eMedicine Specialties > Emergency Medicine > Cardiovascular

Atrial Fibrillation

Author: Pierre Borczuk, MD, Assistant Professor of Medicine, Harvard Medical School, Associate in Emergency Medicine, Massachusetts General Hospital
Contributor Information and Disclosures

Updated: Jul 15, 2009

Introduction

Background

Atrial fibrillation (AF) is the most frequently diagnosed arrhythmia and affects 2.3 million people in the United States. Its prevalence increases with age, and as many as 9% of people older than 80 years are affected.1 Atrial fibrillation is characterized by a lack of coordinated atrial activity, and this loss of organized atrial contraction can lead to a myriad of clinical scenarios that include decompensated congestive heart failure (CHF), embolic cerebrovascular accident (CVA), ischemia, dizziness/weakness, and even asymptomatic patients with tachycardia.

Management of atrial fibrillation includes many modalities: pharmacologic therapy aimed to keep patients in sinus rhythm and to control rate, electrical cardioversion, catheter ablation, as well as anticoagulation to prevent thromboembolic disease.2

The cardiologist's approach to atrial fibrillation is well covered eMedicine’s Cardiology article on Atrial Fibrillation. Emergency physicians are more concerned with the acute or life-threatening problems associated with atrial fibrillation, and this article outlines appropriate ED treatment of these patients; however, readers who are interested in topics such as catheter ablation and clinical electrophysiology of atrial fibrillation are referred to the Cardiology article Atrial Fibrillation. For additional resources, also visit Medscape's Atrial Fibrillation Resource Center.

Pathophysiology

Atrial fibrillation (AF) is caused by multiple reentrant waveforms within the atria, which bombard the atrioventricular (AV) node, commonly leading to a tachycardia that is irregularly irregular. The rate at which atrial fibrillation causes a ventricular contraction is dependent upon the refractory state of the AV node. There is loss of atrial contraction and its contribution to ventricular filling, also referred to as loss of atrial kick. In addition, this loss of contraction can lead to stagnation of blood in the atrium and can promote thrombus formation. Patients may be at risk for embolization when atrial fibrillation converts to sinus rhythm as organized atrial contractions can now cause the dislodging or fragmentation of the atrial thrombus into the systemic circulation.

In summary, clinical presentations are typically due to the following:

  • Loss of atrial kick (synchronized atrial mechanical activity)
  • Irregularity of ventricular response
  • Inappropriately rapid heart rate
Classification of atrial fibrillation

Atrial fibrillation appears to alter the atrial substrate over time, and this electrical remodeling creates a condition in which atrial fibrillation occurs more frequently and is less likely to terminate, hence the phrase "atrial fibrillation begets atrial fibrillation". This notion forms the basis for the following classification:
  • Paroxysmal AF – Episodes of AF that typically lasts less than 24 hours but can last up to 7 days; these terminate spontaneously
  • Persistent AF - Episodes of AF than last more than 7 days and require either pharmacologic or electrical intervention to terminate
  • Permanent AF - Continuous AF, that has failed cardioversion, or where cardioversion has never been attempted
  • Lone AF has been used to describe AF in individuals without structural or cardiac or pulmonary disease, with low risk for thromboembolism. It has traditionally been applied to patients younger than 60 years.
Mechanisms that play a role in atrial fibrillation

The autonomic nervous system may play a role in the initiation of atrial fibrillation. Increased sympathetic innervation in patients with atrial fibrillation may be responsible for remodeling of the atrial substrate and may lead to the development of persistent atrial fibrillation. More recently, tissues at the pulmonary vein and pulmonary vein-left atrial (LA) junction have been demonstrated to play an important role in atrial fibrillation activation and sustaining atrial fibrillation reentrant activity. There is an atrial muscle that extends into the thoracic veins, and this tissue is vagally innervated. These anatomic findings are important in the technique of pulmonary vein isolation in atrial fibrillation catheter ablation.

Common atrial fibrillation clinical scenarios
  • Atrial fibrillation with a structurally normal heart
  • Atrial fibrillation in patients with cardiovascular disease
  • Systemic illness that may predispose to atrial fibrillation (eg, hypothermia, hyperthyroidism)
  • Postoperative atrial fibrillation

Frequency

United States

Approximately 2.5 million Americans, or close to 1% of the total population, currently have atrial fibrillation.

The cost to treat atrial fibrillation in the United States exceeds $6.4 billion per year.3

Atrial fibrillation can be considered a disease of aging, and, with the projected increase in the elderly population in America, the prevalence is expected to more than double by the year 2050.4

Mortality/Morbidity

  • Atrial fibrillation is rarely a life-threatening arrhythmia.
  • Framingham data suggest that patients with atrial fibrillation have a 1.5-2 fold increase in mortality rate when compared with the general population.
  • The rate of ischemic stroke among patients with nonrheumatic atrial fibrillation averages 5% a year, which is somewhere between 2-7 times the rate of stroke in patients without atrial fibrillation. The risk of stroke is not due solely to atrial fibrillation; it increases substantially in the presence of other cardiovascular disease.5
  • The prevalence of stroke in patients younger than 60 years is less than 0.5%; however, in those older than 70 years, the prevalence doubles with each decade.6
  • The attributable risk of stroke from atrial fibrillation is estimated to be 1.5% for those aged 50-59 years, and it approaches 30% for those aged 80-89 years.

Race

  • Atrial fibrillation appears to be more common in whites than in blacks.
  • Blacks have less than half the age-adjusted risk of developing atrial fibrillation than is seen in whites.

Sex

Incidence of atrial fibrillation is significantly higher in men than in women in all age groups.

Age

The prevalence of atrial fibrillation increases almost exponentially with age.

Atrial fibrillation is uncommon in childhood except after cardiac surgery.

  • The prevalence of AF among persons younger than 55 years is 0.1%.
  • The prevalence of AF among persons 60 years or older is 3.8%.
  • The prevalence of AF among persons 80 years or older is 10%.

Clinical

History

Clinical presentation spans the entire spectrum from asymptomatic atrial fibrillation with rapid ventricular response to cardiogenic shock or devastating CVA. When initially evaluating patients in atrial fibrillation, it is useful to determine which patients need immediate stabilization (in minutes, usually cardioversion).

  • Those needing immediate attention include the following:
    • Decompensated CHF
    • Hypotension
    • Uncontrolled angina/ischemia
  • Less severe symptoms and patient complaints may include the following:
    • Palpitations
    • Fatigue or poor exercise tolerance
    • Presyncope, or syncope
    • Generalized weakness, dizziness, fatigue
In addition to eliciting symptoms listed above, history taking of any patient presenting with suspected atrial fibrillation should include questions relevant to temporality, precipitating factors (including hydration status, recent infections, alcohol use), history of pharmacologic or electric interventions and responses, and presence of heart disease. Occasionally, a patient may have a clear and strong belief about the onset of symptoms that may be helpful in determining a course of action.

Physical

Physical examination always begin with airway, breathing, and circulation (ABCs) and vital signs, as these will guide the pace of the intervention.

  • Patients will have an irregularly irregular pulse and will commonly present tachycardic, with heart rates typically in the 110-140 range, but rarely over 160-170 range.
  • Patients with valvular heart disease frequently have coexisting atrial fibrillation, and cardiac murmurs may be appreciated.
  • Pulmonary examination may demonstrate rales consistent with congestive heart failure (CHF) or possibly consistent with a pneumonia that may have precipitated this arrhythmia.
  • In patients with new atrial fibrillation, signs of deep venous thrombosis (DVT) or hyperthyroidism may be found.
  • Because thromboembolic phenomenon is common in atrial fibrillation, signs of transient ischemic attack (TIA)/cerebrovascular accident (CVA) or peripheral embolization (cool/cold pulseless extremity or left upper quadrant pain of splenic infarct) may be discovered.
  • Patients who are hypothermic or those with cardiac drug toxicity may present with bradycardic atrial fibrillation.

Causes

Risk factors for atrial fibrillation (AF) include age, male sex, long-standing hypertension, valvular heart disease, left ventricular hypertrophy, coronary artery disease (with or without depressed left ventricular function), diabetes mellitus, smoking, and any form of carditis.

Causes of atrial fibrillation can be divided into cardiovascular versus noncardiovascular causes.

  • Important cardiovascular causes include the following:
    • Long-standing hypertension
    • Ischemic heart disease
    • CHF
    • Any form of carditis
    • Cardiomyopathy
    • Infiltrative heart disease of any type
    • Sick sinus syndrome
  • Noncardiovascular causes of atrial fibrillation include the following:
  • Noncardiovascular respiratory causes include the following:
    • Pulmonary embolism
    • Pneumonia
    • Lung cancer
    • Idiopathic: Lone atrial fibrillation is idiopathic and defined as the absence of any known etiologic factors plus normal ventricular function by echocardiography. Most patients with lone atrial fibrillation are younger than 65 years, although age is not used to define lone atrial fibrillation.
    • Hypothermia

More on Atrial Fibrillation

Overview: Atrial Fibrillation
Differential Diagnoses & Workup: Atrial Fibrillation
Treatment & Medication: Atrial Fibrillation
Follow-up: Atrial Fibrillation
Multimedia: Atrial Fibrillation
References
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References

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Further Reading

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Keywords

atrial fibrillation, AF, atrial fib, atrial fibrillation treatment, bradyarrhythmia, tachyarrhythmia, arrhythmia, heart disease, acute myocardial infarction, AMI, congestive heart disease, CHD, coronary artery disease, CAD, cardiovascular disease, heart attack, rhythm disturbance, atrioventricular node, AV node, palpitations, dyspnea, chest pain, angina, syncope, hypotension, congestive heart failure, CHF, jugular venous distension, hypertension, valvular heart disease, rheumatic heart disease

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Contributor Information and Disclosures

Author

Pierre Borczuk, MD, Assistant Professor of Medicine, Harvard Medical School, Associate in Emergency Medicine, Massachusetts General Hospital
Pierre Borczuk, MD is a member of the following medical societies: American College of Emergency Physicians
Disclosure: Nothing to disclose.

Medical Editor

William Lober, MD, Associate Professor, Department of Medical Education, Division of Biomedical and Health Informatics, University of Washington School of Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Gary Setnik, MD, Chair, Department of Emergency Medicine, Mount Auburn Hospital; Assistant Professor, Division of Emergency Medicine, Harvard Medical School
Gary Setnik, MD is a member of the following medical societies: American College of Emergency Physicians, National Association of EMS Physicians, and Society for Academic Emergency Medicine
Disclosure: SironaHealth Salary Management position; South Middlesex EMS Consortium Salary Management position

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

David FM Brown, MD, Assistant Professor, Division of Emergency Medicine, Harvard Medical School; Vice Chair, Department of Emergency Medicine, Massachusetts General Hospital
David FM Brown, MD is a member of the following medical societies: American College of Emergency Physicians and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

 
 
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