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Recent data from a landmark trial show that implantable cardioverter defibrillators (ICDs) help prolong the lives of people who have had heart attacks. Results of the Multicenter Automatic Defibrillator Implantation Trial (MADIT II)--which were presented at the American College of Cardiology Annual Scientific Session in March--demonstrated a 31 percent drop in the death rate among heart attack survivors implanted with defibrillators compared to those receiving only drug therapy. The study's findings, published in the New England Journal of Medicine, could have an immediate impact on the treatment and prevention of sudden cardiac death.
"It's big news. It's a major reduction," commented University of Rochester's Dr. Arthur Moss, lead investigator of the multicenter trial. "To get a 31 percent reduction in mortality is pretty unusual and dramatic. This study was done in 76 centers, so it was a very representative population of the patients at risk."
The $7 million trial on the use of ICDs to prevent sudden cardiac death in high-risk cardiac patients, such as Vice President Dick Cheney, was so convincing that an independent review panel decided the device's effectiveness no longer needed to be proven.
While many studies over the years have demonstrated the benefits of ICDs, the MADIT II trial of 1,232 patients convincingly showed the benefits of ICDs implanted in patients who had a prior heart attack and an ejection fraction of less than 30 percent. Ejection fraction is a measure of the function of the left ventricle, representing the percentage of blood ejected from the main pumping chamber with each heartbeat. A normal ventricular ejection fraction is 50 percent or higher; anything less indicates heart muscle damage or weakening.
The damaged tissue can cause abnormal heartbeats, or arrhythmias, placing one at risk for sudden cardiac death. Implanted under the collarbone like a pacemaker, an ICD can detect irregular and potentially fatal arrhythmias--known as ventricular tachycardia or fibrillation--and deliver a shock to restore normal rhythm.
The conclusive findings could significantly enlarge the population considered eligible for the ICD.
"With the new indications for the device, the number of patients who are eligible to receive it will be doubled," said Dr. David S. Cannom of Good Samaritan Hospital in Los Angeles and a member of the trial's Steering Committee. "Physicians are not usually encouraged to look for expensive therapies like the defibrillator. These data, from my standpoint, speak for themselves. The device works--it's incredibly effective at defibrillating the heart."
Under current FDA guidelines, about 300,000 Americans are eligible each year to receive an ICD. Based on the new findings, Dr. Moss estimates that over two million people in the United States could become eligible for the implanted devices.
"MADIT II is a landmark study that demonstrates the further benefit of implantable defibrillator therapy," commented Dr. Moss. "The ICD prolongs lives."
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