Sunday, February 19, 2006

Preventing sudden death with implantable defibrillators

Preventing sudden death with implantable defibrillators: "Preventing sudden death with implantable defibrillators"

In the current issue of the New England Journal of Medicine (March 21), researchers report results from a study in which individuals who had a prior heart attack received an implantable defibrillator to keep their hearts from stopping suddenly, causing sudden death. Implantable defibrillators are devices used in people who have fast heartbeats, conditions called recurrent or sustained ventricular tachycardia or fibrillation. Leads positioned inside the heart sense cardiac rhythm and deliver electric shocks to pace the heart as needed.

Results were released early today at the American College of Cardiology meeting in Atlanta by Arthur Moss, M.D., of the University of Rochester in New York, during the Late-Breaking Clinical Trials session.

The devices are used to prevent sudden death in patients with ventricular fibrillation, but this is the first large study that has tested the devices in individuals who do not have such abnormal rhythms, and who are at high risk for sudden death because their hearts are damaged from prior heart attacks.

The study, called MADIT-II (Multicenter Automatic Defibrillator Implantation Trial), included 1,232 patients who had suffered a heart attack and had an ejection fraction of 30 percent or less. Ejection fraction is a measure of how much blood is pumped from the heart chamber. Normal ejection fraction is between 50 and 75 percent.

Patients were randomly assigned to either receive the implantable defibrillator or treatment with conventional medical therapy. There was a 31 percent reduction in the risk of death in the defibrillator group compared with the conventional-therapy group.

On the downside, more patients treated with the defibrillator suffered worsening heart failure - 19.9 percent compared to 14.9 percent - for the medically-treated group.

According to David Faxon, M.D., president of the American Heart Association, "This study answers some important questions about whether implantable devices are better than medical therapy in preventing sudden death, which accounts for about one half of all deaths from coronary heart disease. The reduction seen in this study is substantial.

"Should patients with these characteristics - prior heart attack and ejection fraction less than 30 - be treated with an implantable defibrillator? It's too soon to make sweeping recommendations without considering the increased costs and complications from heart failure associated with defibrillators.

"The next step is to narrow in on the type of patient who would benefit most, maximizing the benefits, while keeping costs low."

It should also be stressed that the "high tech" approach in treating patients may not be needed if more individuals focused on "low tech" methods to prevent coronary artery disease, such as getting plenty of exercise, not smoking and watching one's diet.

It's also important for individuals to get to the hospital as soon as they have signs of heart attack, because we may be able to limit the amount of heart damage, thus averting the need for a defibrillator, says Faxon.

American Heart Association


Implantable Cardioverter Defibrillator

Implantable Cardioverter Defibrillator

An implantable cardioverter defibrillator is used in patients at risk for recurrent, sustained ventricular tachycardia or fibrillation.

The device is connected to leads positioned inside the heart or on its surface. These leads are used to deliver electrical shocks, sense the cardiac rhythm and sometimes pace the heart, as needed. The various leads are tunnelled to a pulse generator, which is implanted in a pouch beneath the skin of the chest or abdomen. These generators are typically a little larger than a wallet and have electronics that automatically monitor and treat heart rhythms recognized as abnormal. Newer devices are smaller and have simpler lead systems. They can be installed through blood vessels, eliminating the need for open chest surgery.

When an implantable cardioverter defibrillator detects ventricular tachycardia or fibrillation, it shocks the heart to restore the normal rhythm. New devices also provide overdrive pacing to electrically convert a sustained ventricular tachycardia, and "backup" pacing if bradycardia occurs. They also offer a host of other sophisticated functions (such as storage of detected arrhythmic events and the ability to do "noninvasive" electrophysiologic testing).

Implantable cardioverter defibrillators have been very useful in preventing sudden death in patients with known, sustained ventricular tachycardia or fibrillation. Studies are now being done to find out how best to use them and whether they may have a role in preventing cardiac arrest in high-risk patients who haven't had, but are at risk for, life-threatening ventricular arrhythmias.

According to the American Heart Association Heart and Stroke Statistical Update, in 1998 (the most recent statistics available) there were 26,000 ICD procedures.