Researchers in Ireland have discovered a possible problem with a heart defibrillator component made by St. Jude Medical Inc. in which wires that run from the device to the heart may poke through the outer coating of their cable.

The study looked at 212 patients in Ireland who received St. Jude's Riata defibrillator lead and found that 15 percent had suffered such an "insulation breach," which could interfere with the device's life-saving therapy. Normal screening of the device or even X-rays may not pick up the breach, and patients would have no outward clue that their lead wire may be compromised.

"It could ultimately be a big issue, but we're just starting to scratch the tip of the iceberg of what the scope of the problem is," said Dr. Laurence Epstein, chief of the Arrhythmia Service at Brigham and Women's Hospital in Boston. "The downside [of the Irish study] was that it was a very small sample size and it was only one center."

Little Canada-based St. Jude said in a statement, "We are aware of these reports and have been working with this center to learn from their experience."

A defibrillator is a pacemaker-like device implanted in the upper chest that shocks the heart if it senses an irregular heartbeat. A key component in the system is the lead, an insulated cable that contains several coated wires that snake from the defibrillator through blood vessels to the heart. One to three wires may be used with a defibrillator.

The ultra-thin Riata lead was a popular substitute for doctors after a rival product, Medtronic's Sprint Fidelis, was recalled in 2007 following reports that the lead may fracture.

In that case, the malfunction could be picked up during normal monitoring of the device. Still, 13 deaths were linked to the failure of the Fidelis lead, and Fridley-based Medtronic paid $268 million to settle lawsuits that stemmed from the recall.

St. Jude pulled the Riata lead off the market in December after selling 227,000 worldwide and replaced it with a new lead with a different type of insulation. But according to the company's April product performance report, an estimated 76,532 Riata leads are still implanted in U.S. patients.

In mid-December, the company sent a letter to doctors saying the silicone insulation on the Riata leads may be "vulnerable to abrasion," which could result in the device failing to deliver a shock or, conversely, shocking patients unnecessarily.

St. Jude said the rate of abrasion is 0.47 percent nine years after the original implant, with 0.047 percent demonstrating "externalized cables."

Fluoroscopic screening, a type of medical imaging that shows a continuous X-ray image on a monitor, sort of like a movie, should be considered if there is "suspicion of lead failure," the company said.

St. Jude also conceded in the letter "under-reporting of lead complications is well acknowledged throughout the industry."

Regulatory alert

In December, the Medicines and Healthcare products Regulatory Agency (MHRA)-- the British equivalent to the U.S. Food and Drug Administration -- issued an alert on Riata leads, noting that it had found 39 cases of "insulation damage" in patients since 2002.

The FDA said it is "aware of this particular issue based on our review of published information," but no alerts or recalls have been issued for the Riata abrasion issue.

Dr. Robert Hauser, a senior consulting cardiologist with the Minneapolis Heart Institute Foundation who is internationally known for researching defibrillator failures, said his office will likely probe FDA records on Riata. "I've heard about it," he said, "but I don't know the incidence rate."

Various case studies involving individual patients that have been published in medical journals this year have probed the abrasion issue with the Riata lead. All of them suggest fluoroscopic screening of patients with the lead.

Doctors at Queen Elizabeth Hospital in Hong Kong wrote in the journal PACE that St. Jude's "advisory board would be in a better position to strike the right balance between regular fluoroscopic screenings and all inconvenience or anxiety it generates to patients. We personally are more inclined toward the former" as patients with Riata leads are "mostly at high risk of sudden cardiac death to which protection with an intact and reliable ICD system is indispensable."

But even if advanced screening picks up an abrasion problem, Epstein said it's not clear what doctors should do. "It depends entirely on the patient," said Epstein, who is also an associate professor at Harvard Medical School.

Surgery to remove leads in the body can be difficult, since scar tissue can form over the cable. In some cases, the lead can be left inert in the body, after a new one is inserted.

"Do you abandon it and leave it behind, or do you replace it?" Epstein said. "It is an individual decision. It's a case-by-case decision."

Janet Moore • 612-673-7752