MINNEAPOLIS -- One in five devices used to shock hearts back into a normal rhythm fail to work properly after 10 years, a study found.
Electrical wires that connect cardiac defibrillators to the heart were at fault, according to the research. Malfunctioning wires, called leads, sometimes caused the devices to shock the heart unnecessarily, and would sometimes fail to work when the heart began beating abnormally or stopped altogether.
The result may be death, increased costs to repair or remove the device, and increased anxiety for patients, the researchers said. The leads offer a bigger risk for patients than battery failures that triggered recalls since 2005 of thousands of devices made by Medtronic Inc., Boston Scientific Corp., and St. Jude Medical Inc., the researchers said.
"These data emphasize that lead failure may become a prominent concern," in patients who survive past 10 years, said researchers led by Thomas Kleemann, an electrophysiologist at Herzzentrum Ludwigshafen in Germany. "The high incidence of lead complications in these patients should be considered at time of implantation."
The study, published in the May 1 journal Circulation, found the annual failure rates rose with time and occurred in all models. The risk was highest for women and healthier patients who are most likely to live for years.
Many patients didn't make it to the 10-year mark, with researchers calculating a 60 percent survival rate for the leads eight years after implantation.
Kleemann and his colleagues followed 990 consecutive patients who received their first defibrillator in Ludwigshafen between 1992 and 2005. Patients were monitored every three months for an average of 2 1/2 years. Overall, 148 leads, or 15 percent, failed.
The leads are used to track abnormal heart rhythms and transmit an electric shock to the heart to restore proper beat. Almost 70,000 of devices that cost $30,000 or more are implanted each year in the United States, according to the American Heart Association.
The most common complication, responsible for 56 percent of lead defects, stemmed from insulation problems. Others included fractured wires, electrical circuit problems, and sensors.
Officials at Medtronic, the Minneapolis-based industry leader, and Boston Scientific, based in Natick, didn't return phone calls seeking comment.