Atrial Fibrillation¶
Chapter 258 | Part 6: Disorders of the Cardiovascular System
KEY CLINICAL POINTS¶
- Atrial fibrillation (AF) is the most common sustained arrhythmia, with prevalence increasing with age (>95% in patients >60 years).
- AF is associated with a 1.5–1.9-fold increased risk of mortality and is the cause of ~25% of all strokes.
- Stroke risk is assessed using CHADS-VASc score, while bleeding risk is evaluated with HAS-BLED score.
- Management includes rate control, rhythm control, anticoagulation (NOACs or warfarin), and catheter ablation for persistent AF.
- Left atrial appendage thrombus is a critical consideration for cardioversion, requiring anticoagulation or imaging prior to procedure.
1. DEFINITION & OVERVIEW¶
Atrial fibrillation (AF) is a cardiac arrhythmia characterized by disorganized, rapid, and irregular atrial electrical activation, leading to loss of organized atrial mechanical contraction. AF is clinically defined by the pattern of episodes: paroxysmal (self-terminating within 7 days), persistent (>7 days <1 year), or long-standing persistent (>1 year).
Table 258-1: Categorization of Atrial Fibrillation¶
| Type | Definition | LA Size | LA Scar Burden | AAD Efficacy | Ablation Technique |
|---|---|---|---|---|---|
| Paroxysmal AF | Episodes self-terminate or via pharmacologi c/electrical cardioversion within 7 days | Normal to mildly enlarged | Low | Often effective | PV isolation alone usually effective |
| Persistent AF | Episodes lasting >7 days and <1 year | Mild to severely enlarged | Moderate | Not as effective | PV isolation and non-PV AF source ablation |
| Long-standing persistent AF | Persistent AF >1 year | Typically severely enlarged | High | Usually refractory | PV isolation; additional ablation for substrate modification |
1.1 Classification of AF¶
AF is categorized by duration and clinical features: paroxysmal AF (episodes terminate spontaneously or with cardioversion within 7 days), persistent AF (continuous episodes >7 days <1 year), and long-standing persistent AF (>1 year). These categories correlate with left atrial (LA) size, scar burden, and treatment efficacy.
1.2 Pathophysiology¶
AF arises from multifactorial processes leading to electrophysiologic changes in atrial tissue. Key mechanisms include enhanced automaticity in pulmonary vein musculature, abnormal electrical excitability, and tissue remodeling resulting in fibrosis and shortening of atrial refractory periods. Functional reentry and fibrosis contribute to sustained AF.
2. EPIDEMIOLOGY¶
AF prevalence increases with age: >95% in patients >60 years, ~20% in those >80 years. Lifetime risk for men aged 40 is ~25%. Risk factors include age, hypertension, diabetes, obesity, heart failure, sleep apnea, and thyroid disease. AF is more common in men and whites.
2.1 Demographics¶
AF is more prevalent in men than women and in whites than blacks. Risk factors include age >65 years, hypertension, diabetes, obesity, and prior stroke/TIA. Patients with heart failure or structural heart disease have higher risk.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
AF results from a 'final common pathway' of risk factors leading to electrophysiologic changes. Key mechanisms include altered ion channel regulation, enhanced automaticity in pulmonary veins, and atrial remodeling with fibrosis and reentry. Functional reentry and fibrosis sustain AF.
3.1 Molecular Basis¶
Risk factors (age, hypertension, diabetes, etc.) lead to electrophysiologic changes: altered membrane channel regulation, fibrosis, and shortened atrial refractory periods. These changes create substrates for reentry and sustained AF.
4. CLINICAL FEATURES¶
Symptoms include palpitations, fatigue, dyspnea, and presyncope. Signs include irregular pulse, variable ventricular rate, and absence of P waves on ECG. Complications include stroke, heart failure, and thromboembolism. Atrial stunning may delay mechanical function after conversion to sinus rhythm.
4.1 Hemodynamic Consequences¶
Loss of atrial systole reduces cardiac output, leading to exercise intolerance, fatigue, and presyncope. In patients with underlying heart disease, AF may exacerbate heart failure or cause cardiomyopathy.
5. DIFFERENTIAL DIAGNOSIS¶
Differential diagnoses include other supraventricular tachycardias (e.g., atrial flutter, PSVT), ventricular tachycardia, and sinus arrhythmia. ECG findings of irregularly irregular rhythm without P waves are diagnostic for AF.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnosis is confirmed by ECG showing absence of P waves and irregular ventricular response. Additional tests include Holter monitoring, echocardiography (to assess LA size and appendage thrombus), and cardiac MRI/CT for thrombus detection. Ambulatory monitoring is critical for detecting subclinical AF.
6.1 Imaging¶
Transesophageal echocardiography (TEE) and cardiac CT with delayed imaging are used to detect left atrial appendage thrombus. These are critical before cardioversion in patients with prolonged AF.
7. MANAGEMENT & TREATMENT¶
Management includes rate control (beta-blockers, calcium channel blockers), rhythm control (antiarrhythmics, ablation), and anticoagulation (NOACs/warfarin). Cardioversion is indicated for hemodynamic instability or symptoms. Ablation is first-line for paroxysmal AF.
Table 258-2: Novel Oral Anticoagulant Dosing¶
| Drug | Standard Dose | Reduced Dose | Dose Reduction Criteria |
|---|---|---|---|
| Dabigatran | 150 mg bid | 110 mg bid | Age ‡80 years, concomitant verapamil, or increased bleeding risk |
| Rivaroxaban | 20 mg qd | 15 mg qd | Creatinine clearance 15–49 mL/min or ‡2 of 3 criteria (age ‡80, weight £60 kg, serum creatinine ‡1.5 mg/dL) |
| Apixaban | 5 mg bid | 2.5 mg bid | Age ‡80 years, weight £60 kg, or concomitant droned arone/cyclosporine/erythro mycin/ketoconazole |
| Edoxaban | 60 mg qd | 30 mg qd | Creatinine clearance 30–50 mL/min, weight £60 kg, or concomitant drugs |
Anticoagulation is recommended for patients with CHADS-VASc score ≥ 1 (unless female-only risk factor). NOACs (dabigatran, rivaroxaban, apixaban, edoxaban) are preferred over warfarin due to lower bleeding risk. Left atrial appendage closure devices (e.g., Watchman) offer stroke prevention with reduced bleeding risk.
7.2 Ablation¶
Catheter ablation targets pulmonary vein isolation and non-PV foci. Pulsed-field ablation (PFA) is emerging as a safer alternative with reduced tissue damage. Ablation is more effective in paroxysmal AF than persistent/long-standing persistent AF.
8. PROGNOSIS & COMPLICATIONS¶
AF is associated with increased mortality, stroke risk (20% annually without anticoagulation), and heart failure. Complications include thromboembolism, tachycardia-induced cardiomyopathy, and atrial stunning. Subclinical AF increases stroke risk by 2.5-fold.
8.1 Stroke Risk¶
AF increases stroke risk 2–5-fold. CHADS-VASc score predicts annual stroke risk (up to 20% without anticoagulation). Subclinical AF (detected by implantable devices) is associated with 2.5-fold increased stroke risk.
9. SPECIAL CONSIDERATIONS¶
In pregnancy, anticoagulation with low-molecular-weight heparin is preferred. In elderly patients, rate control is often more feasible than rhythm control. Patients with heart failure require careful anticoagulation and monitoring for bleeding risks.
9.1 Anticoagulation in Special Populations¶
Warfarin is required for patients with mechanical heart valves. NOACs are noninferior to warfarin in nonvalvular AF but may have higher bleeding risk. Left atrial appendage closure devices reduce bleeding risk in high-risk patients.
10. KEY POINTS & CLINICAL PEARLS¶
AF management prioritizes anticoagulation (NOACs/warfarin), rate control, and rhythm control strategies. Cardioversion requires anticoagulation for >48 h AF. Pulsed-field ablation offers safer ablation with reduced tissue damage. Subclinical AF detected by implantable devices requires anticoagulation.