What is the most common cause of atrial fibrillation (AFib)?

Most Common Cause of Atrial Fibrillation

Hypertension is the most common cause of atrial fibrillation, present in more than 70% of AF patients who have structural heart disease, and represents the single most important modifiable risk factor due to its high prevalence in the population. 1, 2

Primary Cardiac Causes

Hypertension - The Leading Cause

• Hypertension stands as the main risk factor for developing AF due to its extremely high prevalence in the general population, even though other cardiac conditions may have stronger individual associations. 2
• Hypertension causes left ventricular hypertrophy, increased left atrial pressure, and progressive atrial dilation—all creating the arrhythmogenic substrate for AF. 3, 4
• The mechanism involves structural remodeling through increased wall stress, fibrosis mediated by renin-angiotensin-aldosterone system activation, and altered atrial electrophysiology. 3, 4

Other Major Structural Heart Diseases

• More than 70% of AF patients are older and present with structural heart diseases including left atrial enlargement, coronary artery disease, heart failure, valvular heart diseases, and cardiomyopathies. 1
• Valvular heart disease, especially mitral valve involvement, significantly increases AF risk through left atrial enlargement regardless of stenosis or regurgitation severity. 3, 5
• Coronary artery disease represents a significant risk factor, occurring predominantly in older patients, males, and those with left ventricular dysfunction. 3, 5
• Heart failure creates an arrhythmogenic substrate through both structural and electrical remodeling of the atria. 3, 4

Non-Cardiac Causes to Always Evaluate

Metabolic and Endocrine Disorders

• Hyperthyroidism must always be evaluated in newly diagnosed AF as a potentially reversible cause. 3, 4
• Diabetes mellitus requiring medical treatment is found in 20% of AF patients and contributes to atrial damage through metabolic effects. 1, 4
• Obesity (present in 25% of AF patients) promotes AF through left atrial dilation, with progressive enlargement correlating with increasing body mass index. 1, 4

Pulmonary Conditions

• Chronic obstructive pulmonary disease is found in 10-15% of AF patients. 1
• Pulmonary embolism, sleep apnea syndrome (especially with hypertension and diabetes), and other pulmonary diseases trigger AF through hemodynamic stress and autonomic changes. 3, 4

Reversible Acute Causes

• Acute temporary causes include excessive alcohol intake ("holiday heart syndrome"), surgery, myocardial infarction, pericarditis, myocarditis, and pulmonary embolism—successful treatment of these underlying conditions often eliminates AF. 1, 3
• Postoperative AF is common, occurring in 4.4% after elective colectomy, 9.2-20% after esophagectomy, and 12.6-32% after pulmonary resection. 1

"Lone" Atrial Fibrillation

• Approximately 30-45% of paroxysmal AF and 20-25% of persistent AF occur in younger patients without demonstrable underlying disease. 1, 5
• Even in these cases, inflammatory infiltrates and early fibrosis may be present at the cellular level despite normal standard imaging. 4

Age as a Universal Risk Factor

• AF prevalence increases dramatically with age: <0.5% at age 40-50 years, 4-5% at 65 years, and 12-15% at 80 years or older. 1
• The lifetime risk of developing AF is 25% in those who reach age 40. 1
• Aging causes progressive loss of atrial cardiomyocytes (0.5-1.0% per year) with replacement by fibrous tissue, creating the substrate for AF. 4

Clinical Pitfalls to Avoid

• Do not overlook reversible causes: always screen for hyperthyroidism, acute alcohol intake, infections, and pulmonary conditions in new-onset AF. 3, 4
• Recognize that multiple risk factors often coexist and have additive effects on AF perpetuation—hypertension combined with age, diabetes, or obesity creates particularly high risk. 1
• AF developing during acute myocardial infarction portends worse prognosis compared to pre-infarct AF or sinus rhythm. 1, 3