Atrial Fibrillation

Background

• In AF, the atria are ‘fibrillating’ at a rate of between 350 and 600bpm, and thus are unable to do so in a synchronised manner.
  • They are unable to properly fill or empty their contents, and thus increase the risk of blood stasis, clot formation and stroke.
  • The disorganised electrical activity of the atria occasionally conduct through the AV node, giving rise to an irregularly irregular rate of QRS complexes.
• It is the most common arrhythmia, particularly found in members of the elderly population.

Scheme of atrial fibrillation (top) and sinus rhythm (bottom). The purple arrow indicates a P wave, which is lost in atrial fibrillation. The baseline is ragged and QRS complexes are ‘irregularly irregular’

Classification

1. Paroxysmal AF
   • Terminates spontaneously, usually within a week
   • By definition is not treated (as such)
2. Persistent AF
   • Usually lasts longer than a week and does not self-terminate (i.e. requires treatment)
3. Permanent AF
   • AF that does not revert to sinus rhythm, despite treatment.  Usually lasts >1 year
   • Whilst it can be possible to regress to persistent/paroxysmal status, it is usually very difficult, and management is mostly symptomatic and risk reduction

Aetiology

• Ischaemic and Hypertensive heart disease
  • Haemodynamic stress (most commonly in mitral valve or tricuspid valve disease and left ventricular dysfunction)
    • NB Aortic stenosis is NOT a cause and if AF is present, mitral regurgitation/prolapse should be considered
  • Atrial ischaemia (following MI or in CAD)
• Inflammation (e.g. endocarditis; Dressler’s syndrome (immune mediated pericarditis which classically appears 4 weeks after an MI))
• Alcohol/drug use (particularly stimulants)
• After surgery
• Endocrine disorders e.g. hyperthyroid, diabetes
• Neurological disorders e.g. SAH, stroke
• Age

Presentation

• In many patients, AF is an incidental finding- either on routine examination or investigation with ECG for another reason
• Patients may present with palpitations; syncope; dizziness; chest discomfort; stroke/TIA; worsening symptoms of heart failure

Investigations

• ECG
  • Irregularly irregular rhythm
  • No P waves- replaced by fibrillatory (disorganised) waves that can be fine or coarse
    • Occasionally mimic P waves
  • Absence of isoelectric baseline
  • Variable ventricular rate
• Other investigations include
  • blood tests e.g. FBC, U&Es, LFTs, TFTs (may identify an underlying cause)
    • Coagulation screen also (especially if planned for anticoagulation)
  • CXR
  • Echocardiography- should be performed
    • if a baseline echocardiogram is important for long-term management (such as in younger patients)
    • if you are considering a rhythm-control strategy that includes electrical or pharmacological cardioversion
    • if you suspect underlying structural or functional heart disease (failure or murmur) that would influence management, such as choice of antiarrhythmic drug
    • where needed to help with stratifying stroke risk for antithrombotic therapy, but only where clinical evidence is needed of left ventricular (LV) dysfunction or valve disease

Management (Based on NICE guidelines)

• Always treat an underlying cause (if it can be identified).
• If the patient is unstable i.e. unconscious and requiring acute care, and AF is thought to be the underlying cause:
  • ABCDE
  • Is the AF known to be permanent?
    • If no/not known, Electrical cardioversion (150J DC shock) should be given.  If this fails, try pharmacological cardioversion with IV amiodarone.
    • If yes, pharmacological rate control with beta blockers or verapamil should be tried (amiodarone- second line).
• If the patient is stable:
  • Paroxysmal AF- Rhythm-control
    • ‘Pill-in-the-pocket’ treatment may be appropriate in a sub-group of patients
    • For others, beta blocker is first line
      • If this fails:
        • If there is no CAD/LVD, flecainide or sotalol; if CAD then sotalol is preferred and if LVD (or if others fail), then amiodarone can be used 3rd line
  • Persistent AF in patients who are symptomatic, younger (<65); presenting for the first time; secondary to a treated/corrected cause; with congestive heart failure- Rhythm Control (often more suitable in older patients where cardiac output may not be as high)
    • If the patient requires cardioversion**- do this
      • Ideally patients will have had an echo prior to cardioversion
    • If the underlying cause cannot be treated (or is unknown)
      • treat with a beta-blocker (e.g. bisoprolol) first line
        • If this fails, then as for paroxysmal AF (class 1c agent then amiodarone or amiodarone only if structural disease present)
        • further cardioversion may also be required

**Cardioversion: Make sure to anticoagulate the patient (usually with heparin).  
If the AF began <48 hours ago, perform electrical or pharmacological cardioversion (with flecainide or amiodarone, depending on heart disease).  
If the AF began >48 hours ago, consider trans-oesophageal echo- guided cardioversion.  
If > 48 hours and high risk of failure (e.g. past failure/recurrence), recommend 4 weeks of sotalol/amiodarone prior to electrical cardioversion.
Remember anticoagulation post-cardioversion (esp if AF >48 hours- 4 weeks minimum).
Patients unsuitable include: marked structural heart disease; prolonged AF (>12 months); previous failed attempts/relapses; or a reversible cause

• Persistent AF in older patients >65, patients with CAD, contraindications to pharmacological treatment or who are unsuitable for cardioversion**.  And Permanent AF- Rate control
  • Assess the need for rate-limiting treatment
    • Target HR <90bpm at rest (110bpm for recent onset AF) and an exercise HR of <110bpm (non-active) and <200-age (active)
  • Again, beta blocker is first line, however an alternative is a rate-limiting calcium antagonist e.g. verapamil/diltiazem can also be used
    • If further rate-limiting therapy needed, consider adding digoxin
      • If this is just with exercise, calcium channel blocker and digoxin is recommended over a beta-blocker and digoxin.
      • If digoxin does not help, particularly in those with no underlying cause or evidence of an electrical disorder e.g. WPWS, other drugs e.g. amiodarone can be consider (specialist)

Thromboprophylaxis

• All patients with AF should be considered for thromboprophylaxis therapy (especially persistent/permanent AF)
• Should be started as soon as possible (note that if the patient is on heparin in the hospital setting, further thromboprophylaxis is not required, but should be initiated on discharge)
• Consider risk of thrombo-embolic event (stroke risk factors)
  • High (CHADS2= 2)
    • Previous stroke/TIA
    • Age >=75 with hypertension, diabetes or vascular disease
    • Clinical evidence of valvular disease or heart failure, or evidence on echo
    • Warfarin unless contraindicated, with target INR 2-3
    • Rivaroxaban, apixaban (Both factor Xa inhibitors) or dabigatran (direct thrombin inhibitor) may be a suitable alternative, particularly in patients who might have trouble managing warfarin monitoring/dosing
  • Moderate (CHADS2 =1)
    • Age >=65 with no risk factors
    • Age <75 with risk factors (above)
    • Consider warfarin or aspirin
  • Low risk (CHADS2 <1)
    • Age <65 with no risk factors
    • Aspirin