Atrial fibrillation

Epidemiology

• Incidence
  • <40yo <0.1%
  • >80yo 2% in men, 1.5% women

Risk factors

• Advanced age
• CCF
• Male
• Tall stature
• FHx at <50yo
• Left atrial enlargement
• HTN
• Obesity
• OSA

Aetiology

• Most patients have HTN, usually with LVH, or some other form of structural heart disease
  • Most commonly IHD, mitral valve disease, hypertrophic cardiomyopathy, and dilated cardiomyopathy
  • Also restrictive cardiomyopathies, constrictive pericarditis, cardiac tumours
• Severe pulmonary hypertension
• OSA
• Obesity
• Tachycardia

Presentation

• Symptoms - palpitations, fatigue, dyspnoea, effort intolerance, light-headedness
• 25% asymptomatic
• Syncope - either RVR with neurocardiogenic syncope, or long sinus pause in a patient with sick sinus syndrome
• Irregularly irregular pulse
• 'pulse deficit' - peripheral pulse not as rapid as the apical rate due to low stroke volume

Classification (based on the predominant form of AF)

• Paroxysmal AF: terminates spontaneously within 7 days
  • Vagotonic - occurs in the setting of high vagal tone
  • Adrenergic - occurs with high sympathetic tone
• Persistent AF: present continuously for >7 days
• Longstanding AF: present for >1 year
• Permanent AF: all attempts to restore/maintain sinus rhythm have been abandoned (therapeutic attitude, not characteristic of the disease itself)
• Harder to classify if the disease path has been altered early in the course by cardioversion - don't know what would have happened
• Lone atrial fibrillation: patients <60yo without HTN or any evidence of structural heart disease. Old term, not meaningful. Essentially means low-risk AF.
• Valvular AF: moderate to severe mitral stenosis. Higher risk of stroke.

ECG:

• Low-amplitude baseline oscillations (fibrillating atria) at 300-600bpm
  • Contrast with atrial flutter waves which have a rate of 250-350 beats/min and are constant in timing and morphology
  • Sometimes waves can be very small and not easily seen, and the diagnosis of AF is based on the irregularly irregular ventricular rhythm
• Irregularly irregular ventricular rhythm
  • Typically 100-160bpm when untreated (can be up to 250 with WPW syndrome)
  • Can look more regular when rate >170bpm, or when a junctional tachycardia independently controls the ventricles, or when there is high-degree AV block with a regular escape rhythm, or when the QRS complexes are paced

Management strategy

• Rhythm control (restore sinus rhythm)
  • Methods
    • Anti-arrhythmic drugs
    • Electrical cardioversion
    • RFA of left atrium
    • Surgical ablation
• Rate control
  • Methods
    • Slow conduction through the AV node - beta-blockers, some CCBs, or digoxin
    • AV nodal ablation with ventricular pacing

Complications

• AF with RVR
  • Leads to severe palpitations, cardiac ischaemia, and global haemodynamic compromise
• Stroke