Missing a Beat

Atrial fibrillation is found in about 2.2 million Americans, and the likelihood of developing the heart rhythm disorder increases with age. With people living longer than ever before, Dr. Stephen Hammill is focused on improving the diagnosis and treatment of quivering hearts.

Irregular, rapid beating of the atrial chambers can result in various symptoms. Relatively mild ones include fatigue and cough. More serious ones, however, are angina and stroke. Atrial fibrillation (AF) causes more than 70,000 strokes in the US each year, with 160,000 new cases being diagnosed each year.

Cardiac arrhythmia is most commonly identified at the time of a routine physical examination. A physician will notice an irregular pulse, and to document the cause of the irregular pulse, they will obtain an ECG recording. “That’s the key for making a diagnosis. It’s either a standard 12 lead ECG, an ambulatory Holter monitor or what we call an event recorder,” says Dr. Stephen Hammill, Professor of Medicine at the Mayo Clinic College of Medicine and Director of the Electrocardiography Laboratory.

Advances in electrophysiology testing and mapping have improved the diagnosis of AF remarkably since the mid-1990s. Back then, physicians identified pulmonary vein potentials, recalls Hammill. “The pulmonary veins, which drain blood from the lungs, join the left atrium. And right where they join the atrium can be some abnormal cells that have spontaneous electrical activity causing premature beats. In patients who are susceptible to AF, they will initiate the arrhythmia.”

Only when physicians started to map the left atrium as part of their electrophysiology studies did they identify pulmonary vein potentials, which led to the idea that if these potentials could be eliminated, it might be possible to treat AF or even cure it. “And that is what’s happened with the procedure as it evolved over the last ten years,” summarizes Hammill.

Catheter ablation

For mapping, the catheters that are moved around in the heart chambers are attached to a computer that develops a three-dimensional map. “It’s a sophisticated map,” says Hammill, “similar to the types that are used in animation movies. It creates a three-dimensional model of the electrical activity within the heart, and allows us then to pinpoint these areas of abnormal cells that cause the arrhythmia.”

Other equipment includes specialized catheters that are placed in the heart to record from it and to do an ablation procedure. Hammill: “With ablation we use radio frequency energy, which is the same energy that is used as cautery in the operating room. That energy is delivered to the tip of the catheter. It heats up the catheter and then creates an area of scar, scarring or eliminating these abnormal cells, and also placing scar around the veins to isolate the pulmonary veins.”

Catheter ablation is one of three ways to treat AF once medications have failed. The original approach was the surgical maze procedure, which started in the early 1990s. This open heart surgery requires a sternotomy and is as complex as replacing a heart valve. “It is quite effective, though, with a success rate of around 90 percent,” Hammill points out.

The second treatment option is less invasive, where the heart is approached through the chest wall using thoracoscopy, similar to a laparoscopy for abdominal surgery. This technique, Hammill explains, is still in evaluation. It is used in some centers, but there have not been any longitudinal studies assessing its long-term effectiveness.

Less invasive procedures

With catheter ablation, patients are generally in hospital for about 24 hours, and are able to return to work in about three to five days. The quick recovery time, says Hammill, is a great advantage over open heart surgery. “However,” he adds, “more invasive surgery will continue to play an important role when patients are going for some other type of surgery, such as replacement of a heart valve or coronary bypass, and they have also had problems with atrial fibrillation. It makes sense then to add on a surgical maze procedure. Otherwise, the catheter approach has essentially replaced it.”

And it’s getting better. Advanced catheters, Hammill predicts, will allow easier maneuvering and an improved delivery of energy. “One catheter that testing has been done on, and we’re waiting for approval from the FDA, is a catheter that delivers cold energy. It infuses liquid nitrogen into the tip of the catheter to freeze it. It’s called cryo-ablation and it freezes the cells around the pulmonary veins. It seems to cause less damage or injury, and therefore may be associated with fewer complications.”

Most exciting, Hammill believes, although still to be fully tested, are advancing techniques of incorporating robotics to maneuver catheters within the heart. This may help speed up the procedure and decrease the exposure of radiation to both the physician and the patient. “Stereotaxis is a system that helps with catheter movement. It is tied to and working in conjunction with the mapping systems so that with the one catheter, it would automatically map the heart to identify abnormal cells. Then the system would move the catheter to proceed with the ablation. If it came to pass, it would certainly improve the procedure and make it much more available to patients,” says Hammill.

Implantable devices are also being continuously improved. In use are pacemakers that will detect AF or premature beats that initiate AF and then prevent or terminate it. “In general, these type of pacemakers are not very effective as a single way of treating atrial fibrillation,” Hammill acknowledges, “but they can enhance the effectiveness of medications.”

He hopes that in the near future, more directed medications and AF treatments are found – and one exciting research area, aside from implantable devices and catheter ablation, is in genetics. “We are understanding that there are populations of patients that are genetically predisposed to developing AF. So the research now is being done to find out what the abnormal genes are, or the defects at the cellular level that make it possible for one patient to develop atrial fibrillation while the other patient who’s in the same kind of environment does not. If we can find specific cellular abnormalities at the cellular channel level, then we might be able to target treatment of these genetic defects. But that’s many years away,” says Hammill cautiously.

Targeting AF

Although research is clearly driving continuous improvement in the treatment of AF, Hammill points out that there are still setbacks. “The challenges involved in ablation are trying to balance the risk of complication and duration of the procedure with a desire to eliminate all the potential areas where atrial fibrillation may be coming from. We know that about 95 percent of the time, atrial fibrillation originates from the regions around the pulmonary veins. Five percent of the time, it is initiated from other locations. The challenge is how hard do we target those other locations, and then how do we assess at the time of ablation that we have successfully eliminated the abnormal tissue and isolated the veins?”

About a third of patients continue to have AF in the first one to two months following ablation. After about three months, for 90 percent of patients AF is eliminated. That leaves 10 percent of patients who continue to have AF after everything is healed. “These are the patients we want to work on to figure out what was missed, where their atrial fibrillation was coming from, whether the scars that were created by the ablation weren’t effective, and how we can create better, more thorough scars to decrease this chance of recurrence,” Hammill emphasizes.

Beside ablation, there are other areas of AF treatment that affect a much broader population. This, Hammill, explains, is researcher’s continuous efforts to identify the risk factors for development of AF and treating those risk factors to help reduce the progression in the general population. “We know from research studies that the frequency of atrial fibrillation is definitely increasing, and it’s not just that we’re diagnosing it better, or doing more electrocardiograms. But there is actually more atrial fibrillation occurring.”

This, he believes, is related to AF risk factors, which are similar to those for general cardiac problems, including high blood pressure, diabetes and obesity. By treating those risk factors, AF may be reduced.

There are also studies looking at the relationship of sleep apnea with AF. Hammill: “We know that patients with sleep apnea have an increased risk of atrial fibrillation. Another area of evaluation is with anti-coagulation. The major risk of atrial fibrillation is the risk of developing a blood clot and a stroke. For about half of the patients who come into the emergency department with a new stroke, that stroke is due to atrial fibrillation. And in half of those patients, it’s a severe, disabling stroke. This is an enormous medical problem.”

Anti-coagulation drugs such as warfarin help to reduce the risk of stroke. However, Hammill points out, warfarin is a difficult drug to take. It requires regular blood tests to measure the effectiveness and to adjust the dose. And so research to find better medications is ongoing.

Another option Hammill addresses concerns the atrium in patients with AF. “At the cellular level,” he says, “there seems to be a common theme of inflammation. Treating the inflammation may be a way of treating AF. Inflammation can be treated by medications including the ones that we use for high blood pressure, the so-called ACE inhibitors, and medicines to reduce cholesterol, the statin drugs.”

AF is the most common heart rhythm problem, and for Hammill it is amongst the most intriguing ones. About half of AF patients, he says, have very few or almost no symptoms. “We have professional athletes, and there’s been an astronaut on the moon, who have been in atrial fibrillation and functioned very normally.” Then again, the other half of AF patients are quite debilitated by their symptoms. “We don’t know why some people are so adversely affected, which certainly makes it an interesting problem,” he concludes.

About Stephen Hammill

Dr. Stephen Hammill is a Professor of Medicine at the Mayo Clinic College of Medicine, Director of the Electrocardiography Laboratory and recent past President of the Heart Rhythm Society. Hammill has been a member of the American Board of Internal Medicine Cardiac Electrophysiology Recertification and Certification Test Writing Committee and has published widely in the area of heart rhythm disorders which has included 275 abstracts and 250 scientific manuscripts, book chapters and review articles.