HMI World | Around Harvard

MAY / JUNE 2006

This article originally appeared in the April 2006 Harvard Health Letter and is provided courtesy of Harvard Health Publications.

Atrial fibrillation: Beyond drug therapies

Medications are the first treatment for atrial fibrillation, but if drugs don’t do the job, there are other options.

Atrial fibrillation occurs when the heart’s upper chambers (the atria) race or quiver instead of keeping a normal rhythm. The symptoms include lightheadedness, fatigue, and an erratic or racing heartbeat (palpitations). It’s the most common form of cardiac arrhythmia, affecting some 2.2 million Americans. Unlike ventricular fibrillation, a dysfunction of the heart’s main pumping chambers, atrial fibrillation usually isn’t immediately life-threatening. But as doctors learn more about it, they’re seeing a greater need for treatment.

An older heart is more likely to develop atrial fibrillation than a younger one. In our 50s, only 1 in 200 of us has atrial fibrillation; by the time we reach our 80s, that ratio is 1 in 12. Atrial fibrillation in younger people often has a fairly benign prognosis. But after about age 60, it’s a more serious problem. It can increase the chances of developing heart failure and of having a stroke. If the atria don’t contract properly, blood pools inside them, and clots may form. If a clot breaks free and travels to the brain, it can cause a stroke. Clots can also travel to other parts of the body and cause harmful obstructions in blood vessels supplying the bowels and legs.

Atrial fibrillation is becoming more common for demographic reasons: The baby boom generation is entering its 60s. But even the age-adjusted numbers are going up. Doctors aren’t sure why.

Medications are the first-line treatment, but they don’t work for everyone. Some patients continue to have symptoms. Many cannot tolerate the side effects. Medications that target the arrhythmia directly, such as amiodarone (Cordarone), have a particularly high rate of unacceptable side effects. Often anticlotting medications are necessary, and that means frequent blood tests and a risk for bleeding.

So there is a lot of interest in the alternatives. Each has advocates, and weighing the options isn’t easy. Financial interests cloud the waters. And as is so often the case when it comes to procedures, this isn’t an area where unbiased studies map out a clear-cut course of action. We hope, though, to at least give you the general lay of the land.

Cardioversion
Usually patients go on to nondrug therapies after medications have failed, but cardioversion is an exception. It can be used with, or even before, drug therapy.

Cardioversion is a bit like pushing your heart’s reset button: It allows the heart to reestablish a regular rhythm by interrupting the abnormal one with an electric shock (or sometimes with medications). This isn’t what you may have seen on “ER” and other TV shows. That’s ventricular defibrillation, used to jump-start the heart’s main pumping chambers. Sometimes, though, doctors use the same machine for cardioversion, and the same amount of energy. Patients are anesthetized or sedated for the procedure.

A day or two beforehand, patients are sometimes started on an anti-arrhythmia medication (if they’re not taking one already). The medication improves the chances that the normal rhythm will persist after cardioversion. In some cases, just starting the drug restores the rhythm and makes the shock part of the treatment unnecessary.

The vast majority of the time, cardioversion works to restore a normal rhythm. How long it will last is the wild card. The prospects for long-term success depend partly on how long a patient has had atrial fibrillation. If it has developed recently, within a year or so, the success rate reaches 90%, at least in some studies. After that, the percentages go down. Cardioversion is safe with a low complication rate.

Pacemakers and defibrillators
Pacemakers and implantable cardiac defibrillators (ICDs) are small devices that keep your heart rhythm healthy. Pacemakers emit a signal to regulate the heartbeat; ICDs respond with a strong electrical shock when they detect an irregular heartbeat.

Pacemakers have been used for nearly half a century, but their application to atrial fibrillation is more recent. The main approach involves breaking the electrical link between the atria and the ventricles (a small bundle of tissue known as the atrioventricular, or AV, node) and implanting a pacemaker to regulate the lower chambers — not, as you might expect, the atria. The idea is to isolate the erratic atria and keep them from overtaxing the ventricles, which can lead to heart failure.

Short-term success rates are impressive, but a 2003 study in the journal Heart reported that after six years, fewer than half of patients with pacemakers had a normal heart rhythm. Moreover, the atria continue to fibrillate, so anticlotting medication — usually warfarin (Coumadin) — is still needed.

A hybrid (“pills and pulses”) option combines anti-arrhythmia drugs with a pacemaker. But that may not work for anyone who’s had problems with the drugs. Atrial pacing — using a pacemaker to target the upper chambers rather than the ventricles — has been tried, but the results thus far have been mixed, so it remains experimental.

ICDs haven’t been widely used for atrial fibrillation. The discomfort of repeated shocks is a major drawback. Medicare and Medicaid cover the procedure only for patients with serious ventricular dysfunction.

Problems with judging a procedure
Success rates. The reported success rates for the various nondrug treatments tend to be about the same — somewhere around 90% — so it’s difficult to decide among them on that basis. These rates are often based on relatively few patients in a single “case series” from one hospital, sometimes reported by a single surgeon. Plus, the definition of success varies, as does the follow-up period. View success rate statistics with healthy skepticism.

Invasiveness. All other things being equal, a less invasive procedure is preferable. But smaller incisions don’t help much if the operation isn’t as effective. And judging effectiveness (that is, success rate) can be difficult.

Good candidates. In atrial fibrillation, as in other medical conditions, outcomes tend to be better for patients who are “good” candidates for an operation. Researchers sometimes tilt their studies, choosing patients who are most likely to benefit from the treatment they are studying. Generally speaking, the “good” atrial fibrillation candidate hasn’t had the condition very long (less than a year) and has an intermittent (sometimes termed paroxysmal), not persistent, case.

Cox Maze
The Cox Maze was named for its creator, Dr. James L. Cox at St. Louis’s Barnes Hospital, and the mazelike series of incisions (in both atria) that act like a ring of barrier islands along a seacoast, blocking and channeling the wild electrical signals that cause atrial fibrillation. The surgery also involves removing the left atrial appendage, a little pocket inside the left atrium where blood clots are most likely to form.

Although it was a real breakthrough, the Cox Maze is a complex and demanding operation. It’s open-heart surgery, like the standard coronary artery bypass, so the surgeon has to cut the chest open and stop the patient’s heart, allowing a heart and lung machine to take over during the operation. These days, a full-fledged Cox Maze is usually done only in conjunction with another open-heart procedure, like a coronary artery bypass or a valve repair.

But now surgeons are doing operations billed as partial or, more often, “mini-Mazes.” The basic idea is the same: Partition off the tissue that is causing the fibrillation and channel the electrical activity where it belongs. But many of these procedures have simplified the maze of incisions. In some, the surgeon uses a special tool to quickly burn tissue with radio waves rather than cutting it. The mini-Maze also avoids open-heart surgery. The surgeons work through small incisions in the side of the chest, using slender instruments and tiny videocameras that allow them to see what they are doing.

The surgeons performing these operations are reporting encouraging results. But often the follow-up period has been fairly short, ranging from just a few months to a year or so, and the number of patients involved relatively small. There hasn’t been anything like a large, randomized trial comparing the mini-Maze operations with other treatments. Even as they applaud the spirit of innovation, more conservative surgeons are taking a wait-and-see attitude.

Catheter ablation
Like the Cox Maze, catheter ablation first was performed in the 1980s. But while the Cox Maze remains rare and the mini-Mazes are just getting off the ground, catheter ablation has become increasingly popular. No chest incision is required. Instead, the doctor threads a long, slender wire (the catheter) up a blood vessel, commonly in the groin, and monitors its progress with an imaging device.

The catheter is used to ablate — actually burn — small circles of tissue around the openings of the four pulmonary veins that empty into the left atrium. Usually the ablation is done with radio waves, but technologies under development or in more limited use include ultrasound, laser, and cryothermy (freezing).

In the mid-1990s, French researchers discovered that in some patients the errant signals that cause atrial fibrillation come from small “sleeves” of excitable tissue in and near the pulmonary veins. The idea is to isolate that tissue. The technique got off to a rough start because at first surgeons targeted tissue too far inside the pulmonary veins and caused scarring and narrowing (pulmonary vein stenosis). That problem was largely solved by limiting the ablation to the openings of the veins.

During the procedure, patients are given a sedative and some local anesthesia at the point where the catheter is inserted. Hospital stays are brief.

A fix for afib: Catheter radio-frequency ablation
The tip of the catheter burns tissue with radio waves. By burning tissue around the openings of the four pulmonary veins that empty into the left atrium, the procedure isolates cells that start the erratic electrical activity that leads to atrial fibrillation.

Some of its proponents think catheter ablation will become a first-line treatment. The theory is that drug therapy doesn’t prevent atrial fibrillation from gradually worsening, but early intervention with catheter ablation might. An article in the Journal of the American Medical Association in 2005 concluded that certain types of catheter ablation already offer a “feasible first-line approach” for some patients. Moreover, catheter ablation has good rates of success and few complications.

Still, as with any operation, there are drawbacks to catheter ablation. About 20%–30% of patients must have it done again because the ablated tissue heals so the errant electrical signals “escape.” It is also becoming too popular, with community hospitals and inexperienced surgeons getting into the game. This is a complicated procedure best done at a major medical center by an experienced surgeon.

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