The catheter that Northern Virginia cardiologist Margaret H. Bell threaded into Johnathan Suthard's beating heart was as thin as a strand of linguini, its tip loaded with pressurized frozen nitrous oxide. The solution it would emit was chilled to minus-75 degrees Celsius, a temperature equivalent to the coldest recorded on the Siberian steppes.

Applied precisely to specific spots on the upper right chamber of his heart, the suspected source of Johnathan's potentially fatal heart arrhythmias, the liquid literally froze the targeted tissues to death. The procedure Bell and her partner performed last May known as cardiac cryoablation worked perfectly, restoring the 13-year-old's too-fast heart rate to a normal rhythm.

Doctors at Inova Fairfax Hospital were the first in the Washington area to perform cardiac cryoablation, using a device approved last year by the U.S. Food and Drug Administration (FDA). Specialists at Children's National Medical Center in the District are set to offer it, officials there said, and pediatric cardiac experts predict the procedure will be widely used by next year.

Now liberated from the constraints that have circumscribed his life since age 8, the rising ninth-grader from Manassas Park is immersed in football practice and plans to try out for the track and basketball teams.

And for the first time in six years, his mother says, she is able to relax, without fearing that he might suddenly collapse or forget to take the drug that stabilized his heart rate, but made him dizzy and sluggish. Once, after Johnathan missed two doses, he had to be rushed to the emergency room.

"A lot of the time he couldn't even feel his heart going into arrhythmia," Deborah Suthard said. Her son, she said, desperately wanted to play sports, and his doctors agreed to let him, with certain restrictions.

"I'd stand on the sidelines watching him," Suthard recalled, "and I was just scared to death."

Two years ago Bell tried to treat the boy's heartbeat problem with "radiofrequency ablation," a procedure that uses a heat-tipped catheter to destroy cardiac tissue responsible for the abnormal rhythm.

That procedure had to be aborted because doctors decided after mapping the area that it was too close to the heart's normal conducting system. They worried that if they proceeded they might be forced to implant a pacemaker, a device cardiologists assiduously avoid using in pediatric patients.

A Safer Way

In the past eight months Bell and her partners have performed about 50 cryoablations at Inova Fairfax, about half on pediatric patients. None of the patients has subsequently required a pacemaker or suffered a major complication, Bell said.

"I was an early adopter because this procedure has such a good safety profile," said Phil Saul, chief of pediatric cardiac surgery at the Medical University of South Carolina in Charleston. Saul pioneered ablation procedures a decade ago when he was at Children's Hospital in Boston.

Bell, 43, belongs to a tiny fraternity of physicians -- there are about 100 in the United States -- known as pediatric cardiac electrophysiologists: cardiologists who specialize in treating children with disorders of the heart's electrical system. This system controls the heart rate and provides the energy necessary for the organ's pumping action. Arrhythmia -- a fast, sometimes erratic heartbeat -- can occur when the normal conduction pathways are disrupted.

Like Saul, Bell waited eagerly for the FDA to approve the cryoablation catheter after studies indicated it was safer than radiofrequency ablation and could help patients like Johnathan Suthard.

Cryoablation currently is approved only for patients whose arrhythmias begin in the upper right chamber of the heart near the AV node, a condition called supraventricular tachycardia, or SVT. Children who develop a fast heartbeat are usually born with the condition. In rare cases like Johnathan's, there is a hereditary cause.

Studies are underway to see if cryoablation can treat atrial fibrillation, a rhythm disturbance that produces a fast, erratic heartbeat and is most common in the elderly.

Both radiofrequency ablation and cryoablation are performed using a flexible catheter inserted through a vein in the groin, its placement navigated with continuous images produced by a fluoroscope or X-rays. Electrodes implanted on the tip of the catheter gather data that pinpoint the location of the faulty electrical site in the heart.

If doctors determine the arrhythmia is caused by an SVT and cryoablation is the preferred option, the mapping electrodes are replaced with a tip capable of freezing the defective site inside the heart. The nitrous oxide tip is cooled to minus-30 degrees Celsius, and doctors apply it to the suspected problem area. If they can subsequently induce the fast heartbeat, it's not the right spot and the site can be thawed by stopping the procedure, without causing permanent heart damage.

"Think of the heart as a sponge: If you burn it with a lighter, you damage the sponge," said Jeffrey Silver, product manager for CryoCath, the Montreal-based manufacturer of the ablation catheter. "But if you freeze it, it's okay when you thaw it out."

After the incorrect areas are thawed, testing continues. When they target a site and can't induce the fast heartbeat after freezing it, doctors assume they've found their target. The catheter tip is then cooled to minus 75 degrees Celsius and the area is destroyed, or ablated.

Saul noted that while radiofrequency ablation can be painful because it causes swelling of cardiac tissue, cryoablation is painless, another advantage in treating children. According to CryoCath's Silver, the procedure has been used successfully on a 3-month-old infant.

The chief drawback of cryoablation, according to Bell, is that is does not appear to be as effective as radiofrequency ablation, which works about 95 percent of the time. The success rate for cryoablation is about 90 percent, she added.

"In cases where we're not worried about interfering with the normal conducting system, we like to use the tried-and-true method, which is radiofrequency, and maximize the chances for a cure," Bell said.

But when doctors think the problem area might be too close to the normal electrical conduction system of the heart, as was the case with Johnathan Suthard, cryoablation becomes the preferred option because of its reversibility.

Some doctors say that an additional advantage of cryoablation is its precision. The cold tip adheres better to tissue -- similar to the way a piece of ice adheres to the tongue. Heat-tipped catheters used for radiofrequency ablation tend to move more, some experts say.

Silver said about 6,000 cardiac cryoablations have been performed worldwide and the manufacturer has received no reports of complications serious enough to require a pacemaker.

According to cardiac specialists, recurrences of arrhythmia after cryoablation typically occur within the first month after treatment.

A Cold Cure

Johnathan Suthard noticed that he felt better almost immediately after the procedure, which was performed under general anesthesia. His mother said it took about four hours, followed by another four hours in the recovery room.

"It's made a lot of difference," he said. "Before I would get tired real easy or get real hot and I really couldn't run." He especially disliked the woozy feeling that was a side effect of the drug he had to take.

A few days after the procedure, Johnathan was back in school. A week later he was playing sports without any restrictions. Since May, he said, he has shaved about two minutes off the time it takes him to run a mile.

"I can breathe easier and play harder and run faster," he said. "And I really like that I don't have to get up real early every morning to take my medication."

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Margaret H. Bell of Inova Fairfax Hospital was the first Washington-area cardiologist to perform cardiac cryoablation. A catheter tip, like that at left, is cooled to minus 75 degrees Celcius to destroy defective tissue. Cardiac cryoablation has enabled Johnathan Suthard of Manassas Park, shown here with his parents, Ray and Deborah Suthard, to cure his arrythmia and become active in sports. This cross-sectional view of the heart's right atrium shows the catheter ready to freeze heart tissue.