Summer 2005

Implantable Defibrillators Underused

A number of recent clinical trials have demonstrated that implantable cardioverter defibrillators (ICDs) can significantly reduce the risk of sudden death for people with heart failure. But cardiologists and their patients are not availing themselves of this technology, even when appropriate, cardiovascular researchers at UCSF Medical Center say.

Between 400,000 and 500,000 instances of sudden cardiac deaths occur in the United States each year. Patients with heart failure have long been known to be at much higher risk of sudden death from ventricular fibrillation. For much of the past, the focus has been on treating people who have survived a cardiac arrest. The odds of surviving such an event without an implanted defibrillator are extremely low.

Several previous studies demonstrated that implantable defibrillators save lives in patients who have survived a cardiac arrest. However, two recent studies – the Multicenter Automatic Defibrillator Implantation Trial (MADIT II) and the Sudden Cardiac Death in Heart Failure Trial (SCDHeFT) – demonstrated that defibrillators save lives in patients who are at risk for cardiac arrest, but have not yet had a heart attack.

In those studies, people who had an ejection fraction of 35 percent or less, regardless of whether they had any ventricular arrhythmias, were given implantable defibrillators that sense when ventricular fibrillation is occurring and shock the heart back into rhythm. MADIT II and SCDHeFT demonstrated that patients with defibrillators had a significantly lower chance of dying than those without the devices.

"In the last couple years, we've seen that if we put implanted defibrillators in early enough in high-risk groups, we can have an impact," says Jeffrey Olgin, M.D., director of Cardiac Electrophysiology at UCSF.

The results from MADIT II and SCDHeFT were so good that Medicare and most insurance plans now cover the use of ICDs in these patients.

"It's now becoming apparent that ICD therapy for patients with heart failure should be routinely thought about in the management of patients with heart failure, along with beta-blockers and ACE inhibitors," Olgin says. "ICDs are more invasive than beta-blockers, but have a bigger impact in terms of saving lives."

The procedure that Olgin and his team use to install an ICD is fairly short, lasting about an hour. Patients usually go home after a one-night stay in the hospital. The biggest challenge is to make sure that the device's programming and follow-up therapy are appropriate. The device can be monitored and reprogrammed remotely.

Currently, however, many qualified patients are not given the option of getting an ICD. "Many cardiologists and internists are just not keyed in on this data," Olgin says. "Everyone with an ejection fraction should be seriously considered for an ICD."

A new national trial, called MADIT-III (or MADIT-CRT) will investigate whether an even broader group could benefit from implanted devices and whether a new pacing therapy -- called cardiac resynchronization -- can improve survival and delay the progression of heart failure. Resynchronization therapy involves a biventricular pacemaker, which paces both ventricles, so that the chambers work better together.

In the MADIT-III trial, patients will get a hybrid device that combines a defibrillator with a biventricular pacemaker. The trial will test the hypothesis that both capabilities -- defibrillation and resynchronization therapy -- will benefit these patients.

The MADIT trials and other similar studies investigated the use of ICDs in a relatively small group of patients with a fairly high risk of sudden death. Future trials will look at larger groups at lower risk.

People with coronary artery disease have a very low risk, about 2 or 3 percent, of dying suddenly from an electrophysiological cardiac episode. But because this is such a large cohort, they still account for about 300,000 deaths a year. If the key risk factors for sudden death can be discovered in this group, then ICDs can save many more lives.

Olgin's research and that of his department are focusing on identifying genetic variations and other risk factors associated with a higher risk of cardiac sudden death, so that doctors can more readily identify the most appropriate patients for ICDs.

To contact Dr. Jeffrey Olgin, call (415) 476-5706.

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