Atrial Fibrillation

Common arrhythmia with completely discordant atrial conduction, leading to:

Common terms include:

  • Paroxysmal AF
    Terminates within 7 days (with or without treatment) of onset
  • Persistent AF
    Lasts >7 days.
  • Longstanding AF
    Lasts >1 year.
  • Permanent AF
    When attempts at rhythm control have stopped.

AF requires both:

Epidemiology and Risk Factors

Common:

  • 5% of >70s

Risk factors:

  • Age
  • Obesity
  • OSA
  • Cardiac disease
    • Atrial dilation
      • MR
      • MS
    • LV dysfunction
    • CABG
      25-50%.
    • Cardiac failure
      40%.

Pathophysiology

Aetiology

Clinical Manifestations

Diagnostic Approach and DDx

Investigations

Management

Management of AF has traditionally been divided into two competing strategies:

  • Rate control
    Remain in AF, with controlled ventricular rate. Requires anticoagulation.
  • Rhythm control
    Conversion to sinus rhythm. May be superior to rate control, if it can be achieved, and is desirable in patients:
    • <60
    • Structurally normal hearts
    • Reversible precipitant of AF

The rate/rhythm control debate is made more complex by the fact that rate control strategies result in SR in ~35% of patients, and rhythm control fails in 40-60% of patients. Rhythm control agents (amiodarone, flecainide) also have poorer side effect profiles than rate control agents.

Overall, rhythm control is probably superior if it can be consistently achieved without requirement for heavy-duty antiarrhythmics; and so is most ideal in a young patient, without structural heart disease, and good cardiac reserve.

Resuscitation:

  • Rhythm control

Specific Therapy:

  • Pharmacological
    • Haemodynamic control
      One of:
      • Rhythm control
      • Rate control
    • Anticoagulation
  • Procedural
    • Ablation
      Achieves drug-free rhythm control in >80% after one attempt, and >90% after two attempts.
    • LAA occlusion
    • LAA ligation
    • Left pericardiotomy
    • MAZE

LAA ligation, left pericardiotomy, and MAZE all are performed as an addition to another cardiac surgery to prevent post-operative AF, and are not performed as singular procedures.

Supportive Care:

  • Treat precipitant

Rhythm Control

Urgent electrical cardioversion is recommended for haemodynamically unstable AF with RVR - just as with other unstable tachyarrhythmias.

Cardioversion describes restoration of normal sinus rhythm, and is associated with a temporary ↑ stroke risk, as any clot formed in the static atria may embolise when atrial contraction resumes. Risk significantly elevated if both:

  • Not therapeutically anticoagulated for at least 3 weeks
  • AF duration >48 hours

Cardioversion can be performed either:

  • Electrically
    Synchronised electrical cardioversion indicated if haemodynamically unstable. Requires sedation in the conscious patient.
    • Failure associated with:
      • Greater AF duration
      • LAE
      • Precipitants present
  • Chemically
    A variety of agents:
    • Amiodarone
      Variable dosing strategies described:
      • 2mg/min for 4 hours
      • 5mg/kg over 1 hour
      • 150mg over 30 minutes, followed by infusion
        Can repeat the IV load twice.
    • Flecainide
      • 2mg/kg over 10 minutes.
      • Not suitable in structural heart disease or heart failure
    • Ibutilide
      • 1mg over 10 minutes, followed by a repeat dose after 10 minutes
      • Risk of TDP
    • Vernakalant
      • 3mg/kg over 10 minutes, followed by 2mg/kg over 10 minutes
      • Suitable in structural heart disease or heart failure
      • More effective in the short term than amiodarone, but less effective in maintaining SR at >24 hours.

Rate Control

For acute control:

  • Stable
    • Metoprolol 2.5-5mg IV
    • Diltiazem 30-69mg PO
  • Unstable
    • Amiodarone 5mg/kg
    • Digoxin 0.5-1mg IV

For maintenance:

  • Stable
    • Metoprolol CR 23.75-98mg daily
    • Bisoprolol 2.5-10mg daily
    • Diltiazem 30-60mg PO TDS
  • Unstable
    • Digoxin 125-500ug daily
    • Amiodarone 100-200mg daily

Anticoagulation

Risk depends on aetiology, and therefore is classified into:

No additional benefit seen from adding aspirin in the therapeutically anticoagulated.

  • Valvular AF
    Secondary to rheumatic MV disease. Requires therapeutic anticoagulation with warfarin.
  • Non-valvular AF
    • Aspirin
    • Therapeutic anticoagulation
      • Risk assessment
        Risk-benefit of stroke versus bleeding.
        • Stroke risk assessed with CHA2DS2VASc score
          • 0: Aspirin or no therapy
          • 1: Either aspirin or anticoagulation
          • ⩾2: Anticoagulation
        • Bleeding risk assessed with HAS-BLED score
          ↑ HAS-BLED suggests use of DOAC rather than warfarin.
      • Options
        • Warfarin
          Target INR 2-3.
        • DOAC
        • Heparin infusion
    • DAPT
      Superior to warfarin in the warfarin non-compliant.
CHA2DS2VASc Score
Risk Factor Points
Cardiac Failure
LVEF <40%.		 1
Hypertension 1
Age ⩾75 2
Diabetes Mellitus 1
Previous embolism 2
PVD, CAD, or aortic disease 1
Age 65-74 1
Sex (Female) 1

Other Considerations

High-risk groups:

  • Hypertrophic cardiomyopathy
    • Rhythm control superior
    • Requires therapeutic anticoagulation

Anaesthetic Considerations

Complications

  • C
    • Haemodynamic instability
    • Rate-related cardiomyopathy
      Reversible ↓ in LV function, occurs in ~10%.
  • D
    • Stroke

Prognosis

Prognosis depends on cause:

  • Idiopathic (“lone”) AF
  • Post-surgical
    Significant ↑ risk of stroke, arrhythmia, ↑ hospital length of stay.

Key Studies

Post-operative AF:

  • PALACS (2021)
    • 420 New York cardiac surgical patients with a virgin sternum undergoing CABG, AV, or aortic surgery; without history of AF, arrhythmias, or left pleural disease
    • Randomised, unblinded, mostly one surgeon
    • Posterior left pericardiotomy vs. no intervention
      • Pericardiotomy anticipated to drain pericardial space into left pleural space, ↓ effusion accumulation and arrhythmogenicity
    • Significantly ↓ in intervention group:
      • AF (17% vs. 32%)
        Independent of pre-operative β-blocker use.
      • Anticoagulation (6% vs 14%)
      • Pericardial effusion (12% vs 21%)
    • No change in stroke or MI rate

References

  1. Bersten, A. D., & Handy, J. M. (2018). Oh’s Intensive Care Manual. Elsevier Gezondheidszorg.
  2. Posterior left pericardiotomy for the prevention of atrial fibrillation after cardiac surgery: an adaptive, single-centre, single-blind, randomised, controlled trial. The Lancet. 2021;398(10316):2075-2083. doi:10.1016/S0140-6736(21)02490-9