Atrial Fibrillation

Atrial fibrillation,or AF, is the most common arrhythmia. An arrhythmia is a problem with the speed or rhythm of the heartbeat. A disorder in the heart's electrical system causes AF and other types of arrhythmia. If uncontrolled, AF can cause heart disease or stroke as well as some other cardiovascular conditions.

Other Names

AF is sometimes called the following:

• A fib
• Auricular fibrillation. This term is now considered obsolete

Types

AFs are classified into one of several types.

Paroxysmal

In paroxysmal AF the abnormal electrical signals and rapid heart rate begin suddenly and then stop on their own.

Persistent

Persistent AF is a condition in which the abnormal heart rhythm continues until it’s stopped with treatment.

Permanent

Permanent AF is a condition in which the normal heart rhythm can’t be restored with the usual treatments. Both paroxysmal and persistent atrial fibrillation may become more frequent and eventually result in permanent AF.

Symptoms

AF usually causes the ventricles to contract faster than normal, which prevents them from filling completely with blood. As a result, less blood is pumped into the body. Many symptoms are a consequence of this reduced pumping action:

• palpitations (a strong feeling of a fast heartbeat or a “thumping” in the chest)
• shortness of breath
• weakness or difficulty exercising
• chest pain
• dizziness or fainting
• tiredness
• confusion

Some people with AF don’t have symptoms. In others, the symptoms are mild or severe. The symptoms of paroxysmal AF can last for seconds, minutes, hours, or days.

Most of the symptoms of AF are related to how fast the heart is beating. If medicines or age slow the heart rate, the effect of the irregular beats is minimized.

Causes

AF is caused by abnormal electrical conduction in the heart. Problems with the heart’s structure and some conditions, such as high blood pressure or coronary artery disease can lead to AF. Conditions not related to the heart can also cause AF and these include pneumonia, hyperactive thyroid, blood clot in the lungs etc. Sometimes, the cause of AF is unknown and this is called 'Lone AF'.

Blood flow and electrical conduction in the healthy heart

The heart has two sides, separated by an inner wall called the septum. The right side of the heart pumps blood to the lungs to pick up oxygen. Then, oxygen-rich blood returns from the lungs to the left side of the heart, and the left side pumps it to the body. Veins carry blood from the body to the heart, and arteries carry blood away from the heart to the body.

The illustration shows a cross-section of a healthy heart and its inside structures. The blue arrow shows the direction in which oxygen-poor blood flows from the body to the lungs. The red arrow shows the direction in which oxygen-rich blood flows from the lungs to the rest of the body.

The heart has four chambers: left atrium, right atrium, left ventricle, and right ventricle. The atria are the two upper chambers that collect blood as it comes into the heart, whereas the ventricles are the two lower chambers that pump blood out of the heart to the lungs or the rest of the body.

The heart has an internal electrical system that controls the speed and rhythm of the heartbeat. Each electrical signal begins in a group of cells called the sinoatrial (SA) node. The SA node is located in the right atrium. In a healthy adult heart at rest, the SA node fires off an electrical signal to begin a new heartbeat 60 to 100 times a minute.

From the SA node, the electrical signal travels through special pathways to the right and left atria. This causes the atria to contract and pump blood into the ventricles. The electrical signal then moves down to a group of cells called the atrioventricular (AV) node, located between the atria and the ventricles. Here, the signal slows down just a little, allowing the ventricles time to finish filling with blood.

The electrical signal then leaves the AV node and travels along a pathway called the bundle of His. This pathway divides into a right bundle branch and a left bundle branch. The signal goes down these branches to the ventricles, causing them to contract and pump blood out to the lungs and the rest of the body. The ventricles then relax, and the heartbeat process starts all over again in the SA node.

Electrical conduction and blood flow in AF

In AF, the heart’s electrical signal begins in a different part of the atria or the nearby pulmonary veins and is conducted abnormally. The signals don't travel through normal pathways, but may spread throughout the atria in a rapid, disorganized way. This can cause the atria to beat more than 300 times a minute in a chaotic fashion. The atria’s rapid, irregular, and uncoordinated beating is called fibrillation.

When the atria are fibrillating, the electrical message that starts in the atria spread to the ventricles. The jumbled electrical signals from the atria floods the AV node with electrical impulses. As a result, the ventricles also begin to beat too fast. However, the AV node can’t conduct the signals to the ventricles as fast as they arrive, so even though the ventricles may be beating faster than normal, they aren’t beating as fast as the atria. The atria and ventricles no longer beat in a coordinated way, and this lack of coordination creates a fast and irregular heart rhythm. In AF, the ventricles may beat up to 100–175 times a minute, in contrast to the normal rate of 60–100 beats a minute.

In AF, blood isn’t pumped into the ventricles as well as it should be, and the amount of blood pumped out of the ventricles is based on the randomness of the atrial beats. Thus, instead of the body receiving a constant, regular amount of blood from the ventricles, it receives rapid, small amounts and occasional random, larger amounts, depending on how much blood has flowed from the atria to the ventricles with each beat.

Diagnosis

For those people who don’t have symptoms, AF is often found during a physical exam or electrocardiogram (EKG) done for another purpose. Other times, AF is diagnosed after a person goes to the doctor because of symptoms. Doctors use several methods to diagnose AF, including family and medical history, a physical exam, and several diagnostic tests and procedures.

Family and medical history

In addition to evaluation of symptoms, family and medical histories are used to establish the risk, and therefore likelihood, of AF. Some risk factors include a history of heart disease, high blood pressure, diabetes, or thyroid problems in the patient or in the patient’s family. For a complete description of risks see Chances of Developing Atrial Fibrillation.

Physical exam

Physical exams for detecting AF focus on the heart function. Pulse, blood pressure, and listening to the rate and rhythm of the heartbeat are included in the exams. The lungs are checked for signs of heart failure, and signs of hyperthyroidism, such as swelling in the legs and feet or enlarged thyroid gland, are evaluated.

EKG

An EKG is a simple test that detects and records the electrical activity of the heart. It is the most useful test for diagnosing AF. It shows how fast the heart is beating and its rhythm (steady or irregular). It also records the timing of the electrical signals as they pass through each part of the heart. Portable EKG monitors, such as the Holter monitor or event monitor, are sometimes used to diagnose paroxysmal AF because an episode of AF may not occur during the standard EKG test.

Echocardiogram

Echocardiograms use sound waves to create a moving picture of the heart. An echocardiogram provides information about the size and shape of the heart and how well the heart chambers and valves are functioning. The test also can identify areas of poor blood flow to the heart, areas of heart muscle that aren’t contracting normally, and previous injury to the heart muscle caused by poor blood flow. In most of the cases of atrial fibrillation the left atrial chamber is dilated and this may facilitate the development of thrombosis that may cause thromboembolism in the brain vessels that, in turn, may cause ischemic stroke.

Transesophageal echocardiogram

A transesophageal echocardiogram, or TEE, takes pictures of the heart through the esophagus (the tube leading from the mouth to the stomach). The atria are deep in the chest and often can’t be seen very well on a regular echocardiogram. A doctor can see the atria much better with a TEE.

Blood tests

Blood tests check the levels of electrolytes and thyroid hormone. Electrolytes are minerals in blood and body fluids that are essential for normal health and functioning of the body’s cells and organs.

• TSH(thyroid stimulating hormone)
• chest x-ray
• blood pressure monitoring
• angiography
• TMT(treadmill test)
• BMI
• RBS

Treatment

People with no symptoms and no related heart problems may not need treatment. AF may even go back to a permanent normal heart rhythm on its own. However, some people who have AF for the first time do require intervention.

Repeated episodes of AF tend to cause changes to the electrical system of the heart, leading to persistent or permanent AF. Most people with persistent or permanent AF need treatment to control their heart rate and prevent complications.

Treatment for AF depends on the severity and frequency of symptoms as well as pre-existing heart disease. The treatment of AF has several goals.

• Prevent blood clots that may form in the atria, and thereby reduce the risk for stroke.
• Control how many times a minute the ventricles contract, which is called rate control. This is important because it allows the ventricles enough time to completely fill with blood.
• Restore the heart to a normal rhythm, which is called rhythm control. This allows the atria and ventricles to work together again to efficiently pump blood to the body.
• Treat any underlying disorder that’s causing or raising the risk of AF (e.g., hyperthyroidism).

General treatment options include medicines, medical procedures, and lifestyle changes.

Medications

The risk of a blood clot traveling from the heart to the brain and causing a stroke is increased in people who have AF. Preventing the formation of blood clots is probably the most important part of treating AF. Doctors prescribe blood-thinning medicines to prevent blood clots. These medicines include warfarin, aspirin, and heparin. Warfarin is actually the most effective medicine in people with risk factors for stroke albeit it need strict monitoring of doses to avoid or reduce the risk to develop hemorrhages.

Rate control

Other medicines are used to slow down the rate at which the ventricles are beating. These medicines help bring the heart rate to a normal level. Medicines used to control the heart rate include beta blockers (e.g., metoprolol and atenolol), calcium channel blockers (e.g., diltiazem and verapamil), and digitalis (digoxin). Several other medicines also are available. Ever since two landmark clinical trials, AFFIRM^[1] and RACE^[2], demonstrated that rate control was a safe and effective way to treat atrial fibrillation, rate control is the recommended strategy for most patients with AF—even though the heart rhythm continues to be abnormal and the heart doesn’t work as efficiently as it could. Most people feel better and can function well if their heart rate is well controlled.

Rhythm control

A second use of medications in atrial fibrillation is to control and maintain the heart’s rhythm. This approach is recommended for people who aren’t functioning well with rate control treatment or who have only recently started having AF. Frequently used medicines to control heart rhythm include amiodarone, sotalol, flecainide, propafenone, dofetilide, and ibutilide.

Restoring a normal heart rhythm is more difficult the longer AF is present. This is especially true for people who have had AF for six months or more. Restoring a normal rhythm also becomes less likely if the atria become enlarged or if any underlying heart disease becomes more severe. In these situations, the chance that AF will recur is high, even if medicines are being used.

Underlying causes

Medicine is often used to treat the underlying cause of the AF or risk factors. The medications may target an overactive thyroid, high blood pressure, or excessive weight.

Medical procedures

Although rate control is the preferred strategy to treat atrial fibrillation, there are some patients for whom the normal heart rhythm should be restored. This can be done with medications or with medical procedures.

Several procedures are used to restore heart rhythm in AF.

• Electrical cardioversion, which is a jolt of electricity delivered to the heart to "convert" the rhythm from AF back to a normal heart rhythm. This shock can break the pattern of abnormal electrical signals and restore a normal rhythm.
• Radiofrequency ablation, which is used to restore a normal heart rhythm when medicines or electrical cardioversion don’t work. In this procedure, a wire is inserted through a vein in the leg or arm and threaded to the heart. Radio wave energy is sent through the wire to destroy abnormal tissue that is believed to be disrupting the normal flow of electrical signals.
• Maze procedure, in which a surgeon makes small cuts or burns in the atria to reduce the chances of chaotic electrical activity happening in the atria.

Lifestyle

Lifestyle changes can reduce the risk of worsening AF. Reducing stress, quitting smoking, reducing salt intake, and eating healthily can all reduce risk.

Prevention

Healthy lifestyles lower the risk for heart disease and related complications, such as AF. Healthy lifestyles include the following:

• not smoking
• diets low in saturated fat, trans fat, and cholesterol and that includes a variety of grains, fruits, and vegetables
• regular physical activity
• maintaining a healthy weight

People with existing heart disease, or who have risk factors, may need to make additional lifestyle modifications to reduce the risk of AF:

• follow diets that reduce blood pressure
• keep cholesterol and triglyceride levels within normal ranges by using diet, exercise, and medications
• limit or avoid alcohol
• control blood sugar levels in people with diabetes

Living with Atrial Fibrillation

People who have AF can live normal, active lives. For some people, treatment can cure AF and return their heartbeat to a normal rhythm. For people who have permanent AF, treatment can successfully control symptoms and prevent complications.

Chances of Developing Atrial Fibrillation

AF is more common in people with heart diseases or conditions that affect the cardiovascular system:

• High blood pressure
• coronary artery disease and heart attack
• Heart failure
• Diabetes
• Obesity
• Rheumatic heart disease
• Overactive thyroid
• Chronic obstructive pulmonary disease
• Structural defects, such as mitral valve disorders
• Previous heart surgery
• Viral infections
• Obstructive sleep apnea syndrome
• Stress due to surgery or other severe diseases
• pericarditis (inflammation of the tissues surrounding the heart)
• congenital heart defects
• sick sinus syndrome (a condition in which the heart's electrical signals don't fire properly and the heart rate slows down; sometimes the heart will switch back and forth between a too-slow rate and a too-fast rate).

Recent evidence suggests that patients who receive high-dose steroid therapy are at increased risk of AF. This therapy, which is commonly used for asthma and certain inflammatory conditions, may act as a trigger in people who already have other risk factors for AF.

Related Problems

AF has two major complications: stroke and heart failure. Heart attack is another, rarer complication.

Stroke

During AF, the atria don’t pump all of their blood to the ventricles. Some blood pools in the atria. When this happens, a blood clot (also called a thrombus) can form. If the clot breaks off and travels to the brain, it can cause a stroke.

The illustration shows how a stroke can occur during atrial fibrillation. If a clot (thrombus) forms in the left atrium of the heart, a piece of it can break loose and travel to an artery in the brain, blocking blood flow through the artery. The lack of blood flow to the portion of the brain fed by the artery causes a stroke.

Heart failure

Heart failure occurs when the heart can’t pump enough blood to meet the body’s needs. Because the ventricles are beating very fast and aren’t able to properly fill with blood to pump out to the body, AF can lead to heart failure. Also, if the heart beats too fast for too long it can get weak, resulting in symptoms of congestive heart failure.

A buildup of fluid in the lungs can cause fatigue and shortness of breath, which are common symptoms of heart failure. Fluid also can build up in the feet, ankles, and legs, causing weight gain.

Clinical Trials

U.S.-based clinical trials of atrial fibrillation are ongoing.

Epidemiology

More than 2 million people in the United States have AF, and it affects both men and women. AF generally occurs in older people, mostly because they’re more likely to have heart disease or conditions that increase the risk of AF. AF is uncommon among young people.

References

1. ↑ Wyse DG, Waldo AL, DiMarco JP, et al. A comparison of rate control and rhythm control in patients with atrial fibrillation. N Engl J Med. 2002; 347: 1825–33. Abstract | Full Text
2. ↑ Van Gelder IC, Hagens VE, Bosker HA et al; Rate Control versus Electrical Cardioversion for Persistent Atrial Fibrillation Study Group. A comparison of rate control and rhythm control in patients with recurrent persistent atrial fibrillation. N Engl J Med. 2002 Dec 5;347(23):1834-40. Abstract | Full Text

External Links

Arrhythmia Diseases and Conditions Index from the U.S. National Heart, Lung and Blood Institute

Related Accredited Articles

1. Heart Beat: Unusual Triggers for Atrial Fibrillation
2. Content from Harvard Medical School