New Treatment for Atrial Fibrillation
Mayo Clinic researchers are advancing a less invasive procedure to treat atrial fibrillation – a heart arrhythmia that can limit the health of cardiac patients. How they do it requires the help of Mayo’s leaders in virtual imaging.
Catheter ablation procedure avoids drugs and surgery
Douglas Packer, M.D., is conducting a tour through a patient’s heart. It’s a virtual tour – the patient was successfully treated a month earlier for heart arrhythmia – but Dr. Packer’s excitement is nonetheless palpable.
“When we start a case, it looks like this,” he says, indicating a blank computer screen in a Mayo Clinic cardiac lab in Minnesota. “And then we do this.” He drags the computer mouse. An image blooms onscreen: Layers of vivid green, red and yellow twisting into a 3-D blob. It’s the patient’s heart, the colors pinpointing tiny spots where errant electrical signals are causing atrial fibrillation, the most common arrhythmia.
Dr. Packer simulates directing radiofrequency energy to the hot spots. They sprout red dots, like beads on a necklace, indicating the abnormal tissue is destroyed and heart rhythm restored. During an actual procedure, he would be using long, thin catheters inserted into vessels in the leg to guide tiny electrodes all the way into the patient’s heart.
Long known for its cardiac expertise, Mayo Clinic is targeting the heart in new ways. Researchers are developing non-invasive, non-drug treatments that zero in on the causes and complications of atrial fibrillation.
For patients, catheter ablation offers less risk and faster recovery than open-heart surgery. For cardiologists, the challenge lies in knowing where to ablate when they can’t directly see the heart. Mayo’s latest innovation helps its cardiologists do just that by “immersing” them in a five-dimensional view of the heart.
Like 3D procedures, the new technology uses catheters to insert tiny electrodes into the heart, which send images of the heart’s 3-D anatomic structure to a computer screen. The 5D system, however, uses a unique computational platform to “take the physician inside the heart in 5-D, visualizing the heart walls, the electrical activity within those walls and the catheter as the physician navigates to the treatment site,” says Richard Robb, Ph.D., director of Mayo Biomedical Imaging Resources. “The ablation can actually be observed as it is administered.”
Dr. Robb estimates that the new system potentially increases the effectiveness of catheter ablation to 95 percent – as effective as open-heart surgery. “It is a challenge because the heart is a moving target, dynamically changing shape, position and function as it beats,” he says.
Mayo is known worldwide for its innovative imaging of human body systems and for its efficiency in getting research advances to where they benefit patients at the bedside. Dr. Robb and Douglas Packer, M.D., director of Mayo’s Heart Rhythm Service, are leaders of Catheter ABlation vs. ANti-arrhythmic drug therapy for Atrial Fibrillation or CABANA, a clinical study to evaluate catheter ablation.
“I have had a few opportunities to consider going to other institutions, both academic and industrial,” Dr. Robb says. “But I’m still at Mayo primarily because of the rich collaboration in education, research and clinical practice, and the opportunity that presents for translating research developments to clinical practice. I do not believe there is any other place than Mayo where I could do so readily and efficiently what I love to do - translational research.”
Since 1998, Mayo Clinic doctors have performed this non-invasive procedure, called “catheter ablation,” on about 2,500 patients. “That’s 2,500 patients who otherwise may have required surgery,” says Dr. Packer, director of Mayo’s Heart Rhythm Service. “And we have found catheter ablation to be highly effective at reducing symptoms, improving quality-of-life and, in fact, eliminating the cause of the atrial fibrillation.”
Standard treatment for atrial fibrillation
In atrial fibrillation, the heart’s upper chambers experience chaotic electrical impulses. The resulting rapid and irregular heartbeat causes fatigue, shortness of breath and exercise intolerance. Long-term complications include stroke, serious bleeding, cardiac arrest and death.
About 2.5 million Americans have atrial fibrillation, and it’s becoming more common as the population ages: 2 to 3 percent of 60-year-olds have atrial fibrillation, but the rate rises to 12 percent for 80-year-olds.
“Twenty years ago, atrial fibrillation was viewed as a nuisance, but not necessarily something that required aggressive intervention,” Dr. Packer says. “Now, it’s clear atrial fibrillation plays a role in stroke. It’s also clear that it’s a huge quality-of-life problem.”
For decades, doctors have prescribed medication to treat atrial fibrillation. But several studies show its effectiveness is limited. By the 1990s, doctors began performing surgical ablations – opening the patient’s chest and cutting into heart tissue where the errant electrical signals originate. Although successful, the surgery was complicated and of higher risk.
Around 1993, Mayo began researching non-invasive alternatives, performing its first catheter ablation in a patient five years later. Since then, small-scale trials have indicated catheter ablation is effective for atrial fibrillation.
Future standard treatment?
Mayo’s leadership in this area was recognized recently with a $48 million grant for a major study on catheter ablation. Known as CABANA (Catheter Ablation Versus Anti-arrhythmic Drug Therapy for Atrial Fibrillation), the study involves 3,000 patients and 140 centers worldwide. Led by Mayo, CABANA aims to discover if ablation is more effective than medication for treating atrial fibrillation.
“We think CABANA will be a landmark trial that will guide treatment decisions for years to come,” Dr. Packer says.
Mayo’s breadth of research expertise, encompassing imaging technology and genetics, as well as high-tech treatments, makes it well-suited to lead CABANA. Equally important is the Mayo tradition of the clinician-investigator. “We can ask the right questions because Mayo provides an environment in which some physicians do clinical work as well as basic-science research,” Dr. Packer says.
CABANA is the first large-scale study of the procedure. CABANA’s six-year span allows researchers to examine the procedure’s impact on mortality, hospital costs and a patient’s quality-of-life. Eventually, catheter ablation may be a first-line treatment for atrial fibrillation rather than an option for patients who don’t improve after drug therapy.
“If we demonstrate with CABANA that doing one ablation as the first intervention is much more effective – that it saves patients from time-waste risks and the potential detriments of drug therapy – we will be able to reduce the time to establishing effective therapy,” Dr. Packer says.
Meanwhile, the clinician-researchers at Mayo’s Heart Rhythm Center are already studying further improvements for treating arrhythmia and its complications. One focus is blood clots, which are associated with atrial fibrillation and can cause stroke. To prevent stroke, doctors often prescribe blood thinners, which carry risks of excessive bleeding.
“So one goal for research is to find a way of preventing stroke without taking a systemic blood thinner,” says Samuel Asirvatham, M.D., a specialist at the Heart Rhythm Center.
He is conducting a clinical trial of a new procedure to prevent blood clots. A catheter is used to insert a looped suture into the patient’s left atrial appendage (a muscular pouch attached to the left atrium), where most blood clots form. The procedure excludes that area from blood circulation, so clots can’t arise. Dr. Asirvatham’s innovation is to enter the appendage from outside the heart rather than inside. If successful, “patients would not have to take blood thinners and run the risk of bleeding,” he says. “It could have a really positive impact.”
Atrial fibrillation and inheritance
Another research track is uncovering the genetic basis of atrial fibrillation. A Mayo study in 2003 revealed that “lone” atrial fibrillation (not caused by underlying heart disease) can run in families. Now, investigators in Mayo’s Cardiovascular Genetics Research Laboratory are searching for specific genetic mutations that can lead to atrial fibrillation. Mayo’s painstaking approach involves recruiting family members of atrial-fibrillation patients to give DNA samples. That DNA is compared to the human genome map “to figure out where the culprit gene resides,” says Timothy Olson, M.D., the lab’s director.
This genome-wide approach finds genes that researchers might never have suspected of causing atrial fibrillation. The genes Mayo has identified so far play very different roles in cell biology, indicating that atrial fibrillation’s genetic blueprint is complex. “What we have identified so far is only the tip of the iceberg,” Dr. Olson says. Eventually, he adds, doctors might be able to identify people at risk for atrial fibrillation and prevent its occurrence.
Mayo’s range of work on atrial fibrillation is possible because its researchers routinely cooperate. “The ability to collaborate saves years from the research timeline,” Dr. Packer says. “In any institution, you have to choose whether your default mode for cooperating in research is ‘no’ or ‘yes.’ At Mayo we decided a long time ago the interaction-default mode is ‘yes.’ We will work together to further the science of arrhythmia. The needs of the patient always come first and shape choices in clinical research.”
— November 2010