Atrial Fibrillation

Key points

• Atrial fibrillation is the most common type of cardiac arrhythmia, defined by irregularly irregular ventricular pulse and apical-radial mismatch
• Commonly associated with valvular heart disease, hypertension, increased age, or heart failure
• Evaluate for hemodynamic compromise secondary to rhythm disturbance, which may require urgent electrocardioversion. Other potentially life-threatening associated conditions include myocardial infarction, thromboembolic stroke, thyrotoxicosis, and peripheral emboli. These conditions warrant immediate hospitalization
• Almost all patients should receive anticoagulation, as warfarin has been shown to be effective for primary and secondary prevention of ischemic stroke. The exceptions to anticoagulation would be young patients with lone atrial fibrillation and those with specific contraindications

Background

Description

• Atrial fibrillation is the most common type of cardiac arrhythmia, defined by irregularly irregular ventricular pulse and apical-radial mismatch
• Can be paroxysmal, persistent, or permanent
• Underlying pathology is generally present
• There are multiple causes, and treatment of some causes will result in the patient reverting to sinus rhythm
• Commonly associated with valvular heart disease, hypertension, increased age, or heart failure
• Reversible etiologies such as metabolic derangements and thyroid disease need to be excluded
• Atrial fibrillation is an important cause of thromboembolism, particularly stroke, especially in elderly patients
• Overall, 4,000 per 100,000 patients with atrial fibrillation will have a stroke each year
• Incidence of cerebrovascular accidents may be 5% per year, therefore anticoagulation is warranted in most patients
• Lone atrial fibrillation most often manifests as isolated or recurrent episodes of paroxysmal atrial fibrillation; a few cases have chronic rhythm disturbance

Epidemiology

Prevalence:

• Overall, approximately 2,000 per 100,000 of the U.S. population
• Increases with age
• Among those older than 65 years, 5,000 per 100,000 of the U.S. population

Frequency:

• Incidence is 2% over 20 years

Demographics:

• Uncommon in people younger than 50 years
• Roughly doubles in incidence with each decade over 40 years
• Occurs in 500 per 100,000 people aged 50 to 59 years
• Increases to 8,800 per 100,000 cases in people aged 80 to 89 years
• Rare in children
• More common in men than women
• Rare genetic cases exist. There is an autosomal-dominant form of familial atrial fibrillation, caused by a mutation on chromosome 10; this may be suspected in younger patients who have a strong family history. In an overwhelming majority of patients, however, no specific genetic pattern exists

Causes and risk factors

Common causes

Cardiac causes:

• Most common cause is hypertension, especially where left ventricular hypertrophy is present. Left atrium may dilate secondary to left ventricular dilatation and trigger atrial fibrillation; alternatively, hypertension may be associated with underlying heart disease, itself a risk factor for atrial fibrillation
• Coronary heart disease
• Rheumatic heart disease, especially mitral valve stenosis. This combination increases the risk of stroke 18-fold
• Non-rheumatic valvular heart disease; risk of stroke in these patients is increased 5.6-fold
• Sick sinus syndrome
• Preexcitation syndromes with accessory conduction pathways (eg, Wolff-Parkinson-White [WPW] syndrome), which is recognized by a short PR interval of less than 0.12 seconds and wide QRS complex with delta waves on the electrocardiogram [ECG] when the patient is in sinus rhythm). Should be suspected in a young patient with extremely fast atrial fibrillation
• Idiopathic dilated and hypertrophic cardiomyopathy

Noncardiac causes:

• Thyrotoxicosis, even where classic signs of overactive thyroid are absent
• Acute infections, especially pneumonia in elderly patients
• Acute excess alcohol intake—the 'holiday heart syndrome' in healthy people with otherwise normal hearts. Caused by the release of catecholamines, especially norepinephrine, from the adrenals and epinephrine from cardiac stores. The main metabolite of ethanol increases systemic and myocardial catecholamines; its metabolites also prolong the PR, QRS, and QT intervals directly
• Chronic excess alcohol intake. Alcohol withdrawal also increases catecholamine release
• Lung cancer
• Other thoracic or pulmonary pathology (eg, pleural effusion)
• Postoperative problems (especially after thoracotomy or coronary artery bypass grafting)
• Obstructive sleep apnea—a strong correlation between sleep apnea and atrial fibrillation has been demonstrated, and treatment of sleep apnea may decrease the burden of atrial fibrillation

Rare causes

Cardiac causes:

• Cardiomyopathy—alcoholic and hypertrophic
• Pericardial disease such as effusion and constrictive pericarditis
• Atrial septal defect
• Atrial myxoma

Noncardiac causes:

• Pulmonary embolism
• Drugs (eg, digoxin toxicity, sumatriptan)

Screening

Not applicable.

Primary prevention

Summary approach

• There are no evidence-based or guideline-driven recommendations regarding primary prevention of atrial fibrillation
• The American College of Chest Physicians (ACCP) has issued guideline recommendations on medical and surgical measures to prevent atrial fibrillation following cardiac surgery
• There is general consensus regarding treatment of risk factors underlying the development of atrial fibrillation, such as presence of structural and functional heart disease, hypertension, and hyperthyroidism, and regarding the use of drugs that predispose patients to the arrhythmia

Population at risk

• Approximately 25% of post–cardiac surgery patients; particularly patients of increasing age
• Patients with organic heart disease, or certain pulmonary or endocrine disorders

Preventive measures

• Smoking is a risk factor for coronary heart disease and a cause of atrial fibrillation
• General advice is to avoid smoking in all cardiovascular conditions; coronary heart disease is an important cause of atrial fibrillation
• Acute alcoholic intoxication or alcohol withdrawal may precipitate paroxysmal atrial fibrillation
• Caffeine may induce paroxysmal atrial fibrillation in susceptible individuals
• Patients should be screened for obstructive sleep apnea and referred for treatment. A strong correlation exists between sleep apnea and the burden of atrial fibrillation
• Patient should consult a physician before taking any nonprescription medications, as these may precipitate an attack of atrial fibrillation or interact with prescribed medications
• The 2005 ACCP guidelines regarding prophylaxis following cardiac surgery recommend the use of beta-blockers in patients for whom prophylaxis is indicated. For those patients in whom beta-blockers are contraindicated, amiodarone therapy may be considered. The ACCP recommendations also support the use of biatrial cardiac pacing, continued for 3 days postoperatively, to help prevent postoperative atrial fibrillation