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Jan. 5, 2007 -- As many as one-third of heart patients who get implanted heart defibrillators -- like the one Vice President Dick Cheney has -- might not benefit from them; a simple heart-rhythm test may help identify these patients, new research suggests.
The noninvasive test uses computer technology to gauge a person's risk for sudden cardiac death.
Researchers from the University of Michigan Cardiovascular Center, the VA Ann Arbor Healthcare System, and the Ohio Heart and Vascular Center in Cincinnati found that patients who performed well on the test had the same low risk of death whether they had implanted defibrillators or not.
If the findings are confirmed, the test could save hundreds of millions of dollars annually in health care costs in the U.S. alone, researchers say.
But a heart specialist who spoke to WebMD says many important questions remain unanswered.
"Over the last 10 years or so we have evaluated a lot of tests and a lot of tests have failed," says Virginia Commonwealth University professor of cardiology Kenneth Ellenbogen, MD. "[The tests] looked promising in smaller studies, but in larger studies they missed a lot of patients who had cardiac arrest."
Sudden cardiac death due to electrical problems of the heart accounts for roughly 300,000 deaths a year in the U.S. People with certain heart conditions are at greater risk.
Sudden cardiac death is due to electrical problems in the heart; it is not a heart attackheart attack. Such conditions can include cardiomyopathycardiomyopathy (heart muscle disease) due to past heart attack, among other things.
Implanted cardioverter defibrillators (ICDs) are often recommended for these high-risk patients as a preventive measure. Like pacemakerspacemakers, ICDs are surgically implanted. But while pacemakers deliver mild, continuous electrical impulses to maintain a suitable heart rate and rhythm, defibrillators can deliver a bigger shock of electricity when they detect an abnormal heart rhythm that can lead to sudden cardiac arrest.
The devices work so well that the U.S. government recently expanded coverage for high-risk patients. It is now estimated that 50,000 MedicareMedicare recipients qualify for them annually, at a lifetime cost of roughly $90,000 per recipient.
The problem has been that the strategies for determining who will benefit from ICDs have been inadequate, University of Michigan researcher Paul S. Chan, MD, tells WebMD.
"There is no doubt that these devices are extremely effective for the right patient, but they are also very expensive and not everyone benefits," he says.
In their study involving 768 heart patients considered candidates for ICDs based on conventional testing, Chan and colleagues evaluated the usefulness of a test called microvolt T-wave alternans (MTWA) for predicting who would benefit from the device.
All of the patients had survived heart attacks and had permanent damage to the heart muscle as a result.
Roughly two-thirds had either positive or inconclusive MTWA test results. During up to three years of follow-up, these patients were 70% less likely to die from an abnormal heart rhythm if they had ICDs.
In the remaining one-third of patients with negative MTWA tests, no significant reduction in cardiac arrest-related deaths was seen among patients with the implanted defibrillators.
The study is published in the Jan. 2/9 issue of the Journal of the American College of Cardiology.
Ellenbogen acknowledges that the latest MTWA findings are impressive. But he points out that in another recent study the test did not perform as well.
In that trial, reported last November at the annual meeting of the American Heart Association (AHA), MTWA testing was compared with a more invasive and expensive screening method.
The best results were obtained when the two tests were used together.
"That study definitely did not show to be as useful as a single measure of risk as this trial did," says Ellenbogen, a spokesman for the AHA