Atrial fibrillation

Background

• A dysorganized and rapid atrial electrical activity leading to a loss of coordinated contraction of the atria and an irregularly irregular ventricular rhythm
• May be paroxysmal or persistent

Etiologies

• Cardiac
  • Hypertension
  • Heart failure
  • CAD
  • Hypertrophic, dilated and restrictive cardiomyopathies
  • Valvular heart disease
  • Congenital heart disease
  • Pericardial disease
  • Post-surgical (particularly cardiac surgery)
  • Sick sinus syndrome
  • Atrial fibrillation as a result of ventricular pacing
  • Supraventricular tachycardia
    • Wolf-Parkinson White syndrome
    • Atrial tachycardia
    • Atrial flutter
  • Genetic/Familial
• Non-cardiac
  • Obstructive sleep apnea
  • Obesity
  • Excessive alcohol ingestion (acute or chronic)
  • Hyperthyroidism
  • Vagally-mediated (i.e. habitual aerobic training)
  • Pulmonary disease
    • Pneumonia
    • COPD
    • Pulmonary embolism
    • Pulmonary hypertension
• Idiopathic

Acute Triggers

• Cardiac surgery or transplant
• Acute alcohol intoxication
• Acute illness including infection, myocardial infarction, or pulmonary embolism
• Hyperthyroidism

Epidemiology

• Prevalence by age 80 is approximately 10%
• Lifetime risk of developing AF for individuals 40 years old is approximately 25%

Risk Factors

• Age
• Hypertension
• Diabetes mellitus
• Cardiac disease
• Sleep apnea

Clinical Manifestations

• Feeling of palpitations, acute or paroxysmal
• Syncope
• Examination
  • Irregularly irregular heart rhythm
  • Variable S1

Prognosis

• Risk of stroke by fivefold and is estimated to be the cause of 25% of strokes

Investigations

• Baseline: ECG, echo, CBC, coags, renal and liver function, TSH, lipids, and glucose
• Imaging
  • CXR: to exclude lung disease and heart failure
  • TEE: to rule out thrombus if planning cardioversion
• Labs
  • Serum calcium and magnesium
  • TSH
• Other
  • Holter monitor or loop monitor: to capture paroxysmal atrial fibrillation when it is suspected
  • Treadmill exercise test
  • Electrophysiologic studies
  • Sleep study: to rule out OSA
  • Ambulatory blood pressure monitor
  • Genetic testing

Management

• Cardioversion
  • May cardiovert if onset within 12h or if anticoagulated for at least 3 weeks prior (and 4 weeks after cardioversion)
  • Can consider cardioversion up to 48 hours if low-risk CHADS <2
• Rate control
  • If atrial fibrillation with rapid ventricular response, may need rate control to target resting HR < 100
  • Beta-blockers are first-line
    • Metoprolol, starting at 25mg bid and titrating to effect
  • Non-DHP CCBs are second-line
  • Digoxin may be used in patients who are sedentary or have LV dysfunction
  • Amiodarone is last-line
• Stroke prophylaxis
  • ASA if low risk (CHADS₂=0 or CHA₂DS₂-VASc<2)
  • Warfarin, targeting an INR or 2-3
  • Direct oral anticoagulants such as apixaban or rivaroxaban

Further Reading

• Atrial fibrillation guidelines focussed update 2016