Atrial fibrillation is a heart rhythm disorder in which the upper chambers of the heart (the atria) beat fast and irregularly.
Normally, the muscular walls of the right and left atria contract at the same time, pumping blood into the lower two chambers (the ventricles). Then the walls of the ventricles contract at the same time, pumping blood to the rest of the body.
How is this coordinated? A normal heartbeat starts with an electrical impulse that comes from the sinus node, a cluster of cells in the right atrium. That signal causes the atria to beat, pumping blood into the ventricles. Then it travels to another part of the heart called the atrioventricular node, located in the center of the heart between the atria and the ventricles. From there, the signal travels down to the ventricles, and causes them to beat, sending blood throughout the body.
During atrial fibrillation, many uncoordinated electrical impulses barrage the atria. Instead of contracting in a forceful, coordinated way, the atria quiver.
In atrial fibrillation, the heartbeat is rapid and irregular. A normal heartbeat is 60 to 100 beats per minute, and very regular: beat...beat...beat. In atrial fibrillation, the atria may contract 400 times a minute, and irregularly: beat.beat...beat....beat.....beat.beat.beat....beat.
Quivering atria don't move all of the blood along to the ventricles. When blood sits in the atria, clots can form. Such clots can cause serious problems. They can travel out of the heart and get stuck in an artery to the lungs (causing a pulmonary embolism), an artery to the brain (causing a stroke), or an artery elsewhere in the body.
Symptoms of atrial fibrillation
Atrial fibrillation often doesn't cause any symptoms. When symptoms occur, they can include:
- shortness of breath
- chest pain
Some people with atrial fibrillation have periods of normal heartbeats and periods of atrial fibrillation. In others, atrial fibrillation is constant.
Diagnosing atrial fibrillation
Your story of your symptoms and your and your family's medical history are important for diagnosing atrial fibrillation. Your doctor will check your heart rate and rhythm, as well as your pulse. In atrial fibrillation, the pulse often doesn't match the heart's sounds.
A diagnosis of atrial fibrillation is usually confirmed with an electrocardiogram (ECG). This test records the heart's electrical activity. Because atrial fibrillation can come and go, a standard ECG may be normal.
If that happens, you may be asked to wear a portable ECG machine called a Holter monitor for 24 hours. When symptoms appear less frequently than once a day, you may need an event recorder. It records every heartbeat, but only saves the few seconds worth before and after you push a button to signal you've felt a possible symptom of atrial fibrillation. People may wear an event recorder for a week or more.
Treating atrial fibrillation
Treatments for atrial fibrillation may depend on the cause. If the cause is coronary artery disease, treatment may consist of:
- lifestyle changes
- cholesterol-lowering medications
- blood pressure medications
- coronary artery bypass surgery
Atrial fibrillation caused by an excess of thyroid hormones can be treated with medication or surgery. When rheumatic heart disease is the cause, surgery to replace heart valves damaged by the disease may be needed.
Treating the first attack
When a person develops atrial fibrillation for the first time (or the first few times), doctors generally try to restore a normal heart rhythm. This may be done with medication. Another option is electrical cardioversion: a small shock delivered to the chest. This can reboot the heart and restore a normal rhythm. Although this procedure works in most cases, more than half of people eventually develop atrial fibrillation again.
There are two main medication options for people with atrial fibrillation: rate control and rhythm control.
One way to treat atrial fibrillation is to allow the atria to beat irregularly but to slow how quickly the heart beats. This is called rate control. Medicines used to slow the heart rate include beta blockers, calcium-channel blockers, and digoxin.
Another way to treat atrial fibrillation is to try to restore a normal heart rhythm. This is called rhythm control. Several drugs can help do this, but they often have more harmful side effects than drugs used for rate control.
The most potent drugs for keeping the heart out of atrial fibrillation include amiodarone, flecainide, dofetilide, propafenone, and sotalol.
Rhythm control versus rate control
For the average person with atrial fibrillation, large studies have found that rhythm control and rate control work equally well.
Procedures to halt atrial fibrillation
A nondrug treatment that can keep the heart from repeatedly going back into atrial fibrillation is radiofrequency catheter ablation.
In this procedure, a thin, flexible tube called a catheter is inserted into a vein in the groin and carefully maneuvered into the heart. The tip of the catheter carries a device that can emit radio waves. They zap specific clusters of cells that trigger the abnormal electrical signals that cause atrial fibrillation. If it works, radiofrequency catheter ablation can stop atrial fibrillation and eliminate its symptoms.
Radiofrequency catheter ablation is not always effective, it's effect can wear off over time, and it can cause serious adverse effects. It's important to talk to a doctor about the balance of benefits and risks.
A more invasive procedure, called the maze operation, is done to create scars in the atria. This open-heart surgery prevents abnormal electrical activity from spreading and causing atrial fibrillation.
Atrial fibrillation can cause blood to pool in the atria and form clots. Most people with atrial fibrillation need to take anticoagulant medication to prevent blood clots.
For decades, the drug used most often was warfarin. Like any blood thinning drug, it has risks: a drug that reduces the risk of blood clotting thereby increases the risk of bleeding. Warfarin also needs to be monitored with periodic blood tests to make sure the dose of warfarin has thinned the blood just enough and not too much.
Several newer drugs do not require the periodic monitoring. They include apixaban (Eliquis), dabigatran (Pradaxa), and rivaroxaban (Xarelto). They work as well as warfarin but are considerably more expensive. And less is known about their possible side effects.