An experimental device that uses a catheter-based probe to freeze a tiny area of the heart that causes erratic electrical impulses is much better than drugs at curing atrial fibrillation, researchers reported Monday at the Atlanta meeting of the American College of Cardiology. The device is expected to provide an alternative to current non-invasive techniques that use radio frequency energy to burn away the tissue.
Atrial fibrillation, which affects an estimated 2.7 million Americans and as many as 10 million people worldwide, is the result of aberrant electrical signals that cause the heart to quiver rather than beat strongly. That allows blood to pool in the heart, where it can form clots that cause strokes and heart problems. Patients also suffer chronic fatigue, difficulty breathing and heart failure.
About half of all patients fail drug treatment and require more aggressive approaches. Surgeons used to perform open-chest surgery to access the heart and cauterize the electrically irritable tissue. About a year ago, the Food and Drug Administration approved the first catheter-based system to perform the procedure, Johnson & Johnson's ThermoCool system, which burns away the undesirable tissue with radio frequency (Rf) energy. In this approach, a catheter is threaded through a blood vessel in the groin to the heart, where the tip is used to ablate the tissue. The new instrument, called the Arctic Front Cardiac CryoAblation Catheter System, uses the same approach but employs a balloon that fills with liquid nitrogen to freeze the tissue.
In the new study, called Stop-AF, Dr. Kevin Wheelan of the Baylor Heart and Vascular Hospital in Dallas and his colleagues at 26 U.S. and Canadian centers studied 245 patients with paroxysmal atrial fibrillation, in which the episodes occur intermittently. Two-thirds of the patients were randomized to receive the treatment and the rest received drug therapy. The Johnson & Johnson device had not been approved by the FDA when they began the study, so they had to compare it to the best available approved treatment.
Dr. Douglas Packer of the Mayo Clinic in Rochester, Minn., said at the meeting that 69.9% of the patients receiving cryoablation were free of atrial fibrillation a year after the procedure, compared with 7.3% on drug therapy. About 3% of patients who underwent ablation suffered heart attacks, strokes or other major cardiovascular events, compared with 8.5% of those on drug therapy. The most serious side effect of the procedure was phrenic nerve palsy -- an interference with the electrical pacing of the diaphragm -- in 11.2% of the procedures. The problem resolved within a year in all but four patients.
The safety data is "slightly better" than that for Rf ablation, Wheelan said. The primary advantage of the technique is that it is much easier to learn. Rf ablation requires applying the catheter tip to many points on the tissue, while the cryo-balloon technique engulfs the tissue in the balloon. "The learning curve is greatly simplified," he said.
This trial, along with previous studies of Rf ablation, "is going to push the pendulum more toward considering the option of ablation as a curative strategy earlier on in the disease process," Wheelan said. It could prevent many hospitalizations and complications associated with waiting until the disease has progressed.
A major new trial called CABANA, now underway, will evaluate the different approaches to ablation, looking at overall success, complications and long-term efficacy in more than 5,000 patients. Packer reported on a small pilot study for CABANA that enrolled 60 patients. That study, he said, showed that ablation is better than drugs and justifies proceeding to the larger study.
The Stop-AF trial was sponsored by Medtronic Inc., which already markets the Arctic Front device in Europe. The CABANA pilot trial was sponsored by St. Jude Medical Inc., which manufactures devices for Rf ablation.
-- Thomas H. Maugh II