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Saturday, August 16, 2025

Atrial fibrillation


Atrial fibrillation (AF) is one of the most common types of cardiac arrhythmias, characterized by rapid and irregular electrical activity in the atria, leading to an irregular and often rapid heartbeat. It significantly increases the risk of stroke, heart failure, and other cardiovascular complications.

Pathophysiology

  • In a healthy heart, the sinoatrial (SA) node generates regular electrical impulses that propagate through the atria, atrioventricular (AV) node, and ventricles, producing coordinated contractions.

  • In AF, chaotic electrical signals arise from the atria (often near the pulmonary veins), leading to uncoordinated atrial contractions and ineffective atrial systole.

  • This irregular atrial activity results in an irregular ventricular response, typically 100–175 beats per minute if untreated.

Causes and Risk Factors

  • Cardiac causes: Hypertension, coronary artery disease, valvular heart disease (especially mitral valve disease), heart failure, congenital heart defects.

  • Non-cardiac causes: Hyperthyroidism, diabetes, obesity, chronic kidney disease, sleep apnea, alcohol abuse (“holiday heart”), stimulant use, infections, and lung diseases.

  • Age: Risk increases significantly with age.

  • Genetics: Family history may predispose.

Types of Atrial Fibrillation

  1. Paroxysmal AF – episodes terminate spontaneously or with intervention within 7 days.

  2. Persistent AF – lasts longer than 7 days and requires intervention to restore sinus rhythm.

  3. Long-standing persistent AF – continuous AF lasting more than 12 months.

  4. Permanent AF – accepted as long-term condition; rhythm control attempts are not pursued.

Clinical Features

  • Symptoms:

    • Palpitations (irregular, rapid heartbeat)

    • Fatigue and reduced exercise capacity

    • Shortness of breath

    • Chest pain or discomfort

    • Dizziness or syncope (rare)

  • Asymptomatic AF: Some individuals are diagnosed incidentally during routine check-ups.

Complications

  • Stroke: Blood pooling in atria (especially left atrial appendage) can form clots, leading to embolic strokes. AF increases stroke risk about fivefold.

  • Heart failure: Due to rapid ventricular rates and loss of atrial contribution to ventricular filling.

  • Cognitive decline/dementia: Linked to recurrent microemboli.

Diagnosis

  • Electrocardiogram (ECG): Gold standard, showing absent P waves, irregularly irregular QRS complexes, fibrillatory waves.

  • Holter monitoring: For paroxysmal AF or intermittent episodes.

  • Echocardiography: To assess atrial size, valvular disease, and cardiac function.

  • Blood tests: To evaluate thyroid function, renal function, and electrolytes.

Management

The management of atrial fibrillation focuses on:

  1. Stroke prevention

  2. Rate control

  3. Rhythm control

  4. Management of underlying conditions

1. Stroke Prevention

  • Stroke risk is estimated using CHA₂DS₂-VASc score.

  • Oral anticoagulants are prescribed for most patients except those at very low risk.

Medications (generic names and doses):

  • Warfarin: Dose adjusted to maintain INR 2.0–3.0.

  • Direct oral anticoagulants (DOACs):

    • Apixaban: 5 mg twice daily (2.5 mg twice daily in elderly or renal impairment).

    • Rivaroxaban: 20 mg once daily with food (15 mg daily in renal impairment).

    • Dabigatran: 150 mg twice daily (110 mg in elderly or renal impairment).

    • Edoxaban: 60 mg once daily (30 mg in renal impairment).

2. Rate Control

Objective: Keep ventricular rate <110 bpm at rest.

  • First-line agents:

    • Beta-blockers (e.g., metoprolol 25–100 mg twice daily).

    • Calcium channel blockers (non-dihydropyridines):

      • Verapamil: 120–240 mg/day in divided doses.

      • Diltiazem: 120–360 mg/day.

    • Digoxin: 0.125–0.25 mg once daily (useful in sedentary patients or with heart failure).

3. Rhythm Control

Goal: Restore and maintain sinus rhythm.

  • Electrical cardioversion: Direct current shock under sedation.

  • Pharmacological cardioversion:

    • Amiodarone: 200–400 mg daily (after loading dose).

    • Flecainide: 200–300 mg orally (single dose strategy in selected patients without structural heart disease).

    • Propafenone: 450–600 mg orally (used similarly to flecainide).

  • Maintenance therapy (antiarrhythmics):

    • Amiodarone: 100–200 mg daily.

    • Sotalol: 80–160 mg twice daily.

    • Flecainide: 50–150 mg twice daily.

4. Catheter Ablation and Surgical Options

  • Catheter ablation: Pulmonary vein isolation is an effective option for symptomatic AF not controlled by drugs.

  • Surgical approaches: Maze procedure during cardiac surgery.

Lifestyle and Risk Factor Management

  • Weight reduction in obese patients.

  • Regular physical activity.

  • Limiting alcohol and caffeine.

  • Controlling hypertension, diabetes, and sleep apnea.

  • Avoiding stimulants and excessive thyroid hormone replacement.

Prognosis

  • AF is not usually immediately life-threatening but significantly increases morbidity due to stroke and heart failure.

  • With adequate management, many patients live full and active lives.




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