By Ed Edelson
Monday, April 30, 2007 12:00 AM
MONDAY, April 30 (HealthDay News) -- The wires through which implanted defibrillators deliver the electric jolts that keep hearts beating normally aren't as reliable as many might think, a German cardiovascular research center reports.
Even though the composition of those wires was changed in 1997 to improve reliability, both the newer and older versions of these defibrillators show an annual rate of defect of almost 20 percent a decade after implantation, finds a study in the May 1 issue ofCirculation. Given that these devices are used to treat arrhythmias, dangerously irregular heartbeats that can lead to cardiac arrest, the researchers note that such a significant failure rate poses a public health threat.
"It's a very serious problem, because if the leads [wires] have defects, they have to be changed or the device cannot terminate fibrillation," said study author Dr. Thomas Kleeman, a clinical electrophysiologist at Herzzentrum Ludwigshafen. "Surgery to change them is not so easy," he added.
It is a problem that must be faced by Americans who are walking around with defibrillators inside them, some 68,000 people in 2004, the most recent year for which statistics are available.
Kleeman and his colleagues looked at the reliability of defibrillators implanted in 990 people by the Ludwigshafen center between 1992 and May 2005. They found an average 15 percent defect rate in the wires, with a median time to failure of 4.7 years. A check found that other German institutions were facing the same problem, Kleeman said.
It's generally a simple issue of wear-and-tear, he said. "If the defibrillator is in for many years, the chance to failure increases," Kleeman said, with the likelihood of failure increasing with the number of leads per defibrillator. But, he added, failure appears to be more common in women, younger people and those whose left ventricle was healthier when the device was implanted.
The cause of failure was insulation problems (56 percent); fractured wires (12 percent); loss of ability to detect the abnormal electrical pulse in the heart chamber (11 percent); abnormal impedance, a problem in the electrical circuit (10 percent); or a sensing failure (10 percent).
While 11 percent of those who got defibrillators during the study died, none of the deaths were attributed to lead failure. Of that group, 55 percent died of congestive heart failure, 13 percent died from non-cardiac causes, 9 percent from other cardiovascular problems, and 2 percent from sudden death. In 21 percent of the cases, the cause of death remains unknown.
Manufacturers changed the insulation of defibrillator leads in 1997, switching from polyurethane to silicone insulation, Kleeman noted. The failure rate of the newer leads appears to be higher over the first few years, he said. Slightly more than 90 percent of the older wires survived five years without failure, while only 80 percent of the newer wires accomplished the same feat.
"The newest wires now use polymers of both," Kleeman said. "That started last year, and they might be better."
But the study is a reminder that eternal vigilance is needed in medicine, especially for devices on which life depends, said Dr. Kenneth A. Ellenbogen, director of the department of electrophysiology at Virginia Commonwealth University, and a spokesman for the American Heart Association.
"Several years ago, I wrote an editorial that called the ICD [implantable cardioverter defibrillator] lead the Achilles heel of this therapy," Ellenbogen said. "It is important not to install an ICD and forget about the patient. These patients need to be followed closely and carefully to detect problems many years after they are implanted."
ICDs should be checked frequently, as often as once a month in some cases, Ellenbogen added. "Certainly with patients living longer and longer and newer technology being developed to make the devices last longer, there can be a significant risk of failure," he said.
The latest technology makes it possible to run what amounts to a continual check on ICDs, with bedside monitors that transmit data to manufacturers, Ellenbogen said. And the news about the latest ICDs is not all that bad, he noted.
"That certainly has been my clinical experience, that they are getting better," he said.
The workings of an ICD are explained by the American Heart Association.
SOURCES: Thomas Kleeman, clinical electrophysiologist, Herzzentrum Ludwigshafen, Germany; Kenneth A. Ellenbogen, M.D., director, department of electrophysiology, Virginia Commonwealth University, Richmond; May 1, 2007,Circulation