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Creating order from chaos: Taming atrial fibrillation

Content provided by the Faculty of the Harvard Medical School

Treatment focuses on controlling the heart's rate and rhythm and preventing stroke.

Imagine an orchestra directed by many conductors, all with different scores. Each musician follows whichever conductor and score he or she chooses, and switches when the mood strikes. The result would be noise, not music. That's what happens with atrial fibrillation. Instead of getting a single "beat now" signal from the heart's natural pacemaker every second or so, the upper chambers of the heart (the atria) get bombarded by many signals. The result is a chaotic heart rhythm that can interfere with daily life and increases the chances of having a stroke.

Atrial fibrillation isn't a one-size-fits-all condition. It's always there for some people and comes and goes in others. It causes symptoms in some people; others don't feel a thing.

It would be terrific if this common condition could be easily cured. That isn't currently the case. But there are ways to halt or minimize its symptoms and guard against stroke. How best to do this depends on you, the nature of your atrial fibrillation, and your cardiac and general health.

What is atrial fibrillation?

A normal heartbeat starts in the right atrium in a group of cells known as the pacemaker or sinoatrial node. It generates a pulse of electricity that flashes across the atria, causing them to contract. The contraction forces blood into the two lower chambers (the ventricles). The electrical signal doesn't instantly spread into the ventricles. It enters a cluster of cells known as the atrioventricular node that briefly delays the signal before sending it on to the ventricles. The delay gives the ventricles a chance to fill with blood before contracting.

In people with atrial fibrillation, muscle cells in the atria are activated by stray impulses from the pulmonary veins which carry blood from the lungs to the heart, or from wayward circuits that multiply the signal instead of sending it on a one-way trip to the atrioventricular node. This flurry of electrical activity makes the atria contract hundreds of times a minute. Instead of rhythmically squeezing and relaxing, they quiver and convulse (the medical term is fibrillate), looking like pulsating bags of worms.

Fortunately, the atrioventricular node acts like a circuit breaker. Although it may receive 300 or more signals a minute, it can handle only a maximum of about 180 per minute — even less in older people. Without this check, the ventricles would have little time to fill with blood before contracting. The trickle of blood they send to the body wouldn't sustain life.

Quivering atria do a poor job of pushing blood into the ventricles. Instead, it moves sluggishly through the atria or just sits in them. This allows clots to form. If these get into the bloodstream, they can block arteries in the brain, causing a stroke. The American Heart Association estimates that atrial fibrillation accounts for almost 150,000 strokes a year.

The chaos of atrial fibrillation

The chaos of atrial fibrallation

Stray electrical signals and circuits in the upper chambers of the heart cause the atria to beat fast and erratically.

Causes and consequences

Many cases of atrial fibrillation can be chalked up to the gradual aging of the heart's circuitry. It can arise from anything that raises the pressure inside the atria or makes them work harder, including valve trouble, lung disease, high blood pressure, and heart failure. Other causes include heart attack, drinking too much alcohol, an overactive thyroid gland, stimulants such as caffeine or cocaine, viral infections, dehydration, and stress. In about one in five people, the problem can't be traced to a specific cause. This is called lone atrial fibrillation.

Some people don't notice anything amiss as their atria beat wildly. Others do. Symptoms range from a fluttering sensation in the chest to palpitations (feeling the heart pause or skip a beat), shortness of breath, chest pain, or fainting. Symptoms can range from mildly annoying to disabling. Some people experience them when they are relaxed or falling asleep, or after they've been drinking alcohol. In others, symptoms are triggered by exercise or emotional stress.

Atrial fibrillation is classified by its duration.

  • Paroxysmal atrial fibrillation comes and goes; the abnormal rhythm disappears on its own within a week, and often within a day.

  • Persistent atrial fibrillation lasts longer than seven days and requires medication or other treatment to restore a normal rhythm.

  • Permanent atrial fibrillation endures in spite of attempts to end it (or because no attempts have been made).

There are three main thrusts to treating atrial fibrillation: controlling the heart rate, controlling the heart rhythm, and preventing stroke.

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