Implantable Defibrillators Save Lives

March 17, 2003 -- Implantable defibrillators that shock a misbehaving heart back into sync may be the best way to prevent one of the most common causes of heart-related deaths. A new study shows the expensive electronic devices are more effective than drugs in preventing sudden cardiac death in people most at risk, but determining exactly who fits into that high-risk category remains a difficult issue.

According to researchers, sudden cardiac death accounts for about 50% of all heart-related deaths and remains a considerable threat even though the overall number of deaths due to heart disease is declining. In fact, sudden cardiac death is on the rise among certain groups, such as women between the ages of 35 and 44.

The deadly condition is caused by an abnormal heart rhythm ( arrhythmia) that can cause the heart to stop beating, known as cardiac arrest. An implantable cardioverter defibrillator (ICD) works to prevent sudden cardiac death by stabilizing the heart rhythm and shocking it back into a normal rhythm. The small device is surgically implanted near the heart, and users commonly carry a battery pack to keep it going.

In the study, published in the March 18 issue of the Annals of Internal Medicine, researchers analyzed eight recent trials that compared the effectiveness of the devices with other types of therapy, such as drugs designed to control abnormal heart rhythms.

The study found that ICDs reduced the risk of sudden cardiac death by about 50%, regardless of the person's level of risk. But the effectiveness of the degree of benefit provided by device also varied.

Researchers say up to 90% of sudden cardiac deaths occur in people who experienced an arrhythmia for the first time and the others happen in people who have survived a previous cardiac arrest.

Although the study found ICDs were equally effective in preventing sudden cardiac death in people who had never suffered cardiac arrest and those who had survived a previous episode, researchers say their impact in preventing death depended on the degree of risk each individual faced.

Aside from a previous cardiac arrest, other risk factors for sudden cardiac death include heart disease, unstable heart rhythms, impaired pumping of the heart, and a family history of sudden cardiac death.

This study also helps identify patients who most need an ICD to prevent sudden cardiac deaths. Those who had the greatest degree of risks benefited most from the ICDs.

In an editorial that accompanies the study, Alfred E. Buxton, MD, of Brown Medical School, says it's clear that ICD is the best therapy for people who have survived an episode of cardiac arrest that can't be attributed to another cause. But a greater understanding of the underlying causes of the heart rhythm abnormalities that lead to sudden cardiac death is needed to determine which people with heart disease will benefit most from the costly devices, which also require frequent office visits for follow-up.

"Identifying potential victims in this huge reservoir of lower-risk patients is where the real challenge lies," writes Buxton. "We have only begun to scratch the surface of this more global problem."

SOURCE: Annals of Internal Medicine, March 18, 2003.