Finding your way through the (mini) Maze

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Finding your way through the (mini) Maze

Minimally invasive operations for atrial fibrillation are on the rise. How well they work is up in the air.

In 1987, a St. Louis surgeon created an operation called the Maze that successfully stopped atrial fibrillation, a rapid and uncoordinated beating of the heart’s upper chambers that affects more than two million Americans. Since then, surgeons and inventors have been trying to shrink this complex, open-heart operation into a smaller one that is just as effective but easier on the heart and body.

A handful of “mini-Maze” procedures are now being performed around the country. They don’t always live up to their name — some take liberties with the mini part, others with the Maze. The doctors doing these procedures passionately believe in their effectiveness. Unfortunately, that passion hasn’t yet translated into hard numbers on how well the procedures work.

What is atrial fibrillation?

In a healthy heart, each heartbeat starts with an electrical signal from the sinoatrial node, a bundle of cells in the right atrium that serves as the heart’s pacemaker. The signal flashes along a prescribed pathway across both upper chambers (atria), causing them to contract. It jumps to the lower chambers (ventricles) through a gatekeeper called the atrioventricular node and, after a brief delay, causes them to contract. The result is the familiar two-beat rhythm: The atria contract, filling the ventricles with blood, then the ventricles contract, pumping blood to the body and lungs.

In people with atrial fibrillation, the atria quiver and convulse (the medical term is fibrillate). Instead of rhythmically squeezing and relaxing, the atria look like a pulsating bag of worms.

Sometimes atrial fibrillation goes unnoticed. More often, though, it causes very noticeable problems. One of the most common is a fluttering sensation in the chest, an awareness that the heart is racing. Other symptoms include shortness of breath, dizziness or a lightheaded feeling, weakness, fatigue, and even chest pain.

Quivering atria aren’t very good at pushing blood into the ventricles. When blood sits in the atria, clots can 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. Long-term atrial fibrillation can also lead to heart failure.

There are two basic types of atrial fibrillation. Intermittent, sometimes called paroxysmal, atrial fibrillation comes and goes. Continuous, sometimes called persistent, atrial fibrillation is always present. Each type probably has its own set of causes.

In many people, atrial fibrillation stems from electrical signals leaking into the heart from the pulmonary veins. These vessels carry blood from the lungs to the left atrium. Signals that throw off the heart’s rhythm can also come from the vagal ganglionic plexus. This bundle of nerves branches off from the vagus nerve, which is part of the autonomic (automatic) nervous system. The pulmonary veins and vagal ganglionic plexus are thought to be responsible for many cases of intermittent atrial fibrillation.

Malfunctions in the atria themselves can also give rise to atrial fibrillation. These probably account for much of the continuous type.

Atrial fibrillation has traditionally been treated with medicines that steady the heart’s rhythm or its rate. Warfarin (Coumadin), a drug that makes it harder for blood clots to form, is an integral part of treatment to prevent strokes.

Most people with atrial fibrillation learn how to manage it so it doesn’t interfere much with their lives, even though they would rather stop it forever. For some people, drug therapy doesn’t quell the problem or ease its symptoms. And others can’t — or don’t want to — take powerful medicines, with sometimes powerful side effects, for a lifetime. It is for folks in these last two groups that operations for atrial fibrillation were first developed.

The original Maze

Dr. James L. Cox performed the first Maze procedure at Barnes Hospital in St. Louis. The surgery involves making a series of deep cuts in the right and left atria and immediately sewing them up. This creates a maze-like pattern of scar tissue that essentially corrals each “beat now” signal along a path through the atria. The surgeon also removes the left atrial appendage. This thumblike pocket inside the left atrium is a prime place for blood to stagnate and form clots.

Dr. Cox and his colleagues refined the Maze twice, eliminating a number of the original cuts to the heart. In hospitals where it is performed regularly, the Cox-III Maze stops atrial fibrillation 80%–95% of the time and prevents strokes without the need for warfarin. This has made it the gold standard by which other procedures are measured. Despite its success, the Maze tends to be a procedure of last resort. That’s because it requires splitting the breastbone, then stopping the heart and connecting it to a heart-lung machine. There is a small risk of dying from the operation, and 10%–15% of Maze patients end up needing a pacemaker. Today, the full Maze is usually done only when another operation, such as a valve repair or coronary bypass, is necessary.

Original Maze In the Cox-III maze, the surgeon creates five lines of scar tissue in the left atrium (above), and more in the right atrium.

Mini, not Mazes

The mini-Maze with the most “buzz” is one developed by Dr. Randall Wolf, a cardiac surgeon who heads the University of Cincinnati’s Center for Surgical Innovation. It’s definitely a mini, requiring just two half-inch incisions and a larger three-inch one on each side of the chest. One opening is for a tiny videocamera and light. The surgeon does the entire procedure while watching the beating heart on a TV screen. The heart-lung machine is not used.

The key tool is a clamp-like wand called the AtriCure Hand Piece. It uses radio waves to heat precise lines of heart tissue. With the device, the surgeon encircles a ring of tissue on the left atrium, just below where the pulmonary veins join in, and zaps them with radio waves. The resulting scar tissue creates a barrier against electrical signals from the pulmonary veins.

The Wolf mini-Maze calls for two other steps. The surgeon maps the left atrium, looking for electrical activity from the vagal ganglionic plexus. If any is detected, small burns are used to create a barrier against it. The surgeon also removes the left atrial appendage.

The Wolf mini-Maze appears to be safe, and most people who have it leave the hospital after three days with minimal restrictions. It isn’t really a Maze, though, since it makes just one set of scars compared with the full Maze’s five incisions in the left atrium alone. It should really be called “minimally invasive pulmonary vein isolation with excision of the left atrial appendage.”

Dr. Wolf estimates that 800 such mini-Maze procedures have been done between 2003 and early 2006. The single publication from this group describes the outcomes of 27 patients. Of the 23 followed for three months or more, 21 (91.3%) reported no atrial fibrillation symptoms. More extensive follow-up studies are under way, according to Dr. Wolf.

Wolf mini-Maze This mini-Maze, which requires a few small openings in the side of the chest, creates a circle of scar tissue around each set of pulmonary veins.

At the University of Massachusetts Medical School, Dr. Adam Saltman uses microwaves to create a circle of scars around the pulmonary veins and a scar line that extends toward the left atrial appendage, which is removed. As of early 2006, about 700 of these operations had been done worldwide. According to Dr. Saltman, 82% of the people who have undergone this procedure are free of atrial fibrillation at one year’s follow-up, though these results have not been published or verified elsewhere.

Dr. Cox, the originator of the full Maze, is championing the use of high-intensity focused ultrasound via a device he helped create. A U-shaped probe, which looks like an umbrella handle, is hooked around the left atrium. A zap of ultrasound creates a circular scar that electrically isolates the pulmonary veins. Only a handful of these have been performed.

Surgeons are also working with lasers and cryosurgery (freezing) to stop atrial fibrillation.

A Maze, but not as mini

A smaller version of the true Maze is being done where the original Maze was first performed. Instead of splitting the breastbone, Dr. Ralph Damiano and colleagues gain access to the heart through a four-inch incision between the ribs under the right arm. And instead of cutting and sewing the heart, they use the AtriCure wand to heat precise lines of heart tissue. As is done in the full Maze, the heart is stopped and the patient is connected to a heart-lung machine, although for a much shorter time. In a follow-up study of 40 individuals who had this procedure, 90% had normal heart rhythms at six months.

From the inside out

We would be remiss if we didn’t mention catheter-based pulmonary vein isolation. This isn’t a Maze at all, and it is even less traumatic than minimally invasive surgery.

Instead of working to stop atrial fibrillation from outside of the heart, this procedure works from the inside. A thin, flexible tube (catheter) that emits radio waves is inserted into the femoral vein in the groin and gently maneuvered into the heart. Once in place, it zaps spots on the inner wall of the left atrium around the openings to the pulmonary veins.

Results of an international trial published in 2005 suggest that catheter-based pulmonary vein isolation could rival state-of-the-art drug therapy as a first treatment for atrial fibrillation. After one year, 87% of volunteers who had pulmonary vein isolation were free from symptoms of atrial fibrillation, compared with 37% of those on drug therapy. There were fewer hospitalizations for atrial fibrillation and better quality of life among those who underwent the procedure. Even with these encouraging results, the researchers said that longer, larger studies are needed to see how durable the procedure is and for whom it works best.

Not ready for prime time

As you can see, there’s no such thing as the mini-Maze. Instead, there are different procedures, some of which are minimally invasive but not true Mazes, others of which are Mazes but stretch the meaning of minimally invasive.

What they all have in common are promising results unsupported by hard data about long-term effectiveness. This should set off warning bells for anyone looking for an easy cure for atrial fibrillation.

These procedures could live up to their claims and halt atrial fibrillation in 80% or more of people, freeing them forever of needing a blood thinner or drugs to control their heart’s rhythm or rate. It’s just as possible, though, that they offer little more than a short-term fix. If that’s the case, you expose yourself to all the risks of surgery — which aren’t trivial — for little or no benefit.

We asked the chiefs of cardiac surgery at Harvard’s three main teaching hospitals, all of whom believe in and encourage surgical innovation, if the mini-Mazes are ready for prime time and, if not, what sort of evidence is needed before they become part of mainstream treatment.

Drs. Ralph Morton Bolman III, of Brigham and Women’s Hospital; Frank Sellke, of Beth Israel Deaconess Medical Center; and Gus Vlahakes, of Massachusetts General Hospital, were unanimous in their answers. All said that the hopes for, and marketing of, mini-Maze procedures far exceed the evidence that they work. All three warned against thinking of these operations as acceptable alternatives to drug therapy.

What is needed before mini-Mazes could become part of standard therapy for fighting atrial fibrillation? Ideally, you’d want to see the results of a randomized trial pitting a mini-Maze against the best drug therapy. At a minimum, a study of several hundred patients followed for two or three years with objective measures of their heart rhythms would suffice.

If you can’t wait for this information to be assembled and debated, at least make sure you have the facts.

• No procedure is 100% successful. Depending on who you talk to, the short-term success of mini-Mazes runs from 25%–95%. Results haven’t been independently verified, and the long-term success isn’t known.

• All procedures have risks and side effects. These can include infections, damage to the heart and nearby structures such as the esophagus, and even death. Drugs to control atrial fibrillation have their risks, too. So it’s important to tally up all the benefits and risks.

• Not everyone with atrial fibrillation is a candidate for a mini-Maze. These procedures seem to work best for intermittent (paroxysmal) atrial fibrillation in people with otherwise healthy hearts. They aren’t for those with continuous (persistent) or longstanding atrial fibrillation, large atria, previous heart surgery, or serious breathing problems or lung disease.

Someday doctors may be able to offer a brief operation that permanently stops all types of atrial fibrillation and its right-sided relative, atrial flutter without splitting the breastbone or using the heart-lung machine. At least for now, that day is a ways off.

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Last updated:	August 21, 2006