What are the causes of atrial fibrillation?

Causes of Atrial Fibrillation

Atrial fibrillation is most commonly caused by cardiovascular conditions including hypertension, coronary artery disease, valvular heart disease (especially mitral valve disease), and heart failure, though it can also occur due to non-cardiac causes such as hyperthyroidism, pulmonary conditions, and alcohol consumption. 1

Cardiac Causes

• Hypertension is one of the most prevalent underlying conditions associated with AF development, particularly when left ventricular hypertrophy is present 2
• Valvular heart disease, especially involving the mitral valve, significantly increases AF risk regardless of severity but correlates with left atrial enlargement 1
• Coronary artery disease represents a significant risk factor, with AF being more common in older patients, males, and those with left ventricular dysfunction 1, 3
• Heart failure creates an arrhythmogenic substrate through structural and electrical remodeling of the atria 1, 2
• Cardiomyopathies, including hypertrophic cardiomyopathy and dilated cardiomyopathy, are associated with increased AF risk 1, 2, 3
• Congenital heart disease, especially atrial septal defect in adults, can lead to AF development 1, 3
• Other cardiac conditions associated with AF include restrictive cardiomyopathies (amyloidosis, hemochromatosis, endomyocardial fibrosis), cardiac tumors, constrictive pericarditis, mitral valve prolapse, and calcification of the mitral annulus 1

Non-Cardiac Causes

• Hyperthyroidism is a significant non-cardiac cause that should always be evaluated in newly diagnosed AF 2
• Pulmonary conditions including pulmonary embolism, chronic obstructive pulmonary disease, and sleep apnea syndrome can trigger AF 1, 2
• Alcohol consumption can cause AF through:
  • Acute intake ("holiday heart syndrome") 1, 2
  • Chronic excessive use 2
• Electrolyte abnormalities and metabolic disorders can precipitate AF 1
• Medications (both cardiovascular and non-cardiovascular) can induce AF 2
• Surgery, particularly cardiac or thoracic procedures, commonly leads to postoperative AF 1

Neurogenic and Autonomic Influences

• Vagally-mediated AF is characterized by: 1

  • Higher prevalence in men (4:1 ratio)
  • Onset typically at age 40-50
  • Association with lone AF
  • Occurrence at night, during rest, after eating, or after alcohol ingestion
  • Antecedent progressive bradycardia
  • Worsening with adrenergic blockers and digitalis

• Adrenergically-induced AF features: 1

  • Lower incidence than vagal AF
  • Daytime onset
  • Provocation by exercise or emotional stress
  • Association with polyuria
  • Onset at a specific heart rate for a given patient
  • Improvement with beta-blockers

Pathophysiological Mechanisms

• Structural remodeling of the atria occurs due to: 1, 4

  • Inflammation and fibrosis
  • Hypertrophy
  • Altered wall stress
  • Atrial dilation

• Renin-angiotensin-aldosterone system (RAAS) activation contributes to AF through: 5

  • Promotion of fibrosis via AT1 receptors
  • Increased synthesis of TGF-beta1
  • Release of inflammatory mediators
  • Oxidative stress

• Electrical remodeling creates substrate for reentry circuits and ectopic firing 1, 4

Lone Atrial Fibrillation

• Approximately 30-45% of paroxysmal AF cases and 20-25% of persistent AF cases occur in younger patients without demonstrable underlying disease 1
• May present as isolated or familial arrhythmia 1
• Underlying disease may appear over time, reducing the relative incidence of lone AF in elderly patients 1

Age-Related Factors

• Advanced age is one of the strongest risk factors for AF development 2, 6
• Age-related cardiac changes contributing to AF include: 2
  • Increased myocardial stiffness
  • Fibrosis
  • Atrial dilation

Clinical Considerations

• Always evaluate for potentially reversible causes of AF, particularly thyroid dysfunction, acute alcohol intake, and pulmonary conditions 1, 2
• AF that develops in the setting of acute myocardial infarction portends a worse prognosis compared to pre-infarct AF or sinus rhythm 1
• The risk of developing AF increases with age, presence of valvular heart disease, and congestive heart failure 3, 7
• Treatment of primary arrhythmias like WPW syndrome or AV nodal reentrant tachycardias can reduce the incidence of recurrent AF 1