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Promising Technologies Augur a New Era for Cardiac Medicine

Tests * Researchers are seeking more precise, noninvasive gauges of heart attack risk.


It's a common story: A middle-aged man who has recently received a clean bill of health from a physical exam suddenly drops dead of a heart attack.

Despite great strides in diagnosing heart disease and treating it with a wide range of increasingly sophisticated technologies, doctors still fall short of accurately predicting which patients are at greatest risk of suffering a heart attack. The problem is that it remains difficult to precisely assess the condition of a patient's coronary arteries using current technologies. And most techniques used to explore this question are expensive, invasive, time-consuming, imprecise or sometimes risky.

"Right now, most of our strategy centers around waiting for a heart attack to occur, hoping that the patient survives," says Sidney C. Smith Jr., past president of the American Heart Assn. and director of the Cardiovascular Center at the University of North Carolina in Chapel Hill. "But more than 250,000 don't each year."

At least a third of those who suffer heart attacks never have earlier episodes of chest pain that would alert them to a problem, according to a recent study published in the Journal of the American Medical Assn. And while many have the usual risk factors--high blood cholesterol, diabetes, high blood pressure, obesity, smoking, family history of heart disease--so do a lot of people who never have heart attacks. What's missing is a test that can more accurately predict who is likely to have a heart attack or other cardiac event.

For this reason, researchers are aggressively developing a number of noninvasive tests such as magnetic resonance imaging, ultra-fast CT scans and contrast echocardiograms that can allow them to look inside the hearts of high-risk but asymptomatic patients in bold new ways and better assess risk.

"These are the technologies that are going to have a major impact on how clinical decisions are made in the cardiovascular arena over the next few years," says Robert Balaban, scientific director of the Laboratory Research Program and chief of the Laboratory of Cardiac Energetics at the National Heart, Lung and Blood Institute.

Although still in the research and development phase, the new imaging techniques can already detect unsuspected heart damage, closely examine artery walls and identify the composition of atherosclerotic plaque--the accumulation of fatty material laced with collagen--all of which may help in assessing a patient's risk. The price of these screenings is declining, making them more accessible and likely to be used once they are widely available. Plus, they have the advantage of being noninvasive--and therefore less risky.

The Potential of MRI

With the publication last week in the journal Circulation of the first successful, high-resolution MRI images of coronary artery plaques in humans, scientists moved a step closer to making these new technologies a reality.

Magnetic resonance imaging is a painless, noninvasive technique that uses a highly uniform magnetic field to provide crystal-clear pictures of static body parts, from the brain to the knee. But the constant beating of the heart and blood flow in the coronary arteries have been hurdles to using MRI in real time for cardiac purposes.

Now, researchers at Mount Sinai Medical Center in New York report that they can "black out" blood flow in coronary arteries well enough to accurately visualize blockages and the coronary wall itself. The advance offers the potential to one day use MRI to avoid angiography or even replace it with noninvasive MRI.

Angiography is currently the gold standard for looking inside arteries, and it is used to diagnose and remove blockages via balloon angioplasty or to place stents that keep coronary arteries propped open. But it's an invasive procedure that carries its own risk. Angiography involves making a tiny incision in the femoral artery in the groin, then threading a catheter up the artery into the heart to inject dye.

While the dye is injected, an X-ray image of the heart projected on a monitor reveals the locations and approximate sizes of blockages. Although it can yield essential diagnostic information, angiography misses up to 70% of problems, according to a 1994 Scandinavian study, because it looks at the inside of arteries but can't reliably scan artery walls.

For this reason, the latest MRI findings promise "a much-needed, noninvasive method to identify 'vulnerable' plaques--those most likely to lead to sudden clot formation and an acute heart attack," says Claude Lenfant, director of the heart, lung and blood institute, which funded the study. "The new MRI technique may become an important tool to help physicians identify those individuals who are most likely to suffer a heart attack."

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