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Biology Articles » Microbiology » Implanted Heart Devices Prone To Silent, Dangerous Staph Infection

Implanted Heart Devices Prone To Silent, Dangerous Staph Infection

DALLAS (August 27, 2001) - Pacemakers and other implanted heart devices prolong the lives of people with heart rhythm problems. However, if an individual with one of these devices develops a staph infection it could pose a potentially life-threatening danger, researchers report in today's Circulation: Journal of the American Heart Association.

This study is believed to be the largest prospective evaluation of individuals with permanent pacemakers or implantable cardioverter-defibrillators (ICDs) who have Staphylococcus aureus bacteremia (staph infection in the blood). A pacemaker is a small, battery-operated device that helps the heart beat in a regular rhythm. An ICD monitors heart rhythm and delivers electric shocks to correct abnormal rhythms.

"If a patient has an implanted cardiac device and develops a Staphylococcus aureus infection, the patient's physicians should be worried that the device is infected," says Anna Lisa Chamis, M.D., a cardiology fellow at Duke University Medical Center in Durham, N.C. "Our data suggest that if the infection occurs within one year of implantation, the device ends up being infected in about three-fourths of the cases. The major new finding is that the majority of the device infections showed no obvious signs."

In this study, most of the staph infections did not originate with the device. The most common cause was a tissue infection originating in another part of the body that then spread to the heart device. However, the heart device was thought to cause the staph infection in 18 percent of cases.

Cardiac device infection carries a high risk of serious illness and death. Previous studies have shown that it occurs in up to 20 percent of permanent pacemakers and up to 1.3 percent of ICDs. According to the American Heart Association Heart and Stroke Statistical Update, in 1998 (the most recent statistics available) there were 26,000 ICD procedures and 170,000 pacemaker procedures.

Chamis and her associates evaluated 33 individuals with cardiac pacemakers or defibrillators who had staph infections. In each case, systemic infection was documented by blood tests. The infection had spread to the device in almost half (15) of the cases.

In some cases, device infection will produce redness, inflammation, abnormal growths or deposits on the device or its lead wire. Some of these can be detected by echocardiography, a procedure that produces images from sound waves bounced off the heart. In the absence of obvious signs of infection, blood tests can confirm a staph infection and help guide the decision to remove an implanted device.

The researchers found that 60 percent of the infected devices showed no obvious signs such as redness or pain in the tissues covering the implanted device. Device infection was confirmed only after it was removed for inspection.

Cardiac device infection can be treated by removing the device or by administering antibiotics. However, patients who did not have the devices removed were more likely to die, says Chamis. Removing the device and implanting a replacement is a major surgical procedure, therefore, accurate documentation of infection is essential to avoid unnecessary surgery, according to the researchers.

The findings also showed that 12 of 33 staph infections occurred within a year of device implantation, defined as early infection. Nine of these early infections involved the device. The remaining 21 cases occurred a year or more after device implantation, termed late infection. In six of these cases a device infection was confirmed, and nine others had suspected device involvement.

The researchers conclude that early staph infection carries a high probability of cardiac device involvement. With late infection the device is unlikely to be the initial source of bacteria in the blood, and few signs of device involvement occur. However, the study showed that the device was involved in at least 28 percent of late infections.

Therefore, the researchers support the removal of cardiac devices among most patients who develop staph infection, whether device infection is confirmed or not. Whether the findings apply to infections other than those caused by Staphylococcus aureus is unclear, says Chamis. However, the results probably do apply to other types of implantable devices.

"Other groups have shown that infections, including this specific type of infection, occur in prosthetic joints at rates similar to what we observed," she says. "Catheters that remain in place in the body and other more permanent types of intravenous devices also have been studied, and similar rates of infection have been reported."

Source: American Heart Association. August 2001 


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