Boston, MA - The largest study to date to examine the use of implantable cardioverter-defibrillators (ICDs) in children and those with congenital heart disease has found that the devices do shock appropriately and likely save lives, but they also seem to deliver more inappropriate shocks in children than they do in adults [1]. Dr Charles I Berul (Children's Hospital Boston, MA) and colleagues report their findings in the April 29, 2008 issue of the Journal of the American College of Cardiology.

The findings "are no big surprise," Berul told heartwire, indicating that, overall, ICDs are of benefit in children. "But it would be nice to be able to reduce the number of inappropriate shocks," he said, pointing out that this is "always going to be a problem, and it is probably worse for pediatric patients."

Currently, "it's a complex decision-making process, with a lot of clinical testing" to determine which pediatric patients get ICDs, he says, adding that it would be good to have "better risk stratification to identify those that are more likely to use the devices."

Berul et al explain that advances in the technology of ICDs have allowed the downsizing of devices and leads, making them more suitable for application in children. Still, their use in pediatric patients accounts for only a very small percentage of overall use (<1%).

They wanted to examine a contemporary cohort of patients and so retrospectively analyzed data from 443 individuals who received ICDs between 1992 and 2004, including both pediatric patients and adults with congenital heart disease, taken from four centers (mean age 16 years). They identified implant characteristics, shock frequency, and long-term complications. Implant indication was primary prevention in 52% of cases.

Shock data were available on 409 patients. Of these, 105 (26%) received a mean of four appropriate shocks each (range one to 29 shocks per patient), making it "highly probable that at least some of these shocks were potentially life-saving," say the researchers. However, they point out that the overall all-cause mortality rate of 4% and sudden cardiac death rate of 1% over a relatively long follow-up period—mean of 7.5 years—were "strikingly low" compared with similar adult series.

At least some of these shocks were potentially life-saving.

And children in the study were more likely to receive inappropriate shocks than the adults they looked at. Overall, 87 patients (21%) received inappropriate shocks—an average of six per patient (range one to 60 per patient). But when broken down by age, 24% of children under 18 had inappropriate shocks vs 14% of adults. While such shocks are not life-threatening, they are not pleasant, says Berul, who describes them as "like being kicked in the chest."

One reason for the children receiving more inappropriate shocks is that they often have spikes in heart rates that aren't usually seen in adults, due to their higher levels of activity, Berul says. The devices might have difficulty differentiating between normal increases in heart rate and abnormal rhythms, he suggests.

The main reason for inappropriate shocks was failure of the ICD wires, which caused 14% of such shocks. This is a particular problem in children, who live much longer with their ICDs than adults do and whose leads can stretch due to activity and growth, says Berul. Lead failure also requires periodic surgery to replace the wires, he notes.

Berul's team is working with device manufacturers to change ICD programming to minimize unnecessary shocks in children and to provide more durable and longer-lasting leads.

The researchers also showed that those who were sickest—those who had already had an arrest—were more likely to have appropriate shocks. In practice, this group is the obvious one in whom to use such devices, says Berul. But most pediatric patients fall into "level 2" in terms of the guidelines on indications for ICDs, he says: there is no agreement one way or another as to whether they should receive an ICD.

As such, a pediatric ICD registry and consensus development of guidelines and definitions in pediatric and congenital heart disease ICD recipients would be of use, the researchers say. Berul told heartwire that just one paragraph of the lengthy current guidelines on indications for ICDs is specific to children.