Atrial fibrillation overview

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Sinus rhythm

Atrial fibrillation

Atrial Fibrillation Microchapters
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Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Atrial Fibrillation from other Diseases
Epidemiology and Demographics
Risk Factors
Screening
Natural History, Complications and Prognosis
Special Groups Postoperative AF Acute Myocardial Infarction Wolff-Parkinson-White Preexcitation Syndrome Hypertrophic Cardiomyopathy Hyperthyroidism Pulmonary Diseases Pregnancy ACS and/or PCI or valve intervention Heart failure
Diagnosis
History and Symptoms
Physical Examination
Laboratory Findings
Electrocardiogram EKG Examples A-Fib with LBBB
Chest X Ray
Echocardiography
Holter Monitoring and Exercise Stress Testing
Cardiac MRI
Treatment
Rate and Rhythm Control
Cardioversion Overview Electrical Cardioversion Pharmacological Cardioversion
Anticoagulation Overview Warfarin Converting from or to Warfarin Converting from or to Parenteral Anticoagulants Dabigatran
Maintenance of Sinus Rhythm
Surgery Catheter Ablation AV Nodal Ablation Surgical Ablation Cardiac Surgery
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

Atrial fibrillation (AF or afib) is a cardiac arrhythmia (abnormal heart rhythm) that involves the two upper chambers (atria) of the heart. Atrial fibrillation is an irregularly irregular heart beat due to chaotic firing of the impulses in the atrium. In this rhythm, the atrium is stimulated chaotically by a wide number of ectopic foci of electrical activity.

Classification

Although several clinical classification plans and protocols have been proposed, none of them fully account for all aspects of atrial fibrillation. The American Heart Association, American College of Cardiology, and the European Society of Cardiology have proposed a classification system based on simplicity and clinical relevance. This classification system contains four main categories which are: first detected or diagnosed, paroxysmal, persistent, and permanent atrial fibrillation.

Pathophysiology

In atrial fibrillation, the normal electrical impulses that are generated by the sinoatrial node are overwhelmed by disorganized electrical impulses that originate in the atria and pulmonary veins, leading to conduction of irregular impulses to the ventricles. This results into an irregular heartbeat which may occur in episodes lasting from minutes to weeks or continuously for many years.

Causes

The most common cause of atrial fibrillation is atrial dilation associated with hypertension. Approximately 1/3 of patients have familial atrial fibrillation which is due to an underlying genetic disorder. Given the number of patients who undergo coronary artery bypass grafting in the developed world, this is an increasing underlying cause of atrial fibrillation. Other general causes include: the advancing age of the population, the hemodynamic stress of heart failure and valvular heart disease, myocardial ischemia, a variety of inflammatory disorders, pulmonary diseases, alcohol and drug abuse, and endocrine disorders.

Differentiating Atrial Fibrillation from other Diseases

Atrial fibrillation must be distinguished from other common atrial arrhythmias which include atrial flutter, atrial tachycardia, atrioventricular nodal reentry tachycardia, paroxysmal supraventricular tachycardia, and Wolff-Parkinson-White syndrome.

Epidemiology and Demographics

AF is the most common arrhythmia. The risk of atrial fibrillation increases with age, and 8% of people over the age of 80 have AF. It accounts for 1/3 of hospital admissions for cardiac rhythm disturbances, and the rate of admissions for AF has risen in recent years.

Risk Factors

Atrial fibrillation (AF) affects millions of people, and the number increases with increasing age. Men are more likely than women to have the condition. In the United States, AF is more common among Caucasians than African-Americans or Hispanic Americans. The risk of AF increases with age. This is mostly because the risk for heart disease and other conditions that can cause AF also increases with increasing age.

Screening

Screening for atrial fibrillation is generally not performed, although a study of routine pulse checks or electrocardiograms during routine office visits found that the annual rate of detection of atrial fibrillation in elderly patients improved from 1.04% to 1.63%.

Natural History, Complications and Prognosis

Atrial fibrillation can be complicated by embolic events including stroke and systemic embolization. The atrial kick (active filling of the left ventricle by atrial contraction) often contributes importantly to the filling of the left ventricle, and the loss of the atrial kick can be associated with the development of congestive heart failure.

Diagnosis

History and Symptoms

Atrial fibrillation is often asymptomatic, and is not in itself generally life-threatening, but may result in palpitations, fainting, chest pain, or congestive heart failure.

Physical Examination

Atrial fibrillation is often be identified by taking the pulse and observing that the heartbeats occur at regular intervals. The pulse is classically irregularly irregular.

Electrocardiogram

The absence of P waves on the electrocardiogram with an irregularly irregular atrial rhythm is diagnostic of atrial fibrillation.

Chest X-Ray

A chest X-ray is useful in the setting of atrial fibrillation only when the cause is suspected to be pulmonary in origin.

Echocardiogram

Performing an echocardiogram in the setting of atrial fibrillation is essential to evaluate certain pathologies of the heart such as valvular heart disease, hypertrophy, presence of thrombus, presence of pericardial disease; some parameters of cardiac functionality including the size and function of the left ventricle, the size of the atria.

Cardiac MRI

Cardiac magnetic resonance imaging may be used to assess the structure and the function of the atria in patients with atrial fibrillation. Further studies are needed to determine whether CMR is useful for detecting atrial thrombi in persons with atrial fibrillation.

Other Imaging Studies

Other diagnostic studies include the holter monitor to assess symptomatic episodes of atrial fibrillation over a 24 hour period, and exercise stress testing to assess a how a patient's heart rate responds to exertion. The main benefits to performing an exercise stress test are to reproduce exercise induced atrial fibrillation, and to exclude ischemia before initiating treatment with type 1C antiarrhythmic medications.

Treatment

Atrial fibrillation may be treated with medications which either slow the heart rate or revert the heart rhythm back to normal sinus rhythm. Synchronized electrical cardioversion may also be used to convert AF to a normal heart rhythm. Surgical and catheter-based therapies may also be used to prevent recurrence of AF in certain individuals. People with AF are often given anticoagulants such as warfarin to reduce the risk of stroke.

Among patients in whom there is normal atrioventricular conduction, fibrillatory or irregular impulses that vary in timing, amplitude and shape are present which are in turn associated with the rapid irregular ventricular response that characterizes atrial fibrillation.

Cardioversion

Cardioversion is a medical procedure by which an abnormally fast heart rate (tachycardia) or cardiac arrhythmia is converted to a normal rhythm, using electricity or drugs.

Anticoagulation

Oral anticoagulation is a mainstay of atrial fibrillation management. For both primary and secondary prevention of stroke, there is a 61% relative risks reduction in the incidence of all cause stroke (both ischemic and hemorrhagic) associated with adjusted-dose oral anticoagulation.

Rate Control

Atrial fibrillation with rapid ventricular rate is a common finding in many hospitalized patients. The ventricular rate may be increased upto 150-170. It is essential to bring the ventricular rate down to less than 100 because a rapid ventricular response can cause hemodynamic instabilities and tachycardia mediated cardiomyopathies (heart failure). AF can cause disabling and annoying symptoms. Palpitations, angina, lassitude (weariness), and decreased exercise tolerance are related to rapid heart rate and inefficient cardiac output caused by AF. This can significantly increase mortality and morbidity, which can be prevented by early and adequate treatment of the AF.

Rhythm Control

Prophylactic antiarrhythmic drug therapy may be required to maintain sinus rhythm, reduce frequency of symptoms, improve hemodynamic function and exercise capacity and prevent tachycardia-induced cardiomyopathy secondary to atrial fibrillation. In patients with heart failure, pharmacological maintenance of sinus rhythm has shown to reduce morbidity.

Surgery

Radiofrequency Ablation

Ablation is a newer technique and has shown some promise for cases of recurrent AF that are unresponsive to conventional treatments. Radiofrequency ablation (RFA) uses radiofrequency energy to destroy abnormal electrical pathways in heart tissue. The energy emitting probe (electrode) is placed into the heart through a catheter inserted into veins in the groin or neck. Electrodes that can detect electrical activity from inside the heart are also inserted, and the electrophysiologist uses these to map an area of the heart in order to locate the abnormal electrical activity before eliminating the responsible tissue.

Maze Procedure

A surgical option for some patients with atrial fibrillation is the maze procedure. In this procedure, a series of incisions in a cross like pattern are made on the atria, which blocks the abnormal atrial circuits, hence eliminating the atrial fibrillation. A number of improvements have been made to this surgical procedure since it was first invented.

Secondary Prevention

In patients with paroxysmal atrial fibrillation, or after conversion of persistent AF, dronedarone is a medication that may be used to decrease the need for hospitalization, and can be started as an outpatient therapy. It can not be given in patients with class IV heart failure, decompensated heart failure, or depressed left ventricular function. A permanent pacemaker is not recommended in patients who do not have another indication for placement of a pacemaker.