Atrial fibrillation: beyond drug therapies

Medication may be a first-line treatment, but it doesn't work for everyone. For some patients, surgery could be the answer

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By  Joanne Bladd Published  May 8, 2006

Atrial fibrillation: beyond drug therapies|~|atrial2.jpg|~|Medications that target the arrhythmia directly have a high rate of unacceptable side effects|~|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).

Atrial fibrillation is the most common form of cardiac arrhythmia. 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 one in 200 of us has atrial fibrillation; by the time we reach our 80s, that ratio is one 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 partly becoming more common for demographic reasons; as the world’s population ages, more people are entering their 60s. But even the age-adjusted numbers are showing an increase and doctors aren’t sure why.
Medications are the first-line treatment, but they don’t work for everyone. Some patients continue to have symptoms and 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 anti-clotting medications are necessary, and that means frequent blood tests and a risk of bleeding.

Consequently, there is a lot of interest in the alternatives. Each method has its advocates, and weighing up 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.

Usually patients go on to non-drug therapies after medications have failed, but cardioversion is an exception. It can be used with, or even before, drug therapy.
Cardioversion acts by 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). Patients are anaesthetised 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 of the normal rhythm persisting 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 on 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 continued to fibrillate, so anticlotting medication, usually warfarin (Coumadin), was still needed.
A hybrid (known as the ‘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.

Cox Maze
The Cox Maze was named for its creator, Dr James Cox at St. Louis’s Barnes Hospital, and for 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.

However, surgeons are now 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 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, randomised 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 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 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.

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). The 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 usually brief.

Some proponents of catheter ablation believe it will become a first-line treatment, suggesting that while drug therapy doesn’t prevent atrial fibrillation from gradually worsening, 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. As a treatment, catheter ablation offers good rates of success and few complications.

However, as with any operation, there are drawbacks. Between 20% to 30% of patients must have the procedure repeated, because the ablated tissue heals, allowing the errant electrical signals to ‘escape’. It is also becoming too popular, with community hospitals and inexperienced surgeons getting into the game. Catheter ablation is a complicated procedure best done at a major medical center by an experienced surgeon.

This article is provided courtesy of Harvard Medical International.© 2006 President and Fellows of Harvard College||**||

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