Atrial fibrillation is a common heart rhythm problem. More than 2 million Americans have this condition, which can cause palpitations, shortness of breath, fatigue and stroke. The condition is increasingly common with advancing age. It affects less than 1 percent of Americans younger than 60, but as many as one in 10 people older than 80.
In atrial fibrillation, the heart's two upper chambers beat chaotically. And they don't beat in coordination with the two lower chambers of the heart. The result is an irregular and often rapid heart rate.
Atrial fibrillation is often caused by changes in your heart that occur with age or as a result of heart disease or high blood pressure. Atrial fibrillation may be a sporadic condition, or it may be chronic.
Although atrial fibrillation usually isn't life-threatening, it can lead to complications. Treatments for atrial fibrillation vary from person to person. But they may include medications and other interventions to try to alter the heart's electrical system.
Signs and 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.
Although some people with atrial fibrillation have no symptoms, other people experience:
• Palpitations, which are sensations of a racing, uncomfortable, irregular heartbeat or a flopping in your chest
• 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 last until they're treated.
• Some people with atrial fibrillation have no symptoms and are unaware of their condition until their doctor discovers it during a physical examination.
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 pacemaker. The sinus node produces the impulse that starts each heartbeat.
During a normal rhythm, 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 to the ventricles, the ventricles contract, pumping blood out to your body. Each contraction is a heartbeat.
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.
Abnormalities in the heart's structure are the most common cause of atrial fibrillation. Diseases affecting the heart's valves or pumping system also are likely causes, as is long-term high blood pressure. However, some people who have atrial fibrillation don't have underlying heart disease, a condition called lone atrial fibrillation. In lone atrial fibrillation, the cause is often initially unclear.
Possible causes of atrial fibrillation include:
• High blood pressure
• Abnormal heart valves
• Congenital heart defects
• An overactive thyroid or other metabolic imbalance
• Exposure to heart stimulants, such as 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
The older you are, the greater your risk of 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.
Anyone with heart disease faces an increased risk of atrial fibrillation. Also, people with thyroid problems, diabetes and high blood pressure have an elevated risk of atrial fibrillation. Obesity also may play a role in the development of atrial fibrillation.
Screening and diagnosis
To make a diagnosis of atrial fibrillation, your doctor may conduct cardiac tests such as:
• 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 testing. This is a portable version of an ECG. It's especially useful in diagnosing rhythm disturbances that occur at unpredictable times. 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.
• Echocardiogram. In this test, sound waves are used to produce a video 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.
• Blood tests. These help your doctor rule out thyroid problems or blood chemistry abnormalities that may lead to atrial fibrillation.
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 blood flow, causing a stroke. The risk of stroke in atrial fibrillation depends on your age (you have a higher risk as you age), on whether you have high blood pressure, a history of heart failure or a previous stroke, and other factors. People with atrial fibrillation have a much greater risk of stroke than do those who don't have atrial fibrillation. A blood clot can also lodge in other blood vessels, such as those supplying the kidneys or legs. Medications such as blood thinners can greatly lower your risk of stroke or damage to other organs caused by blood clots.
• Congestive heart failure. Atrial fibrillation alone 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 for atrial fibrillation include medications and procedures to regulate heart rhythm. The goals of treating atrial fibrillation include:
• Restoring the heart to a normal rhythm (rhythm control)
• Slowing the heart rate (rate control)
• Preventing blood clots
Cardioversion: Restoring the heart to a normal rhythm
In order to correct atrial fibrillation — to reset your heart to its regular rhythm (sinus rhythm) — doctors often perform a procedure called cardioversion. This can be done in two ways:
• Cardioversion with drugs. This uses medications called anti-arrhythmics, which are designed to stop the atria's quivering and restore normal sinus rhythm. Commonly used medications include amiodarone (Cordarone, Pacerone), propafenone (Rythmol), procainamide (Procanbid), sotalol (Betapace) and dofetilide (Tikosyn). Although these drugs can effectively restore sinus rhythm in many people, they can cause side effects, such as nausea, dizziness and fatigue. In rare instances, they may actually cause an increase in heart rate. These medications may be needed indefinitely.
• 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 it begins again, it may resume normal rhythm. The procedure is performed under light anesthesia. Beforehand, doctors occasionally prescribe ibutilide (Corvert). This anti-arrhythmic medication can improve the procedure's success rate, especially if electrical cardioversion alone hasn't achieved sinus rhythm.
Before undergoing cardioversion, you may be given a blood-thinning medication for several weeks to reduce the risk of blood clots in the atria and the risk of 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.
After electrical cardioversion, anti-arrhythmics are often prescribed to help prevent future episodes of atrial fibrillation. Unfortunately, even with medications, the chance of another episode of atrial fibrillation is high.
Slowing the heart rate
When atrial fibrillation can't be converted, 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. These more consistently control heart rate both at rest and during activity. 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.
Preventing blood clots
You may be at especially high risk of stroke if you have atrial fibrillation and heart disease. In this situation, your doctor may prescribe blood-thinning medications (anticoagulants), such as warfarin (Coumadin) or aspirin, in addition to medications designed to treat your irregular heartbeat.
In some situations, people with difficult-to-control atrial fibrillation who haven't been helped by other treatments may benefit from more-invasive techniques, such as:
• AV nodal ablation with pacemaker implantation. This involves applying radiofrequency 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.
• Maze procedure. In this open-heart surgery, a maze of incisions made in the atria blocks the flow of excess electrical impulses within the atria. Some people require a pacemaker after the procedure.
• Pacemaker implantation. A pacemaker is a medical device that helps regulate the heartbeat. The device, smaller than a matchbox, is placed under the skin near the collarbone. A wire extends from the device to the heart. If a pacemaker detects a heart rate that's too slow or no heartbeat at all, it emits electrical impulses that stimulate your heart to speed up or begin beating again. The most common use of pacemakers is for people with atrial fibrillation in one of two situations. First, if the medications used to prevent atrial fibrillation or control the heart rate lead to excessively slow heartbeats, then you need a pacemaker. Second, pacemakers are needed after AV nodal ablation.
• Pulmonary vein ablation. In many people who have atrial fibrillation and an otherwise relatively 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. Catheter ablation (cautery) to electrically isolate the veins can stop them from starting atrial fibrillation. In the procedure, energy is applied through the tip of the catheter at the junction of the pulmonary veins and the left atrium. This eliminates the arrhythmia without the need for medications or implantable devices.
Many people with atrial fibrillation need to make important lifestyle changes that improve the overall health of their heart. Your doctor may advise that you:
• Eat heart-healthy foods
• Reduce your salt intake, which can help lower blood pressure
• Increase your physical activity
• Quit smoking
Mental stress can exacerbate atrial fibrillation. Taking steps to reduce stress in your life may help calm your nerves — and your heart. Cutting back on caffeine and alcohol, which can overstimulate the heart and trigger an episode of atrial fibrillation, may also be beneficial.
It's also important to be careful when taking over-the-counter (OTC) medications. Some, such as cold medicines containing pseudoephedrine, contain stimulants that can trigger atrial fibrillation. Also, some OTC medications adversely interact with anti-arrhythmic medications.
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