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.
Cardiac cryoablation has enabled Jonathan Suthard of Manassas Park, shown here with his parents, Ray and Deborah Suthard, to cure his arrythmia and become active in sports.
(Jahi Chikwendiu - The Washington Post)
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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."•
