Silicone wires in newer defibrillators less reliable than older polyurethane-insulated leads

German researchers say the newer wire leads now used in implantable cardioverter defibrillators (ICDs) are not as reliable as first thought.

The researchers at the Herzzentrum Ludwigshafen Cardiovascular Research Center say the annual defect rate was as high as 20% after 10 years of use for the silicone wire leads now used in implantable cardioverter defibrillators (ICDs) compared to 7% for the older polyurethane-insulated leads.

The silicone leads had initially promised to be more reliable, but in fact according to the German study they are less reliable than earlier versions.

Researcher Dr. Thomas Kleemann, says the findings are surprising as it appears that the silicone-coated wires develop problems even earlier than the polyurethane-coated wires.

As many as 68,000 ICDs were implanted in the U.S. in 2004; the technology is designed to continuously monitor heart rhythms and shock the heart back into its normal rhythm when an arrhythmia occurs or the heart stops beating altogether.

The wire leads that connect the defibrillator to the heart are threaded through the blood vessels and in 1997 silicone-insulated leads replaced polyurethane ones in the hope that they would present fewer problems.

For their study Kleemann and colleagues examined the annual lead defect rate among 990 patients who received the implantable devices at a heart clinic in Ludwigshafen, Germany, between 1992 and May 2005.

They found a total of 148 (15%) experienced a lead defect during follow-up, and the average time to failure was 4.7 years; a lead defect is a severe lead failure that needs surgery to fix the problem.

The researchers found that lead defects occurred in both newer and older ICD models, but they occurred more often in younger patients, female patients, and those with better pumping function of the heart.

This is the case because these were the patients who tended to live long enough to experience the lead defects.

Although 207 patients died during the follow-up, the researchers found that 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.

Experts say patients with either of the ICDs need not panic but should have their device checked by a doctor every three to six months.

The researchers confirm that most problems can be detected during routine visits to the doctor and they say in their study 65% of the lead defects were found during routine evaluation of the devices.

Experts say the technology used in ICDs has improved and they are becoming more reliable but patients need to recognise that an implantable device such as an ICD or a pacemaker, just like any other technology will at times need to be fixed.

They say the latest technology now makes it possible to run what amounts to a continual check on ICDs, with bedside monitors that transmit data to manufacturers.