Atrial Fibrillation: Diagnosis and Management

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and a favourite of examiners because it ties together a memorable ECG, a two-limbed management plan, and a genuinely important decision about stroke prevention. Get the framework, control the rate or rhythm, and decide on anticoagulation, and you have covered most of what the UKMLA asks.

This is a revision guide, not a clinical protocol. Always check management against current NICE guidance, the BNF and your local trust policy.

Key points

• AF is an irregularly irregular rhythm with absent P waves on the ECG.
• Management has two separate limbs: controlling the ventricular rate or rhythm, and preventing stroke.
• Rate control (usually a beta-blocker or a rate-limiting calcium-channel blocker) is first-line for most patients.
• Stroke risk is assessed with the CHA2DS2-VASc score; bleeding risk with a tool such as ORBIT.
• A DOAC is first-line for anticoagulation in most patients; aspirin is not used for stroke prevention in AF.

What atrial fibrillation is

In AF, disorganised electrical activity in the atria replaces coordinated contraction, so the atria quiver rather than contract and the ventricles respond irregularly. This produces an irregular pulse, loss of the atrial contribution to filling, and blood stasis in the left atrium, which is why AF raises the risk of thromboembolic stroke.

AF is usually classified by its time course:

• Paroxysmal: episodes that stop on their own, typically within 48 hours and by definition within 7 days.
• Persistent: lasting longer than 7 days, or requiring cardioversion to terminate.
• Permanent: ongoing AF where a decision has been made not to attempt to restore sinus rhythm.

Common causes

Look for a precipitant. Frequently examined associations include ischaemic heart disease, hypertension, mitral valve disease, thyrotoxicosis, sepsis and other acute infection, alcohol excess, pulmonary embolism, and electrolyte disturbance. Some AF is "lone" with no identifiable cause.

Presentation

AF may be asymptomatic and found incidentally, or cause palpitations, breathlessness, chest discomfort, dizziness or syncope. It can precipitate or worsen heart failure. Some patients present for the first time with a stroke or TIA. On examination the classic sign is an irregularly irregular pulse.

Diagnosis

The diagnosis is made on the ECG:

• Irregularly irregular R-R intervals.
• Absent P waves, with a fibrillatory (chaotic) or flat baseline.
• The QRS complexes are usually narrow unless there is co-existing bundle branch block.

For suspected paroxysmal AF with a normal resting ECG, ambulatory monitoring (for example a 24-hour tape or longer) is used to capture an episode. Baseline investigations typically include thyroid function, urea and electrolytes, full blood count, and an echocardiogram to assess structure and valves.

Management: the two limbs

Think of AF management as two independent questions. First, how do we control the heart? Second, how do we protect the brain? They are decided separately.

Limb 1: rate or rhythm control

Rate control is first-line for most patients. Options include a standard beta-blocker (not sotalol) or a rate-limiting calcium-channel blocker such as diltiazem or verapamil. Digoxin is generally reserved for sedentary patients or as an add-on, and can be useful where there is co-existing heart failure. Note that rate-limiting calcium-channel blockers such as verapamil and diltiazem should be avoided in heart failure with reduced ejection fraction.

Rhythm control (aiming to restore and maintain sinus rhythm) is considered in specific situations, for example new-onset AF, AF with a reversible cause, AF causing heart failure, or symptoms that persist despite adequate rate control. It may involve cardioversion (electrical, or pharmacological with an agent such as flecainide or amiodarone), long-term antiarrhythmic drugs, or catheter ablation in selected patients. Flecainide is avoided where there is structural or ischaemic heart disease.

A crucial safety point around cardioversion: if AF has been present for more than 48 hours (or the duration is unknown), the patient should be anticoagulated for at least 3 weeks before elective cardioversion, or a transoesophageal echocardiogram used to exclude atrial thrombus, because restoring sinus rhythm can dislodge a clot and cause a stroke.

When AF is an emergency

If a patient with AF is haemodynamically unstable, for example with shock, syncope, myocardial ischaemia or acute heart failure, this is a peri-arrest situation and emergency electrical cardioversion is indicated. Escalate to seniors immediately.

Limb 2: stroke prevention

This is the highest-yield decision. Estimate stroke risk with the CHA2DS2-VASc score:

• C — Congestive heart failure (1)
• H — Hypertension (1)
• A2 — Age 75 or over (2)
• D — Diabetes mellitus (1)
• S2 — prior Stroke, TIA or thromboembolism (2)
• V — Vascular disease (1)
• A — Age 65 to 74 (1)
• Sc — Sex category female (1)

The higher the score, the higher the annual stroke risk, and the stronger the case for anticoagulation. In broad terms, anticoagulation is offered as the score rises (and is generally recommended for a score of 2 or more); a female sex point on its own, with no other risk factors, does not by itself mandate anticoagulation. Assess bleeding risk alongside this, for example with the ORBIT score, and address modifiable bleeding risk factors, but a high bleeding score is not an automatic reason to withhold anticoagulation.

For anticoagulation itself, a direct oral anticoagulant (DOAC) such as apixaban, rivaroxaban, dabigatran or edoxaban is first-line for most patients. Warfarin is used where a DOAC is unsuitable, for example with a mechanical heart valve or moderate-to-severe mitral stenosis. Aspirin should not be used for stroke prevention in AF.

Exam pearls

• Irregularly irregular pulse with absent P waves is the giveaway.
• Management splits into rate/rhythm control and stroke prevention; decide them separately.
• CHA2DS2-VASc estimates stroke risk; ORBIT (or similar) estimates bleeding risk.
• DOAC first-line; warfarin for mechanical valves or moderate-to-severe mitral stenosis.
• Unstable AF means emergency electrical cardioversion.
• AF over 48 hours needs anticoagulation before elective cardioversion (or a TOE first).

The bottom line

Atrial fibrillation is a structured, high-yield topic: recognise the irregularly irregular, P-wave-less ECG, look for a precipitant, then work through the two limbs, control the rate (or rhythm where indicated), and make a deliberate anticoagulation decision using CHA2DS2-VASc with a DOAC first-line.

If the rate-versus-rhythm decision and the CHA2DS2-VASc score feel like lists to memorise, they make far more sense when a doctor walks you through the reasoning on real examples. SyncMed runs free, live cardiology tutorials with GMC-verified NHS doctors who turn algorithms into understanding, and you can see how the sessions work before you join.

Learn atrial fibrillation live with SyncMed. Free, live UKMLA and OSCE tutorials from GMC-verified NHS doctors who make cardiology click. Join SyncMed for free and book your seat.