Minimally Invasive Cure For Abnormal Heart Rhythm On The Horizon

Researchers at Washington University School of Medicine in St. Louis showed for the first time that, in sheep, applying bipolar radiofrequency yields similar results in less time and with less extensive surgery than the more invasive Maze procedure, the traditional curative treatment for this condition.

Even more importantly, the procedure can be done without using the heart-lung machine and stopping the heart. Sunil M. Prasad, M.D., postdoctoral surgery fellow, will present these findings at the American College of Surgeons’ 2001 Clinical Congress on Tuesday, Oct. 9 at the Morial Convention Center in New Orleans. Ralph J. Damiano Jr., M.D., professor of surgery and chief of cardiac surgery, led the study.

At the end of October, the surgical team plans to be the first in the United States to use bipolar radiofrequency in a patient with atrial fibrillation. Atrial fibrillation affects more than 2 million Americans. The condition causes painful symptoms and may account for roughly 15 percent of all strokes in the United States. Medications can alleviate symptoms in some patients, but they cannot cure the problem.

Normally, electric signals trigger the synchronized contraction of muscles in the heart’s two upper chambers, the atria. During atrial fibrillation, a chaotic web of electric impulses spreads throughout the atria, causing the chambers to quiver rather than contract in unison.

In 1985, researchers at the School of Medicine developed a surgical cure called the Maze procedure to control these erratic impulses. In this procedure, surgeons make small, strategically placed incisions in the atria. The slits generate scar tissue that serves as barriers, trapping abnormal electric signals in a “maze” of barricades. Only one path remains intact, guiding impulses to their correct destination.

With a success rate of over 90 percent, the Maze procedure revolutionized the treatment of atrial fibrillation. However, it is technically difficult and therefore is not performed frequently.

Surgeons also must temporarily stop the heart and use a heart-lung machine to support the circulation in order to make the incisions. Not all patients, therefore, are healthy enough to endure the operation.

So researchers developed an alternative using bipolar radiofrequency to achieve the same result as the Maze procedure without needing to rely on a heart-lung machine and without the surgical complexities of creating a maze of incisions.

The bipolar radiofrequency method uses two electrodes that pass a current through a section of heart tissue. The current heats and kills the band of clamped tissue. Like Maze procedure incisions, radiofrequency energy causes scar tissue that blocks the abnormal impulses responsible for atrial fibrillation.

“We felt bipolar radiofrequency energy would be able to create linear scars with less injury to surrounding tissue than even an incision,” says Damiano. “We also realized that we could measure the electric current between the two electrodes and, by looking at changes in the resistance to the flow of electricity, we could tell when the tissue was successfully ablated.”

The team tested the procedure on five sheep at four of the standard incision locations for the traditional Maze. Each lesion only took nine seconds to complete as compared with Maze incisions which take five to 10 minutes to create.

According to Damiano, “the real test of success is whether the effect is permanent.” Their preliminary findings suggest it is. The affected areas were incapable of transmitting electric signals for up to 30 days. Special staining and post-mortem analysis revealed that all the lesions extended from the outside layer of the heart to the inner layer, confirming that the disruption was complete.

“This study indicates to us that the procedure is safe to do in patients,” Damiano says. “We are refining the technique so it can be done on the beating heart without placing patients on the heart-lung machine, which should minimize complications and accelerate recovery. After undergoing the traditional Maze procedure, patients typically stay in the hospital for seven to 10 days. Bipolar radiofrequency should not only dramatically reduce the time of surgery, but should also decrease the hospital stay and hopefully speed up recovery. Most importantly, it may allow us to offer this curative operation to many more patients with atrial fibrillation.”

Reference: Prasad SM, Maniar HS, Schuessler RB, Damiano RJ. Transmural epicardial radiofrequency ablation on the beating heart: Progress towards a minimally invasive operation for atrial fibrillation. American College of Surgeons’ 2001 Clinical Congress, October, 2001.

Funding from Atricure, Inc., the National Institutes of Health and Washington University in St. Louis supported this research.

BACKGROUND: Washington University's Surgical Efforts To Treat Atrial Fibrillation

Atrial fibrillation is the most common type of irregular heart rhythm, affecting more than two million Americans alone. In addition to causing painful symptoms, atrial fibrillation accounts for roughly 15 percent of all strokes in the United States.

The first cure for this condition, the surgical Maze procedure, was developed in 1985 at Washington University School of Medicine in St. Louis by James Cox, M.D., and revolutionized the treatment of this common form of arrhythmia. However, the Maze procedure remains a technically difficult surgery to perform and requires patients to be on the heart-lung machine for several hours, decreasing the percentage of patients who qualify for surgery.

So researchers have begun to develop variations of the Maze concept that are safer and easier to perform. Washington University’s efforts in this endeavor include:

* A Fremont, Calif., company called AFx has developed a way to surgically treat atrial fibrillation using microwave energy as opposed to the traditional method of creating a “maze” of incisions to block electrical activity. The tool was approved by the Food and Drug Administration in May 2001 and now is being used by a few institutions around the country, including the School of Medicine. This is the first use of microwave energy to treat heart arrhythmias.

* Researchers at the School of Medicine are collaborating with Atricure Inc. in Cincinnati to perfect the use of bipolar radiofrequency energy for a minimally invasive Maze procedure. This new technique can be used on the beating heart, thereby drastically reducing the time needed for surgery and recovery. Researchers at Washington University plan to use this technique for the first time in a human at the end of October.