Atrial Fibrillation

KEY FEATURES

ESSENTIALS OF DIAGNOSIS

• Irregularly irregular ventricular rhythm usually at rates > 100 bpm

• Absence of distinct P waves on the ECG

GENERAL CONSIDERATIONS

• The most common chronic arrhythmia

• Prevalence increases with age from 0.1% for those < 55 years old to 9% in those > 80 years old. Nearly 70% of those with atrial fibrillation are > 65 years old

• Common causes include:

  • – Hypertensive heart disease

  • – Coronary heart disease

  • – Rheumatic heart disease

  • – Systolic dysfunction of any cause

  • – Mitral valve disease

  • – Cardiac surgery

  • – Hyperthyroidism

  • – Idiopathic

• Atrial fibrillation associated with Wolff-Parkinson-White syndrome may lead to very rapid ventricular rates and be life threatening

• QRS complex is usually narrow (< 100 ms) but may be wide (> 120 ms) if there is aberrant conduction, a preexisting bundle branch block, or an accessory pathway

• Long, short cycle length fluctuations are common

• Faster ventricular rates may minimize cycle length fluctuation

• Atrial fibrillation is classified as paroxysmal (self-terminating within 7 days), persistent (fails to terminate within 7 days and commonly requires cardioversion), long-standing persistent (episodes lasting longer than 12 months), or permanent, in which a decision has been made to not pursue rhythm control strategy. The term lone atrial fibrillation describes those with atrial fibrillation and no structural heart disease; however, this term is no longer commonly used

• Paroxysmal, persistent, and permanent forms of atrial fibrillation all increase the risk of stroke

• Atrial fibrillation is a leading cause of stroke; this risk is mitigated by anticoagulation therapy

• Other causes of rapid regular ventricular rate include atrial flutter, junctional rhythm, and ventricular tachycardia

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

• Palpitations, chest pain, shortness of breath, fatigue, and dizziness

• Symptoms of precipitating or associated conditions may mask symptoms of atrial fibrillation

• Alternatively, atrial fibrillation may produce symptoms in otherwise asymptomatic conditions

• Syncope is uncommon

• Atrial fibrillation may be an incidental finding in some patients (asymptomatic)

PHYSICAL EXAM FINDINGS

• Variable S₁, occasional S₃, and absent S₄

• Absence of a waves in the jugular venous pulse

• Pulse deficit (difference between the auscultated or palpated apical heart rate and palpated rate at the wrist) is common, particularly at fast heart rates

• Irregularly irregular pulse

• Signs of precipitating conditions like thyrotoxicosis, rheumatic mitral stenosis, and heart failure

DIFFERENTIAL DIAGNOSIS

• Multifocal atrial tachycardia (P waves present but irregular)

• Atrial flutter with variable atrioventricular (AV) block (P waves present but irregular)

• Sinus rhythm with consecutive premature atrial contractions (P waves present but irregular)

• Junctional rhythm (P waves absent but regular)

DIAGNOSTIC EVALUATION

LABORATORY TESTS

• CBC, basic metabolic panel

• Thyroid function (serum thyroid-stimulating hormone and free thyroxine)

• Arterial blood gas analysis to ...