Freezing abnormal electrical pathways in the hearts of young patients may be a safer alternative to zapping them with powerful radiofrequency probes in order to treat tachycardias and other arrhythmias, according to a new study in the April 5, 2005, issue of the Journal of the American College of Cardiology.
“If you have a child with a supraventricular tachycardia due to a reentry circuit, or a target very close to the atrioventricular node or the His bundle, try to do a cryoablation first, then if it is unsuccessful, you can do a radiofrequency ablation, if there aren’t any other alternatives,” said Fabrizio Drago, M.D., at the Bambino Gesù Hospital in Rome, Italy.
The use of a catheter probe chilled to -75° Celsius to destroy or ablate abnormal electrical circuits in adult heart arrhythmia patients is becoming increasingly popular, but this is the first study of its type that involved children. Currently, radiofrequency ablation, which uses a probe emitting very powerful electromagnetic energy, is the treatment of choice for these patients.
While usually effective, ablation of electrical pathways in the heart can create new problems, including atrioventricular block, which is an impairment in the transmission of electrical signals from the upper to lower chambers through the atrioventricular node. Radiofrequency ablation is permanent, but cryoablation has the potential advantage of being reversible during the procedure. Cardiologists can set the freezing probe to -30° Celsius and test its effect on the patient. If a problem appears in the heart’s electrical pattern, the probe can be removed and the chilled nerves can recover. If the test freeze appears successful, the probe temperature is lowered to -75° Celsius to achieve a permanent ablation.
Twenty-six pediatric patients (age range 5 to 20 years) were treated; 16 had tachycardia and 10 had Wolff-Parkinson-White syndrome, a condition in which electrical signals to the heart’s pumping chambers arrive too early, thus interfering with normal pumping action. No permanent cryo-related complications or adverse outcomes were reported. The procedure was successful in 24 patients (92 percent). However, during follow-up (range: 1 to 22 months), arrhythmias returned in seven of these 24 patients.
“This report is important because it describes the first single-institution experience about the use of cryoablation in a pediatric population in an attempt to eliminate reentry circuits located near the atrioventricular junction without any complications. This is the critical point,” Dr. Drago said. “Our acute success was very high, but we had many recurrences, maybe more than those reported in adult patients.”
Dr. Drago said he considers the higher rate of recurrences an acceptable trade-off for increased safety in these young patients, as compared to the usual experience with radiofrequency ablation.
“We do think that in dealing with children, it's better to do a procedure with a little bit lower success rate and no risks, than to do a procedure with an higher long-term success rate, but with the risk, even if low, of severe complications,” he said.
Dr. Drago noted that this study was not a randomized, controlled trial; it did not directly compare cryoablation to radiofrequency ablation; and it reports the experience of only one hospital.
Paul C. Gillette, M.D., F.A.C.C., at Cook Children's Health Care System in Fort Worth, Texas, who was not connected with this study, noted that he and his colleagues began investigating cryoablation more than a decade ago, in part because of the complications sometimes caused by radiofrequency ablation. He said their experience with cryoablation has been positive.
“In our pediatric electrophysiology lab, we decided that since cryoablation was so inherently safe, we would focus on eliminating all evidence of abnormal condition. Cryoablation is now our technique of choice for any septal pathways or atrioventricular node reentry,” Dr. Gillette said.
George F. Van Hare, M.D., F.A.C.C., at the Stanford University Medical Center in Palo Alto, Calif., who also was not connected with this study, called for the optimism about cryoablation to be tempered with caution, until more studies are done.
“This report, while preliminary and only involving a limited number of patients, shows that cryoablation is effective. There are far too few patients reported to make any definite statements concerning safety, however. Still, there are important reasons to believe that cryoablation will eventually turn out to be a safer method of ablation when working in the region of the compact atrioventricular node, and therefore this method of ablation deserves attention, particularly in the pediatric population. Ideally, additional experience will be reported from large multiinstitutional registry studies, and the results of cryoablation in children will be compared to previously reported benchmarks for efficacy and safety of radiofrequency ablation,” Dr. Van Hare said.
The American College of Cardiology, a 31,000-member nonprofit professional medical society and teaching institution, is dedicated to fostering optimal cardiovascular care and disease prevention through professional education, promotion of research, leadership in the development of standards and guidelines, and the formulation of health care policy.