Atrial Fibrillation: Causes, Symptoms, and Treatment of AFib

The Quivering Heart: America's Most Common Arrhythmia

Atrial fibrillation (AFib) affects approximately 6 million Americans, and prevalence is rising sharply as the population ages. By 2030, the American Heart Association projects that more than 12 million Americans will have the condition. AFib is not a minor electrical nuisance: it causes roughly 20 to 25 percent of all ischemic strokes and is associated with a 1.5 to 3.5-fold increased risk of death compared with patients who maintain normal sinus rhythm.

In AFib, the normal orderly electrical activation of the atria — the heart's upper chambers — breaks down into chaotic, disorganized electrical impulses. Instead of contracting rhythmically to push blood into the ventricles, the atria quiver. The ventricular rate becomes irregular. Blood can pool in the left atrial appendage, forming clots that may embolize to the brain.

Normal Conduction vs. AFib Physiology

The healthy heart's rhythm begins in the sinoatrial (SA) node — a cluster of specialized cells in the right atrium that fires at 60 to 100 times per minute. Each electrical impulse spreads through the atria, causes atrial contraction, passes through the atrioventricular (AV) node, and then activates the ventricles in a coordinated sequence.

In AFib, multiple chaotic electrical wavelets re-enter atrial tissue in disorganized circuits. The SA node loses control. The AV node receives a barrage of impulses — up to 400 to 600 per minute — but due to its refractory period, transmits only a fraction to the ventricles, resulting in an irregular ventricular rate typically between 100 and 180 beats per minute in untreated AFib.

Two major electrophysiological mechanisms drive AFib initiation and maintenance:

• Triggered activity: Spontaneous electrical discharges from pulmonary vein sleeves (myocardial extensions into the pulmonary veins) initiate most paroxysmal AFib episodes. This insight drives catheter ablation strategy.
• Reentrant circuits: Structural changes in atrial tissue — fibrosis, hypertrophy, inflammation — create the substrate that sustains AF once initiated.

Types of Atrial Fibrillation

Causes and Risk Factors

Multiple conditions predispose to atrial structural and electrical remodeling that promotes AFib:

• Hypertension: The most common risk factor; causes left ventricular hypertrophy and atrial pressure elevation
• Heart failure: Increased atrial wall stress promotes fibrosis and electrical instability
• Valvular heart disease: Mitral stenosis and mitral regurgitation increase left atrial pressure and size
• Coronary artery disease and prior myocardial infarction
• Obstructive sleep apnea: Hypoxia and autonomic fluctuations promote AFib; treatment of OSA reduces AFib recurrence
• Obesity: Every 5 kg/m² increase in BMI raises AFib risk by approximately 29%; pericardial fat may directly infiltrate and remodel atrial tissue
• Hyperthyroidism and excessive alcohol consumption ("holiday heart")
• Age: Prevalence rises from 0.1% in those under 55 to greater than 9% in those over 80

Symptoms and Diagnosis

Symptoms of AFib vary widely. Many patients are entirely asymptomatic — their AFib is detected incidentally on an electrocardiogram. Symptomatic patients may experience:

• Palpitations (awareness of an irregular or rapid heartbeat)
• Fatigue and reduced exercise tolerance
• Dyspnea (shortness of breath)
• Lightheadedness or near-syncope
• Chest discomfort

Diagnosis requires an electrocardiogram (ECG) showing the characteristic findings: absence of distinct P waves, irregularly irregular QRS complexes, and a fibrillatory baseline. When AFib is paroxysmal and not captured on a standard ECG, ambulatory monitoring — Holter monitor (24–48 hours), extended loop recorder, or implantable cardiac monitor — may be required.

Stroke Risk Stratification: The CHA₂DS₂-VASc Score

Anticoagulation is recommended for men with scores ≥2 and women with scores ≥3. Direct oral anticoagulants (DOACs) — apixaban, rivaroxaban, dabigatran, edoxaban — are preferred over warfarin for non-valvular AFib due to lower intracranial hemorrhage risk and comparable or superior stroke prevention.

Treatment Strategies

Management of AFib pursues three simultaneous goals: rate control, rhythm control (when appropriate), and stroke prevention.

Rate control slows the ventricular response using AV-nodal blocking agents — beta-blockers (metoprolol), non-dihydropyridine calcium channel blockers (diltiazem, verapamil), or digoxin — targeting a resting heart rate below 110 bpm (lenient control) or below 80 bpm (strict control).

Rhythm control aims to restore and maintain sinus rhythm through pharmacological cardioversion (flecainide, propafenone, amiodarone), electrical cardioversion, or catheter ablation. Catheter ablation — electrically isolating the pulmonary veins from the left atrium — achieves freedom from AF in approximately 70 to 80 percent of paroxysmal AFib patients after a single procedure. The EAST-AFNET 4 trial (2020) demonstrated that early rhythm control (initiated within one year of diagnosis) reduced cardiovascular outcomes compared with rate control in patients with cardiovascular risk factors.

For patients with left atrial appendage thrombus on imaging, anticoagulation must precede cardioversion, or transesophageal echocardiography must exclude clot before the procedure. For patients who cannot tolerate long-term anticoagulation, left atrial appendage occlusion with the Watchman device (FDA-approved 2015) provides an alternative stroke prevention strategy.

This article is for informational purposes only. Consult a qualified healthcare professional before making any health decisions.