Atrial Fibrillation - Comprehensive Review

Definition

Classification (Types)

Epidemiology

Pathophysiology

1. Triggers - Most commonly arise from the pulmonary veins (PV). Rapid ectopic firing from PV sleeves initiates AF. In some cases, other sites (coronary sinus, superior vena cava, posterior left atrium) serve as triggers.
2. Substrate - Age-related atrial fibrosis, conduction heterogeneity, and electrical remodeling create a substrate for multiple re-entrant wavelets and rotors. Structural heart disease (hypertension, mitral stenosis, heart failure) accelerates atrial remodeling. Left atrial (LA) dilation and fibrosis are key.
3. Electrical remodeling ("AF begets AF") - Sustained AF shortens atrial effective refractory periods, promotes further atrial remodeling, and stabilizes the arrhythmia over time.
4. Autonomic triggers - Vagally mediated AF tends to occur at night/rest (bradycardia-dependent); adrenergically mediated AF occurs with exercise or emotional stress.
5. Inflammation and oxidative stress - Both play a role, especially in postoperative AF (seen in 25-40% after open heart surgery), where adrenergic activation, atrial ischemia, and electrolyte disturbances converge. (Braunwald's, p. 1820)

Risk Factors / Associated Conditions

• Hypertension (most common modifiable risk factor)
• Coronary artery disease
• Heart failure (HFpEF, HFrEF)
• Valvular heart disease (especially mitral stenosis - in MS + AF, thromboembolic risk is as high as with prosthetic valves)
• Obesity and obstructive sleep apnea
• Hyperthyroidism
• Alcohol ("holiday heart")
• Diabetes mellitus
• Chronic kidney disease
• Advancing age

Clinical Presentation

• Palpitations (most classic, though less prominent in the elderly)
• Dyspnea, fatigue, reduced exercise tolerance
• Lightheadedness, presyncope
• Chest discomfort
• Acute pulmonary edema (especially in HFpEF with rapid ventricular rate - abrupt loss of atrial contribution to LV filling)
• Silent AF - Common in older adults; may first present as stroke or cognitive decline

ECG Features

• Irregularly irregular RR intervals
• Absent distinct P waves - replaced by fibrillatory (f) waves (best seen in V1 and lead II)
• Narrow QRS (unless bundle branch block or pre-excitation is present)
• Rapid ventricular response typically 110-160 bpm if untreated
• WPW + AF is dangerous: broad, irregular, very rapid QRS complexes due to antegrade conduction down the accessory pathway (can degenerate to VF)

Complications

1. Stroke / Thromboembolism

• Nonvalvular AF increases stroke risk 5-fold
• Stroke mechanism: blood stasis in the left atrial appendage (LAA) forms thrombus, which embolizes
• Strokes in AF tend to be more severe and disabling
• In MS + AF: risk is even higher - OACs (warfarin, NOT DOACs) are indicated regardless of CHA₂DS₂-VASc score (Braunwald's, p. 750-760)

2. Heart Failure

• Loss of atrial kick reduces cardiac output by 15-30%
• Rapid ventricular rates cause tachycardia-mediated cardiomyopathy if sustained

3. Cognitive Impairment / Dementia

• Independent association with cognitive decline, even without clinical stroke

4. Reduced Quality of Life and Increased Mortality

Stroke Risk Assessment - CHA₂DS₂-VASc Score

• Score = 0: Anticoagulation can be omitted
• Score = 1 (male) or 2 (female): May consider anticoagulation (shared decision)
• Score ≥2 (male) or ≥3 (female): Anticoagulation recommended

Management

Anticoagulation

• Dabigatran (direct thrombin inhibitor)
• Rivaroxaban, Apixaban, Edoxaban (factor Xa inhibitors)

• Mitral stenosis (valvular AF) - DOACs are NOT recommended
• Mechanical heart valves
• Target INR 2.0-3.0 (lower range 2.0-2.5 in elderly)

Rate Control

• Beta-blockers (metoprolol, atenolol, carvedilol) - first-line for most patients, especially with HFrEF or post-MI
• Non-dihydropyridine calcium channel blockers (diltiazem, verapamil) - effective but avoid in HFrEF
• Digoxin - useful in HF with reduced EF when other agents fail; limited by reduced efficacy with exertion and significant toxicity risk. Toxicity: nausea, vision changes, arrhythmias (PAT with block, bidirectional VT)

Rhythm Control

• Symptomatic patients despite rate control
• First episode of AF in younger patients
• AF-related cardiomyopathy
• Paroxysmal AF with long intervals of sinus rhythm

• IV ibutilide - ~60-70% efficacy for recent-onset AF (<2-3 days); avoid if EF <35% (risk of torsades de pointes)
• IV amiodarone - 40-50% efficacy; preferred if structural heart disease present
• IV procainamide - 30-40% efficacy
• Oral flecainide or propafenone - "pill in the pocket" for patients without structural heart disease; for AF <7 days duration

• More effective than pharmacologic cardioversion
• Requires sedation/anesthesia
• If AF duration >48 hours or unknown: TEE to exclude LAA thrombus before cardioversion, OR 3-4 weeks of therapeutic anticoagulation first
• If hemodynamically unstable: Immediate cardioversion without waiting for TEE
• Anticoagulation required before and for ≥4 weeks after cardioversion (regardless of CHA₂DS₂-VASc)

• Flecainide, propafenone - for AF without structural heart disease
• Sotalol - for AF with coronary artery disease; requires QT monitoring
• Amiodarone - most effective AAD; use when others have failed or in presence of structural heart disease (HF, LVH); limited by significant extracardiac toxicities (pulmonary, thyroid, hepatic, ophthalmic)
• Dronedarone - for paroxysmal/persistent AF; CONTRAINDICATED in permanent AF and HFrEF (ANDROMEDA trial)
• Dofetilide - effective; requires in-hospital initiation for QT monitoring

Catheter Ablation (Pulmonary Vein Isolation - PVI)

• Symptomatic paroxysmal or persistent AF refractory/intolerant to AADs
• AF with HFrEF (CASTLE-AF trial showed mortality reduction with ablation vs. medical therapy)
• Younger patients who prefer ablation over lifelong AADs

Special Scenarios

AF with Heart Failure

• AF and HF are bidirectionally linked: each worsens the other
• In HFrEF: rhythm control with ablation has shown mortality and HF hospitalization reduction (CASTLE-AF)
• In HFpEF/HFmrEF: Both rate and anticoagulation are indicated; the benefit of rhythm control is less clearly established by RCT data, though symptomatic patients deserve a trial of sinus rhythm restoration. (Braunwald's, p. 329-331)
• Beta-blockers: preferred for rate control in HFrEF; neutral in HFpEF

AF with Mitral Stenosis

• Combination of MS + AF dramatically increases stroke risk (equivalent to prosthetic valves)
• Warfarin only (DOACs not recommended)
• Even transient AF episodes (<30 seconds) on ambulatory monitoring significantly increase thromboembolic risk in MS
• Rate control is difficult; ivabradin has been used with some success
• Rhythm control improves quality of life especially with small LA and short AF duration (Braunwald's, p. 750-760)

Postoperative AF

• Occurs in 25-40% after CABG or valve surgery; peaks on day 2
• Prevention: prophylactic amiodarone, sotalol, or beta-blockers; magnesium supplementation; possibly botulinum toxin injection into epicardial fat pads (reduces AF burden for up to 3 years)
• Management: rate or rhythm control both acceptable; most resolve within 3 months
• Anticoagulation continued post-discharge; if no recurrence after 60-90 days (confirmed by monitoring), anticoagulation can be discontinued (Braunwald's, p. 1820-1841)

AF in the Elderly (≥75 years)

• More likely to be asymptomatic or present atypically
• Increased risk of both stroke AND bleeding with age
• HAS-BLED score helps assess bleeding risk but should not replace anticoagulation when indicated
• DOACs preferred over warfarin
• WATCHMAN device for those intolerant of anticoagulation
• Screening: ESC recommends pulse palpation + ECG at age ≥65; systematic ECG screening at ≥75 (Class IIb) (Braunwald's, p. 2817)

Screening

• ESC: Pulse taking or ECG rhythm strip at age ≥65 (Class I); systematic ECG screening at ≥75 (Class IIb)
• US Preventive Services Task Force: Insufficient evidence for routine ECG screening for AF
• Wearable devices (smartwatches, patches) are increasingly used for opportunistic AF detection

Sources

• Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine - Chapters 66, 75 (Valvular Heart Disease), Chapter 64
• Washington Manual of Medical Therapeutics - Chapter 7 (p. 2217-2252)
• PMID: 38727662 - Rhythm vs Rate Control Meta-Analysis, JACC Clinical Electrophysiology (2024)
• PMID: 39918465 - Anticoagulation + Antiplatelet in AF + Stable Coronary Disease, JACC (2025 Mar)