"Two and a half million people in the United States suffer from atrial fibrillation, a chaotic rhythm of the top chambers (atria) of the heart that causes the whole heart to beat rapidly and irregularly," said Dr. Donahue, assistant professor of medicine at The Johns Hopkins University School of Medicine in Baltimore. "The two conventional treatment strategies are to either try to keep the rhythm from becoming irregular, or to try to maintain a controlled heart rate. But we are still far from having an optimal therapy. There is a tremendous need for new ways to treat this condition.
"A number of innovative approaches are in different stages of development," said Dr. Donahue. He spoke today at an American Medical Association media briefing on cardiology in New York City.
Radio frequency ablation is an experimental treatment that is currently having some success, according to Dr. Donahue. In this treatment, catheters (thin tubes) are put in the heart, and radiofrequency energy is used to isolate the area that causes the fibrillation. "In patients who have simple AF -- that is, there is no other heart disease -- this technique is very effective. At the end of one year, 60 to 80 percent of patients are cured; they have no more problem with irregular rhythm," said Dr. Donahue. "More commonly, though, patients with AF have other heart disease. But even in those patients, we see a success rate in the range of 20 to 40 percent.
"There are a number of different drugs in early clinical trials (phase I or phase II)," said Dr. Donahue. "These drugs are designed to block a special ultra-rapid potassium channel that is isolated to the atria. (Potassium channels are part of the system that regulates the excitability of the heart.) There are currently potassium channel blockers used to control AF. But, because they affect channels in both the upper and lower (ventricular) chambers of the heart, they can have dangerous side effects and must be carefully controlled. By targeting a channel that is unique to the upper chambers, the hope is that they will control the AF without posing a danger to the ventricular chambers."
Gene transfer techniques, although not as far along in their development, are showing promise in animal models, according to Dr. Donahue. Gene transfer would not have the side effects that drugs do. One technique would regulate heart rate by inserting a gene that would modify the atrial/venticular node, the point at which they meet. The modified node would not be able to conduct impulses from the upper to the lower chambers of the heart. "This has been shown to work in animal models of chronic disease and would be in line for clinical trials in perhaps three to five years," said Dr. Donahue.
"In another ongoing investigation in our lab we are transferring a gene for a mutant potassium channel to the atria to eliminate the ability of the atria to fibrillate," said Dr. Donahue. "This is in an earlier stage of development."
"AF is a very active area of research, with a number of very different modes of attack in different stages of development, that should pay off in improved patient care," said Dr. Donahue.
Media Advisory: To contact Kevin Donahue, M.D., call Joanna Downer at 410-614-5105 or e-mail at email@example.com. On the day of the briefing, call the AMA's Science News Department at 312/464-2410.