Atrial fibrillation

Atrial fibrillation is increasingly common with advancing age. During atrial fibrillation, the heart's two upper chambers (the atria) beat chaotically and irregularly — out of coordination with the two lower chambers (the ventricles) of the heart. The result is an irregular and often rapid heart rate that causes poor blood flow to the body and symptoms of heart palpitations, shortness of breath and weakness. Most people with atrial fibrillation have an increased risk of developing blood clots that may lead to stroke.

Atrial fibrillation is a common heart rhythm problem. More than 2 million Americans have atrial fibrillation, which can cause palpitations, shortness of breath, fatigue and stroke.

Atrial fibrillation is often caused by changes in your heart that occur as a result of heart disease or high blood pressure. Episodes of atrial fibrillation can come and go, or you may have chronic atrial fibrillation.

Although atrial fibrillation usually isn't life-threatening, it can lead to complications. Treatments for atrial fibrillation may include medications and other interventions to try to alter the heart's electrical system.

Symptoms

A heart in atrial fibrillation doesn't beat efficiently. It may not be able to pump an adequate amount of blood out to your body with each heartbeat, causing a drop in your blood pressure.

Some people with atrial fibrillation have no symptoms and are unaware of their condition until their doctor discovers it during a physical examination. Those who do have symptoms may experience:

• Palpitations, which are sensations of a racing, uncomfortable, irregular heartbeat or a flopping in your chest
• Weakness
• Lightheadedness
• Confusion
• Shortness of breath
• Chest pain

Atrial fibrillation may be:

• Sporadic. In this case it's called paroxysmal (par-ok-SIZ-mul) atrial fibrillation. You may have symptoms that come and go, lasting for a few minutes to hours and then stopping on their own.
• Chronic. With chronic atrial fibrillation, symptoms may last until they're treated.

Causes

To pump blood, your heart muscles must contract and relax in a coordinated rhythm. Contraction and relaxation are controlled by electrical signals that travel through your heart muscles.

Your heart consists of four chambers — two upper chambers (atria) and two lower chambers (ventricles). Within the upper right chamber of your heart (right atrium) is a group of cells called the sinus node. This is your heart's natural pacemaker. The sinus node produces the impulse that starts each heartbeat.

Normally, the impulse travels first through the atria, then through a connecting pathway between the upper and lower chambers of your heart called the atrioventricular (AV) node. As the signal passes through the atria, they contract, pumping blood from your atria into the ventricles below. A split second later, as the signal passes through the AV node through the right and left bundle branches to the ventricles, the ventricles contract, pumping blood out to your body.

In atrial fibrillation, the upper chambers of your heart (atria) experience chaotic electrical signals. As a result, they quiver. The AV node — the electrical connection between the atria and the ventricles — is overloaded with impulses trying to get through to the ventricles. The ventricles also beat rapidly, but not as rapidly as the atria. The reason is because the AV node is like a highway on-ramp — only so many cars can get on at one time. The result is an irregular and fast heart rhythm. The heart rate in atrial fibrillation may range from 100 to 175 beats a minute. The normal range for a heart rate is 60 to 100 beats a minute.

Possible causes
Abnormalities or damage to the heart's structure is the most common cause of atrial fibrillation. Diseases affecting the heart's valves or pumping system are common causes, as is long-term high blood pressure. However, some people who have atrial fibrillation don't have underlying structural heart disease, a condition called lone atrial fibrillation. In lone atrial fibrillation, the cause is often unclear. Serious complications are usually rare in lone atrial fibrillation.

Possible causes of atrial fibrillation include:

• High blood pressure
• Heart attacks
• Abnormal heart valves
• Congenital heart defects
• An overactive thyroid or other metabolic imbalance
• Exposure to stimulants, such as medications, caffeine or tobacco, or to alcohol
• Sick sinus syndrome — this occurs when the heart's natural pacemaker stops functioning properly
• Emphysema or other lung diseases
• Previous heart surgery
• Viral infections
• Stress due to pneumonia, surgery or other illnesses
• Sleep apnea

Risk factors

• Age. The older you are, the greater your risk of developing atrial fibrillation. As you age, the electrical and structural properties of the atria can change. This may lead to the breakdown of the normal atrial rhythm.
• Heart disease. Anyone with heart disease, including valve problems, history of heart attack and heart surgery, faces an increased risk of atrial fibrillation.
• Other chronic conditions. People with thyroid problems, high blood pressure, sleep apnea and other medical problems have an elevated risk of atrial fibrillation.
• Alcohol use. Use of alcohol, especially binge drinking, can trigger an episode of atrial fibrillation.
• Family history. An increased risk of atrial fibrillation runs in some families. In some of these cases, specific genes have been identified as the likely cause of atrial fibrillation.

Tests and diagnosis

To make a diagnosis of atrial fibrillation, your doctor may do tests that involve the following:

• Electrocardiogram (ECG). Patches with wires (electrodes) are attached to your skin to measure electrical impulses given off by your heart. Impulses are recorded as waves displayed on a monitor or printed on paper.
• Holter monitor. This is a portable machine that records all of your heartbeats. You wear the monitor under your clothing. It records information about the electrical activity of your heart as you go about your normal activities for a day or two. You can press a button if you feel symptoms, and then your doctor can figure out what heart rhythm was present at that moment.
• Event recorder. This device is similar to a Holter monitor except all of your heartbeats are not recorded. There are two recorder types: One uses a phone to transmit signals from the recorder while you're experiencing symptoms. The other type is worn all the time (except while showering) for as long as a month. Event recorders are especially useful in diagnosing rhythm disturbances that occur at unpredictable times.
• Echocardiogram. In this test, sound waves are used to produce a video image of your heart. Sound waves are directed at your heart from a wand-like device (transducer) that's held on your chest. The sound waves that bounce off your heart are reflected back through your chest wall and processed electronically to provide video images of your heart in motion to detect underlying structural heart disease.
• Blood tests. These help your doctor rule out thyroid problems or blood chemistry abnormalities that may lead to atrial fibrillation.

Complications

Sometimes, atrial fibrillation can lead to the following complications:

• Stroke. In atrial fibrillation, the chaotic rhythm may cause blood to pool in your atria and form clots. If a blood clot forms, it could dislodge from your heart and travel to your brain. There it might block arterial blood flow, causing a stroke. The risk of stroke in atrial fibrillation depends on your age (you have a higher risk as you age) and on whether you have high blood pressure or a history of heart failure or previous stroke, and other factors. Most people with atrial fibrillation have a much greater risk of stroke than do those who don't have atrial fibrillation. Medications such as blood thinners can greatly lower your risk of stroke or damage to other organs caused by blood clots.
• Heart failure. Atrial fibrillation alone, especially if not controlled, may weaken the heart, leading to heart failure — a condition in which your heart can't circulate enough blood to meet your body's needs.

Treatments and drugs

Treatments for atrial fibrillation include medications and procedures that attempt to either reset the heart rhythm back to normal or control the heart rate so that the heart doesn't beat dangerously fast, though it may still beat irregularly. Treatments also include blood thinners to prevent blood clots.

The treatment option best for you will depend on how long you've had atrial fibrillation, how bothersome your symptoms are and the underlying cause of your atrial fibrillation. Generally, the goals of treating atrial fibrillation are to:

• Reset the rhythm — or — control the rate
• Prevent blood clots

Sometimes atrial fibrillation will correct or "reset" itself. In some people, a specific event or an underlying condition, such as a thyroid disorder, may trigger atrial fibrillation. If the condition that triggered your atrial fibrillation can be treated, you might not have any more heart rhythm problems — or at least not for quite some time. If your symptoms are bothersome or if this is your first episode of atrial fibrillation, your doctor may attempt to reset the rhythm. Or it may be best to simply take medications to control the heart rate and prevent blood clots.

The best strategy for you depends on many factors, including whether you have other problems with your heart and how well you tolerate the medications available to treat atrial fibrillation or control the rate. In some cases, you may need a more invasive treatment, such as catheter or surgical techniques.

Resetting the rhythm
Ideally, to treat atrial fibrillation, the heart rate and rhythm are reset to normal. This can be accomplished in some cases, depending on the underlying cause of atrial fibrillation and how long you've had it. To correct atrial fibrillation, doctors may be able to reset your heart to its regular rhythm (sinus rhythm) using a procedure called cardioversion. Cardioversion can be done in two ways:

• Cardioversion with drugs. This form of cardioversion uses medications called anti-arrhythmics to help restore normal sinus rhythm. Depending on your heart condition, your doctor may recommend trying intravenous or oral medications to return your heart to normal rhythm. This is often done in the hospital with continuous monitoring of your heart rate. If your heart rhythm returns to normal, your doctor often will prescribe the same anti-arrhythmic or a similar one long term to try to prevent recurrent spells of atrial fibrillation.
• Electrical cardioversion. In this brief procedure, an electrical shock is delivered to your heart through paddles or patches placed on your chest. The shock stops your heart's electrical activity for a split second. When your heart begins again, the hope is that it resumes its normal rhythm. The procedure is performed under anesthesia.

Before undergoing cardioversion, you may be given a blood-thinning medication, such as warfarin (Coumadin), for several weeks to reduce the risk of blood clots and stroke. Alternatively, you may undergo transesophageal echocardiography — a test to exclude the presence of a blood clot — just before cardioversion. In transesophageal echocardiography, a tube is passed down your esophagus and detailed ultrasound images are made of your heart. Unless the episode of atrial fibrillation lasted less than 24 hours, you will require warfarin for at least four to six weeks after cardioversion to prevent a blood clot from forming even after your heart is back in normal rhythm.

Maintaining normal rhythm
After electrical cardioversion, anti-arrhythmics often are prescribed to help prevent future episodes of atrial fibrillation. Commonly used medications include amiodarone (Cordarone, Pacerone), propafenone (Rythmol), procainamide (Procanbid) and dofetilide (Tikosyn). Although these drugs can help maintain sinus rhythm in many people, they can cause side effects, such as nausea, dizziness and fatigue. In rare instances, they may cause ventricular arrhythmias — life-threatening rhythm disturbances originating in the heart's lower chambers. These medications may be needed indefinitely. Unfortunately, even with medications, the chance of another episode of atrial fibrillation is high.

Rate control
Sometimes atrial fibrillation can't be converted back to a normal heart rhythm. Then the goal is to slow the heart rate (rate control). Traditionally, doctors have prescribed the medication digoxin (Lanoxin). It can control heart rate at rest but not as well during activity. Most people require additional or alternative medications, such as calcium channel blockers or beta blockers. In general, your heart rate should be between 60 and 100 beats a minute when you're at rest. Your doctor can give you guidelines for your maximal heart rate.

Some people may not be able to tolerate medications, or medications don't work to control the heart rate. In these cases, AV node ablationmay be an option.

AV node ablation involves applying radio frequency energy to your atrioventricular (AV) node through a long, thin tube (catheter) to destroy this small area of tissue. The procedure prevents the atria from sending electrical impulses to the ventricles. The atria continue to fibrillate, though, and anticoagulant medication is still required. A pacemaker is then implanted to establish a normal rhythm.After AV node ablation, you'll need to continue to take anticoagulant medications to reduce the risk of stroke because your heart is still in atrial fibrillation.

Surgical and catheter interventions
Sometimes medications or cardioversion to control atrial fibrillation doesn't work. In those cases, your doctor may recommend a procedure to destroy the area of heart tissue responsible for the erratic electrical signals and restore your heart to a normal rhythm. These options can include:

• Radiofrequency catheter ablation. In many people who have atrial fibrillation and an otherwise normal heart, atrial fibrillation is caused by rapidly discharging triggers, or "hot spots." These hot spots are like abnormal pacemaker cells that fire so rapidly that the atria fibrillate. When present, these triggers are most commonly found in the pulmonary veins, the veins that return blood from the lungs to the heart. Radio frequency energy directed to these hot spots through a catheter (called radiofrequency ablation, pulmonary vein ablation or pulmonary vein isolation) may be used to destroy these hot spots, scarring the tissue and thereby disrupting the erratic electrical signals. This eliminates the arrhythmia without the need for medications or implantable devices. In some cases, additional spots are treated in your heart — depending on the electrical circuits found — and sometimes other types of catheters that can freeze the heart tissue (cryotherapy) are used.

• Surgical maze procedure. The maze procedure is often done during an open-heart surgery. Using a scalpel, doctors create several precise incisions in the atria to create a pattern or maze of scar tissue. Because scar tissue doesn't carry electricity, it interferes with stray electrical impulses that cause atrial fibrillation. Radio frequency or cryotherapy can also be used, and there are several variations of the surgical maze technique. The procedure has a high success rate, but because it usually requires open-heart surgery, it's generally reserved for people who don't respond to other treatments or when it can be done during other necessary heart surgery, such as coronary artery bypass surgery or heart valve repair. Some people require a pacemaker after the procedure.

  Newer and less invasive techniques are being developed to create the atrial scar tissue. Doctors at some centers use radio frequency or cryotherapy applied to the outside surface of the heart through a small chest incision or through a scope placed into the chest cavity (thorascopic approach). Microwave, laser and ultrasound energy are also being studied as options to perform the maze procedure.

Preventing blood clots
Most people who have atrial fibrillation or who are undergoing certain treatment for atrial fibrillation are at especially high risk of blood clots that can lead to stroke. The risk is even higher if other heart disease is present along with atrial fibrillation. Your doctor may prescribe blood-thinning medications (anticoagulants), such as warfarin (Coumadin) or aspirin, in addition to medications designed to treat your irregular heartbeat. Many people have spells of atrial fibrillation and don't even know it — so you may need lifelong anticoagulants even after your rhythm has been restored to normal.

Atrial flutter
Atrial flutter is similar to atrial fibrillation, but slower. If you have atrial flutter, the abnormal heart rhythm in your atria is more organized and less chaotic than in the abnormal patterns common with atrial fibrillation. Sometimes you may have atrial flutter that develops into atrial fibrillation and vice versa. The symptoms, causes and risk factors of atrial flutter are similar to atrial fibrillation. For example, strokes are a common concern in someone with atrial flutter.

One difference between atrial flutter and atrial fibrillation is that many people with atrial flutter respond better to treatment such as catheter ablation. As with atrial fibrillation, atrial flutter is usually not life-threatening when it's properly treated.