Mar. 1, 2004 ANN ARBOR, MI -- Two-thousand times a day, Austin Miller’s heart rate would race – sometimes in excess of 200 beats per minute, nearly twice the rate of a normal child’s heart.
His abnormal heart rhythm, a rare arrhythmia in children known as Junctional Ectopic Tachycardia (JET), took a toll on Austin’s young life. It caused him to feel irritable and affected his performance at school. When he was first diagnosed at age 3, doctors also told Austin’s parents that his rapid heart rhythm would prevent him from playing sports and require him to take medication for the rest of his life.
But just a few months ago, Austin’s future dramatically changed when, at the age of 7, he was able to stop his irregular heart rhythm cold. Thanks to a new minimally invasive tissue freezing technique called cryoablation performed by the University of Michigan C.S. Mott Children’s Hospital Pediatric Cardiology Arrhythmia Service, Austin now has a normal heart rhythm and no longer needs to use medication for his heart.
The U-M Pediatric Cardiology Arrhythmia Service at Mott was the first to use this new technique in Michigan, and is currently the only hospital in Michigan to offer cryoablation for children with heart arrhythmias.
Cryoablation has been used for several years to treat arrhythmias in adult and pediatric patients, but originally required open-heart surgery for physicians to gain access to the heart. But now, cryoablation can be performed during an outpatient heart catheterization procedure, making it a much safer technique to use with young patients like Austin.
“It’s truly amazing to see what an impact this procedure has had on his life after living with the condition for so many years,” says Tamara Miller, Austin’s mother. “Just a few weeks after the procedure, I saw a huge change in his personality – he’s happier and doing much better in school now.”
Cryoablation eliminates abnormal conduction pathways within the heart by freezing heart muscle and eliminating its ability to carry electrical signals. This allows the normal conduction system to work effectively and returns the heart to having a normal activation sequence, says pediatric cardiologist Peter S. Fischbach, M.D., the director of the U-M Pediatric Electrophysiology Laboratory.
“This is a very promising new technology,” says Fischbach, an assistant professor in the Department of Pediatrics and Communicable Diseases at the U-M Medical School. “Cryoablation adds a level of safety for trans-catheter treatment of arrhythmias. It is especially useful for individuals with smaller hearts because it allows us to see the electrical effects of the process before there is any permanent tissue damage to the heart. Due to the size of many of the pediatric patients, the abnormal electrical pathways we are trying to eliminate are geographically very close to many vital structures within the heart.”
Patients who undergo cryoablation are either sedated or put under general anesthesia, depending upon their age, before a catheter is inserted through the groin and guided up toward the heart.
To locate the target area, or ablation site, a procedure called cryomapping is first used to cool – but not freeze - the heart muscle. This process safely suspends the electrical conduction of the area without producing any permanent damage to the tissue, which allows Fischbach and his colleagues to determine if the site is causing the arrhythmia. The tissue is re-warmed and able to regain normal function if it is found not to be the affected area.
Once the ablation site has been confirmed, the temperature at the tip of the catheter is lowered to -70 degrees Celsius, which freezes the tissue and eliminates the cells responsible for the arrhythmia. When freezing is complete, the catheter is removed and the patient is monitored in the hospital for four to six hours. Children are able to return to their normal daily activities within 48 hours of the procedure.
A similar procedure that heats the heart muscle instead of freezing it, called radiofrequency ablation, is another option available for pediatric and adult patients with heart arrhythmias. Radiofrequency ablation aims to counteract irregular electrical impulses in heart muscle by delivering tiny bursts of intense radiofrequency waves to the areas of disorganized electrical activity through the catheter, cauterizing the tissue in the immediate vicinity of the catheter without harming nearby tissue.
Cryoablation and radiofrequency ablation have both successfully worked to correct heart arrhythmias at U-M. In fact, a recent report from experts at the U-M Cardiovascular Center show that more than 85 percent of patients with intermittent atrial fibrillation, a type of heart arrhythmia, were cured after a single session of radiofrequency ablation. Those patients also no longer need medications to stabilize their heartbeat, and their risk of clotting and strokes were decreased.
But for sensitive pediatric arrhythmia cases like Austin, Fischbach says cryoablation is the safest and most effective option available.
“Austin had a very uncommon congenital condition in which the arrhythmia focus was living immediately adjacent to the atrioventricular node, the normal electrical connection between the top and the bottom chambers of the heart,” he says. “With cases like this, cryoablation is the best option to avoid the high risk of damaging the AV node that could lead to a condition called complete heart block, which would necessitate a pacemaker for the remainder of the patients life. Cryoablation certainly affords the patient a level of safety for treating certain types of arrhythmias that is not present with traditional radiofrequency ablation.”
Since October, the U-M Pediatric Cardiology Arrhythmia Clinic has performed 20 cryoablation procedures on pediatric patients. Arrhythmias can cause irregularities with the rhythmic beating of the heart, causing it to beat too fast or too slow.
To learn more about the U-M Pediatric Cardiology Arrhythmia Service, visit http://www.med.umich.edu/cvc/mchc/index.html. For more information about cryoablation, visit Cryo Cath at http://www.cryocath.com.
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