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Atrial Fibrillation (AF)

Atrial fibrillation occurs when there's uncoordinated, irregular atrial contractions, which leads to irregular ventricular contractions. Its causes include: SMITH

  • Sepsis

  • Mitral valve stenosis/regurgitation - If due to this, AF is classed as Valvular AF (rest is classed as non-valvular AF)

  • IHD

  • Thyrotoxicosis

  • HTN


N.B. HTN and Mitral regurgitation cause the atria to stretch, therefore affecting the conductive pathways of the chamber.


N.B. It can also be due to alcohol consumption, which can lead to myocarditis and damage to the heart’s electrical conduction system.


It's differentials include:

  • Atrial flutter (saw-tooth pattern on ECG)

  • Ventricular ectopics

  • Atrial extrasystoles

  • Sinus tachycardia


Complications

Either due to uncontrolled heart rate, embolism, or anticoagulation:

  • HF (poor diastolic ventricular filling)

  • Systemic emboli - Ischaemic stroke, Mesenteric ischaemia, Acute limb ischaemia

  • Bleeding - Intracranial, GI (usually due to the patient being on anticoagulants)


Presentation

In the elderly, it's usually asymptomatic, and therefore diagnosed at routine checks. In others, it can present with:

  • Palpitations

  • SOB

  • Dizziness

  • Syncope

  • Features suggestive of the underlying cause


O/E - Irregularly irregular pulse, and features suggestive of the underlying cause e.g. pan-systolic murmur with MR, weight loss and diarrhoea with hyperthyroidism.


The differential for an irregularly irregular pulse is Ventricular ectopics. The way to differentiate it from AF is by doing a Stress ECG. With ventricular ectopics, the ECG will normalise when HR is raised over a threshold, whereas it stays abnormal in AF.


Investigations

  • ECG - Irregularly irregular ventricular contractions + Absent P waves

    • AF tends to show a fibrillating baseline w/no discernible p waves. This can resemble flutter, but atrial flutter would be more widespread over multiple leads.

  • Bloods - FBC (anaemia), TFT (hyperthyroidism), U&E

  • Echo - look for structural defects

  • CXR - look for lung problems

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Management

If HR > 100 bpm, it's classified as Fast AF, which requires immediate treatment. An A-E approach needs to be done to assess for any haemodynamic instability, and if the patient is unstable, they should be sent for immediate DC Cardioversion.


Rate control - Usually 1st line, expect those whose AF has a reversible cause, or have HF primarily caused by the AF. Options here are B-blockers (1st line), Non-DHP CCB, or Digoxin.

  • B-blockers avoided in COPD, Asthma, Postural hypotension

  • CCB avoided in HF due to negative inotropic effect

  • Digoxin avoided in young pts due to risk of cardiac mortality


Rhythm control - This is achieved with Cardioversion, which can be done in 2 ways:

  • Electrical/DC - If onset is acute (< 48 hours), pt can be DC cardioverted under GA. If onset > 48 hours/unknown, the patient has to be anticoagulated for 3 weeks prior to being DC cardioverted.

  • Pharmacological - Flecanide (1st line), Amiodarone

    • Flecanide is avoided in older patients with structural heart abnormalities, so is preferred in younger patients


N.B. Anticoagulation is needed for 3 weeks if the patient has been in AF for > 48 hours because, if they’re cardioverted, there’s a risk of throwing off a clot and causing more damage. The DOAC will help reduce the risk of this prior to cardioversion.


N.B. Flecainide works by blocking rapid Na influx, therefore preventing the production of an action potential, and slowing down the heart.


If the patient's symptoms are still uncontrolled and there's an identifiable locus in their left atrium, Ablation therapy can be done.


Anticoagulation

In AF patients, the risk of a cardioembolic stroke is much higher, therefore it's extremely important that anticoagulation therapy is started. There are 2 important scores to know here:

  • CHA2DS2-VASc¹ - Assesses the patients risk of stroke

    • Score 0 - no anticoagulation

    • Score 1+ (Male), 2+ (Female) - give anticoagulation

  • ORBIT² - Assesses the bleeding risk if the patient is given anticoagulation


N.B. ORBIT score is recommended by NICE to be used instead of the previous HASBLED score.


1st line - DOAC e.g. apixaban, rivaroxaban, dabigatran

  • Doesn’t require INR monitoring

  • Has a half-life of 12 hrs, therefore if a dose is missed, the patient won’t be covered

2nd line - Warfarin

  • Requires INR monitoring

  • Has a half-life of 40 hrs, therefore its effect lasts days

  • The only oral drug licensed for valvular AF


AF in Pre-excitation

AF occurs in 20% of patients with a Wolff-Parkinson-White (WPW) pattern

  • A HR > 200 bpm is way too fast to be conducted by the AVN

  • AF + WPW is usually mistaken for AF + LBBB instead. This can be distinguished by:

    • A variable beat-to-beat QRS width = WPW

    • A fixed beat-to-beat QRS width = LBBB




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