained cardiac arrhythmia — an abnormal heart rhythm in which the upper chambers of the heart (the atria) beat chaotically and very rapidly instead of with the coordinated, regular contractions of a normal heartbeat. AF affects an estimated 33–40 million people globally and its prevalence rises sharply with age.

AF is not immediately life-threatening in most cases, but it carries a significant risk of stroke — five times higher than in people without AF — and can lead to heart failure when left untreated over years.

How the Normal Heart Rhythm Works

In a healthy heart, each beat is initiated by an electrical impulse from the sinoatrial (SA) node — the heart's natural pacemaker — located in the right atrium. This impulse spreads across both atria, causing them to contract and push blood into the ventricles. It then passes through the atrioventricular (AV) node to trigger coordinated ventricular contraction.

This sequence produces the regular pulse felt at the wrist: 60–100 beats per minute at rest, with each beat efficient and rhythmic.

What Happens in Atrial Fibrillation

In AF, instead of a single ordered electrical impulse from the SA node, multiple chaotic electrical signals fire simultaneously from many sites within and around the atria. The atria quiver (fibrillate) rather than contract properly, losing up to 10–15% of their pumping contribution.

Because the AV node cannot conduct every disorganised signal to the ventricles, only some signals get through — unpredictably. This produces the hallmark of AF: an irregularly irregular pulse, often rapid (140–160 beats per minute in untreated AF).

Atrial Flutter

Closely related to AF, atrial flutter involves a single, fast but organised circuit of electrical activity cycling around the right atrium, causing very rapid atrial contractions (250–350 per minute). The ventricles typically respond to every second or third atrial beat, producing a rapid but often regular pulse of around 150 beats per minute. Many people with atrial flutter also experience AF at other times.

Causes and Risk Factors

AF can occur in people with structurally normal hearts, but it is more commonly associated with underlying conditions:

• Hypertension (high blood pressure) — the single most common risk factor; causes left atrial enlargement
• Coronary artery disease — reduces blood supply to the atrial tissue
• Heart failure — raised atrial pressure promotes AF; AF worsens heart failure, creating a vicious cycle
• Heart valve disease — particularly mitral valve stenosis or regurgitation (enlarges the left atrium)
• Cardiomyopathy — disease of the heart muscle
• Congenital heart defects
• Obstructive sleep apnoea — intermittent oxygen desaturation triggers electrical changes in atrial tissue
• Hyperthyroidism (overactive thyroid) — excess thyroid hormone overstimulates the heart
• Excess alcohol — "holiday heart" syndrome; acute or chronic alcohol use is a well-established trigger
• Obesity — an independent risk factor independent of associated hypertension and diabetes
• Age — risk doubles with each decade over 55; AF affects around 9% of people over 80

Types of AF by Duration

Symptoms

Symptoms vary widely — some people are unaware they have AF; others are significantly disabled by it.

Common symptoms include:

• Palpitations — an awareness of the heartbeat, often described as fluttering, racing or irregular
• Breathlessness — on exertion or at rest, particularly when the ventricular rate is rapid
• Fatigue and reduced exercise tolerance
• Dizziness or light-headedness
• Chest tightness or discomfort
• Weakness

Symptoms are typically worse when the ventricular rate is rapid. When rate is well-controlled (60–80 bpm at rest), many patients are largely asymptomatic.

In some patients, the first presentation of AF is a stroke — often devastating and entirely preventable with appropriate anticoagulation.

Why Atrial Fibrillation Increases Stroke Risk

When the atria fibrillate rather than contract, blood stagnates within them — particularly in the left atrial appendage (LAA), a small pouch in the left atrium. Stagnant blood tends to clot. These clots can break off, travel through the circulation, and block a cerebral artery, causing a stroke.

AF increases stroke risk fivefold compared with people in sinus rhythm. AF-related strokes tend to be more severe and disabling than strokes from other causes. The annual stroke risk in AF is estimated by the CHA₂DS₂-VASc score, which weighs age, sex, blood pressure, diabetes, prior stroke, vascular disease and heart failure.

Diagnosis

Electrocardiogram (ECG)

AF is confirmed by ECG, which shows:

• Absence of distinct P waves (replaced by irregular, low-amplitude fibrillatory activity)
• Irregularly irregular R-R intervals — no pattern to when ventricles contract
• Rapid ventricular rate in untreated AF

A single 12-lead ECG captures the rhythm if AF is ongoing. A 24-hour or 7-day Holter monitor is used to detect paroxysmal AF that comes and goes.

Additional Investigations

• Echocardiogram — assesses cardiac structure, valve function, left atrial size, and clot within the left atrial appendage
• Thyroid function tests — to exclude hyperthyroidism as a reversible cause
• Full blood count, kidney function, liver function — baseline before starting anticoagulation
• Sleep study — if obstructive sleep apnoea is suspected

Treatment

Treatment of AF has three main goals:

1. Rate control — prevent the ventricles from beating too fast
2. Rhythm control — restore and maintain normal sinus rhythm where appropriate
3. Anticoagulation — prevent stroke

Rate Control

For many patients, particularly older adults with few symptoms, controlling the ventricular rate (targeting 60–80 bpm at rest) is adequate management. Medications include:

• Beta-blockers (e.g. metoprolol, bisoprolol) — first-line
• Calcium channel blockers (e.g. diltiazem, verapamil) — alternative
• Digoxin — useful when other agents are not tolerated, particularly in heart failure

Rhythm Control

Restoring normal sinus rhythm is preferred in younger patients, those with significant symptoms, and those in whom AF may be reversible. Options include:

• Cardioversion — a controlled electric shock delivered under brief sedation, which resets the heart to normal rhythm; effective and safe
• Antiarrhythmic drugs — flecainide (in structurally normal hearts), amiodarone (broadly effective but with side effects requiring monitoring), sotalol, dronedarone
• Catheter ablation — the most effective intervention for maintaining long-term sinus rhythm in paroxysmal and persistent AF

Catheter Ablation for Atrial Fibrillation

Catheter ablation is a minimally invasive procedure performed under sedation or light general anaesthesia. Thin catheters are passed through the femoral vein to the heart, where radiofrequency energy (or cryotherapy) creates scar lines that electrically isolate the pulmonary veins — the most common triggers of AF — from the left atrium.

Success rates (freedom from AF at 12 months without antiarrhythmic drugs) are approximately:

• Paroxysmal AF: 70–80%
• Persistent AF: 50–70% (often requiring repeat procedures)

Ablation is increasingly recommended as first-line therapy for symptomatic paroxysmal AF, particularly in younger patients, following evidence that early rhythm control reduces cardiovascular events compared with rate control alone.

Anticoagulation

Anticoagulants (blood thinners) substantially reduce stroke risk and are recommended for most patients with AF and a CHA₂DS₂-VASc score of 2 or above.

Direct oral anticoagulants (DOACs) — rivaroxaban, apixaban, dabigatran, edoxaban — are preferred over warfarin due to:

• Predictable dosing (no routine INR monitoring)
• Lower risk of intracranial haemorrhage
• Similar or superior efficacy in preventing stroke

In patients who cannot tolerate anticoagulants, percutaneous left atrial appendage occlusion (LAAO) — sealing off the LAA with a device (e.g. Watchman, Amulet) — is an alternative to prevent clot formation.

AF Management in China

China's major cardiac electrophysiology centres perform among the highest volumes of AF ablation procedures globally:

• State-of-the-art ablation laboratories: 3D mapping systems (CARTO, EnSite NavX), contact-force catheters, and cryoballoon ablation are all available
• High-volume operators: leading centres in Beijing, Shanghai and Guangzhou perform hundreds of AF ablations annually, with outcomes comparable to top European and North American institutions
• One-stop AF assessment: ECG, echocardiogram, Holter monitoring, CHA₂DS₂-VASc scoring and anticoagulation initiation within a single-day appointment
• Left atrial appendage occlusion (LAAO): available for patients unsuitable for long-term anticoagulation
• Cost: AF ablation in China typically costs 30–40% of UK private rates
• Full English support throughout consultation, procedure and discharge planning

Contact a ChinaMedicalTour care navigator to arrange an AF assessment or ablation consultation.

Medical content based on MSD Manuals, authored by L. Brent Mitchell MD (Libin Cardiovascular Institute, University of Calgary), reviewed by Jonathan G. Howlett MD. Last reviewed September 2024, updated July 2025.