Recalled St. Jude Medical Inc. wires, still in use to connect life-saving defibrillators to the hearts of 79,000 patients, had multiple defects that led to melted conductors, electrical abnormalities and shocks, a study found.
St. Jude stopped selling its Riata wires in December, 2010, and recalled them last year on reports they could break through their insulation. Surgery to remove the leads may present higher risks than keeping them in, U.S. regulators have said.
A study of 105 reports on failed wires found that two-thirds had multiple defects, often up and down their length. The wires can produce noise, like static on a television set, which may result in unnecessary shocks or reduce the energy needed to stimulate the heart, according to the study reported today at the American College of Cardiology meeting in Chicago.
“The problem with this whole defect is there is no easy way to pick it up until an event happens,” said Robert Hauser, the Minneapolis Heart Institute cardiologist who authored the report, in a telephone interview. “It’s an all or nothing situation. We are trying to figure out how to manage these patients, or a way to monitor them safely and effectively.”
A separate analysis from researchers in Northern Ireland presented at the meeting found 2.6 percent of patients with the leads develop protruding wires each year, and 19 percent of patients have the complication.
Mark Carlson, chief medical officer for St. Paul, Minnesota-base St. Jude, said the extruding wires have another coating of insulation and most still work properly.
The company is conducting a clinical trial with more than 500 patients to determine how frequently the problem occurs and what happens to the wires over time, Carlson said in an interview at the meeting.
The appearance of a protruding wire shouldn’t be cause for alarm or an overreaction, Carlson said. Among the devices returned to St. Jude because of electrical abnormalities that had protruding wires, the cables still functioned normally 85 percent of the time. Twelve percent had another abnormality that was likely responsible for the device’s breakdown, he said.
“Seeing this does not mean an electrical malfunction,” he said in an interview. “This is the opposite of a picture is worth a thousand words. We still need to focus on the electrical function of the lead.”
Cardiac defibrillators are devices about the size of a deck of cards that are implanted in the chest and connected to the heart via wires, called leads. They are used to shock the heart back into a normal rhythm if it starts beating erratically or stops entirely. They are typically used in patients who have survived a cardiac arrest or have dangerous heart rhythms.
Next Generation Wires
One risk for St. Jude is that doctors will stop using the company’s next generation Durata leads because of concerns stemming from the Riata findings, said Raj Denhoy, an analyst with Jefferies & Co. in New York. While there are no reports of similar failures with Durata, that may not stop physicians from shying away from it, he wrote in a note to investors.
“This thesis doesn’t require a smoking gun on Durata, and as the mechanism of failure is likely time dependent, it may take a year or more to see a higher failure rate in this newer lead,” he wrote in a March 21 note to investors. “We believe clinicians will increasingly become unwilling to take the chance that the Durata could fail at a higher rate over time.”
Researchers have speculated that the movement of the Riata wires within the insulated cord frays the coating and allows them to break free.
Hauser theorizes that once the wire is exposed, it starts to flex and causes additional damage that worsens over time. The most damage may come in the heart, where the flexing is greatest, he said. The silicone coating may also creep away from pressure points over time, thinning the insulation, he said.
“This is the most difficult and challenging device problem I’ve seen in 40 years,” Hauser said. “It’s a very unique failure mode. It’s never been seen before in a defibrillator or pacemaker lead. And it’s very troubling because no one knows what the natural history of this will be.”
The study was funded by the Minneapolis Heart Foundation and Abbott Northwestern Hospital Foundation.