New hope for children with abnormal heart rhythm

University of Michigan Health System
Tuesday, 1 June 2004

Freezing technique offered at UMHS proves effective for arrhythmias

From age 3 to 8 , Austin Miller's heart would race up to 200 beats per minute about double a normal heart rate.

"We noticed when he was in preschool he would get a kind of bluish appearance to his face and he would be winded. Every year it seemed to get worse and worse," says Tamara Miller, Austin 's mother.

Doctors prescribed different medications to control the cardiac arrhythmia, or abnormal heartbeat. But the medications slowed his heart rate too much, at times to as low as 40 beats per minute.

The Millers then came to the University of Michigan Health System 's C.S. Mott Children's Hospital, where doctors offered a unique treatment option that would freeze the small bit of heart tissue causing the arrhythmia. Austin underwent the procedure, called cryoablation, four months ago.

"We didn't want him to be on medication, because we were worried about long-term effects. So we were hoping to get him off that and give him more of a normal life," Miller says.

While arrhythmias are more commonly associated with adults, they can affect children as well.

"These arrhythmias can affect children in many different ways. It can range from a nuisance that just slows them down on the playing field or makes them stop what they're doing for a moment or two to potentially life threatening," says Peter Fischbach, M.D., director of the Pediatric Electrophysiology Lab at UMHS.

Arrhythmias can cause the heart to beat too fast or too slow. Symptoms can start in infancy and can manifest themselves as poor feeding or irritability. Older children may complain of their heart beating too fast or feeling unwell. In adolescence, arrhythmias cause a racing heart rate, dizziness or chest discomfort.

Treatment for arrhythmia is done in the cardiac catheterization laboratory and involves identifying where the short circuit occurs within the heart. Doctors then put a catheter in that circuit and turn on energy, either heating or cooling. Radiofrequency ablation, the standard catheterization procedure, involves passing a small current through the tip of a catheter and burning the affected heart tissue.

In cryoablation, the catheter tip is cooled, instead of heated, and a portion of the heart muscle is frozen, eliminating its ability to carry electrical signals. This lets the heart's normal conduction system work the way it's supposed to, creating a normal heartbeat.

"Cryoablation may not be indicated for every arrhythmia that we treat in a catheterization laboratory," says Fischbach, clinical assistant professor of Pediatrics at U-M Medical School. "There are some arrhythmias that are amenable to treatment with standard radiofrequency ablation. It's the tried and true technique. Cryoablation certainly is going to have a very important role in treating young children."

Because children are smaller, the abnormal electrical pathways are often close to many vital structures within the heart. In cryoablation, the first step is to cool, but not freeze, the area suspected of causing the arrhythmia in a process called cryomapping. At this point, the heart loses its electrical function without losing any mechanical function, so the heart cells are alive and recoverable. This provides a measure of safety which is not available in radiofrequency ablation.

Cryoablation is offered for both children and adults. It once required open heart surgery but is now being done in the catheterization laboratory at Mott Hospital as an outpatient procedure. Mott is currently the only hospital in Michigan offering cryoablation for pediatric heart arrhythmias.

Austin 's surgery took about five hours, after which he was required to lay flat for 6 hours. He was released from the hospital that same evening. The procedure has a 95 percent to 98 percent success rate.

While Austin 's condition had progressed from several hundred episodes of arrhythmia each day to several thousands, the cryoablation procedure has stopped the arrhythmias.

"The cryoablation was four months ago and he is doing wonderfully," Miller says. "He's allowed to play organized sports on teams and he's thrilled. He's a normal 8-year-old. He has absolutely no restrictions."

About arrhythmias:

An arrhythmia is an abnormal beating of the heart caused by a change in the electrical signals. They may cause the heart to beat abnormally fast or abnormally slow.

  • Tachycardia refers to an excessively fast heart rate.

  • Bradycardia refers to an extremely slow heart rate.

A newborn's heart rate is around 120-140 beats per minute. An adolescent at rest will have a heart rate around 70 beats per minute. Exercise makes the heart beat faster; it beats slower during sleep.

Resources:

Facts about arrhythmia

Children and arrhythmia

UMHS Pediatric Arrhythmia clinic

U-M Congenital Heart Center

For more information, or to contact University of Michigan Health System, see their website at: www.med.umich.edu

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