Atrial Fibrillation (AF)
Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and is characterised by rapid, irregular atrial electrical activity, leading to an irregularly irregular pulse and increased risk of stroke, heart failure, and thromboembolism.
This page covers the definition, causes, risk factors, classification, symptoms, ECG findings, diagnosis, investigations, management, and complications of atrial fibrillation, with emphasis on anticoagulation, rate control, and rhythm control.
The content is based primarily on NICE guideline [NG196] Atrial fibrillation: diagnosis and management.
Background Information
Definition
AF is a chaotic, rapid (300-500 bpm While the atria fire chaotically at 300-500 bpm, the AV node acts as a gatekeeper that limits how many impulses reach the ventricles, resulting in a ventricular rate (heart rate) that is typically much slower (though still often rapid and irregular when untreated).
Classification
| Type | Description |
|---|---|
| Paroxysmal AF | AF that self-terminates, lasts <7 days (but usually within 48 hours) |
| Persistent AF | AF episode lasts >7 days or requires cardioversion to restore sinus rhythm |
| Permanent AF | Rhythm control strategy is abandoned, and it is accepted that the person will remain in permanent AF |
Pathophysiology
AF is often triggered by electrical activity originating from ectopic foci, most commonly generated in the pulmonary veins.
Causes and Risk Factors
Risk factors for developing chronic AF: [Ref1, Ref2]
- Advancing age
- Causes of left atrial dilation
- Mitral valve disease
- Heart failure
- Obstructive sleep apnoea
- Hypertension
- Metabolic syndrome
- CKDChronic kidney disease
Risk factors for developing acute AF episodes: [Ref1, Ref2]
- Any acute illness or infection (e.g. sepsis, pneumonia)
- Acute alcohol intoxication (holiday heart syndrome)
- Thyrotoxicosis
- Post-operative state
Complications
Major complications of AF: [Ref]
- Embolic stroke (ischaemic) – most important complication
- Systemic thromboembolism (renal infarct, splenic infarct, mesenteric ischaemia)
- Heart failure
Pulmonary embolism can occur if there is an intracardiac shunt (e.g. atrial septal defect, PFOPatent Foramen Ovale )
Diagnosis
Be aware that the heart rate (ventricular rate) during active AF varies; it can be normal, slow, or fast depending on how the AV node filters the chaotic atrial impulses.
Generally, fast AF is more common in symptomatic patients. Normal / slow AF typically occurs in those with high vagal tone (e.g. athletes, during sleep), underlying AV conduction disease, older adults, and patients on rate-controlling medications. [Ref]
Clinical Features
Symptoms
10-40% of patients are asymptomatic [Ref]
Symptoms are highly non-specific:
- Palpitations – typical description is ‘irregular heartbeat’, ‘fluttering’, ‘pounding’
- Exertional dyspnoea
- Exercise intolerance
- Fatigue
The relationship between AF rhythm and symptoms is complex and inconsistent: [Ref]
- Patients can be symptomatic only when in AF and asymptomatic when in sinus rhythm
- But even while actively in AF, they can have symptoms or be completely asymptomatic
Examination Findings
Typical findings when the patient is actively in AF:
- Irregularly irregular pulse
- Variable 1st heart sound intensity
Features of the associated cause can also be present concurrently:
- Mitral stenosis → malar flush, mid-diastolic murmur with loud S1, history of rheumatic fever (see the Heart Valve Disease article for more information)
- Mitral regurgitation → pansystolic murmur that radiates to the axilla (see the Heart Valve Disease article for more information)
- Chronic heart failure → exertional dyspnoea, bi-basal crackles, history of ischaemic heart disease (see the Chronic Heart Failure article for more information)
To accurately comment on the pulse rate in AF at the bedside:
- Palpate the radial pulse for a full 60 sec
- Auscultate the apex for a full 60 sec (apical pulse method) – preferred
Investigation and Diagnosis
Test of choice: resting 12-lead ECG
- ECG is always required to confirm the diagnosis
- If paroxysmal AF is suspected, or the initial ECG is inconclusive despite ongoing clinical suspicion of AF → 24-hour Holter monitoring
- Last resort for maximum sensitivity: implantable loop recorders
Implantable loop recorders (ILRs) are small, subcutaneous cardiac monitoring devices that provide continuous, long-term ECG monitoring for up to 3-5.5 years to detect infrequent arrhythmias and correlate symptoms with cardiac rhythm.
[Ref]
Additional investigations after AF is diagnosed:
- Transthoracic echocardiography (to assess for structural heart disease and cardiac function)
- Blood tests
Important to determine stroke and bleeding risk factors, as well as underlying conditions that will guide further management.
(FBC, U&E, LFT, TFT, HbA1c)
ECG Findings in AF
- Irregularly irregular R-R intervals
- Absence of discrete P waves preceding QRS complexes
- Narrow QRS complexes (unless aberrancy
In atrial fibrillation, QRS complexes are narrow because impulses conduct through the normal His-Purkinje system; however, aberrancy (functional or fixed bundle branch block) can cause transient or persistent QRS widening despite the supraventricular origin of the arrhythmia.
is present) - Heart rate can vary (normal / slow / fast)
Management
Acute Management
The following points are the same as those covered in the Tachycardia (Peri-Arrest) Management article.
The first step is to check for ANY of the life-threatening features:
- Shock – hypotension (SBP < 90 mmHg) and/or features of sympathetic compensation
- Tachycardia
- Cold pale skin
- ↓ CRT
- Symptoms of ↓ cerebral blood flow (confusion, ↓ GCS)
- Syncope
Only syncope is considered an unstable feature in the context of periarrest tachycardia guidelines; presyncope (near-syncope) does not qualify as an unstable feature. Syncope is defined as a transient, complete loss of consciousness with inability to maintain postural tone and rapid recovery, whereas presyncope refers to symptoms such as extreme lightheadedness or altered consciousness without complete loss of consciousness.
– due to ↓ cerebral blood flow - Myocardial ischaemia – chest pain and/or 12-ECG findings
- Heart failure – pulmonary oedema (LV failure) and/or raised JVP (RV failure)
- Immediately post-ROSC
ROSC: return of spontaneous circulation
The unstable, high-risk period right after a pulse is regained (following a cardiac arrest), before the patient is physiologically stabilised.
Subsequent management:
| Life-threatening feature(s) present → | Immediate synchronised DC shockShock must be synchronised to occur with the R wave of the ECG to avoid R on T phenomena which can induce ventricular arrhythmias up to 3 attempts, under sedation or anaesthesia (initial shock at maximum defibrillator output is reasonable)
|
| No life-threatening features → | There are 2 management approaches (depending on the onset of AF):
|
In acute AF of onset that is <48 hours, there is NO clean-cut guidance on choosing between rate and rhythm control:
- NICE and international guidelines recommend considering BOTH rate of rhythm control, as they yield comparable outcomes
- Shared decision making between the patients and the doctor is recommended (i.e. depends on the patient’s wish and concerns, also local resources)
- A few key points to note: [Ref1][Ref2]
- Rate control is reasonable for those who are asymptomatic (or minimally symptomatic), especially when spontaneous conversion is likely and acute triggers (e.g. infection, alcohol, dehydration) are addressed
- Rhythm control is preferred for those with persistent symptoms or inability to achieve adequate rate control despite optimal therapy
- Rhythm control may also be considered in those with heart failure secondary to AF or younger patients
The key exam culprit is that if the onset of AF is >48 hours (or uncertain) → do NOT offer acute rhythm control (i.e. cardioversion), as these patients would require prior anticoagulation.
In exams, apart from an unstable patient needing immediate cardioversion, it is uncommon for the question to ask the student to choose between methods of rhythm control. Instead, it is more common for the question to test one’s knowledge on individual cardioversion methods, such as which drug to use and precautions.
Rate Control in Acute AF
Offer any of the following:
- Beta blocker (e.g. bisoprolol, metoprolol, carvedilol), or
- Rate-limiting CCB (verapamil or diltiazem), or
- Digoxin
Rate-limiting CCBs (verapamil and diltiazem) should be avoided if there is heart failure or if there is ↓ ejection fraction. Beta blocker or digoxin should be used instead.
This is because rate-limiting CCBs (specifically non-DHP CCBsNon-dihydropyridine calcium-channel blocker) have a strong -ve inotropic and -ve chronotropic effects, which can depress myocardial contractility, worsening heart failure, and potentially triggering cardiac arrest.
A common reason to avoid beta blocker is if the patient is asthmatic.
Rhythm Control in Acute AF
Either pharmacological OR electrical cardioversion is appropriate for rhythm control in acute AF – NICE recommends considering the choice depending on clinical circumstances and resources.
- Electrical cardioversion is more effective and provides rapid restoration of sinus rhythm, but requires sedation [Ref]
| Pharmacological cardioversion | Electrical cardioversion | |
|---|---|---|
| Reasons to choose one over another [Ref] |
|
|
| Choice of drug / approach |
|
|
Long Term Management
There are 2 main aspects of the long-term management of AF:
- Symptom management (with rate or rhythm control)
- Assessing and reducing risk of stroke (if indicated)
It is important to note that NOT all patients with AF automatically need symptom management. Asymptomatic patients without tachycardia do NOT routinely require rate/rhythm control and can be managed with active observation.
However, assessment for the need of anticoagulation (to reduce risk of stroke) is necessary for ALL patients diagnosed with AF, irrespective of the type of atrial fibrillation OR presence of symptoms.
1. Symptom Management
Symptoms of AF can be managed by either 1) rate or 2) rhythm control.
Rate control should be offered as 1st line to most patients. A few exceptions where rate control should NOT be offered as 1st line:
- New onset AF (<48 hours onset) (→ rate OR rhythm control is appropriate)
- AF causing heart failure (→ rhythm control preferred)
- Presence of a reversible cause (→ treat the underlying cause)
- AF with atrial flutter deemed suitable for ablation strategy (→ catheter ablation preferred)
Rate Control
1st line: monotherapy of standard cardioselective beta blocker or rate-limiting CCB (diltiazem / verapamil)
- If AF + heart failure: beta blocker is preferred
- Digoxin monotherapy is a 1st line alternative in those who do little physical activity
Digoxin is less effective during exertion
If monotherapy is ineffective in controlling the rate → offer dual therapy with ANY 2 of the following:
- Standard beta blocker or
- Diltiazem or
- Digoxin
The treatment goal for ongoing rate control in AF is to alleviate symptoms and target a resting HR of <100-110 bpm. [Ref]
Do not offer amiodarone for long-term rate control.
Rhythm Control
Precautions Before Cardioversion
If AF onset is <48 hours → cardioversion can be carried out now with a heparin infusion prior
If AF onset is >48 hours (or uncertain), precautions must be taken:
- Delay cardioversion until patient has been on at least 3 weeks of anticoagulation, or
- Perform TOETransoesophageal echocardiography to exclude a left atrial thrombus → then give heparin and cardiovert now (if immediate cardioversion is desired)
The reason extra precautions are needed prior to cardioversion in those with AF onset >48 hours is because after 48 hours it is likely that a left atrial thrombus has formed.
If the patient is cardioverted immediately without any anticoagulation, the cardioversion is likely to dislodge the left atrial thrombus and cause an embolic stroke.
Details on Various Rhythm Control Methods
Choosing between various rhythm control methods (if opted for):
- If AF has persisted for >48 hours → electrical cardioversion is preferred due to its superior efficacy and rapid conversion
- Some reasons to avoid electrical cardioversion: 1) patient prefers not to 2) patient unable to tolerate sedation / anaesthesia
- AF with atrial flutter deemed suitable for ablation strategy → catheter ablation preferred
In exams, apart from an unstable patient needing immediate cardioversion, it is uncommon for the question to ask the student to choose between methods of rhythm control. Instead, it is more common for the question to test one’s knowledge on individual cardioversion methods, such as which drug to use and precautions.
| Rhythm control option | Sub-options | Recommendations |
|---|---|---|
| Electrical | n/a | Synchronised DC cardioversion
Consider amiodarone starting 4 weeks before and continuing for up to 12 months after electrical cardioversion to maintain sinus rhythm |
| Pharmacological | Long-term rhythm control |
|
| As required (pill in the pocket) / no drug treatment | Consider if there is infrequent paroxysmal AF AND minimally symptomatic or induced by known precipitants
The “pill in the pocket” approach refers to the self-administration of a single oral dose of an antiarrhythmic drug at the onset of symptomatic AF, to achieve pharmacological cardioversion outside the hospital |
|
| Cardiac catheterisation interventions | Left atrial ablation (pulmonary vein isolation) |
|
| Pace and ablate | Pacemaker implanted before AV node ablation
|
2. Stroke Risk Reduction
The drug class of choice to reduce stroke risk in AF is anticoagulants (not antiplatelets), the decision is mainly influenced by balancing the risk of stroke and risk of bleeding.
Assessing the need for anticoagulation in AF is very important; all patients with AF should be assessed (even after a single AF episode or paroxysmal AF).
Assessing Risk of Stroke
The CHA2DS2VSc score is recommended to assess the risk of stroke in AF:
| Male |
|
| Female |
|
Do not offer anticoagulation to a person aged under 65 years with AF and no risk factors other than their sex (a very low risk of stroke equating to a CHA2DS2-VASc score of 0 for men or 1 for women)
| CHA2DS2VSc score component | Score |
|---|---|
| Congestive heart failure | 1 |
| Hypertension | 1 |
| Age (65-74 y/o) | 1 |
| Age (≥75 y/o) | 2 |
| Diabetes | 1 |
| Stroke / TIATransient ischaemic attack / thromboembolism (arterial) | 2 |
| Vascular disease (IHDIschaemic heart disease, PADPeripheral arterial disease) | 1 |
| Sex (female) | 1 |
Extra information:
The 2024 ESC guidelines now recommend using the CHA2DS2VA score, removing the 1 point previously assigned to “Female Sex” in the original CHA2DS2VSc model.
However, this is yet to be reflected in NICE guideline. Therefore, this is unlikely to be examined in the UKMLA, but one may encounter this in clinical practice.
Assessing Risk of Bleeding
NICE recommends the ORBIT score
- But there are no recommendations on using the score to guide the decision of whether to give anticoagulation or not
- Clinical judgement should be used, while taking the patient’s wishes into account
Choice of Anticoagulation
There are 2 main patient populations:
| Patients with valvular AF (i.e. AF with a mechanical heart valve or moderate to severe mitral stenosis) | 1st line: warfarin |
| Other patients | 1st line: DOACsDirect oral anticoagulants (apixaban / rivaroxaban / dabigatran / edoxaban)
2nd line: warfarin |
If anticoagulation is not appropriate → consider left atrial appendage occlusion Left atrial appendage occlusion (LAAO) is a percutaneous or surgical procedure that mechanically seals off the left atrial appendage, the source of >90% of cardiac thrombi in nonvalvular AF, to reduce stroke risk as an alternative to oral anticoagulation.
Do not withhold anticoagulation solely because of a person’s age or their risk of falls.
References
NICE guideline [NG196] Atrial fibrillation: diagnosis and management. Last updated: Jun 2021.