Atrial Fibrillation: Junior Doctor Guide & Clerking Template

Q: What are the red flags for fast atrial fibrillation (AF)?

Shock, syncope, ischaemia, HF — think unstable — DC cardioversion; Irregular, broad, very fast — think pre-excited AF — no AV blockers; Fever, sepsis, dehydration — think secondary AF — treat cause; Tremor, weight loss, goitre — think thyrotoxicosis; Sudden cold pale limb — think acute limb ischaemia; New neuro deficit — think embolic stroke

Q: What is the initial management of fast atrial fibrillation (AF)?

12-lead ECG (confirm AF, look for ischaemia, pre-excitation, QRS width); Unstable → electrical cardioversion (emergency synchronised DC cardioversion without delaying for anticoagulation); Look for a trigger (sepsis, hypovolaemia, PE, thyroid, alcohol, electrolytes, ischaemia); Establish the onset (under 48 h vs over 48 h or unknown); Anticoagulate (start heparin or a DOAC if cardioversion is planned (unless contraindicated)); Correct electrolytes (K⁺ and Mg²⁺)

Q: What diagnoses must you not miss in fast atrial fibrillation (AF)?

Unstable AF (shock · ischaemia · HF); Pre-excited AF (WPW); Embolic complications (stroke · limb · gut); Thyrotoxicosis / sepsis-driven AF (treat the trigger)

Q: What investigations should a junior doctor order for fast atrial fibrillation (AF)?

ECG: AF, rate, pre-excitation, ischaemia, LVH.; Bloods: U&E, K, Mg, TFT, FBC, CRP, glucose, clotting (before anticoagulation).; Imaging: Heart failure, infection.

Q: Admit or discharge: how is the plan decided for fast atrial fibrillation (AF)?

Home: Stable, rate controlled (resting HR under 110), trigger dealt with, anticoagulation decided and started, follow-up arranged (GP/AF clinic).; Admit: Unstable, uncontrolled rate, heart failure, significant trigger (sepsis), new stroke, or pre-excitation.

Settle them, and check the basics

stable or unstable?

Red flags — what each should make you think

Shock, syncope, ischaemia, HFunstable — DC cardioversion Irregular, broad, very fastpre-excited AF — no AV blockers Fever, sepsis, dehydrationsecondary AF — treat cause Tremor, weight loss, goitrethyrotoxicosis Sudden cold pale limbacute limb ischaemia New neuro deficitembolic stroke

🩺

Pearl

Fast AF is often a symptom, not the disease. A septic, dehydrated patient in AF at 150 needs fluids and antibiotics, not a beta-blocker. Treat the trigger and the rate often settles on its own.

First actions

ECG12-lead ECG
⚡Unstable → electrical cardioversion
🔍Look for a trigger
⏱Establish the onset
HepAnticoagulate
K/MgCorrect electrolytes

Understand the patient — rate, rhythm, anticoagulation

NICE NG196

Rate or rhythm?

Onset clearly under 48 h — rate or rhythm control; rhythm options are electrical cardioversion or pharmacological (flecainide if no structural heart disease, or amiodarone if structural heart disease). Anticoagulate with heparin while deciding.
Onset over 48 h or unknown — rate control. Cardioversion only after at least 3 weeks of therapeutic anticoagulation (or TOE-guided).
Rate control drugs — beta-blocker (not sotalol) or rate-limiting CCB (diltiazem, verapamil — avoid in heart failure with reduced EF). Digoxin for sedentary patients or with heart failure. Amiodarone may be used in the acute setting with heart failure.

Stroke and bleeding risk

CHA₂DS₂-VASc — CHF, Hypertension, Age ≥75 (2), Diabetes, Stroke/TIA/thromboembolism (2), Vascular disease, Age 65–74, Sex (female)
NICE: offer anticoagulation (a DOAC first-line) with a score of 2 or more; consider it for men with a score of 1
ORBIT to assess bleeding risk — address modifiable risks (BP, alcohol, NSAIDs) rather than withholding anticoagulation
Don't use aspirin alone for stroke prevention in AF

Source: NICE NG196

Work A–E — assess and act as you go

AAirway. Patent.—

BBreathing. Pulmonary oedema, pneumonia, PE.oxygen if hypoxic, CXR

CCirculation. Apical rate, BP, perfusion, murmurs, fluid status.unstable → DC cardioversion

DDisability. Focal neurology (embolic stroke), confusion.stroke pathway if new deficit

EExposure. Thyroid signs, limbs (emboli), infection source, alcohol.temperature

The diagnoses you must not miss

tap to open each

What points toward it, what would rule it in, and how to manage it.

points toward it

AF with hypotension, syncope, chest pain/ischaemia or acute heart failure.

rule in

Clinical + ECG.

manage it

Emergency synchronised DC cardioversion (sedation/GA); amiodarone if it fails or recurs. Don't delay for anticoagulation.

Source: NICE NG196 · Resus Council UK

points toward it

Very fast, irregular, broad bizarre complexes of varying width.

rule in

ECG; expert review.

manage it

No AV-node blockers. Cardioversion or expert-guided drugs.

Source: Tachyarrhythmias page

points toward it

New focal neurology; a cold, painful, pulseless limb; abdominal pain out of proportion (mesenteric ischaemia).

rule in

CT head / CT angiogram.

manage it

Stroke pathway (thrombolysis/thrombectomy decisions), vascular surgery for limb ischaemia, surgical review for mesenteric ischaemia.

Source: NICE NG128 — stroke

points toward it

Fever, infection source, weight loss, tremor, goitre.

rule in

TFT, CRP, cultures, lactate.

manage it

Treat the cause; beta-blockers help thyroid-driven AF (with endocrine input). Avoid rate control in compensatory tachycardia.

Source: senior review

Investigate — what to order, when, and what it tells you

test with a question in mind

ECG

Look for

AF, rate, pre-excitation, ischaemia, LVH.

Bloods

Must-do

U&E, K, Mg, TFT, FBC, CRP, glucose, clotting (before anticoagulation).

If indicated

Troponin, LFT, cultures.

Imaging

CXR

Heart failure, infection.

Echo

Structure, valves, LV function — especially if rhythm control planned.

How the plan comes together

disposition · handover

home

Stable, rate controlled (resting HR under 110), trigger dealt with, anticoagulation decided and started, follow-up arranged (GP/AF clinic).

admit

Unstable, uncontrolled rate, heart failure, significant trigger (sepsis), new stroke, or pre-excitation.

Hand over: onset time, rate/rhythm strategy, anticoagulation, CHA₂DS₂-VASc and ORBIT.

🩺

Pearl

Unstable means shock. Stable means find the trigger, decide rate or rhythm by the 48-hour rule, and never forget the stroke risk. Nicely done getting here.

✎

Clerking template

copy or download

Atrial fibrillation — documentation structure

A structure and prompt list to help you document and think systematically. It is not a completeness check and cannot guarantee nothing is missed — use your trust's own proforma, your seniors, and your clinical judgement.

AF — CLERKING TEMPLATE PRESENTING COMPLAINT: HISTORY OF PRESENTING COMPLAINT Palpitations — onset (time / date — is it under 48 h?): Symptoms — breathlessness / chest pain / syncope: Triggers — infection / alcohol / thyroid / dehydration: Previous AF / anticoagulation / cardioversion: Bleeding history / falls: RED FLAGS ASKED (record present or absent) [ ] Shock, syncope, ischaemia, HF -> unstable — DC cardioversion [ ] Irregular, broad, very fast -> pre-excited AF — no AV blockers [ ] Fever, sepsis, dehydration -> secondary AF — treat cause [ ] Tremor, weight loss, goitre -> thyrotoxicosis [ ] Sudden cold pale limb -> acute limb ischaemia [ ] New neuro deficit -> embolic stroke SCORES / KEY CHECKS Adverse features: Y / N Onset: under 48 h / over 48 h / unknown Strategy: rate / rhythm CHA2DS2-VASc: ORBIT: Anticoagulant started (drug / dose): PAST MEDICAL HISTORY: DRUG HISTORY: ALLERGIES: SOCIAL HISTORY (smoking / alcohol / function / who's at home): FAMILY HISTORY: OBSERVATIONS: RR SpO2 ( % O2) HR BP Temp GCS NEWS2 EXAMINATION A - B - C - D - (GCS pupils glucose ) E - INVESTIGATIONS ORDERED: IMPRESSION: DIFFERENTIALS CONSIDERED: [ ] Unstable AF [ ] Pre-excited AF [ ] Embolic complications [ ] Thyrotoxicosis / sepsis-driven AF [ ] Atrial flutter [ ] Multifocal atrial tachycardia [ ] Sinus rhythm with ectopics PLAN: 1. 2. 3. ESCALATION / SENIOR DISCUSSION: Discussed with: Time: Advice: SAFETY NET / IF DETERIORATES: Documented by: Grade: Date/Time:

Test yourself

active recall

Cover the answer, say it out loud, then reveal. Retrieval beats re-reading.

0 / 10 known

Red flag

Shock, syncope, ischaemia, HF — what should it make you think?

unstable — DC cardioversion

Red flag

Irregular, broad, very fast — what should it make you think?

pre-excited AF — no AV blockers

Red flag

Fever, sepsis, dehydration — what should it make you think?

secondary AF — treat cause

Red flag

Tremor, weight loss, goitre — what should it make you think?

thyrotoxicosis

Red flag

Sudden cold pale limb — what should it make you think?

acute limb ischaemia

Red flag

New neuro deficit — what should it make you think?

embolic stroke

Must not miss

How do you rule in unstable AF?

Clinical + ECG.

Must not miss

How do you rule in pre-excited AF?

ECG; expert review.

Must not miss

How do you rule in embolic complications?

CT head / CT angiogram.

Must not miss

How do you rule in thyrotoxicosis / sepsis-driven AF?

TFT, CRP, cultures, lactate.

Frequently asked questions

quick answers

What are the red flags for fast atrial fibrillation (AF)?

Shock, syncope, ischaemia, HF — think unstable — DC cardioversion
Irregular, broad, very fast — think pre-excited AF — no AV blockers
Fever, sepsis, dehydration — think secondary AF — treat cause
Tremor, weight loss, goitre — think thyrotoxicosis
Sudden cold pale limb — think acute limb ischaemia
New neuro deficit — think embolic stroke

What is the initial management of fast atrial fibrillation (AF)?

12-lead ECG — confirm AF, look for ischaemia, pre-excitation, QRS width
Unstable → electrical cardioversion — emergency synchronised DC cardioversion without delaying for anticoagulation
Look for a trigger — sepsis, hypovolaemia, PE, thyroid, alcohol, electrolytes, ischaemia
Establish the onset — under 48 h vs over 48 h or unknown
Anticoagulate — start heparin or a DOAC if cardioversion is planned (unless contraindicated)
Correct electrolytes — K⁺ and Mg²⁺

Always alongside senior support and your local guideline.

What diagnoses must you not miss in fast atrial fibrillation (AF)?

Unstable AF — shock · ischaemia · HF
Pre-excited AF — WPW
Embolic complications — stroke · limb · gut
Thyrotoxicosis / sepsis-driven AF — treat the trigger

Open each one in the must-not-miss section for what points toward it, how to rule it in, and how to manage it.

What investigations should a junior doctor order for fast atrial fibrillation (AF)?

ECG — AF, rate, pre-excitation, ischaemia, LVH.
Bloods — U&E, K, Mg, TFT, FBC, CRP, glucose, clotting (before anticoagulation).
Imaging — Heart failure, infection.

Admit or discharge: how is the plan decided for fast atrial fibrillation (AF)?

Home — Stable, rate controlled (resting HR under 110), trigger dealt with, anticoagulation decided and started, follow-up arranged (GP/AF clinic).
Admit — Unstable, uncontrolled rate, heart failure, significant trigger (sepsis), new stroke, or pre-excitation.

Is there a clerking template for fast atrial fibrillation (AF)?

Yes — there is a free clerking template for fast atrial fibrillation (AF) on this page, structured as presenting complaint, red flags asked, history, examination (A–E), investigations, differentials, plan and escalation. You can copy it or download it as a Word document. Jump to the template.

→

Keep going

one more?

Next in CardiologyHypertensive emergencyWhen high BP is an emergency. · 6 min