The defibrillator leads pulled off the market this week by Medtronic Inc. may pose a higher risk of fracture in younger adults and children, a population for whom the devices were particularly popular in part because of their small diameter.

Children make up a relatively small share of patients who receive the implanted devices. But leads — wires that attach defibrillators to patients’ hearts — tend to come under greater stress in more-active people, including kids, adolescents and younger adults.

Monday, Medtronic, based in Minneapolis, announced it would stop selling its Sprint Fidelis leads because of a risk of fractures that could erroneously dispatch jolts of electricity. The company said that of the 268,000 Sprint Fidelis leads implanted, 2,085 were in patients under the age of 21. About 235,000 patients still have the leads, and the company said the fractures may have contributed to five deaths. The deceased patients’ ages haven’t been made public.

Preliminary data from physicians at 32 institutions who specialize in treating pediatric patients and adults with congenital heart disease showed a fracture rate of 6.7% among 569 patients with Sprint Fidelis leads over 30 months. The “vast majority” of the patients are likely to be under the age of 21, given the physicians involved, says Wayne H. Franklin, an associate professor at Northwestern University’s Feinberg School of Medicine, who gathered the physician reports.

Medtronic has reported a lower failure rate, 2.3% after 30 months, for all patients implanted with one particular Sprint Fidelis model. For that same model, Dr. Franklin saw a fracture rate of 4.9% among 304 patients in his survey. The real difference may be slightly greater, because the failure rate from Medtronic includes more than just fractures.

“It’s fairly concerning,” said Dr. Franklin, a pediatric cardiac electrophysiologist. He began gathering the data from colleagues belonging to a society of similar specialists after leads in two of his own young patients fractured, leading to shocks.

He and other doctors say that despite the potentially higher risk for young people, they aren’t currently suggesting patients replace the wires pre-emptively, which involves surgery that can carry more risk than that of a lead’s fracturing. They said they will urge young patients to monitor their leads closely. They also say they don’t have pediatric data for other leads; all lead models tend to have higher fracture rates in young patients.

If a lead is found to be fractured, patients can have the lead extracted or a new lead may be able to be threaded through the same vein.

“To actually remove one of these things is not just difficult, but can be dangerous,” said George Van Hare, a professor at Stanford Medical School who knows of two fractures among 40 pediatric patients who got Sprint Fidelis leads at his center. The center gets some research and training funding from Medtronic, and he consults for one rival device maker.

When a lead fractures, patients can get unnecessary and massive shocks, or not get the shock when they need it to save their lives after cardiac arrest.

Dr. Franklin’s data add to those released Monday by Medtronic. The company said that in patients younger than 21, the failure rate of one Sprint Fidelis model after 30 months was higher than that for all patients: 3.8% compared with 0.8%. That finding was based only on data gathered from devices returned to the company and thus likely doesn’t paint a full picture. The more-definitive Medtronic data for that same model, in the entire patient population, show a failure rate of 2.3% over the same period.

A Medtronic spokesman said the company “broke it out individually to make sure that physicians knew what we knew,” and “thought it was meaningful to point it out.” But, he said, “we don’t have enough data on that subset to give any more advice,” leaving physicians and families to decide what should be done.

A Food and Drug Administration spokeswoman said the agency is reviewing all the reports it received of potential problems with the leads.

Doctors say the Sprint Fidelis leads were especially useful in children, adolescents and young adults because of their narrow girth, which made them easier to thread into small veins. They also left space for replacement leads as patients needed updates over time.

A lead prone to fracture might break more often in younger, more active people, whose hearts beat faster and place more stress on the leads. Even at rest, children’s hearts tend to beat more quickly than those of adults.

Parents are faced with a dilemma as they weigh how active their children should be, given the potential risk. “We have to make choices that are best for the whole person, not a piece of the person,” said Lisa Salberg, chief executive of the Hypertrophic Cardiomyopathy Association, a group for patients with a heart condition, which gets some funding from a charity foundation affiliated with Medtronic. Her 12-year-old daughter has a Sprint Fidelis lead, she says.

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