What is Atrial Fibrillation (A-Fib)?
Atrial fibrillation (atrial fibrillation or A-fib) is an abnormal heart rhythm characterized by rapid and irregular beating.
Most episodes have no symptoms. Occasionally there may be heart palpitations, fainting, lightheadedness, shortness of
breath, or chest pain.
High blood pressure and valvular heart disease are the most common alterable risk factors for atrial fibrillation. Other heart-
related risk factors include heart failure, coronary artery disease, cardiomyopathy, and congenital heart disease.
A diagnosis is made by feeling the pulse and may be confirmed using an electrocardiogram (EKG).
Atrial fibrillation is often treated with medications to slow the heart rate to a near normal range (known as rate control) or to convert the rhythm to normal sinus rhythm (known as rhythm control).
Electrical cardioversion can also be used to convert atrial fibrillation to a normal sinus rhythm and is often used emergently if the person is unstable.
Ablation may prevent recurrence in some people. Depending on the risk of stroke either aspirin or anti-clotting medications may be recommended.
Signs and symptoms
Atrial fibrillation is usually accompanied by symptoms related to a rapid heart rate. Rapid and irregular heart rates may be perceived as palpitations or exercise intolerance and occasionally may produce anginal chest pain (if the high heart rate causes ischemia).
Other possible symptoms include congestive symptoms such as shortness of breath or swelling. The arrhythmia is sometimes only identified with the onset of a stroke or a transient ischemic attack (TIA). It is not uncommon for a patient to first become aware of atrial fibrillation from a routine physical examination or EKG, as it often does not cause symptoms.
Since most cases of atrial fibrillation are secondary to other medical problems, the presence of chest pain or angina, signs and symptoms of hyperthyroidism (an overactive thyroid gland) such as weight loss and diarrhea, and symptoms suggestive of lung disease can indicate an underlying cause.
Rapid heart rate
Presentation is similar to other forms of rapid heart rate and may be asymptomatic. Palpitations and chest discomfort are common complaints. Common symptoms of uncontrolled atrial fibrillation may include shortness of breath, shortness of breath when lying flat, dizziness, and sudden onset of shortness of breath during the night.
This may progress to swelling of the lower extremities, a manifestation of congestive heart failure. Due to inadequate cardiac output, individuals with atrial fibrillation may also complain of light-headedness, may feel like they are about to faint, or may actually lose consciousness.
Atrial fibrillation can cause respiratory distress due to congestion in the lungs.
Low blood pressure is most concerning and a sign that immediate treatment is required. Many of the symptoms associated with uncontrolled atrial fibrillation are a manifestation of congestive heart failure due to the reduced cardiac output.
Respiratory rate will be increased in the presence of respiratory distress. Pulse oximetry may confirm the presence of hypoxia related to any precipitating factors such as pneumonia.
Examination of the jugular veins may reveal elevated pressure (jugular venous distention). Lung exam may reveal crackles, which are suggestive of pulmonary edema. Heart exam will reveal a rapid irregular rhythm.
Atrial fibrillation is linked to several forms of cardiovascular disease, but may occur in otherwise normal hearts.
Cardiovascular factors known to be associated with the development of atrial fibrillation include high blood pressure, coronary artery disease, mitral stenosis (e.g., due to rheumatic heart disease or mitral valve prolapse), mitral regurgitation, left atrial enlargement, hypertrophic cardiomyopathy (HCM), pericarditis, congenital heart disease, and previous heart surgery.
Additionally, lung diseases (such as pneumonia, lung cancer, pulmonary embolism, and sarcoidosis) are thought to play a role in certain people. Disorders of breathing during sleep such as obstructive sleep apnea (OSA) are also associated with atrial fibrillation.
A 12-lead ECG showing atrial fibrillation at approximately 150 beats per minute.
The evaluation of atrial fibrillation involves a determination of the cause of the arrhythmia, and classification of the arrhythmia. Diagnostic investigation of atrial fibrillation typically includes a complete history and physical examination, ECG,
transthoracic echocardiogram, complete blood count, and serum thyroid stimulating hormone level.
If a patient presents with a sudden onset of severe symptoms, other forms of abnormal heart rhythm with high heart rate must be ruled out, as some may be immediately life-threatening, such as ventricular tachycardia. While most patients will be placed on continuous cardiorespiratory monitoring, an ECG is essential for diagnosis.
History and physical examination
The history of the individual's atrial fibrillation episodes is probably the most important part of the evaluation. Distinctions should be made between those who are entirely asymptomatic when they are in atrial fibrillation (in which case the atrial fibrillation is found as an incidental finding on an ECG or physical examination) and those who have gross and obvious symptoms due to atrial fibrillation and can pinpoint whenever they go into atrial fibrillation or revert to sinus rhythm.
While many cases of atrial fibrillation have no definite cause, it may be the result of various other problems. Hence, kidney function and electrolytes are routinely determined, as well as thyroid-stimulating hormone (commonly suppressed in hyperthyroidism and of relevance if amiodarone is administered for treatment) and a blood count.
EKG of atrial fibrillation (top) and normal sinus rhythm (bottom). The purple arrow indicates a P wave, which is lost in atrial fibrillation.
Atrial fibrillation is diagnosed on an electrocardiogram (EKG).
In general, a chest X-ray is performed only if a pulmonary cause of atrial fibrillation is suggested, or if other cardiac conditions are suspected (in particular congestive heart failure.) This may reveal an underlying problem in the lungs or the
blood vessels in the chest.
In particular, if an underlying pneumonia is suggested, then treatment of the pneumonia may cause the atrial fibrillation to terminate on its own.
Management of atrial fibrillation
The main goals of treatment are to prevent circulatory instability and stroke. Rate or rhythm control are used to achieve the former, whereas anticoagulation is used to decrease the risk of the latter.
Anticoagulation can be used to reduce the risk of stroke from atrial fibrillation. Anticoagulation is recommended in most people other than those at low risk of stroke or those at high risk of bleeding.
Rate versus rhythm control
There are two ways to approach atrial fibrillation using medications: rate control and rhythm control. Both methods have similar outcomes.
Rate control lowers the heart rate closer to normal, usually 60 to 100 bpm, without trying to convert to a regular rhythm.
Rhythm control tries to restore a normal heart rhythm in a process called cardioversion and maintains the normal rhythm with medications. Studies suggest that rhythm control is more important in the acute setting atrial fibrillation, whereas rate control is more important in the chronic phase.
Cardioversion is the attempt to switch an irregular heartbeat to a normal heartbeat using electrical or chemical means.
Electrical cardioversion involves the restoration of normal heart rhythm through the application of a DC electrical shock.
Chemical cardioversion is performed with drugs.
Surgery - Ablation
Atrial fibrillation increases the risk of heart failure. Women have a worse outcome overall than men. Evidence increasingly suggests that atrial fibrillation is independently associated with a higher risk of developing dementia.
In atrial fibrillation, the lack of an organized atrial contraction can result in some stagnant blood in the left atrium (LA) or left atrial appendage (LAA). This lack of movement of blood can lead to thrombus formation (blood clotting). If the clot becomes mobile and is carried away by the blood circulation, it is called an embolus.
An embolus proceeds through smaller and smaller arteries until it plugs one of them and prevents blood from flowing through the artery. This process results in end organ damage due to loss of nutrients, oxygen, and removal of cellular waste products. Emboli in the brain may result in an ischemic stroke or a transient ischemic attack (TIA).
Atrial fibrillation has been independently associated with a higher risk of dementia. Several mechanisms for this association have been proposed including silent small blood clots (subclinical microthrombi) traveling to the brain resulting in small ischemic strokes without symptoms, altered blood flow to the brain, inflammation, and genetic factors.
Active anticoagulation with direct oral anticoagulants or warfarin appears to be protective against atrial fibrillation-associated dementia and evidence of silent ischemic strokes on MRI.
Atrial fibrillation is the most common arrhythmia.
It also accounts for one-third of hospital admissions for cardiac rhythm disturbances.
It is more common in men than in women. In men, coronary disease is more frequent, while in women, high systolic blood pressure or valvular heart disease are more prevalent.