Over the past several years, atrial fibrillation, the most common type of irregular heartbeat, has been increasingly recognized as a potentially serious condition. Physicians used to think it was a relatively harmless cardiac arrhythmia that didn't need to be treated unless it caused symptoms or was associated with valvular heart disease.

But all that has changed. Atrial fibrillation (AF) is well known to be an independent risk factor for stroke and death. Indeed, stroke risk is increased more than fivefold in people with AF, and their strokes are nearly twice as likely to be fatal as those in people without the rhythm abnormality.

AF has become an active area of research: some studies are comparing the efficacy of drug treatments that control heart rhythm or rate; others are evaluating the risks and benefits of electrical therapies and surgery.

The condition affects about 2 million Americans, and its incidence rises with age. Although AF does occur in middle-aged adults and some younger ones, it is uncommon. Data from the Framingham Heart Study indicate that 6.5% of people 50-59 have the condition and that the rate rises steadily to 31% in people 80 and older.

When the heart is functioning properly, its four chambers beat in a well-orchestrated way. (The upper two chambers are called the right and left atria; the lower two are the right and left ventricles.) A chamber contracts, or beats, when triggered by an electrical impulse. This signal is generated by the sinus node, a small bundle of specialized cells in the wall of the right atrium.

In AF, the heart's electrical impulses get out of whack. This causes the atria to quiver erratically instead of beating forcefully at a regular rate. As a result, blood isn't pumped completely out of the atria, allowing it to pool and clot. If a piece of a clot breaks off and travels to an artery that feeds the brain, the blockage of blood flow will likely cause a stroke.

Unfortunately, stroke is the leading cause of disability in the United States and the third most common cause of death. Although strokes can be prevented, they usually cannot be treated. (For more on stroke, see Harvard Health Letter, July 1998.) Indeed, stroke prevention is a vital component of AF treatment.

The root of the problem

Several conditions can trigger AF. The most common are high blood pressure, congestive heart failure, and prior heart attack. Other causes include valvular heart disease, an overactive thyroid, infections, and excessive alcohol consumption. Sometimes, doctors can find no apparent cause.

In most cases of AF, a person will experience such symptoms as heart palpitations, chest discomfort, shortness of breath, exercise intolerance, fatigue, or lightheadedness.

Although the condition is chronic for most people who have it, in some it occurs intermittently and is known as paroxysmal. This type is characterized by recurrent episodes that either resolve on their own or in response to medical treatment. People with episodic palpitations are often asked to wear a portable heart monitor for 24 hours to document the duration and frequency of the episodes.

Often, AF can go on for hours or even a day or two without causing harm; however, the risk of clots is highest when AF has not stopped on its own or has gone untreated for 48 hours or more. Evidence suggests that many people with intermittent AF will eventually develop the chronic form.

Treating it right

There are three goals in treating AF: slowing the heart rate, preventing clots and strokes, and restoring a normal heart rhythm when possible. Digoxin is generally used to slow the heart rate either alone or in combination with other drugs such as beta-blockers (propranolol, atenolol) or calcium channel blockers (verapamil).

Although these medications reduce discomfort in many people, they may have side effects and they do not reduce stroke risk. Long-term use of warfarin (Coumadin), an anticoagulant, has been shown to prevent up to 80% of strokes in people with AF, but there is evidence that the medication is underused. A study published last year in the journal Stroke found that of 272 patients with AF, only 38% were receiving warfarin. Many experts believe that the majority of people with AF should be taking the anti-clotting drug. Aspirin, which also prevents clots, is far less effective than warfarin but is sometimes used when the risk of stroke is very low.

Some doctors have been hesitant to prescribe warfarin because it increases the risk for bleeding complications. Increased bleeding from a nick or a cut may be inconsequential, but if it results from a stomach ulcer or serious fall, for example, it could be life-threatening. Unfortunately, warfarin use is often seen by both doctors and patients as an inconvenience because people who take the medication must get periodic blood tests so that the physician can monitor and adjust the dose to keep it at a safe level.

Although testing may be a bit of a nuisance and bleeding problems are a possibility, experts do not consider these good enough reasons for anyone at high risk for stroke to forego warfarin. Someone defined as high risk has AF and more than one additional risk factor for stroke, such as congestive heart failure, a history of hypertension, previous stroke, or blood clots. A person at moderate risk may have AF and one additional risk factor; people in this category should weigh the pros and cons of warfarin use with their physician. In some cases, aspirin may be the drug of choice. Those at low risk, who have AF but no other risk factors for stroke, are the best candidates for aspirin therapy.

The third goal of treatment, establishing a normal heart rhythm, is difficult to achieve in people with AF. Doctors sometimes use cardioversion, in which a brief jolt of electricity is applied to the patient's heart. Most people require medication afterward to maintain a normal heart rhythm, but it is not always effective.

Because drugs can only control, not cure, AF, researchers are setting their sights on therapies such as implantable pacemakers and surgery. Occasionally, an open-heart operation called the "maze" procedure is performed in which a surgeon creates tiny maze-clike orridors in the heart; this seems to stop its chaotic electrical activity. Investigators are hoping to develop less invasive catheter-based versions of this procedure that could be widely used and would cure AF altogether. Until then, the best medicine for most people with AF is therapy to slow the heart rate and warfarin or aspirin for stroke prevention.

courtesy: Health Allianace