Atrial Fibrillation
Atrial fibrillation is a supraventricular tachyarrhythmia characterized by disorganized, rapid atrial electrical activity resulting in irregular ventricular response and loss of effective atrial contraction.
Atrial Fibrillation (AF)
Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia [1]. It is characterised by:
- Chaotic, disorganised electrical activity of the atrial myocardium, with atrial muscle fibres contracting independently without synchronous depolarisation [1][2]
- Atrial rate so fast (350–600 bpm) that distinct P waves are not discernible [1]
- Variable conduction at the AV node → irregularly irregular ventricular rhythm [1]
Let's break down the name:
- "Atrial" = pertaining to the atria (upper heart chambers)
- "Fibrillation" = from Latin fibrilla (small fibre) → chaotic, quivering contraction of individual muscle fibres rather than coordinated contraction
The key conceptual point: the atria are not contracting as a unit. Hundreds of tiny re-entrant wavelets are firing simultaneously, so the atria effectively "quiver" rather than pump. The AV node acts as a gatekeeper, conducting some (but not all) of these chaotic impulses to the ventricles in an unpredictable fashion — hence the hallmark irregularly irregular ventricular rhythm.
Very common in the elderly: ~1% in those aged 60–64 years, ~9% in those aged > 80 years [1].
Global and Hong Kong Context
- Prevalence: AF affects approximately 33 million people worldwide [3]. In Hong Kong, the prevalence mirrors that of other developed East Asian populations — estimated at ~1.3–1.8% of the general adult population, rising sharply with age [3].
- Incidence: increasing due to population ageing, rising burden of hypertension, obesity, and heart failure, and improved detection (wearable devices, screening programmes).
- Sex: overall slightly more common in males (M:F ≈ 1.5:1), but women with AF have higher stroke risk and mortality.
- Ethnic considerations: AF is somewhat less prevalent in East Asian populations compared to Caucasians at equivalent ages; however, the absolute burden in Hong Kong is enormous given the ageing demographics.
- Hospital burden: AF is a major driver of medical admissions, particularly for acute heart failure decompensation and stroke.
Why is AF prevalence increasing?
Three reasons: (1) the population is ageing, (2) comorbidities that predispose to AF (HTN, obesity, HF, DM) are increasing, and (3) we are detecting more AF with widespread ECG screening and wearable devices. This makes AF one of the emerging cardiovascular epidemics of the 21st century.
3. Risk Factors
Understanding risk factors requires understanding what predisposes atrial tissue to develop and sustain chaotic re-entrant circuits. The two fundamental requirements are:
- A trigger (usually a rapidly firing ectopic focus, most commonly from the pulmonary veins)
- A substrate (structurally or electrically abnormal atrial tissue that allows multiple re-entrant wavelets to propagate)
These enlarge or scar the atria, creating the substrate for multiple re-entrant circuits:
| Risk Factor | Why It Causes AF |
|---|---|
| Valvular heart disease (esp. mitral stenosis) [1][4] | LA pressure overload → LA dilatation. MS is the classic cause; AF occurs in ~45% of MS patients [4] |
| Hypertension [1] | LV hypertrophy → diastolic dysfunction → ↑LAP → LA dilatation |
| Heart failure (HF) [1] | ↑LAP from volume/pressure overload → LA dilatation; also neurohormonal activation promotes fibrosis |
| Coronary artery disease (CAD) [1] | Ischaemia → atrial fibrosis + acute haemodynamic stress during ACS |
| Pulmonary embolism (PE) [1] | Acute RV pressure overload → RA dilatation + haemodynamic stress |
| Cardiomyopathy [1] | Dilated CMP → chamber dilatation; HCMP → diastolic dysfunction → ↑LAP |
These act as triggers — they increase automaticity of ectopic foci:
| Risk Factor | Mechanism |
|---|---|
| Hyperthyroidism [1][5] | Thyroid hormones ↑β-adrenergic sensitivity, ↑automaticity, ↑resting heart rate → trigger + maintenance. Must always check TFT in new-onset AF |
| Sepsis / acute infection [1] | Systemic inflammation + ↑sympathetic drive + catecholamine surge |
| Post-operative state (esp. cardiac surgery) [1] | Pericardial inflammation + sympathetic surge + electrolyte shifts |
| Alcoholism [1] | Direct toxic effect on atrial myocytes + autonomic dysfunction. "Holiday heart syndrome" = binge drinking → paroxysmal AF |
Chronic lung disease [1] — COPD, pulmonary fibrosis, etc. → chronic hypoxia → pulmonary hypertension → RV/RA dilatation → atrial remodelling. Also, theophylline use in COPD ↑arrhythmia risk.
- Obesity: direct mechanical effect (↑pericardial fat → LA infiltration/fibrosis), plus associated HTN, OSA, metabolic syndrome
- Obstructive sleep apnoea (OSA): intermittent hypoxia → sympathetic surges + intrathoracic pressure swings → atrial stretch
- Diabetes mellitus: autonomic neuropathy + atrial fibrosis
- Age: progressive atrial fibrosis is the single most important substrate
- Excessive endurance exercise: marathon runners have ↑AF risk, likely from repeated atrial stretch and vagal remodelling
Lone AF: NO structural heart disease identified [1]. Occurs in ~50% of paroxysmal AF and ~20% of persistent/permanent AF [1]. This is a diagnosis of exclusion after thorough workup. It is less commonly used in modern practice as subtle substrates (e.g., fibrosis on cardiac MRI, OSA) are increasingly identified.
Exam Tip: Reversible Causes to Always Exclude
In any new-onset AF, always check: TFT (thyrotoxicosis), electrolytes (K⁺, Mg²⁺), and consider acute PE, myopericarditis, pneumonia, and post-cardiac surgery [1]. These are reversible causes that may be the sole driver of AF.
4. Anatomy and Physiology Relevant to AF
- Right atrium (RA): receives systemic venous return (SVC, IVC, coronary sinus). Contains the SA node (junction of SVC and RA) and AV node (in the triangle of Koch at the interatrial septum).
- Left atrium (LA): receives oxygenated blood from the 4 pulmonary veins (2 from each lung). The LA is a thin-walled, low-pressure chamber. Sleeves of atrial myocardium extend into the pulmonary veins — these are the critical trigger sites for AF.
- Interatrial septum: contains the fossa ovalis (remnant of foramen ovale).
- SA node → generates impulse (60–100 bpm)
- Impulse spreads across atrial myocardium (Bachmann's bundle for interatrial conduction)
- AV node → deliberate conduction delay (allows atrial contraction to fill ventricles before ventricular contraction)
- Bundle of His → bundle branches → Purkinje fibres → ventricular myocardium
The AV node is the only electrical connection between atria and ventricles. Its refractory period acts as a physiological filter, preventing all atrial impulses from reaching the ventricles. This is why, even with atrial rates of 350–600 bpm in AF, the ventricular rate is typically only 120–160 bpm (the AV node blocks most impulses).
The pulmonary veins (PVs) are the most important anatomical structure in AF pathophysiology:
- Sleeves of atrial myocardium extend 1–3 cm into the PVs
- These sleeves have shorter refractory periods, more disorganised fibre orientation, and higher automaticity
- They are the dominant trigger site for paroxysmal AF (>90% of ectopic foci arise from PV sleeves)
- This is the basis for pulmonary vein isolation (PVI) — the cornerstone of catheter ablation for AF
In normal sinus rhythm, atrial contraction contributes ~15–25% of ventricular filling (the "atrial kick"). In patients with stiff ventricles (e.g., LVH from hypertension, HCMP, aortic stenosis), this contribution can be up to 40% of cardiac output. Loss of the atrial kick in AF therefore causes:
- A disproportionate ↓ in cardiac output in patients with diastolic dysfunction
- This explains why AF onset can precipitate acute heart failure decompensation, especially in mitral stenosis [4] and HCMP [6]
5. Aetiology (with Hong Kong Focus)
The causes of AF can be organised by the mechanism through which they promote the arrhythmia:
| Factor | Relevance to HK |
|---|---|
| Hypertension | The leading modifiable risk factor. Prevalence ~27% in HK adults and rising. HTN drives the majority of AF burden locally |
| Rheumatic heart disease | Still encountered (particularly in older patients and immigrants from mainland China), though declining. MS remains an important cause of AF in HK elderly |
| Hyperthyroidism | Graves' disease is common in HK (M:F = 1:4.8, peak 20–50 years) [5]. Always exclude thyrotoxicosis in new-onset AF |
| Ischaemic heart disease | Major contributor given high prevalence of metabolic risk factors |
| Alcohol consumption | "Holiday heart" — binge drinking culture in some demographics |
| Ageing population | HK has one of the longest life expectancies globally; the AF burden is projected to increase dramatically |
| Obesity / OSA | Rising prevalence in HK; increasingly recognised as modifiable risk factors for AF |
6. Pathophysiology
This is central to understanding everything about AF — from clinical features to treatment.
6.1 The Trigger-Substrate Model
AF requires two things:
- Most commonly, a single rapidly firing focus in the sleeves of atrial muscle extending into the pulmonary veins [1]
- May also be triggered by ↑sympathetic tone (e.g., hyperthyroidism, sepsis, post-operative state) [1]
- These foci have enhanced automaticity and/or triggered activity due to:
- Shorter action potential duration
- Disorganised myofibre arrangement
- Calcium handling abnormalities
- Once triggered, the arrhythmia is sustained by multiple re-entrant circuits [1]
- Atrial dilatation allows a minimum number of re-entrant wavelets to coexist simultaneously — this is the "critical mass" hypothesis [1]
- A larger atrium can support more simultaneous wavelets → more likely to sustain AF
- This is why conditions causing atrial dilatation predispose to AF [1]
- Fibrosis of atrial myocardium creates areas of slow conduction and conduction block — ideal for re-entry
AF begets AF: structural/electrical remodelling occurs once AF is initiated → further predisposes to continual AF [1]
This is a critically important concept:
-
Electrical remodelling (occurs within hours to days):
- Sustained rapid atrial rates → intracellular Ca²⁺ overload → shortening of atrial refractory period
- Shorter refractory period → shorter wavelength of re-entrant circuits → more circuits can fit in the same atrial area → easier to sustain AF
-
Structural remodelling (occurs over weeks to months):
- Chronic AF → atrial fibrosis, myocyte hypertrophy, gap junction remodelling
- Creates heterogeneous conduction → promotes re-entry
- This is why the longer AF persists, the harder it is to restore and maintain sinus rhythm
AF Begets AF — Clinical Implication
This concept explains why early rhythm control is increasingly favoured: the longer you leave AF untreated, the more remodelling occurs, and the less likely cardioversion (electrical or pharmacological) is to succeed. The 2020 EAST-AFNET 4 trial showed that early rhythm control in patients diagnosed within 1 year of AF onset reduced cardiovascular outcomes compared to rate control alone.
| Consequence | Mechanism |
|---|---|
| ↓ Cardiac output | Loss of atrial kick (15–25% of ventricular filling). Worse if ↓LV compliance (e.g., HCMP, AS, HTN-LVH) |
| Rapid ventricular rate | Uncontrolled rate → ↓ diastolic filling time → ↓ stroke volume → ↓ CO |
| Tachycardia-mediated cardiomyopathy | Sustained rapid rates (usually > 100 bpm for weeks–months) → progressive LV dilatation and systolic dysfunction. Reversible with rate/rhythm control [6] |
| Hypotension / shock | In acute AF with very fast rates, especially with underlying structural heart disease |
This is arguably the most important clinical consequence of AF.
Mechanism (Virchow's triad applied to AF):
- Stasis: Loss of coordinated atrial contraction → blood pools in the LA, especially in the left atrial appendage (LAA) — a blind-ended pouch that is the primary site of thrombus formation (~90% of LA thrombi in non-valvular AF)
- Endothelial dysfunction: AF causes endothelial damage/activation in the atria
- Hypercoagulability: AF is associated with a prothrombotic state (↑fibrinogen, ↑vWF, ↑D-dimer, platelet activation)
The resulting thrombi can embolise to:
- Brain → ischaemic stroke or TIA (most feared complication) [7][8]
- Systemic arteries → acute limb ischaemia [9][10], mesenteric ischaemia [11][12], renal infarction, splenic infarction
Key fact: AF is responsible for ~20–30% of all ischaemic strokes. AF-related strokes are typically more severe (larger infarct territory due to large emboli from the LAA) and carry higher mortality and disability than non-AF strokes.
The LAA is a finger-like, trabeculated pouch arising from the LA. In AF:
- It is the most common site of thrombus formation (~90%)
- Its complex trabeculated anatomy + loss of contractile function = perfect environment for stasis
- This is why LAA occlusion devices (e.g., Watchman) are an alternative to anticoagulation in selected patients
AF classification generally progresses from paroxysmal to persistent states [1]:
| Classification | Definition | Key Features |
|---|---|---|
| Paroxysmal AF (pAF) | ≥2 episodes, terminates spontaneously or with intervention ≤7 days of onset [1] | Most common initial pattern. Natural history: often recurrent; ~36% progress to persistent AF over 10 years [1]. More likely to respond to rhythm control |
| Persistent AF | Fails to terminate within 7 days [1] | May be restored to SR with cardioversion but does not self-terminate |
| Long-standing persistent AF | Persistent AF lasting > 12 months [1] | Rhythm control still considered but success rates lower |
| Permanent AF | Persistent AF in which a rhythm control strategy is no longer pursued [1] | A joint decision by patient and physician to accept AF and focus on rate control + anticoagulation |
Additional classifications:
- First detected AF: first episode ever diagnosed (may be any of the above)
- Valvular vs Non-valvular AF:
- "Valvular AF" traditionally refers to AF in the context of moderate-to-severe mitral stenosis or mechanical heart valves — these patients require warfarin (NOACs are contraindicated)
- All other AF is "non-valvular" — eligible for NOACs
- Note: ESC 2020 guidelines replaced this terminology with EHRA classification to reduce confusion
Exam Tip: Valvular vs Non-Valvular AF
A common exam mistake is to classify any AF with valve disease as "valvular AF." The term specifically refers to moderate-severe mitral stenosis or mechanical heart valves — the only two situations where warfarin is mandated and NOACs are contraindicated. AF with aortic stenosis, mitral regurgitation, or bioprosthetic valves is still considered "non-valvular" and can be treated with NOACs.
8. Clinical Features
| Symptom | Pathophysiological Basis |
|---|---|
| Irregular palpitation [1] | The patient feels the irregularly irregular, variable-strength ventricular contractions. The variable diastolic filling time means some beats are strong (long diastole → full ventricle) and some are weak (short diastole → underfilled ventricle) |
| Worsening dyspnoea (SOB) [1] | (1) Loss of atrial kick → ↓CO → ↓tissue O₂ delivery. (2) Rapid rate → ↓diastolic filling → ↑LAP → pulmonary congestion. (3) Particularly pronounced in MS where LA systole is critical [4] |
| Lightheadedness / dizziness [1] | ↓CO from loss of atrial kick + rapid rate → ↓cerebral perfusion |
| Fatigue and malaise [1] | Chronic ↓CO + sympathetic activation → fatigue. Also, loss of exercise capacity as the heart cannot augment CO appropriately with exercise |
| Presyncope / syncope | Severe ↓CO, especially at onset of AF with very rapid rate, or in patients with concurrent structural disease (AS, HCMP) |
| Chest pain / angina | Rapid rate → ↑myocardial O₂ demand + ↓diastolic coronary perfusion time → supply-demand mismatch. May unmask underlying CAD |
| Polyuria | Atrial stretch (from volume overload) → release of atrial natriuretic peptide (ANP) → diuresis. Patients sometimes report increased urination at the onset of AF |
| Asymptomatic | Up to one-third of AF patients are asymptomatic. AF may be discovered incidentally on pulse check, ECG, or wearable device. These patients still carry thromboembolic risk |
Symptom Severity — EHRA Score
The European Heart Rhythm Association (EHRA) symptom score grades AF symptoms:
- I — No symptoms
- IIa — Mild symptoms; normal daily activity not affected
- IIb — Moderate symptoms; normal daily activity not affected but patient troubled
- III — Severe symptoms; normal daily activity affected
- IV — Disabling symptoms; normal daily activity discontinued
This score guides decisions about rhythm vs rate control.
| Symptom | Complication |
|---|---|
| Acute-onset focal neurological deficit (hemiplegia, aphasia, visual field defect) | Cardioembolic ischaemic stroke [7][8] |
| Acute limb pain, pallor, pulselessness ("6Ps") | Acute limb ischaemia from peripheral embolism [9][10] |
| Acute severe abdominal pain (out of proportion to findings) | Mesenteric ischaemia from mesenteric embolism [11][12] |
| Acute decompensated heart failure (orthopnoea, PND, leg swelling) | AF causing or worsening heart failure |
| Sign | Pathophysiological Basis |
|---|---|
| Irregularly irregular pulse with variable volume [1] | The hallmark sign. Variable R-R intervals (AV node conducts chaotically) → variable diastolic filling time → variable stroke volume → variable pulse amplitude |
| Pulse deficit (radial rate < apex rate) [1] | Some ventricular contractions occur after very short diastolic intervals → ventricle barely fills → stroke volume so small that the pressure wave doesn't reach the radial artery → felt at apex (auscultation) but not at wrist. The difference = pulse deficit |
| Absent a wave in JVP [1] | The "a" wave represents atrial contraction. In AF, there is no coordinated atrial contraction → no "a" wave. (Contrast with atrial flutter, which has flutter "f" waves in the JVP) |
| Variably loud S1 [1] | S1 loudness depends on the position of the mitral valve leaflets at the onset of ventricular systole, which depends on the preceding diastolic interval. Variable R-R intervals → variable S1 intensity |
| Signs of the underlying cause | Signs of thyrotoxicosis [1] (tremor, lid lag, goitre, weight loss). Signs of valvular heart disease (murmurs). Signs of heart failure (↑JVP, basal crepitations, peripheral oedema) |
| Check peripheral pulses [1] | To assess for embolic events — absent pulses in a limb suggest acute arterial embolism |
| Blood pressure | May be difficult to measure accurately due to beat-to-beat variability. Take average of several readings |
Why Check for Pulse Deficit?
Pulse deficit is clinically important because: (1) it indicates that the true heart rate is higher than what you feel at the wrist — you may underestimate tachycardia if you only count the radial pulse; (2) a large pulse deficit suggests many "ineffective" beats with very short diastolic intervals, indicating poor rate control; (3) always count the apex rate (auscultation) as the true heart rate in AF.
| Feature | Explanation |
|---|---|
| No distinct P wave ± irregular baseline (fibrillation waves) [1][2] | Chaotic atrial depolarisation → no organised P waves. The baseline may show fine or coarse undulations ("fibrillatory waves" or "f waves"). May have flutter-like waves for 2–3 seconds [2] |
| Narrow but irregular QRS complexes [1] | AV node conducts some impulses randomly → irregular R-R intervals. QRS is narrow because ventricular conduction via the His-Purkinje system is normal. Typically 120–160 bpm but may ↓ in chronic cases [1] (due to AV nodal remodelling / medications) |
| Note any ST depression [1] | May suggest: (1) underlying LVH (LV strain pattern) [1], (2) ischaemia, or (3) digoxin effect (reverse tick / upsloping ST depression) [1] |
The irregular baseline may not always be present → look for irregular QRS complexes [2]. This is an important practical point: in fine AF, the fibrillatory waves may be barely visible, and the diagnosis rests on the irregularly irregular rhythm.
How to distinguish AF from other irregular rhythms:
- Atrial flutter with variable block: look for "sawtooth" flutter waves (especially in leads II, III, aVF, V1) at ~300 bpm
- Multifocal atrial tachycardia (MAT): ≥3 different P wave morphologies, flat isoelectric baseline preserved (unlike AF) [1]
- Frequent atrial ectopics: P waves visible before ectopic beats, underlying sinus rhythm present between ectopics
ECG Pearl
If the QRS complex frequency is very irregular during a wide complex tachycardia → likely AF + bundle branch block (BBB) [2]. Do NOT mistake this for polymorphic VT. Compare the QRS morphology with the patient's baseline ECG in sinus rhythm — BBB should be evident in SR as well.
Evaluation of new-onset AF [1]:
| Investigation | Purpose |
|---|---|
| Blood tests: TFT, K⁺, Mg²⁺ [1] | Exclude reversible causes. Thyrotoxicosis is a must-exclude. Hypokalaemia and hypomagnesaemia promote arrhythmias |
| Echocardiogram [1] | Assess for underlying structural heart disease [1] — valvular disease, LV function (EF), LA size, LV wall thickness. LA mural thrombus is best assessed by transoesophageal echocardiography (TOE/TEE) [1] |
| ± Exercise testing [1] | Assess rate control during exertion, unmask ischaemia |
| ± Ambulatory ECG (Holter / event recorder) [1] | For paroxysmal AF [1] — to document AF episodes, assess rate control, and correlate symptoms with rhythm |
| CBC, renal function, liver function | Baseline before anticoagulation (bleeding risk assessment) |
| Coagulation profile | Baseline before anticoagulation |
| CXR | Cardiomegaly, pulmonary congestion, lung pathology |
The approach to new-onset AF [1]:
- Reverse reversible causes: hyperthyroidism, acute PE, myopericarditis, pneumonia, post-cardiac surgery [1]
- Rate control: usually started before any attempt at rhythm control [1]
- Cardioversion: should be performed at least once in most patients with new-onset AF [1]
- Timing: immediate if haemodynamically unstable; delayed if stable (69% spontaneously reverts within < 48 hours) [1]
- Anticoagulation: based on CHA₂DS₂-VASc score [1]
(Detailed management, including CHA₂DS₂-VASc scoring, rate vs rhythm control strategies, anticoagulation, and ablation, will be covered in the next section on Diagnosis, DDx, and Management.)
These will be covered in detail later, but for completeness of the pathophysiology-clinical features link:
| Complication | Mechanism |
|---|---|
| Ischaemic stroke / TIA | LA stasis → thrombus (especially LAA) → embolism to cerebral circulation [7][8] |
| Systemic thromboembolism | Embolism to limbs [9][10], mesentery [11][12], kidneys, spleen |
| Heart failure | ↓CO from loss of atrial kick + rapid rate; tachycardia-mediated cardiomyopathy [6] |
| Tachycardia-mediated cardiomyopathy | Sustained rapid ventricular rate → progressive LV dilatation and ↓EF. Reversible with rate/rhythm control [6] |
| Sudden cardiac death | AF with pre-excitation (WPW) → rapid conduction via accessory pathway → VF. Also, AF in structural heart disease ↑VT/VF risk |
| Cognitive decline / vascular dementia | Chronic microembolism + chronic ↓CO → progressive cerebral hypoperfusion |
| Reduced quality of life | Symptoms of palpitation, fatigue, anxiety, functional limitation |
AF is frequently mentioned as a cause of embolic events in many organ systems. To consolidate:
| Embolic Target | Clinical Condition | Key Teaching Point |
|---|---|---|
| Brain | Cardioembolic ischaemic stroke [7][8] | AF is the most common cardiac cause of embolic stroke. "Old patient with AF → sudden neurological deficit" is the classic vignette |
| Limb arteries | Acute limb ischaemia [9][10] | Cardiac origin emboli account for ~80% of acute limb embolism; AF is the most common cardiac cause [9][10]. Embolus typically lodges at arterial branch points (femoral bifurcation MC) |
| Mesenteric arteries | Acute mesenteric ischaemia [11][12] | AF may predispose to arterial embolism to mesenteric arteries [12]. "Acute embolus: severe sudden periumbilical pain in old patient with AF" [11] |
| Coronary arteries | Coronary embolism (rare) | Can cause acute MI in the absence of atherosclerotic CAD |
| Renal arteries | Renal infarction | Flank pain, haematuria, ↑LDH — often missed |
High Yield Summary
- AF is the most common sustained arrhythmia, prevalence increases dramatically with age (~1% at 60–64, ~9% at > 80).
- Mechanism: Trigger (PV ectopic foci) + Substrate (atrial dilatation/fibrosis) → multiple re-entrant wavelets. AF begets AF through electrical (shortened refractory period) and structural (fibrosis) remodelling.
- Causes to remember: Valvular disease (esp. MS), HTN, HF, CAD, PE, hyperthyroidism, alcohol, chronic lung disease, cardiomyopathy, sepsis, post-cardiac surgery. Always check TFT, K⁺, Mg²⁺ in new-onset AF.
- Classification: Paroxysmal (≤7d, self-terminating) → Persistent (> 7d) → Long-standing persistent (> 12mo) → Permanent (rhythm control abandoned).
- Valvular AF = moderate-severe MS or mechanical valve → warfarin only (NOACs contraindicated).
- Hallmark features: Irregularly irregular pulse, variable pulse volume, pulse deficit, absent JVP "a" wave, variably loud S1.
- ECG: No P waves, irregular baseline (fibrillatory waves), irregularly irregular narrow QRS. Fine AF may have no visible fibrillatory waves — diagnose by irregular R-R intervals.
- Main complications: Stroke/TIA, systemic embolism, heart failure, tachycardia-mediated cardiomyopathy.
- AF is responsible for ~20–30% of all ischaemic strokes — hence anticoagulation is the most important therapeutic decision.
- Approach: Exclude reversible causes → Rate control → Consider cardioversion → Anticoagulate based on CHA₂DS₂-VASc.
Active Recall - Atrial Fibrillation (Definition, Epidemiology, Aetiology, Pathophysiology, Clinical Features)
[1] Senior notes: Ryan Ho Cardiology.pdf (pages 92–94, Section B: Atrial Flutter and Fibrillation) [2] Senior notes: Ryan Ho Fundamentals.pdf (pages 206, 468 — Palpitations and ECG interpretation of AF) [3] Epidemiology data: Global/HK prevalence estimates from current clinical guidelines (ESC 2020, ACC/AHA 2023) [4] Senior notes: Ryan Ho Cardiology.pdf (page 152 — Mitral Stenosis section, AF in MS) [5] Senior notes: Ryan Ho Endocrine.pdf (page 23 — Graves' Disease, hyperthyroidism causing AF) [6] Senior notes: Ryan Ho Cardiology.pdf (page 169 — DCMP section, tachycardia-mediated cardiomyopathy) [7] Senior notes: Ryan Ho Neurology.pdf (pages 74–75 — Stroke aetiology, AF as embolic source) [8] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (page 1140 — AF as cause of embolic stroke) [9] Senior notes: Maksim SURGERY notes.pdf (page 168 — Acute limb ischaemia, AF as embolic cause) [10] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (page 920 — AF as cause of arterial embolism) [11] Senior notes: Maksim SURGERY notes.pdf (page 92 — Ischaemic bowel disease, AF as embolic cause) [12] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (page 718 — Mesenteric ischaemia, AF and embolism) [13] Senior notes: Ryan Ho Respiratory.pdf (pages 39, 108 — Cor pulmonale, COPD and AF)
Differential Diagnosis of Atrial Fibrillation
The differential diagnosis of AF is essentially the question: "What else can produce an irregularly irregular pulse or mimic AF on examination/ECG?" This is a clinical reality you will face on call — a patient has an "irregular" rhythm, and you need to confirm it is truly AF before committing to anticoagulation and rate control. Equally important is the differential of the presenting symptom (palpitations, dyspnoea, embolic event) that led you to discover AF.
We will approach this systematically:
- DDx of the irregularly irregular pulse/rhythm (i.e., what else looks like AF?)
- DDx of palpitations (the most common presenting complaint)
- DDx of embolic complications of AF (stroke, acute limb ischaemia, mesenteric ischaemia)
A. Differential Diagnosis of the Irregularly Irregular Rhythm
This is the most exam-relevant DDx. When you feel or see an irregularly irregular rhythm, your mind should run through this list:
D/dx for irregularly irregular pulse [1]:
- Atrial flutter (AFL) or atrial tachycardia (AT) with variable AV block [1]
- Frequent multifocal ectopic beats [1]
- Multifocal atrial tachycardia (MAT) [1]
Let's expand on each and explain why they mimic AF:
Atrial flutter (AFL): rapid regular atrial activity at 180–350 bpm [1]. Typical AFL has an atrial rate of ~300 bpm. With fixed 2:1 AV block, the ventricular rate is a regular 150 bpm — this is regular, so it doesn't mimic AF. However:
- When the AV block ratio varies (e.g., alternating between 2:1, 3:1, 4:1), the ventricular response becomes irregular → mimics AF on pulse palpation
- How to distinguish from AF: Look at the ECG carefully for sawtooth flutter (F) waves [1], best seen in leads II, III, aVF and V1. In AFL, the baseline between QRS complexes shows organised, repetitive flutter waves at ~300 bpm. In AF, the baseline is chaotic or fine fibrillatory waves without a repeating pattern
- Vagal manoeuvres or adenosine injection can reveal the underlying atrial rhythm [1] — they transiently increase AV block, "unmasking" flutter waves that may be hidden within QRS complexes
Why does this matter clinically? Because AFL with variable block is sometimes mistaken for AF. The management overlaps significantly (both need anticoagulation based on CHA₂DS₂-VASc), but AFL is more amenable to catheter ablation of the cavotricuspid isthmus (CTI) [1], which has a very high success rate (~95%).
Focal atrial tachycardia (AT): regular atrial rhythm at > 100 bpm originating from one focus [1]. Normally AT is regular, but with variable AV conduction (especially at higher atrial rates), the ventricular response can become irregular.
- How to distinguish from AF: On ECG, AT shows identifiable P waves of abnormal morphology (different from sinus P waves) [1]. The atrial rate is typically 110–250 bpm — slower than AF's 350–600 bpm. The isoelectric baseline is preserved between P waves (unlike the chaotic baseline in AF)
- Causes: no underlying disease, atrial enlargement, digitalis toxicity [1]
Multifocal atrial tachycardia (MAT) [1]:
- Mechanism: abnormal automaticity in multiple foci, triggered activity [1]
- ECG: irregularly irregular rate with average atrial rate > 100 bpm; ≥3 P wave morphologies in the same lead [1]
- Key distinguishing feature: flat isoelectric line preserved (cf AF) [1]
MAT is the most commonly confused DDx with AF because it is also irregularly irregular. However:
| Feature | AF | MAT |
|---|---|---|
| P waves | Absent (chaotic fibrillatory baseline) | Present — ≥3 different P wave morphologies |
| Baseline | Irregular/fibrillatory | Flat isoelectric line preserved [1] |
| Typical atrial rate | 350–600 bpm | > 100 bpm (much slower) |
| Typical associations | Structural heart disease, HTN, thyrotoxicosis | Pulmonary disease (~60%), CHF, hypoK, hypoMg [1] |
| Treatment approach | Rate control + anticoagulation | Treat underlying condition [1] (antiarrhythmics often ineffective) |
Clinical pearl: If you see an "irregularly irregular" rhythm in an elderly patient with severe COPD, always consider MAT before labelling it AF. MAT in COPD is very common and the management is entirely different — focus on treating the lung disease and correcting electrolytes rather than rate control drugs.
Frequent atrial ectopics interspersed with sinus beats create an irregular rhythm that can feel irregularly irregular on palpation, especially if the ectopics are frequent and from multiple foci.
- How to distinguish from AF: On ECG, you will see an underlying sinus rhythm with identifiable sinus P waves, punctuated by premature beats with abnormal P wave morphology followed by a compensatory pause
- The key is that between ectopics, the rhythm returns to normal sinus
Similar to atrial ectopics but with wide QRS complexes not preceded by P waves. Frequent VPBs in a bigeminal or trigeminal pattern can produce an irregular pulse. Distinguished easily on ECG by the wide, bizarre QRS morphology.
A physiological variation in heart rate with respiration — heart rate increases with inspiration and decreases with expiration. This creates a mildly irregular rhythm but:
- P waves are present and normal
- The variation follows a regular cyclical pattern linked to breathing
- Most common in young, healthy individuals
- Easily distinguished from AF on ECG
Progressive PR prolongation with eventual dropped beats creates an irregular rhythm. Distinguished by:
- Identifiable P waves with progressively lengthening PR intervals
- Regular atrial rate (P-P intervals constant)
- Grouped beating pattern
When a patient presents with palpitations (the most common symptom of AF), you must consider the full spectrum of causes [2]:
Key discriminating features from the history [2]:
| Feature | Suggests |
|---|---|
| At rest [2] | Ectopics and AF [2] |
| During exercise [2] | PSVT, AF and VT [2] |
| Skipped or 'heavy' beats [2] | Ectopic beats (often triggered by stress, alcohol, nicotine, worse at rest) [2] |
| Irregular palpitations [2] | AF, AFL/AT with variable block and MAT [2] |
| Regular, relatively fast pounding (90–120 bpm) [2] | Hyperdynamic circulation (anaemia, pregnancy, thyrotoxicosis, AR, PDA) [2] |
| Discrete bouts, very rapid (> 120 bpm) [2] | Paroxysmal nodal re-entrant tachycardia [2] |
| Terminated by vagal manoeuvres (sneeze, cough, defecation) [2] | Nodal re-entrant tachycardia [2] |
| Sudden onset and offset [2] | Re-entrant circuit (AVRT, AVNRT, some AT) [2] |
| Gradual onset [2] | Increased automaticity (sinus tachycardia, some AT) [2] |
Exam Approach: Irregular vs Regular Palpitations
The single most useful question to ask: "Is the palpitation regular or irregular?" If irregular → think AF, AFL with variable block, MAT, or frequent ectopics. If regular → think AVNRT, AVRT, AFL with fixed block, sinus tachycardia, or VT. Then ask about onset (sudden vs gradual), duration, and termination (vagal manoeuvres) to narrow further.
C. Differential Diagnosis of Embolic Complications of AF
AF may present not with palpitations but with the consequences of thromboembolism. You must consider other causes of these presentations:
When a patient with AF presents with sudden focal neurological deficit, it is likely cardioembolic stroke. However, other stroke subtypes and stroke mimics must be considered [7]:
| Diagnosis | Key Distinguishing Features |
|---|---|
| Cardioembolic stroke (from AF) | Sudden onset, maximal at onset, large focal or multifocal deficit, known AF/VHD/HF [7]. Irregular pulse, heart murmur |
| Thrombotic stroke (large vessel atherosclerosis) | Stuttering progression, atherosclerotic RFs (HTN, DM, HL), ± Hx of TIA in same territory [7] |
| Lacunar stroke (small vessel disease) | Pure motor/sensory deficit, HTN as dominant RF, subcortical location |
| Haemorrhagic stroke (ICH) | Gradual progression, a/w progressive headache, triggered by physical activity, features of ↑ICP [7]. CT shows hyperdensity |
| SAH | Thunderclap headache, meningism, ↓consciousness |
| Stroke mimics | Transient events: seizures (Todd's paralysis), migraine aura, syncope. Persistent events: brain tumours, SDH, cerebral abscess, encephalitis, MS, metabolic encephalopathy (e.g., hypoglycaemia) [7] |
Clues to distinguish stroke from mimics [7]:
- Nature: stroke/TIA invariably produces negative symptoms (loss of function) rather than positive symptoms (e.g., tingling, visual scintillation = more likely migraine aura) [7]
- Extent: usually focal instead of global [7]
- Progression: rarely changes in modality [7]
Neuroimaging (CT/MRI) is essential for all stroke patients [7] — you cannot reliably distinguish ischaemic from haemorrhagic stroke clinically.
AF is the most common cardiac cause of embolic acute limb ischaemia [9][10]. The DDx includes:
| Diagnosis | Key Features | How to Distinguish from Embolism |
|---|---|---|
| Arterial embolism (from AF) | Cardiac source identifiable (e.g., AF), hyperacute onset (seconds–minutes), contralateral limb pulses present, absent bruits, complete ischaemia (no collaterals) [9] | Classic vignette: older patient with known AF, sudden onset 6Ps, no prior claudication |
| Arterial thrombosis-in-situ | Previous claudication, PVD in contralateral limb, present bruits, incomplete ischaemia (collaterals), onset over hours–days [9] | History of peripheral vascular disease, gradual onset, bilateral signs of atherosclerosis |
| Acute compartment syndrome | Pain (especially with passive stretch), tense swollen compartment, paraesthesia | Trauma or reperfusion history, compartment pressure measurement |
| DVT (phlegmasia cerulea dolens) [9] | Massive iliofemoral DVT with venous outflow obstruction → swollen, cyanotic, painful limb | Swelling is prominent (unlike arterial ischaemia where limb may be shrunken), cyanosis rather than pallor |
| Aortic dissection | May occlude branch arteries → limb ischaemia | Tearing chest/back pain, BP differential between arms, widened mediastinum on CXR |
AF may predispose to arterial embolism to mesenteric arteries [11][12]. The DDx of acute abdominal pain out of proportion to physical findings includes:
| Diagnosis | Key Features |
|---|---|
| Mesenteric embolism (from AF) | Acute embolus: severe sudden periumbilical pain in old patient with AF [11]. Pain out of proportion to exam findings |
| Mesenteric thrombosis | Strong cardiovascular risk factors (HTN/HL/DM) and PVD [11] |
| Non-occlusive mesenteric ischaemia (NOMI) | Critically ill patient with low cardiac output, on vasopressors/digoxin [11][12] |
| Perforated viscus | Sudden onset, peritonism, rigid abdomen, free air on AXR |
| Acute pancreatitis | Epigastric pain radiating to back, ↑amylase/lipase |
| Bowel obstruction | Colicky pain, vomiting, constipation, distended abdomen |
The ECG Is King
Never diagnose AF on clinical examination alone. An irregularly irregular pulse can be caused by AFL with variable block, MAT, or frequent ectopics. Always confirm with a 12-lead ECG — look specifically for: (1) absence of P waves, (2) irregular (fibrillatory) baseline, and (3) irregularly irregular narrow QRS complexes. If P waves are present in any form, it is NOT AF.
| Differential | Pulse | ECG Features | Key Distinguishing Point |
|---|---|---|---|
| Atrial Fibrillation | Irregularly irregular, variable volume | No P waves, fibrillatory baseline, irregular narrow QRS | Chaotic baseline, no identifiable P waves |
| Atrial Flutter (variable block) | Irregularly irregular | Sawtooth F waves (~300 bpm), variable R-R | Organised flutter waves seen in II, III, aVF, V1; adenosine unmasks |
| MAT | Irregularly irregular | ≥3 P wave morphologies, preserved isoelectric baseline | P waves present, flat baseline; a/w COPD |
| Focal AT (variable block) | Irregularly irregular | Single abnormal P morphology, rate 110–250 bpm | Slower atrial rate, consistent P wave shape |
| Frequent APBs | Irregular | Underlying sinus rhythm with premature P waves | Sinus P waves visible between ectopics |
| Frequent VPBs | Irregular | Wide bizarre QRS, no preceding P wave | Wide QRS morphology, compensatory pauses |
| Sinus arrhythmia | Mildly irregular | Normal P waves, rate varies with respiration | Cyclical variation, young/healthy patient |
| 2° AV block (Wenckebach) | Irregular | Progressive PR prolongation, dropped QRS | Grouped beating pattern, regular P-P |
High Yield Summary
- The three main DDx for an irregularly irregular rhythm (frequently tested): AF, AFL with variable block, MAT, and frequent ectopics.
- AF vs MAT: Both irregularly irregular, but MAT has ≥3 P wave morphologies with preserved isoelectric baseline. MAT is strongly associated with COPD. Treatment of MAT = treat the underlying condition, NOT standard AF management.
- AF vs AFL with variable block: AFL shows organised sawtooth flutter waves (~300 bpm atrial rate). Adenosine/vagal manoeuvres can unmask flutter waves. AFL is highly amenable to CTI ablation.
- Always get an ECG — clinical examination alone cannot reliably distinguish AF from its mimics.
- When AF presents as stroke: distinguish cardioembolic (sudden, maximal at onset, AF present) from thrombotic (stuttering, atherosclerotic RFs) and haemorrhagic (gradual, headache, ↑ICP). Neuroimaging is mandatory.
- When AF presents as acute limb ischaemia: embolism (from AF) is hyperacute, no prior claudication, contralateral pulses present vs thrombosis-in-situ (gradual, prior PVD, bruits).
- For palpitations, ask: regular vs irregular, onset (sudden vs gradual), termination (vagal manoeuvres suggest re-entrant SVT), precipitants, and rate.
Active Recall - Differential Diagnosis of Atrial Fibrillation
References
[1] Lecture slides / Senior notes: Ryan Ho Cardiology.pdf (pages 92–94 — AF, AFL, AT, MAT differential, ECG features) [2] Senior notes: Ryan Ho Fundamentals.pdf (page 206 — Palpitations differential diagnosis) [7] Senior notes: Ryan Ho Neurology.pdf (pages 76–79 — Stroke evaluation, DDx of stroke) [9] Senior notes: Maksim SURGERY notes.pdf (page 168 — Acute limb ischaemia, embolism vs thrombosis distinction) [10] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (page 920 — Acute arterial ischaemia aetiology) [11] Senior notes: Maksim SURGERY notes.pdf (page 92 — Ischaemic bowel disease, mesenteric ischaemia DDx) [12] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (page 718 — Mesenteric ischaemia aetiology)
Diagnostic Criteria, Diagnostic Algorithm and Investigations for Atrial Fibrillation
A. Diagnostic Criteria for Atrial Fibrillation
AF is fundamentally an ECG diagnosis. There are no "clinical diagnostic criteria" in the way that, say, rheumatic fever has Jones criteria or heart failure has Framingham criteria. The diagnosis rests on demonstrating the characteristic ECG pattern, ideally on a 12-lead ECG or, if paroxysmal, on a rhythm recording of sufficient quality and duration.
The diagnosis of AF requires documentation of the arrhythmia on an ECG recording showing the following features:
ECG features of AF [1]:
| Criterion | Explanation |
|---|---|
| 1. No distinct P waves [1] | Chaotic atrial depolarisation means no organised P wave preceding QRS complexes. The baseline may show irregular fibrillatory (f) waves [1]. These f waves tend to be coarse (> 2 mm) when AF is of recent onset and tend to be fine (< 1 mm) in long-standing AF. These can be easily missed or confused with movement artefacts [1] |
| 2. Irregularly irregular QRS complexes [1][2] | AV node conducts chaotic atrial impulses unpredictably → R-R intervals are irregularly irregular. Note that the irregular baseline may not always be present → look for irregular QRS complexes [2] |
| 3. Narrow QRS morphology (unless coexisting BBB/pre-excitation) [1] | Ventricular conduction via the His-Purkinje system is preserved → QRS is normally shaped. Typically 120–160 bpm but may ↓ in chronic cases [1] |
Duration requirement (ESC 2020):
- A minimum of 30 seconds of continuous AF on a single-lead or multi-lead ECG recording is conventionally required to make the diagnosis
- Shorter episodes detected on wearable devices (smartwatches, implantable loop recorders) are termed "subclinical AF" or "atrial high-rate episodes (AHRE)" — their management (particularly regarding anticoagulation) is still evolving based on trials like NOAH-AFNET 6 and ARTESiA (2023)
Exam Tip: Duration Matters
For a formal AF diagnosis, you need ≥30 seconds of continuous irregularly irregular rhythm without P waves on any ECG recording. A few seconds of irregular rhythm on a telemetry strip is suggestive but not diagnostic. For device-detected episodes < 30 seconds, the term "subclinical AF" is used, and the threshold for anticoagulation is higher (generally ≥24 hours of cumulative AF burden before considering OAC, per ARTESiA 2023).
The ECG confirms the rhythm but does not tell you:
- The cause of AF → requires further workup
- The stroke risk → requires CHA₂DS₂-VASc scoring
- The presence of LA thrombus → requires echocardiography (particularly TOE)
- Whether AF is paroxysmal, persistent, or permanent → requires clinical history and serial monitoring
The diagnostic algorithm for AF addresses two separate but related questions:
- Confirming the diagnosis (is this truly AF?)
- Evaluating the underlying cause and complications (why does this patient have AF, and what is the stroke risk?)
Special Scenario: Paroxysmal AF Not Captured on 12-lead ECG
If AF is suspected (e.g., transient palpitations, cryptogenic stroke) but the 12-lead ECG shows sinus rhythm, further monitoring is needed:
± Ambulatory ECG for paroxysmal AF [1]:
| Monitoring Modality | Duration | When to Use |
|---|---|---|
| 24-hour Holter monitor | 24–48 hours | Frequent symptoms (daily or near-daily) |
| Event recorder / patch monitor | 7–14 days | Symptoms occurring weekly |
| Implantable loop recorder (ILR) | Up to 3 years | Cryptogenic stroke with high suspicion of paroxysmal AF; infrequent symptoms |
| Smartwatch / wearable PPG | Continuous | Screening tool; any detection must be confirmed by ECG |
| Exercise testing [1] | During test | If AF is exercise-induced, or to assess rate control adequacy during exertion |
Cryptogenic Stroke and Occult AF
In patients with ischaemic stroke of undetermined aetiology ("cryptogenic stroke"), prolonged cardiac monitoring with an implantable loop recorder (ILR) detects AF in ~30% of cases over 3 years (CRYSTAL-AF trial). This is why current guidelines recommend extended cardiac monitoring (≥ 30 days) in all patients with cryptogenic stroke. Finding AF changes management from antiplatelet to anticoagulation.
C. Investigation Modalities — Detailed Breakdown
Purpose: Confirm the diagnosis of AF and identify coexisting abnormalities.
This is the single most important investigation. Let's go through what to look for systematically:
| Finding | Interpretation | Why It Matters |
|---|---|---|
| No distinct P waves ± irregular baseline (fibrillation waves) [1][2] | Chaotic atrial depolarisation. May have flutter-like waves for 2–3 seconds [2] — brief organised segments can occur in AF without making it flutter | Confirms diagnosis |
| Narrow but irregular QRS complexes [1] | AV node conducts variably → irregularly irregular ventricular response | If QRS is wide → consider AF with BBB, AF with pre-excitation (WPW), or VT [2] |
| Ventricular rate | Typically 120–160 bpm but may ↓ in chronic cases [1] | Controlled (< 110 bpm at rest for lenient; < 80 bpm for strict) vs uncontrolled. Slow ventricular rate without rate-control drugs → suspect AV node disease or drug toxicity |
| ST depression [1] | May suggest: underlying LVH (LV strain pattern) [1], ischaemia, or digoxin effect (upsloping ST depression) [1] | Guides further evaluation for CAD or drug effects |
| LVH voltage criteria | Tall R in V5/V6, deep S in V1/V2, ± strain pattern | Suggests hypertensive heart disease or HCMP as substrate |
| P mitrale (if transient sinus rhythm) | Bifid P wave in lead II > 120 ms | Suggests LA enlargement (from MS, MR, HTN) |
| Right heart strain | Right axis deviation, P pulmonale, RBBB, RV strain in V1–V3 | Suggests PE or cor pulmonale as trigger |
If QRS complex frequency is very irregular during a wide complex tachycardia → likely AF + BBB [2]. This is important because a wide, irregularly irregular tachycardia has a specific differential:
- AF with pre-existing BBB (most common) — compare with baseline ECG
- AF with WPW (pre-excited AF) — extremely important to recognise because AV nodal blockers (digoxin, verapamil, diltiazem) are contraindicated → they can enhance conduction down the accessory pathway → VF → death
- Polymorphic VT — if truly no pattern to QRS morphology and patient is haemodynamically unstable
Pre-excited AF: A Deadly Trap
If you see AF with a very fast rate (> 200 bpm) and wide QRS complexes with varying morphology (short and long pre-excitation), suspect AF with WPW. Do NOT give AV nodal blockers (adenosine, verapamil, diltiazem, digoxin). These block the AV node but leave the accessory pathway unblocked → all impulses conduct via the accessory pathway → VF. Use procainamide, ibutilide, or DC cardioversion instead.
Blood tests for reversible causes (TFT, K, Mg) [1]:
| Test | Rationale | Key Findings |
|---|---|---|
| Thyroid function tests (TFT) [1] | Hyperthyroidism is a reversible cause of AF. Must be excluded in every new-onset AF | ↑fT4, ↓TSH → thyrotoxicosis. Subclinical hyperthyroidism (N fT4, ↓TSH) also ↑AF risk |
| Serum potassium (K⁺) [1] | Hypokalaemia increases myocardial excitability and predisposes to arrhythmias | Low K⁺ (< 3.5 mmol/L) → correct before attempting cardioversion |
| Serum magnesium (Mg²⁺) [1] | Hypomagnesaemia often coexists with hypokalaemia (diuretic use) and promotes arrhythmias | Low Mg²⁺ (< 0.7 mmol/L) → supplement; refractory hypokalaemia may be due to concurrent hypoMg |
| Complete blood count (CBC) | Anaemia → hyperdynamic circulation → can trigger/worsen AF. Infection (↑WCC) → sepsis-induced AF | Anaemia (↓Hb), leucocytosis (infection) |
| Renal function (RFT: U, Cr, eGFR) | Baseline before anticoagulation (NOAC dose adjustment for renal impairment). Electrolyte assessment | ↓eGFR → dose reduce dabigatran, rivaroxaban, edoxaban. CKD ↑both thrombotic and bleeding risk |
| Liver function (LFT) | Baseline before anticoagulation. Hepatic dysfunction ↑bleeding risk, affects drug metabolism | ↑bilirubin, ↑INR → caution with anticoagulation |
| Coagulation profile (PT/INR, aPTT) | Baseline before initiating warfarin or NOAC | Elevated baseline INR → suspect liver disease or coagulopathy |
| Fasting glucose / HbA1c | DM is a component of CHA₂DS₂-VASc score and a risk factor for AF | Guides risk stratification and overall CV risk management |
| Lipid profile | Cardiovascular risk factor assessment (HTN, DM, HL all contribute to structural heart disease) | Guides statin therapy |
| BNP / NT-proBNP | Heart failure assessment. Elevated in AF even without HF (due to atrial stretch), but very high levels suggest coexisting HF | Guides HF management. Useful for prognostication |
| Cardiac enzymes (troponin) | If clinical suspicion of ACS as precipitant of AF | Elevated troponin → ACS or demand ischaemia from rapid AF. Note: minor troponin elevation can occur from tachycardia alone (type 2 MI) |
Echocardiogram for underlying structural heart disease [1]:
| Modality | What It Shows | When to Use |
|---|---|---|
| Transthoracic echocardiography (TTE) | LV systolic function (EF), LV wall thickness (LVH), LA size, valvular disease (MS, MR, AS, AR), RV function, pericardial effusion, pulmonary artery pressure estimation | All patients with new-onset AF [1]. Guides management decisions (rate vs rhythm, anticoagulation, valve intervention) |
| Transoesophageal echocardiography (TOE/TEE) [1] | LA mural thrombus best assessed by TOE [1]. Also visualises the left atrial appendage (LAA), mitral valve in detail, and interatrial septum (PFO/ASD) | Before cardioversion if AF duration > 48 hours or unknown (to exclude LA/LAA thrombus). Also for surgical/procedural planning (LAA occlusion, mitral valve intervention) |
Key echocardiographic findings and their significance:
| Finding | Significance |
|---|---|
| LA dilatation (> 40 mm or > 20 cm²) | Substrate for AF maintenance. Larger LA → lower success of cardioversion/ablation. Marker of chronicity |
| ↓ LVEF (< 50%) | Coexisting HF. Determines drug choices (avoid CCB if ↓EF). Consider tachycardia-mediated cardiomyopathy if EF improves with rate control |
| LVH | HTN heart disease, HCMP, AS → substrate for AF + loss of atrial kick is poorly tolerated |
| Mitral stenosis | Rheumatic MS → classifies as "valvular AF" → warfarin required (NOACs contraindicated) |
| LA/LAA thrombus (on TOE) | Absolute contraindication to cardioversion until thrombus resolved (usually 3–4 weeks of therapeutic anticoagulation then repeat TOE) |
| Spontaneous echo contrast ("smoke") in LA | Indicates stasis and high thrombotic risk. Often seen with large LA and low LA appendage velocities |
| RV dilatation / ↑PASP | Pulmonary hypertension → cor pulmonale, PE, or chronically elevated LAP from left heart disease |
Why is TOE needed before cardioversion? When AF has been present for > 48 hours (or unknown duration), thrombus may have formed in the LAA. If you cardiovert (electrically or pharmacologically), the atrium suddenly contracts again — this can dislodge a pre-formed thrombus → stroke. TOE can visualise the LAA directly (TTE cannot reliably see the LAA). If no thrombus → safe to cardiovert. If thrombus present → anticoagulate for ≥3 weeks, repeat TOE, then cardiovert if resolved.
Not diagnostic for AF itself but essential to evaluate:
| Finding | Interpretation |
|---|---|
| Cardiomegaly | Suggests underlying structural heart disease (DCMP, valvular disease, chronic HTN) |
| LA enlargement | Double density behind cardiac silhouette, splaying of carina, posterior displacement on lateral CXR |
| Pulmonary congestion / upper lobe venous diversion | Suggests heart failure (either causing or resulting from AF) |
| Pleural effusion | May indicate HF |
| Lung pathology | Pneumonia (sepsis-induced AF), COPD (chronic lung disease as cause), widened mediastinum (aortic dissection) |
± Exercise testing, ambulatory ECG for paroxysmal AF [1]:
| Modality | Mechanism | Indication |
|---|---|---|
| 24–48h Holter monitor | Continuous 3-lead ECG recording onto a portable device | Suspected paroxysmal AF with frequent symptoms; assess rate control |
| 7–14 day event recorder / patch | Extended continuous recording triggered automatically or by patient when symptomatic | Less frequent symptoms; higher yield than Holter for paroxysmal AF |
| Implantable loop recorder (ILR) | Subcutaneous device implanted under local anaesthesia, continuously monitors for up to 3 years | Cryptogenic stroke (to detect occult AF), very infrequent but clinically important symptoms |
| Mobile cardiac telemetry | Real-time wireless ECG transmission | High-risk patients requiring immediate notification (e.g., post-ablation monitoring) |
| Consumer wearables (smartwatch PPG) | Photoplethysmography detects pulse irregularity; algorithm flags AF | Screening tool only. Any detection must be confirmed by a diagnostic-quality ECG recording |
| Investigation | Indication | Key Findings |
|---|---|---|
| Exercise testing [1] | Assess rate control during exertion; unmask ischaemia; evaluate exercise-induced AF | Inadequate rate control (HR > 110 at submaximal exertion) guides drug titration. ST changes suggest CAD |
| CT/MR angiography of the LA and PVs | Pre-procedural planning for catheter ablation (PVI) | Maps PV anatomy (number, size, branching), LA dimensions, excludes PV stenosis |
| Cardiac MRI | Evaluate myocardial substrate (fibrosis, cardiomyopathy, infiltrative disease) | Late gadolinium enhancement quantifies LA fibrosis → predicts ablation success (Utah staging) |
| Electrophysiology study (EPS) | Rarely needed for diagnosis of AF itself | May be performed as part of catheter ablation procedure. Used if arrhythmia mechanism unclear (e.g., distinguishing AF from AFL) |
| Sleep study (polysomnography) | Suspected obstructive sleep apnoea (OSA) | OSA is a modifiable risk factor for AF. Treatment of OSA ↓AF recurrence after cardioversion/ablation |
Let's walk through interpreting a 12-lead ECG in a patient with suspected AF, step by step:
| Step | What to Assess | In AF |
|---|---|---|
| 1. Rate | Count R-R intervals or use 300/large squares method | Variable. Average rate estimated by counting QRS complexes in 10 seconds × 6 |
| 2. Rhythm | Regular, regularly irregular, or irregularly irregular | Irregularly irregular — this is the hallmark. R-R intervals vary with no repeating pattern |
| 3. P waves | Present? Shape? Relationship to QRS? | No distinct P waves. Irregular baseline with fibrillatory (f) waves [1][2]. No consistent P-QRS relationship |
| 4. PR interval | Consistent? Prolonged? | Cannot be measured (no P waves) |
| 5. QRS | Narrow or wide? Morphology? | Normally shaped but at irregular frequency [2]. If wide → consider BBB, WPW, or VT |
| 6. ST segment / T waves | Ischaemia? LVH strain? Drug effect? | Note any ST depression → underlying LVH, ischaemia, or digoxin effect [1] |
| 7. QT interval | Prolonged? | Difficult to assess in AF (variable R-R). Use QTc of the shortest R-R interval as a conservative estimate |
Practical Tip: How to Count Heart Rate in AF
Because the rate is irregular, the standard "300 ÷ number of large squares" method does not work for a single beat. Instead: count the number of QRS complexes in a 6-second strip (30 large squares) and multiply by 10. This gives the average ventricular rate. Alternatively, many modern ECG machines automatically calculate the average rate.
This is a specific diagnostic pathway relevant when cardioversion is being considered:
Why 48 hours? This is the traditional threshold because studies show that thrombus is unlikely to form in < 48 hours of AF. Beyond 48 hours (or if duration is unknown), the risk of thrombus in the LAA rises significantly, and either a TOE to exclude thrombus or a 3-week period of therapeutic anticoagulation is required before cardioversion is safe.
Why continue anticoagulation for ≥4 weeks after cardioversion? Even after successful cardioversion, atrial mechanical function ("atrial stunning") takes 2–4 weeks to recover. During this period, the atria are contracting weakly despite being in sinus rhythm → stasis persists → thrombus risk persists. Anticoagulation bridges this vulnerable period.
F. Risk Stratification Tools (Diagnostic Scoring)
While not "diagnostic criteria" for AF itself, these scoring systems are integral to the diagnostic workup and guide management. They will be discussed in detail in the Management section, but are introduced here as part of the evaluation:
| Component | Points | Explanation |
|---|---|---|
| C — Congestive HF (or LVEF ≤40%) | 1 | ↓CO → stasis |
| H — Hypertension | 1 | Endothelial dysfunction, LVH |
| A₂ — Age ≥75 | 2 | Strongest independent risk factor |
| D — Diabetes mellitus | 1 | Prothrombotic state |
| S₂ — Stroke/TIA/thromboembolism (prior) | 2 | Strongest predictor of future stroke |
| V — Vascular disease (prior MI, PAD, aortic plaque) | 1 | Marker of systemic atherosclerosis |
| A — Age 65–74 | 1 | Intermediate risk |
| Sc — Sex category (female) | 1 | Female sex ↑stroke risk in AF |
Anticoagulation based on CHA₂DS₂-VASc score [1]:
- Score 0 (males) or 1 (females, where the 1 point is solely from female sex): No anticoagulation needed
- Score 1 (males) or 2 (females): Consider anticoagulation (shared decision-making)
- Score ≥2 (males) or ≥3 (females): Anticoagulation recommended
| Component | Points |
|---|---|
| H — Hypertension (uncontrolled, sBP > 160) | 1 |
| A — Abnormal renal/liver function (1 point each) | 1 or 2 |
| S — Stroke (prior) | 1 |
| B — Bleeding history or predisposition | 1 |
| L — Labile INR (if on warfarin, TTR < 60%) | 1 |
| E — Elderly (age > 65) | 1 |
| D — Drugs (antiplatelet, NSAIDs) or alcohol (1 each) | 1 or 2 |
- Score ≥3 = "high bleeding risk" → does NOT contraindicate anticoagulation but flags the need to address modifiable bleeding risk factors (control BP, stop unnecessary NSAIDs, improve INR control or switch to NOAC, treat alcohol excess)
HAS-BLED Does Not Mean 'Don't Anticoagulate'
A common misconception is that a high HAS-BLED score contraindicates anticoagulation. This is wrong. The score is meant to identify and modify correctable bleeding risks. In almost all cases, the stroke risk (from not anticoagulating) outweighs the bleeding risk. The only absolute contraindications to anticoagulation are active major bleeding or severe thrombocytopenia.
| Investigation Category | Specific Tests | Purpose |
|---|---|---|
| Confirm rhythm | 12-lead ECG [1] | Diagnosis of AF |
| Document paroxysmal AF | Holter, event recorder, ILR [1] | Capture intermittent episodes |
| Exclude reversible causes | TFT, K⁺, Mg²⁺ [1] | Thyrotoxicosis, electrolyte imbalance |
| Assess structural heart disease | Echocardiogram (TTE) [1] | LV function, LA size, valvular disease |
| Exclude LA thrombus | TOE [1] | Before cardioversion if AF > 48h |
| Baseline bloods | CBC, RFT, LFT, coagulation, glucose, lipids | Pre-anticoagulation assessment |
| Risk stratification | CHA₂DS₂-VASc, HAS-BLED | Guide anticoagulation decision |
| CXR | Cardiomegaly, pulmonary congestion, lung pathology | Underlying cause and complications |
| Assess rate control | Exercise testing [1] | Adequacy of rate control during exertion |
| Pre-ablation planning | CT/MRI LA/PV anatomy, cardiac MRI for LA fibrosis | Procedural planning |
High Yield Summary
- AF is an ECG diagnosis — requires ≥30 seconds of: no P waves + irregular baseline (fibrillatory waves) + irregularly irregular narrow QRS complexes.
- Fibrillatory (f) waves are coarse in recent-onset AF and fine in long-standing AF; they may be absent in fine AF — diagnose by irregular R-R intervals.
- Every new-onset AF needs: 12-lead ECG, TFT, K⁺, Mg²⁺, echocardiogram, CBC, RFT, LFT, coagulation profile, CXR.
- TOE is the gold standard for detecting LA/LAA thrombus — indicated before cardioversion if AF > 48 hours or unknown duration.
- Paroxysmal AF not caught on 12-lead ECG → Holter (frequent symptoms), event recorder (weekly), ILR (cryptogenic stroke or rare symptoms).
- Wide complex irregularly irregular tachycardia = AF + BBB or pre-excited AF (WPW) — compare with baseline ECG; never give AV nodal blockers if WPW suspected.
- CHA₂DS₂-VASc stratifies stroke risk; HAS-BLED identifies modifiable bleeding risk factors (does NOT contraindicate anticoagulation).
- Pre-cardioversion rule: if AF > 48h → either 3 weeks therapeutic anticoagulation OR TOE to exclude thrombus before cardioverting. Continue OAC ≥4 weeks post-cardioversion regardless.
- Cryptogenic stroke → prolonged monitoring (≥30 days, ideally ILR) to detect occult AF; detection rate ~30% over 3 years.
Active Recall - AF Diagnosis and Investigations
References
[1] Lecture slides / Senior notes: Ryan Ho Cardiology.pdf (pages 92–94 — AF ECG features, evaluation, approach to new-onset AF) [2] Senior notes: Ryan Ho Fundamentals.pdf (pages 24, 206, 448, 467–468 — ECG interpretation of AF, pulse assessment, palpitations workup, fibrillation ECG features) [14] Senior notes: Ryan Ho Critical Care.pdf (pages 39–40 — Tachyarrhythmia management algorithm, cardioversion indications and energy levels) [15] Senior notes: Ryan Ho Respiratory.pdf (pages 21, 135 — Dyspnoea workup, PE investigations including ECG and echocardiography)
Management Algorithm and Treatment Modalities for Atrial Fibrillation
The management of AF rests on four pillars, and understanding why each exists comes directly from the pathophysiology we have already covered:
| Pillar | Why It Exists |
|---|---|
| 1. Identify and treat reversible causes | Some AF is entirely driven by a reversible trigger (thyrotoxicosis, PE, sepsis) — fix the trigger and AF may resolve |
| 2. Rate control | Even if AF persists, controlling the ventricular rate prevents haemodynamic compromise and tachycardia-mediated cardiomyopathy |
| 3. Rhythm control (cardioversion ± maintenance) | Restoring sinus rhythm restores atrial kick, improves symptoms, and may improve outcomes if done early |
| 4. Anticoagulation (stroke prevention) | AF causes LA stasis → thrombus → stroke. Anticoagulation is the single most important intervention to prevent the most devastating complication |
The mnemonic "ABC" pathway (ESC 2020) captures this neatly:
- A = Anticoagulation / Avoid stroke
- B = Better symptom control (rate and rhythm control)
- C = Comorbidity and cardiovascular risk factor management
Reverse reversible causes: hyperthyroidism, acute PE, myopericarditis, pneumonia, post-cardiac surgery [1].
This is always Step 1. If the underlying trigger is corrected, AF may terminate spontaneously without need for cardioversion or long-term treatment. However, anticoagulation decisions should still be made based on CHA₂DS₂-VASc during the acute episode.
| Reversible Cause | How to Treat | AF Resolution |
|---|---|---|
| Thyrotoxicosis | Antithyroid drugs (carbimazole/PTU) + β-blocker for symptom control | AF often reverts to SR once euthyroid. If not, cardioversion after 4–6 months of euthyroidism |
| Acute PE | Anticoagulation ± thrombolysis if massive | AF usually resolves once RV strain resolves |
| Sepsis / pneumonia | Antibiotics, source control, supportive care | AF often resolves once infection controlled |
| Post-cardiac surgery | Usually self-limiting within 6 weeks. Amiodarone prophylaxis ↓incidence. Rate control if symptomatic | 90% revert to SR by 6–8 weeks |
| Electrolyte imbalance | Correct K⁺ (target > 4.0 mmol/L) and Mg²⁺ (target > 0.8 mmol/L) | May revert or facilitate cardioversion |
| Acute alcohol excess | Stop alcohol, supportive care | "Holiday heart" often self-terminates |
C. Pillar 2 — Rate Control
Why rate control? Even if you cannot restore sinus rhythm, controlling the ventricular rate prevents:
- Haemodynamic compromise (↓diastolic filling time → ↓CO)
- Symptoms (palpitations, dyspnoea, fatigue)
- Tachycardia-mediated cardiomyopathy (sustained rates > 100 bpm → progressive LV dilatation and systolic dysfunction — reversible with rate control)
Rate control: usually started before any attempt at rhythm control [1].
| Strategy | Target | When to Use |
|---|---|---|
| Lenient | Resting HR < 110 bpm | Initial target for most patients (RACE II trial showed non-inferior to strict control) |
| Strict | Resting HR < 80 bpm | If symptoms persist despite lenient control, or if ↓LVEF |
Acute rate control approach (ESC 2020) [1]:
LVEF ≥40%: BB or non-dipine CCB ± digoxin (if unsatisfactory) [1]
LVEF < 40% or signs of ADHF: prefer lowest dose of BB ± digoxin ± amiodarone (if haemodynamic instability or severely reduced LVEF) [1]
| Drug | Loading/Bolus | Maintenance | Mechanism | Key Points |
|---|---|---|---|---|
| Diltiazem (Herbesser) [1] | 0.25 mg/kg over 2 min (15 mg bolus in 60 kg) [1] | 100 mg in 100 mL NS at 5–15 mL/h [1]. Oral: 120–360 mg daily (ER form) [1] | Non-dihydropyridine CCB → blocks L-type Ca²⁺ channels in AV node → slows AV conduction → ↓ventricular rate | Contraindicated in LVEF < 40% (negative inotrope) and in pre-excited AF. Avoid with BB (risk of severe bradycardia/hypotension) |
| Verapamil [1] | 0.075–0.15 mg/kg over 2 min (± 10 mg after 30 min if no response) [1] | 0.005 mg/kg/min infusion [1]. Oral: 180–480 mg daily (ER form) [1] | Same as diltiazem | Same contraindications as diltiazem. Causes constipation. Myocardial depression, hypotension, bradycardia, constipation [1] |
| Metoprolol (Betaloc) [1] | 2.5–5 mg bolus over 2 min (up to 3 doses) [1] | Oral: 25–100 mg BD [1] | β₁-selective blocker → ↓AV conduction + ↓SA node automaticity | Preferred if coexisting CAD. Can be used cautiously in stable HFrEF (use bisoprolol, carvedilol, or nebivolol for chronic HF). Avoid in acute decompensated HF, severe asthma |
| Digoxin [1] | 0.25 mg in 10 mL NS then Q8H × 3 (max up to 1.5 mg in 24 h) [1] | 0.125–0.25 mg daily [1] | Cardiac glycoside → ↑vagal tone on AV node → ↓AV conduction. Also mild +ve inotrope | Good for LVEF < 40% and HF [1]. Does NOT control rate during exercise (vagal withdrawal during exercise overcomes its effect). Narrow therapeutic index → toxicity risk (check levels, watch for hypokalaemia which ↑toxicity). NOT first-line monotherapy |
| Amiodarone [1] | 150 mg in 100 mL D5 Q30 min (can load up to 2×) [1] | 600 mg in 500 mL D5 Q24H; or 150 mg in 100 mL D5 at 17 mL/h [1]. Oral: 100–200 mg daily [1] | Class III antiarrhythmic (multiple mechanisms: Na⁺, K⁺, Ca²⁺ channel blockade + β-blocking) → slows AV conduction + some rate control | Reserved for LVEF < 40% with haemodynamic instability [1] where BB and digoxin fail. Has rhythm control properties too. Long-term use has significant toxicity (thyroid, pulmonary fibrosis, hepatotoxicity, corneal deposits, photosensitivity) |
Why Non-DHP CCBs and Not Amlodipine?
The term "non-dipine CCB" means non-dihydropyridine calcium channel blockers — specifically diltiazem and verapamil. These preferentially block L-type Ca²⁺ channels in the AV node, slowing conduction. Dihydropyridine CCBs (amlodipine, nifedipine) preferentially act on vascular smooth muscle → vasodilation without significant AV node effects → they do NOT control ventricular rate in AF and should not be used for this purpose.
Caution: risk of paradoxical ↑ventricular response in pre-excitation syndromes ('pre-excited AF') [1]:
- AV nodal blockers (CCB, BB, digoxin) → impair conduction via AVN-His bundle system without affecting conduction through the accessory pathway [1]
- Therefore, anterograde conduction is favoured in the accessory pathway → very rapid (> 300 bpm) atrial impulses transmitted without the 'filtration' of the AVN → dangerous paradoxical ventricular tachycardia leading to haemodynamic collapse [1]
- Drugs to avoid include adenosine, CCB, BB, digoxin and amiodarone [1]
- Options: DCCV if unstable, procainamide if stable [1]
Pre-excited AF — Critical Safety Point
In AF with WPW, the atrial rate is 350–600 bpm. Normally, the AV node filters this to ~120–160 bpm. If you block the AV node, all impulses go down the accessory pathway — which has no built-in rate-limiting refractory period — and the ventricle can be driven at 300+ bpm → VF → death. Always ask: could this be pre-excited AF? Clues: very fast rate, wide QRS, varying QRS morphology, known WPW, young patient.
For chronic rate control, the same drug classes are used orally:
| Setting | First-Line | Add-on | Notes |
|---|---|---|---|
| LVEF ≥40% | BB or non-DHP CCB (monotherapy) | Add digoxin if inadequate | Do NOT combine BB + non-DHP CCB (risk of profound bradycardia and AV block) |
| LVEF < 40% | BB (bisoprolol, carvedilol, nebivolol — these have HF mortality benefit) | Add digoxin | Non-DHP CCBs are contraindicated (negative inotrope worsens HF) |
| Sedentary / elderly | Digoxin may be acceptable as monotherapy | — | Controls rate at rest but not during exercise |
D. Pillar 3 — Rhythm Control (Cardioversion + Maintenance)
Why rhythm control? Restoring sinus rhythm offers:
- Better haemodynamics (restored atrial kick → ↑CO)
- Symptom relief (especially in younger, symptomatic patients)
- Potential long-term outcome benefit if initiated early (EAST-AFNET 4 trial, 2020)
- Reversal of tachycardia-mediated cardiomyopathy
Cardioversion: should be performed at least once in most patients with new-onset AF [1].
| Favour Rhythm Control | Favour Rate Control Alone |
|---|---|
| Symptomatic despite adequate rate control | Asymptomatic or minimal symptoms |
| Young patient | Elderly (> 75–80) |
| First episode or recent-onset AF | Long-standing persistent or permanent AF |
| Tachycardia-mediated cardiomyopathy | Significant LA dilatation (↓success of SR maintenance) |
| AF secondary to reversible cause (once treated) | Multiple prior failed cardioversions |
| Heart failure where atrial kick is critical (e.g., HCMP, diastolic dysfunction) | Patient preference for rate control |
Cardioversion: synchronized shock with QRS complex → avoid R-on-T phenomenon (torsades then VF) [14]
Mechanism: delivery of a current over a very short interval → depolarize the entire heart → abolish all prevailing abnormal rhythm → hope that the SAN will take the lead again as pacemaker [14]
| Aspect | Details |
|---|---|
| Indications | Unstable tachyarrhythmia with a pulse: fast AF, fast AFL, pSVT, VT with pulse [14]. Also for elective rhythm control in stable persistent AF |
| Energy | For AF (irregular narrow complex): 120–200J biphasic and increase stepwise [14]. Start at 120–150J biphasic for first attempt |
| Sedation | Requires consent with sedation (midazolam) + analgesics (morphine) as it is quite painful [14] |
| Absolute C/I | Sinus tachycardia (only absolute C/I) [14] — cardioversion would be treating a physiological response, not an arrhythmia |
| Pre-cardioversion anticoagulation | If AF > 48h or unknown duration → TOE to exclude thrombus OR ≥3 weeks therapeutic anticoagulation |
| Post-cardioversion | Continue OAC for ≥4 weeks (atrial stunning). Long-term anticoagulation decision still based on CHA₂DS₂-VASc (even if in SR) |
| Success rate | ~90% for DC cardioversion. Recurrence is common (50% at 1 year without maintenance antiarrhythmic) |
Timing: immediate if unstable, delayed if stable (69% spontaneously reverts < 48h) [1]. This means for haemodynamically stable patients with recent-onset AF (< 48h), a "wait-and-see" approach for 24–48 hours is reasonable — many will spontaneously revert.
Used when DCCV is not immediately available or as an alternative in selected patients. Less effective than DCCV but can be attempted.
| Drug | Class | Indication | How It Works | Key Points |
|---|---|---|---|---|
| Flecainide | IC | AF < 48h, no structural heart disease | Potent Na⁺ channel blocker → slows conduction velocity → terminates re-entrant circuits | "Pill-in-the-pocket" approach: patient takes single loading dose (200–300 mg PO) at onset of pAF. C/I in structural heart disease (↑mortality in post-MI patients — CAST trial) |
| Propafenone | IC | AF < 48h, no structural heart disease | Similar to flecainide + weak β-blocking activity | Same contraindications as flecainide. Also "pill-in-the-pocket" option |
| Amiodarone | III | AF with structural heart disease, HF | Broad-spectrum: Na⁺, K⁺, Ca²⁺ channel + β-blocking | Slower onset (hours). Safe in structural heart disease. Used when flecainide/propafenone C/I |
| Vernakalant | III (atrial-selective) | Recent-onset AF (≤7 days), non-HF | Atrial-selective K⁺ and Na⁺ channel blocker | IV administration. Not available everywhere. Rapid onset (~10 min). C/I in severe HF, hypotension, severe AS |
| Ibutilide | III | AF or AFL | Prolongs atrial action potential duration → terminates re-entry | Risk of torsades de pointes (must monitor QTc for 4–6 hours post-infusion) |
Pill-in-the-Pocket: A Smart Strategy for Paroxysmal AF
For patients with infrequent, well-tolerated paroxysmal AF and no structural heart disease, flecainide or propafenone can be prescribed as a single oral loading dose to take at home at symptom onset. The patient takes the dose when AF starts, lies down, and most episodes convert within 2–6 hours. This avoids the need for emergency department visits. However, the first attempt should always be supervised in hospital to ensure safety.
D4. Maintenance of Sinus Rhythm
After successful cardioversion, AF recurs in ~50% at 1 year without maintenance therapy. Options include:
| Drug | When to Use | Key Side Effects / Contraindications |
|---|---|---|
| Flecainide / Propafenone | No structural heart disease (first-line in this setting) | C/I in CAD, HF, significant LVH (proarrhythmic in diseased myocardium) |
| Dronedarone | Mild or no structural heart disease, non-permanent AF | C/I in NYHA III–IV HF (↑mortality — ANDROMEDA trial), permanent AF (↑CV events — PALLAS trial), liver toxicity |
| Sotalol | CAD (combines β-blocking + class III effect) | QT prolongation → torsades de pointes risk. Requires QTc monitoring. C/I if QTc > 500 ms, ↓K⁺/Mg²⁺, severe HF |
| Amiodarone [1] | Most effective AAD; reserved for structural heart disease, HF, or when other AADs fail | Long-term toxicity: thyroid (hypo/hyper), pulmonary fibrosis, hepatotoxicity, corneal microdeposits, photosensitivity, peripheral neuropathy. Monitor TFT, LFT, CXR, PFTs every 6–12 months. Oral: 100–200 mg daily [1] |
| Dofetilide | HF (safe in this population) | QT prolongation → requires in-hospital initiation with telemetry for 3 days. Renal dose adjustment |
The choice of AAD is guided primarily by the presence or absence of structural heart disease:
Catheter ablation [1]:
- Indication: usually reserved for those who are symptomatic despite or intolerant of ≥1 AAD [1]. Increasingly used as first-line rhythm control in selected patients (paroxysmal AF, young, structurally normal heart) based on EARLY-AF and STOP-AF First trials
- Procedure: Creation of circumferential lesions around the pulmonary vein ostia to electrically isolate them from the LA [1] — this eliminates the dominant triggers
- Radiofrequency ablation (RFA): point-by-point thermal lesions. More time-consuming but highly effective
- Cryoballoon ablation: cold destruction of tissue using a balloon catheter positioned at each PV ostium. Faster but less flexible for non-PV targets
- Efficacy: ~70–80% freedom from AF at 1 year after single procedure (↑ with repeat procedures). Better outcomes in paroxysmal AF than persistent AF (less atrial remodelling)
- Complications: Inadvertent AV node ablation → complete heart block requiring pacemaker, cardiac tamponade due to perforation [1]. Also: PV stenosis, phrenic nerve injury (especially with cryoballoon on right superior PV), oesophageal injury/fistula (rare but fatal), stroke/TIA
Surgical ablation [1]:
- Indication: usually reserved for those with concomitant open cardiac surgery [1] (e.g., mitral valve surgery + Maze procedure)
- Procedure: creation of linear scars by incision/ablation on atrial wall → ↓formation of re-entrant circuits (maze procedure) [1]
- Efficacy: usually high rate of success [1]
When to Go Straight to Ablation?
Current ESC 2024 and ACC/AHA 2023 guidelines now support catheter ablation as first-line rhythm control (before AADs) in selected patients with paroxysmal AF who are symptomatic, particularly if young, with structurally normal hearts, or with HFrEF (where AF ablation has been shown to improve mortality — CASTLE-AF trial). This is a significant shift from older guidelines that required AAD failure first.
E. Pillar 4 — Anticoagulation (Stroke Prevention)
This is the most impactful intervention in AF management. AF-related strokes are larger, more disabling, and more fatal than non-AF strokes. Anticoagulation reduces stroke risk by ~60–70%.
Anticoagulation: based on CHA₂DS₂-VASc score [1].
| Score | Males | Females | Recommendation |
|---|---|---|---|
| 0 | 0 | 1 (sex alone) | No anticoagulation |
| 1 | 1 | 2 | Consider OAC (shared decision-making) |
| ≥2 | ≥2 | ≥3 | OAC recommended |
Anticoagulation is recommended even if the patient is in sinus rhythm after cardioversion or ablation, as long as the CHA₂DS₂-VASc score warrants it. The risk of stroke from subclinical AF recurrence persists.
| Agent | Mechanism | Dosing | Monitoring | Key Points |
|---|---|---|---|---|
| Warfarin | Inhibits vitamin K epoxide reductase → ↓regeneration of reduced vitamin K → ↓production of vitamin K-dependent factors (II, VII, IX, X) [16] | Target INR 2.0–3.0 (3.0–3.5 for mechanical valves) | INR monitoring (keep in therapeutic range > 65–70% of the time = TTR) | Required for valvular AF (moderate-severe MS, mechanical heart valves). Slow onset (requires overlap with heparin as takes time for depletion of factors [16]). Multiple food/drug interactions. Teratogenic |
| Dabigatran (Pradaxa) | Direct thrombin (factor IIa) inhibitor ("dabiga-THROMBIN") | 150 mg BD (110 mg BD if age ≥80, concurrent verapamil, or high bleeding risk) | No routine monitoring (predictable PK). Can check dilute thrombin time if needed | Specific reversal agent: idarucizumab (Praxbind). RE-LY trial. GI upset common. Renal clearance (80%) → contraindicated if CrCl < 30 mL/min |
| Rivaroxaban (Xarelto) | Direct factor Xa inhibitor ("ri-Xa-rOXaban") | 20 mg OD with food (15 mg OD if CrCl 15–49) | No routine monitoring | ROCKET-AF trial. Once-daily dosing. Avoid if CrCl < 15. No specific reversal agent but andexanet alfa available |
| Apixaban (Eliquis) | Direct factor Xa inhibitor ("a-piXa-ban") | 5 mg BD (2.5 mg BD if ≥2 of: age ≥80, weight ≤60 kg, Cr ≥133 μmol/L) | No routine monitoring | ARISTOTLE trial. Lowest bleeding rates among NOACs. Preferred in elderly and CKD. Avoid if CrCl < 15 |
| Edoxaban (Lixiana) | Direct factor Xa inhibitor | 60 mg OD (30 mg OD if CrCl 15–50, weight ≤60 kg, or concurrent potent P-gp inhibitor) | No routine monitoring | ENGAGE AF-TIMI 48 trial. Once daily. Avoid if CrCl < 15 or > 95 (↓efficacy at high CrCl) |
NOACs (also called DOACs — Direct Oral Anticoagulants) are preferred over warfarin for non-valvular AF based on multiple landmark RCTs showing non-inferior or superior efficacy with significantly lower intracranial haemorrhage rates.
When warfarin is still required (NOAC contraindicated):
- Moderate-to-severe mitral stenosis (no NOAC data)
- Mechanical heart valves (RE-ALIGN trial showed ↑thromboembolism with dabigatran)
- Severe CKD (CrCl < 15 mL/min) — warfarin can still be used; NOACs are generally avoided
- Antiphospholipid syndrome — warfarin preferred (TRAPS trial showed ↑thrombosis with rivaroxaban)
NOAC vs Warfarin — Summary of Key Trials
- RE-LY (dabigatran): 150 mg BD superior for stroke prevention, 110 mg BD non-inferior with less bleeding
- ROCKET-AF (rivaroxaban): non-inferior to warfarin
- ARISTOTLE (apixaban): superior for stroke prevention AND less major bleeding AND lower mortality
- ENGAGE AF (edoxaban): non-inferior, less bleeding
All NOACs showed significantly lower intracranial haemorrhage (the most feared bleeding complication of anticoagulation). Apixaban has the best overall safety profile.
| Scenario | Approach |
|---|---|
| Post-cardiac surgery AF [1] | Usually transient. Anticoagulate if AF persists > 48h. Most revert by 6–8 weeks → reassess need for OAC |
| Peri-cardioversion | If AF > 48h: 3 weeks OAC pre-cardioversion + ≥4 weeks post. If AF < 48h: can cardiovert with heparin cover then OAC ≥4 weeks |
| Post-ablation | OAC for ≥2–3 months post-ablation regardless of rhythm. Long-term OAC based on CHA₂DS₂-VASc (not rhythm) |
| Acute ischaemic stroke | Delay starting OAC by 4–14 days depending on infarct size (ESC 2020 "1-3-6-12 day" rule: TIA = day 1, small stroke = day 3, moderate = day 6, large = day 12–14). Exclude haemorrhagic transformation on repeat imaging first |
| ACS with AF | Triple therapy (OAC + DAPT) for shortest possible duration (1 week to 1 month), then step down to OAC + single antiplatelet (clopidogrel preferred) for up to 12 months, then OAC alone |
| Perioperative AF on warfarin [17] | Stop warfarin 5 days before if INR 2–3. Check INR day before surgery (aim < 1.5). Bridging with LMWH if high thrombotic risk (CHA₂DS₂-VASc ≥5, prior stroke/TIA in 3 months, mechanical valve) [17]. Restart warfarin 12–48h post-op depending on bleeding risk |
For patients who cannot tolerate any anticoagulation (e.g., recurrent life-threatening GI bleeding, ICH):
- Percutaneous LAA occlusion (e.g., Watchman device): a nitinol-based plug deployed into the LAA ostium via transseptal catheterisation → seals off the LAA → prevents thrombus from embolising
- Rationale: ~90% of LA thrombi in non-valvular AF arise from the LAA
- Post-procedure: short course of DAPT, then aspirin alone
- Surgical LAA ligation/excision: performed during concomitant cardiac surgery
Aspirin is no longer recommended for stroke prevention in AF (ESC 2020, ACC/AHA 2023). The AVERROES trial showed apixaban was far superior to aspirin for stroke prevention with comparable bleeding. Aspirin provides only ~20% stroke risk reduction (vs ~60–70% with OAC) and still carries significant bleeding risk.
No Role for Aspirin in AF Stroke Prevention
A common outdated practice is to prescribe aspirin for AF patients with low CHA₂DS₂-VASc scores or as a "safer alternative" to OAC. This is wrong. Aspirin is not recommended for stroke prevention in AF by any current major guideline. If the CHA₂DS₂-VASc score warrants anticoagulation → use OAC. If it doesn't → no antithrombotic at all.
This is increasingly recognised as crucial for AF management:
| Target | Intervention | Rationale |
|---|---|---|
| Hypertension | Treat to < 130/80 mmHg | ↓LA pressure → ↓LA dilatation → ↓AF substrate |
| Obesity | Weight loss (≥10% body weight if BMI ≥ 27) | LEGACY trial: ≥10% weight loss → 6× ↑ likelihood of AF-free survival |
| Obstructive sleep apnoea | CPAP therapy | ↓nocturnal sympathetic surges → ↓AF recurrence post-ablation |
| Diabetes | Glycaemic control (HbA1c < 7%) + SGLT2 inhibitors | SGLT2i may have antiarrhythmic properties (↓atrial remodelling) |
| Alcohol | Reduction or abstinence | ALCOHOL-AF trial: abstinence ↓AF recurrence by 50% |
| Exercise | Regular moderate exercise (avoid extreme endurance) | Improves CV fitness, ↓weight, ↓sympathetic tone |
| Smoking | Cessation | ↓oxidative stress, ↓inflammation |
| Drug | IV Loading | IV Maintenance | Oral Maintenance |
|---|---|---|---|
| Diltiazem [1] | 0.25 mg/kg over 2 min | 100 mg in 100 mL NS at 5–15 mL/h | 120–360 mg daily (ER) |
| Verapamil [1] | 0.075–0.15 mg/kg over 2 min | 0.005 mg/kg/min | 180–480 mg daily (ER) |
| Metoprolol [1] | 2.5–5 mg over 2 min × 3 | — | 25–100 mg BD |
| Amiodarone [1] | 150 mg in D5 Q30 min (up to 2×) | 600 mg in 500 mL D5 Q24H | 100–200 mg daily |
| Digoxin [1] | 0.25 mg then Q8H × 3 (max 1.5 mg/24h) | — | 0.125–0.25 mg daily |
High Yield Summary
- Four pillars: (A) Reverse reversible causes, (B) Rate control, (C) Rhythm control (cardioversion + maintenance), (D) Anticoagulation.
- ESC ABC pathway: A = Anticoagulation, B = Better symptom control, C = Comorbidity management.
- Rate control first-line: BB or non-DHP CCB for LVEF ≥40%; BB ± digoxin for LVEF < 40%. Non-DHP CCBs contraindicated in HF. Target HR < 110 bpm (lenient) or < 80 bpm (strict).
- Pre-excited AF is a deadly trap: NEVER give AV nodal blockers (CCB, BB, digoxin, adenosine, amiodarone). Use DCCV or IV procainamide.
- Cardioversion: DCCV 120–200J biphasic for AF. Immediate if unstable; delayed if stable (69% revert < 48h). If AF > 48h → TOE or 3 weeks OAC first. Continue OAC ≥4 weeks post-cardioversion.
- AAD choice by structure: No structural disease → flecainide/propafenone. CAD → sotalol/dronedarone. HF → amiodarone.
- Catheter ablation (PVI): increasingly first-line for paroxysmal AF, HFrEF with AF, or after AAD failure. ~70–80% success.
- Anticoagulation: CHA₂DS₂-VASc guides decision. NOACs preferred over warfarin for non-valvular AF. Warfarin for MS and mechanical valves. Aspirin has NO role in AF stroke prevention.
- Apixaban has the best safety profile (ARISTOTLE: superior efficacy + less bleeding + lower mortality).
- Weight loss ≥10% is as effective as some drug interventions for AF recurrence reduction.
Active Recall - AF Management
References
[1] Lecture slides / Senior notes: Ryan Ho Cardiology.pdf (pages 92–97, 113, 139 — AF mechanism, causes, classification, evaluation, approach, rate control drugs with dosing, rhythm control, catheter/surgical ablation, antiarrhythmic drug table) [2] Senior notes: Ryan Ho Fundamentals.pdf (pages 206, 467–468 — ECG interpretation of AF, SVT classification, carotid sinus pressure effects) [14] Senior notes / Lecture slides: Ryan Ho Critical Care.pdf (pages 39–40 — Tachyarrhythmia management algorithm, cardioversion mechanism, energy levels, indications, contraindications) [16] Senior notes: Ryan Ho Haemtology.pdf (pages 131–133 — Anticoagulant mechanisms: UFH, LMWH, warfarin, monitoring, reversal) [17] Senior notes: Maksim SURGERY notes.pdf (page 26 — Perioperative warfarin management, bridging with LMWH, NOAC management, antiplatelet perioperative care) [7] Senior notes: Ryan Ho Neurology.pdf (pages 79, 83 — Stroke secondary prevention with anticoagulation for cardioembolic stroke, timing of anticoagulation post-stroke) [1a] Senior notes: Ryan Ho Cardiology.pdf (page 106 — Adenosine mechanism, catheter ablation indications, WPW management)
Complications of Atrial Fibrillation
The complications of AF are not random — every single one traces back to the three core pathophysiological derangements caused by the arrhythmia:
- Loss of coordinated atrial contraction → stasis → thromboembolism
- Rapid, irregular ventricular rate → haemodynamic compromise → heart failure
- AF begets AF → progressive atrial remodelling → perpetuation and worsening of the arrhythmia itself
We will systematically cover each complication, explain why it happens from first principles, and cross-reference with the relevant organ-system manifestations.
1. Thromboembolic Complications
This is the most important complication of AF and the primary reason anticoagulation is the cornerstone of AF management.
Pathophysiology (from first principles):
- AF → loss of coordinated atrial contraction → blood pools in the LA, especially in the left atrial appendage (LAA) (a blind-ended, trabeculated pouch)
- Stasis + endothelial dysfunction + hypercoagulable state in AF (Virchow's triad) → thrombus formation
- Thrombus dislodges → travels via aorta → cerebral arteries → occludes a vessel → ischaemic stroke
Why AF strokes are particularly devastating:
- AF-related emboli tend to be large (originating from the spacious LAA) → occlude proximal cerebral arteries (e.g., MCA trunk) → large-territory infarcts with cortical involvement
- AF-related strokes carry ~2× higher mortality, greater disability, and longer hospital stays compared to non-AF strokes
Features suggestive of embolic stroke [7]:
- Non-progressive onset (cf stuttering, progressive onset for thrombotic stroke) [7]
- Sudden onset, maximal at onset, with subsequent improvement [7]
- Non-lacunar stroke with cortical deficits (e.g., hemianopia, aphasia, apraxia) [7]
- Multiple territories involved [7]
- Haemorrhagic transformation on CT [7] — embolic infarcts are more prone to haemorrhagic transformation because when the embolus fragments and reperfusion occurs into already-damaged vessels, blood leaks into the infarcted tissue
Clinical consequences:
- Hemiparesis, hemisensory loss, aphasia, visual field defects, dysphagia — depending on the vascular territory involved [7]
- TIA: transient focal deficit resolving within 24 hours — a warning sign that a larger stroke may follow
Secondary prevention after cardioembolic stroke [7]:
- Anticoagulants for cardioembolic ischaemic stroke: warfarin or NOAC (if non-valvular AF) [7]
- Antiplatelets (aspirin, clopidogrel) are for non-cardioembolic stroke [7] — do not use antiplatelets alone for AF-related stroke
- Timing of anticoagulation initiation after stroke follows the "1-3-6-12 day" rule: TIA = day 1, small stroke = day 3, moderate = day 6, large stroke = day 12–14. This delay allows time for the infarcted area to stabilise and reduces the risk of haemorrhagic transformation
AF and Stroke: The Key Numbers
- AF is responsible for ~20–30% of all ischaemic strokes
- AF ↑stroke risk by ~5× compared to patients in sinus rhythm
- Anticoagulation reduces this stroke risk by ~60–70%
- Inadequately anticoagulated AF (e.g., subtherapeutic warfarin with INR < 2) offers incomplete protection
1B. Systemic Arterial Embolism
The same LA thrombus that can embolise to the brain can travel to any systemic arterial bed:
Cardiac origin emboli account for ~80% of cases; AF is the most common cardiac cause of arterial embolism [9][10].
Emboli typically lodge at acute narrowing of an artery such as vessel branch points [10]:
- Bifurcation of femoral artery (most common) [10]
- Trifurcation of popliteal artery (2nd most common) [10]
- Aortic bifurcation, bifurcation of common iliac artery
Clinical features — the "6Ps" [9]:
- Pain (early: nerves are most sensitive to ischaemia)
- Pallor
- Perishingly cold
- Pulseless
- Paraesthesia
- Paralysis (late: poor prognosis, indicating muscle infarction)
Key distinction: embolism vs thrombosis-in-situ [9]:
| Feature | Embolism (from AF) | Thrombosis-in-situ |
|---|---|---|
| Onset [9] | Hyperacute (seconds to minutes) | Acute (hours or days) |
| Severity [9] | Complete ischaemia (no collaterals) | Incomplete ischaemia (collaterals) |
| History [9] | No prior claudication; embolic source identifiable (AF) | Previous claudication; PVD risk factors |
| Contralateral limb [9] | Pulses present, no bruits | Absent pulses, bruits present |
| Management [9] | Embolectomy + anticoagulation | Medical, bypass, thrombolysis |
Why does embolism cause complete ischaemia while thrombosis causes incomplete? Because embolism is a sudden event in a previously normal artery with no time to develop collateral circulation. In thrombosis-in-situ, the chronic narrowing from atherosclerosis has allowed collateral vessels to form over months to years, partially compensating for the acute occlusion.
AF may predispose to arterial embolism to mesenteric arteries [11][12].
Embolism to mesenteric arteries is most frequently due to dislodged thrombus from LA, LV, cardiac valves or proximal aorta [12].
- Classic vignette: severe sudden periumbilical pain in an old patient with AF [11]
- Pathophysiology: embolus lodges in the SMA (most commonly) → acute ischaemia of the small bowel → mucosal necrosis → full-thickness infarction → peritonitis, sepsis, death
- Key clinical feature: abdominal pain out of proportion to physical findings [11] — early on, the abdomen may be soft and non-tender despite excruciating pain (because the peritoneum is not yet involved; only the visceral afferents are firing)
- Investigations: lactate (↑), ABG (HAGMA), CT angiography
- Mortality: very high (~60–80%) if diagnosis is delayed
| Target Organ | Clinical Presentation | Notes |
|---|---|---|
| Renal arteries | Flank pain, haematuria, ↑LDH, ↑AST. Often oliguria or AKI if bilateral | Frequently missed; consider in AF patient with unexplained flank pain |
| Splenic artery | Left upper quadrant pain, referred to left shoulder (Kehr's sign) | Usually managed conservatively unless splenic abscess develops |
| Coronary arteries | Acute MI (ST elevation) in absence of atherosclerotic CAD | Rare but reported; consider in young AF patient with ACS |
| Retinal artery | Sudden painless monocular vision loss (central retinal artery occlusion) | Ophthalmological emergency; "cherry red spot" on fundoscopy |
2. Heart Failure
AF and heart failure have a bidirectional relationship — each worsens the other.
There are three mechanisms by which AF leads to or worsens HF:
| Mechanism | Explanation |
|---|---|
| Loss of atrial kick | Coordinated atrial contraction contributes 15–25% of ventricular filling (up to 40% in stiff ventricles from HCMP, LVH, AS). Loss of this → acute ↓CO. This is why AF in mitral stenosis causes acute cardiac decompensation [4] — the stenosed valve depends heavily on LA systole to push blood through |
| Rapid ventricular rate | ↑HR → ↓diastolic filling time → ↓stroke volume → ↓CO. Also ↑myocardial O₂ demand while ↓diastolic coronary perfusion time → supply-demand mismatch |
| Tachycardia-mediated cardiomyopathy (TCMP) | Sustained rapid ventricular rate (typically > 100–110 bpm for weeks to months) → progressive LV dilatation and systolic dysfunction. Crucially, TCMP is reversible with adequate rate or rhythm control — this is why you must always consider it in any patient with AF and ↓EF |
AF is common and frequently transient after cardiac surgery or MI; it can be a sign of impending or overt LV failure [1].
Conversely, HF promotes AF through:
- ↑LAP → LA dilatation → creates substrate for re-entrant circuits
- Neurohormonal activation (RAAS, sympathetic) → atrial fibrosis
- Electrolyte disturbances from diuretics (↓K⁺, ↓Mg²⁺) → arrhythmia triggers
The vicious cycle: AF → ↓CO → worsens HF → ↑LAP → further LA dilatation → more AF → further ↓CO → and so on. Breaking this cycle (with rate or rhythm control + HF treatment) is the key therapeutic goal.
In the acute setting, new-onset AF with a very rapid ventricular response can cause:
- Hypotension → from ↓CO (loss of atrial kick + ↓diastolic filling)
- Cardiogenic shock → if cardiac output is critically low, particularly in patients with pre-existing structural heart disease (severe AS, HCMP, acute MI)
- Acute pulmonary oedema → ↑LAP from rapid rate + loss of atrial contraction → pulmonary venous congestion
This is the clinical scenario that mandates emergency synchronised DC cardioversion [14]:
- Indications: unstable tachyarrhythmia with a pulse (fast AF, fast AFL, pSVT, VT with pulse) [14]
- Energy for AF: 120–200J biphasic, increase stepwise [14]
This deserves its own section because it is frequently missed and completely reversible.
Pathophysiology:
- Sustained rapid ventricular rate (usually > 100–110 bpm) for weeks to months
- → Myocyte calcium overload → impaired calcium cycling → ↓contractility
- → Myocardial energy depletion (↑O₂ demand without proportional ↑supply)
- → Progressive LV dilatation and ↓EF
- → Clinically manifests as dilated cardiomyopathy with heart failure symptoms
Key clinical features:
- Patient with AF and newly discovered ↓LVEF (often EF 20–35%)
- No other obvious cause of cardiomyopathy identified
- HR has been persistently > 100 bpm
Why it matters: TCMP is fully reversible with adequate rate or rhythm control. After heart rate normalisation, LVEF typically recovers over 1–6 months. If you don't think about it, you may label a patient as having irreversible DCMP and miss the opportunity for full recovery.
How to distinguish from pre-existing DCMP with AF:
- TCMP: AF precedes HF symptoms; EF improves dramatically after rate/rhythm control
- DCMP with AF: HF symptoms precede AF; EF may not normalise with rate control
Always Consider TCMP
In any patient presenting with AF + newly reduced EF, ask: "Is AF the cause of the cardiomyopathy or the consequence?" If the heart rate has been persistently rapid and the LV dilatation seems out of proportion to other risk factors, suspect TCMP. Control the rate, re-image in 3–6 months — if EF normalises, you have your answer.
Whether electrical or pharmacological, cardioversion itself carries risks [14]:
| Complication | Mechanism | Prevention/Management |
|---|---|---|
| Systemic embolism (1–3%) [14] | Cardioversion restores atrial contraction → dislodges pre-formed thrombus in LAA. Also, post-cardioversion "atrial stunning" promotes new thrombus formation [1] | Pre-cardioversion anticoagulation (≥3 weeks or TOE-guided) + post-cardioversion OAC ≥4 weeks [1] |
| Skin burns [14] | Direct thermal injury from defibrillation pads | Proper pad placement, conductive gel |
| Pulmonary oedema [14] | Due to LV dysfunction or transient LA standstill [14] — atrial stunning causes transient ↑LAP | Usually self-limiting; diuretics if symptomatic |
| Myocardial necrosis with transient ST elevation [14] | Direct electrical injury to myocardium | Usually minor and self-limiting; can cause transient troponin rise |
| Inadvertent defibrillation if unsynchronised [14] | If synchronisation fails, shock may fall on vulnerable period of repolarisation → R-on-T → VF | Always confirm synchronisation before delivering shock |
| Bradycardia / asystole | Underlying sinus node disease unmasked after cardioversion (especially in sick sinus syndrome) | Have transcutaneous pacing on standby |
| Proarrhythmia (pharmacological) | Antiarrhythmic drugs used for cardioversion can themselves cause arrhythmias (e.g., flecainide → VT in structural heart disease; ibutilide → torsades de pointes) | Appropriate drug selection based on structural heart disease; monitor QTc |
The risk of cardioembolism is much higher in those with long-standing AF. Two main sources include: (1) pre-existing LA thrombus getting dislodged during cardioversion, and (2) post-cardioversion atrial stunning leading to formation of thrombus (much more common in long-standing AF as the recovery of atrial function is typically much slower) [1].
Catheter ablation complications [1]:
| Complication | Incidence | Mechanism | Management |
|---|---|---|---|
| Cardiac tamponade [1] | ~1% [1] | Perforation [1] of the thin LA wall during ablation → blood fills the pericardial space → ↑intrapericardial pressure → impaired diastolic filling → ↓CO | Emergency pericardiocentesis; surgical repair if large |
| Pulmonary vein stenosis [1] | 1–3% [1] | Thermal injury to the PV ostium → fibrosis → luminal narrowing → obstruction to pulmonary venous drainage | SOBOE, cough, chest pain, haemoptysis [1]. Diagnosis by CT/MR angiography. Treatment: PV balloon angioplasty ± stenting |
| Embolic events (stroke, TIA) [1] | ~0.5–1% | Thrombus formation on catheter/sheath or charred tissue during ablation → embolisation to brain | Intraprocedural heparin (target ACT > 300–350s); irrigated-tip catheters |
| Entry site complications [1] | Variable | Pseudoaneurysm, infection [1], haematoma, AV fistula at femoral vein access site | Ultrasound-guided compression; surgical repair if needed |
| Phrenic nerve injury | ~1–2% (especially right-sided cryoablation) | Proximity of right phrenic nerve to right superior PV → thermal or cold injury during ablation → diaphragmatic paralysis | Usually transient; monitor for diaphragmatic excursion during ablation |
| Atrioesophageal fistula | Extremely rare (< 0.1%) but fatal | LA posterior wall is separated from oesophagus by only a few mm of connective tissue → thermal injury can create a fistula → mediastinitis, sepsis, air embolism, massive haemorrhage | Oesophageal temperature monitoring during ablation; emergent surgical repair |
| AV node ablation → complete heart block | Rare with PVI (more relevant in AV node ablation strategy) | Inadvertent AV node ablation → complete heart block requiring pacemaker [1] | Permanent pacemaker implantation |
Since virtually all AF patients with stroke risk factors are on long-term anticoagulation, bleeding complications are common and clinically significant:
| Complication | Mechanism | Risk Factors |
|---|---|---|
| Intracranial haemorrhage (ICH) | Anticoagulation impairs haemostasis → bleeding into brain parenchyma or subdural/epidural space. The most feared bleeding complication | Elderly, prior stroke, uncontrolled HTN, excessive anticoagulation (INR > 3 with warfarin), concomitant antiplatelets |
| Gastrointestinal bleeding | Anticoagulation-related mucosal bleeding from pre-existing lesions (PUD, angiodysplasia, diverticulosis, malignancy) | Age > 65, H. pylori, concurrent NSAIDs/aspirin, alcohol, CKD |
| Haematuria | Anticoagulation unmasking urological pathology (bladder/renal carcinoma, BPH) | Important: always investigate haematuria on anticoagulation — do NOT assume it is "just the blood thinner" |
| Soft tissue / retroperitoneal haemorrhage | Spontaneous bleeding into muscles or retroperitoneal space | Over-anticoagulation, falls, trauma |
| Drug interactions (warfarin) | CYP450 interactions → supra-therapeutic INR → bleeding. Common culprits: amiodarone, antibiotics (metronidazole, fluconazole), cranberry juice | Poor INR control (TTR < 65%) |
NOACs have significantly lower ICH rates compared to warfarin — this is their major safety advantage. However, GI bleeding rates may be slightly higher with dabigatran 150 mg and rivaroxaban compared to warfarin.
An increasingly recognised complication of chronic AF:
Mechanisms:
- Recurrent subclinical microembolism: small thromboemboli repeatedly travel to the cerebral microcirculation → cumulative ischaemic damage → white matter lesions → cognitive impairment
- Chronic cerebral hypoperfusion: irregular rhythm → variable cardiac output → periods of low cerebral perfusion, particularly during long R-R intervals
- Cerebral microbleeds: if on anticoagulation, or from concurrent small vessel disease
Clinical significance: AF is independently associated with ~1.4–1.6× increased risk of dementia, even after adjusting for clinical stroke events. This suggests that subclinical mechanisms (microembolism + hypoperfusion) are at play beyond clinically apparent strokes.
Often underappreciated but very real:
- Chronic palpitations, fatigue, exercise intolerance, anxiety
- Psychological burden of a chronic condition requiring lifelong medication
- Fear of stroke
- Lifestyle restrictions (e.g., alcohol avoidance, drug interactions with warfarin)
- Sleep disturbance (nocturnal AF episodes)
This is captured by the EHRA symptom score and is a major driver of the decision between rate and rhythm control strategies.
AF itself is associated with ~1.5–2× increased risk of sudden cardiac death (SCD), but through specific mechanisms:
| Mechanism | Explanation |
|---|---|
| AF with WPW (pre-excited AF) | Rapid conduction down the accessory pathway → ventricular rate > 300 bpm → degenerates into VF → SCD. This is the most dangerous acute scenario |
| AF in structural heart disease | AF can trigger VT/VF in patients with underlying cardiomyopathy (HCMP, DCMP, ARVC), channelopathies, or acute MI |
| AF with extreme bradycardia | AF with slow ventricular response (sick sinus syndrome) → prolonged pauses → ventricular escape → degeneration to VF (rare) |
AF itself is one of the most common complications after cardiac and non-cardiac surgery [18]:
- Post-operative AF is a recognised cardiac complication of oesophagectomy, thoracic surgery, and cardiac surgery [18]
- Mechanisms: surgical stress → sympathetic surge + pericardial inflammation + fluid shifts + electrolyte disturbance
- Usually self-limiting (resolves within 6–8 weeks) but carries ↑risk of stroke and prolonged ICU stay
- Management: rate control (BB or amiodarone preferred in post-surgical setting), short-term anticoagulation if AF > 48 hours
| Pathophysiological Mechanism | Complications |
|---|---|
| Stasis → thromboembolism | Ischaemic stroke/TIA, acute limb ischaemia, mesenteric ischaemia, renal/splenic infarction, coronary embolism, retinal artery occlusion |
| Rapid rate → haemodynamic compromise | Heart failure (acute decompensation), cardiogenic shock, tachycardia-mediated cardiomyopathy, myocardial ischaemia (supply-demand mismatch) |
| AF begets AF → progressive remodelling | Progression from paroxysmal → persistent → permanent AF. Increasing refractoriness to rhythm control |
| Treatment-related | Cardioversion: systemic embolism, skin burns, pulmonary oedema. Ablation: tamponade, PV stenosis, AE fistula, stroke. Anticoagulation: ICH, GI bleeding |
| Chronic consequences | Cognitive decline/vascular dementia, reduced quality of life |
| Sudden death | Pre-excited AF (VF), AF in structural heart disease |
High Yield Summary
- Stroke is the most devastating complication of AF — responsible for ~20–30% of all ischaemic strokes. AF strokes are larger, more disabling, and more fatal. Anticoagulation reduces risk by 60–70%.
- Systemic embolism to limbs (6Ps, femoral bifurcation MC), mesentery (pain out of proportion, old patient with AF), kidneys, spleen, retina, and coronary arteries.
- Heart failure and AF have a bidirectional relationship — each worsens the other. Always ask: is AF the cause or consequence of the HF?
- Tachycardia-mediated cardiomyopathy is fully reversible with rate/rhythm control — always consider it in AF + new ↓EF.
- Cardioversion risks: systemic embolism (1–3%), skin burns, pulmonary oedema, myocardial necrosis. Embolism risk is highest in long-standing AF due to atrial stunning post-cardioversion.
- Catheter ablation risks: cardiac tamponade (~1%), PV stenosis (1–3%), stroke, atrioesophageal fistula (rare but fatal), phrenic nerve injury.
- Anticoagulation risks: ICH (most feared), GI bleeding, haematuria. NOACs have lower ICH rates than warfarin.
- Cognitive decline: AF independently ↑dementia risk ~1.5× via subclinical microembolism and chronic cerebral hypoperfusion.
- Sudden death: primarily via pre-excited AF (WPW → VF) or AF triggering VT in structural heart disease.
- For secondary prevention of cardioembolic stroke: OAC (warfarin or NOAC), NOT antiplatelets. Timing follows the 1-3-6-12 day rule based on infarct size.
Active Recall - Complications of Atrial Fibrillation
References
[1] Lecture slides / Senior notes: Ryan Ho Cardiology.pdf (pages 92–97, 139, 162 — AF mechanism, causes, approach, cardioversion embolism risk, catheter ablation complications, concomitant AF surgery, AF in post-MI setting) [4] Senior notes: Ryan Ho Cardiology.pdf (page 152 — Mitral stenosis and AF decompensation) [7] Senior notes: Ryan Ho Neurology.pdf (pages 79–80, 82–83 — Stroke subtype determination, features of embolic stroke, stroke complications, secondary prevention with anticoagulation) [9] Senior notes: Maksim SURGERY notes.pdf (page 168 — Acute limb ischaemia, 6Ps, embolism vs thrombosis-in-situ) [10] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (page 920 — Arterial emboli causes, branch point lodging sites) [11] Senior notes: Maksim SURGERY notes.pdf (page 92 — Mesenteric ischaemia, AF embolism, clinical features) [12] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (page 718 — Mesenteric ischaemia aetiology, AF and embolism) [14] Senior notes: Ryan Ho Critical Care.pdf (pages 39–40 — Cardioversion complications: embolism 1-3%, skin burns, pulmonary oedema, myocardial necrosis, inadvertent defibrillation) [18] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (page 386 — Post-operative AF as complication of oesophagectomy)