Atrial fibrillation overview


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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.

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.

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 that generate the heartbeat. The result is an irregular heartbeat which may occur in episodes lasting from minutes to weeks, or atrial fibrillation may be present continuously for 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 this 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.

Complications
Due to the lack of coordination of atrial activation, there is a decline in the mechanical pumping action of the atrium. The decline in mechanical function of the atrium may or may not lead to inadequate filling of the ventricle(s) depending upon the importance of the atrial "kick" or atrial contribution to ventricular filling in a given patient. In patients with a stiff left ventricle, the atrial kick may be critical to achieve adequate ventricular filling.

Patients with atrial fibrillation usually have a significantly increased risk of stroke (up to 7 times that of the general population). Stroke risk increases during AF because blood may pool and form clots in the poorly contracting atria and especially in the left atrial appendage (LAA). The level of increased risk of stroke depends on the number of additional risk factors. If the AF patient has none, the risk of stroke is similar to that of the general population. However, many patients do have additional risk factors and AF is a leading cause of stroke.

Chronic AF leads to a small increase in the risk of death.

Natural History
Atrial fibrillation may be continuous (persistent or permanent AF) or alternating between periods of a normal heart rhythm (paroxysmal AF). The natural tendency of atrial fibrillation is to become a chronic condition. Chronic AF leads to a small increase in the risk of death.

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 don't occur at regular intervals. the pulse is classically irregularly irregular.

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

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.