Carotid IMT en USC

BY Brenda Maceo MAY 1, 1996

Most health-conscious Americans know the best strategy for avoiding heart disease-a low-cholesterol, low-fat diet and regular exercise. But what has been difficult to know was just how well these efforts were paying off. Until now.

A remarkable and reliable new test developed by researchers in the division of cardiology at the USC School of Medicine and the Jet Propulsion Lab in Pasadena, California, can peer directly into the arteries without needles, catheters, or drugs. And because this test, called IMT, can be completed in 15 or 20 minutes, people who have never had the health of their arteries closely examined can now do so over the course of a lunch hour. (See “IMT in 1-2-3.”)

The new test uses an ultrasound device, similar to ones used during pregnancy, to create an image of the innermost layer of a major artery in the neck. Sophisticated computers then calculate the thickness of the blood vessel’s wall-the intima-media thickness (IMT)-with a high degree of precision. The thickness of the artery wall is a good indicator of coronary artery disease. Increasing thickness, or “hardening,” signals the beginnings of atherosclerosis.

Hardening arteries have traditionally been detected by cardiac catheterization, or angiogram, in which a hollow tube is inserted into the heart’s blood vessels to inject them with dye. Because this procedure is invasive and cannot be performed on patients who do not show symptoms of disease, it has no role in prevention.

IMT was the realization of a goal of the USC Atherosclerosis Research Unit to develop a technique that could noninvasively detect and monitor atherosclerosis.

In 1993, 1994, and most recently in March of 1996, Howard N. Hodis, M.D., director of the USC Atherosclerosis Research Unit, and assistant professor of medicine, preventive medicine, molecular pharmacology and toxicology, and his colleagues published a series of studies indicating that high-resolution ultrasound of the carotid artery was an excellent non-invasive option for tracking atherosclerosis and treatment effectiveness. Their findings built upon the pioneering work of David H. Blankenhorn, M.D., USC chief of cardiology from 1963-80, who, in addition to other seminal research, was the first to produce evidence that human atherosclerosis was reversible.

Until his death in 1993, Blankenhorn worked with Robert Selzer, a senior scientist and biomedical engineer at the Jet Propulsion Lab, to apply sophisticated image analysis techniques used in space to medical applications. Together, they were the first to develop techniques to quantitatively analyze angiographic images and devise a method for measuring arterial walls by automated computer analysis.

And while the image analysis is complex, the simplicity of the IMT procedure makes it available to people who are not candidates for angiograms-healthy individuals with no outward signs of heart disease.

By looking directly at the arterial wall, IMT can detect trouble years before other techniques, which means before any dangerous plaques form and begin to block the flow of blood around the heart.

“IMT is in keeping with the direction of where USC cardiology is headed in general-preventive care, early detection and early treatment of disease,” says David Faxon, M.D., professor of medicine, and chief of the USC division of cardiology. “It also is in keeping with the trend toward less invasive and more cost-effective procedures.”

Jacques Barth, M.D., associate professor of medicine and preventive medicine who, because of his involvement in the early development of the IMT procedure with Blankenhorn, was recruited to USC to build a preventive cardiology program, concurs: “Emergency rooms used to be the entry point for cardiology patients-now we have the ability to detect potential problems before they become life-threatening.”

“IMT gives us a window of opportunity to discriminate between individuals who should and should not be treated, as well as the ability to determine how well the treatments are working,” adds Hodis.

Faxon says he would recommend the IMT procedure to anyone with a family history of heart disease or with contributing factors such as smoking or high cholesterol. “In fact, it is our hope that some day this procedure will become part of the regular physical examinations for those at risk.

“Up until now,” continues Faxon, “it has not been well appreciated that heart disease is really advanced when it presents symptoms. Now, as part of the technological advances that are sweeping medicine, we know far more about the disease process. By the time most atherosclerosis or heart disease is symptomatic, it is very advanced and treatment is difficult. Early detection methods like IMT mean that we can have a greater impact on the disease.”