Causes of Atrial Fibrillation
Atrial fibrillation results from a complex interplay of cardiac structural disease, medical comorbidities, reversible precipitants, genetic factors, and autonomic dysfunction, with the most common causes being hypertension (particularly with left ventricular hypertrophy), heart failure, valvular disease (especially mitral), coronary artery disease, and obesity. 1, 2
Structural Heart Disease
The majority (70-80%) of AF occurs in patients with underlying cardiac pathology 1. The primary cardiac causes include:
- Valvular disease: Mitral valve disease is the most common valvular etiology, but mitral valve prolapse, mitral regurgitation, and mitral annular calcification also predispose to AF 1, 2
- Hypertension: Particularly when left ventricular hypertrophy is present, creating increased atrial pressure and promoting atrial remodeling 1, 2
- Heart failure: Both systolic and diastolic dysfunction significantly increase AF risk through atrial pressure elevation and structural changes 1, 2
- Coronary artery disease: Causes atrial ischemia and increases AF susceptibility 1, 2
- Cardiomyopathies: Including hypertrophic cardiomyopathy, dilated cardiomyopathy, and restrictive cardiomyopathies (amyloidosis, hemochromatosis, endomyocardial fibrosis) 1, 2
- Congenital heart disease: Especially atrial septal defect in adults 1, 2
Reversible and Acute Causes
These causes are critical to identify because successful treatment often eliminates AF 2:
- Alcohol intake: "Holiday heart syndrome" from acute intoxication 2, 3
- Postoperative state: Common after cardiac, thoracic, or esophageal surgery 1, 2
- Acute myocardial infarction: Portends worse prognosis than pre-infarct AF 2
- Inflammatory conditions: Pericarditis, myocarditis 2, 3
- Pulmonary embolism and other acute pulmonary diseases 2, 3
- Hyperthyroidism and other metabolic disorders 2, 3
- Electrocution 2
- Drugs: Including caffeine, certain cardiovascular and non-cardiovascular medications 1, 4
Medical Comorbidities
Obesity is an especially important modifiable risk factor, with excess AF risk mediated by left atrial dilation that increases progressively from normal to overweight to obese categories 1, 2, 1. Weight reduction has been linked to regression of left atrial enlargement 1.
Sleep apnea syndrome is commonly associated with AF, though the exact mechanism—whether hypoxia, biochemical changes, pulmonary dynamics, autonomic tone changes, or systemic hypertension—remains undetermined 1, 2.
Lone Atrial Fibrillation
Approximately 30-45% of paroxysmal AF and 20-25% of persistent AF occurs in younger patients without demonstrable underlying disease 2. However, underlying disease may appear over time, and in elderly patients, age-related changes (increased myocardial stiffness, atrial fibrotic changes) may be associated with AF 1.
Familial and Genetic Factors
Familial AF is more common than previously recognized 1, 2. The likelihood of developing AF increases among offspring of parents with AF, suggesting familial susceptibility 2. This relationship extends to patients with family history of hypertension, diabetes, or heart failure, indicating mechanisms are not purely electrical 2. Specific chromosomal loci have been linked to AF in some families 1.
Autonomic Influences
Autonomic tone plays a crucial role in AF initiation 2. The balance between sympathetic and vagal influences is as important as absolute tone levels 2:
- Vagally-mediated AF: Occurs at night, after meals, or alcohol intake; more common in men; associated with lone AF 3
- Adrenergically-induced AF: Occurs during daytime, with exercise or emotional stress 3
Electrophysiological Mechanisms
The underlying substrate involves 1, 2:
- Enhanced automaticity (focal AF)
- Conduction abnormalities (reentry)
- Atrial pressure elevation
- Age-induced atrial fibrotic changes
- Ion channel dysfunction
- Calcium handling abnormalities
Neurogenic Causes
Subarachnoid hemorrhage and major non-hemorrhagic stroke can precipitate AF 1.
Clinical Pitfall
Do not assume AF in elderly patients is simply age-related—systematically evaluate for reversible causes, particularly hyperthyroidism, alcohol use, sleep apnea, and uncontrolled hypertension, as treating these conditions may eliminate the arrhythmia 2, 3. Similarly, in younger patients labeled with "lone AF," maintain vigilance for emerging structural heart disease over time 2.