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Wednesday, February 4, 2009
When a vulnerable plaque ruptures in a coronary artery, the result for the patient can sometimes be catastrophic. A ruptured fatty plaque can block blood flow to the heart, and many cardiologists predict they cause two-thirds to three-quarters of all fatal heart attacks.
"The thing about vulnerable plaques is that they are commonly present, and with conventional means are next to impossible to identify,” says James Januzzi, MD, medical director of the Cardiac Intensive Care Unit at the Massachusetts General Hospital Heart Center. "Any means by which early and reliable identification of a vulnerable plaque could be achieved, would be soon followed by the next important step - if we can identify them, can we do anything about them? Can we prevent a heart attack before it occurs?"
Massachusetts General Hospital, under the direction of Ik-Kyung Jang, M.D., Ph.D., has been exploring these possibilities using optical coherence tomography (OCT), an intravascular imaging technology that researchers hope will give doctors a better means to identify these dangerous plaques - and eventually save lives.
Looking inside the artery
Vulnerable plaques, first described by cardiologists 10 years ago based on autopsies of heart attack victims, are difficult to recognize. Cholesterol tests do not always identify those at risk for rupture because the amount of cholesterol in the arterial wall is not always reflected in the amount in the bloodstream. Computed tomography (CT) and magnetic resonance imaging (MRI) scans may also miss them because of their low resolution.
Researchers decided that going inside the artery may be the best way to diagnose the problem.
By creating extremely high-resolution images from within the artery, OCT can pinpoint the microscopic characteristics of a vulnerable plaque, such as a larger lipid pool covered by a thin fibrous cap.
Using near-infrared light, OCT bounces light off the vessel wall and collects details down to 10 microns, a resolution 20 times better than CT. The resulting image of the coronary artery - rendered in a matter of seconds - offers a clear depiction of the plaque’s architecture.
“The development of OCT and the demonstration of its feasibility for intravascular imaging could enable the ability to capture in vivo what was previously seen only through a pathologist’s microscope,” says Dr. Jang.
Second generation OCT
Mass General demonstrated the first-ever use of OCT in a human subject in 2000. Since then, the understanding of vulnerable plaques has developed along with the technology. Dr. Jang is the national principal investigator to evaluate the second generation OCT system. Mass General is joined by Columbia University Medical Center and Stanford University Medical Center in this trial.
OCT images are taken in patients undergoing a percutaneous coronary intervention (PCI), such as a stent placement. Previously, the blood flow had to be interrupted by inflating a balloon and flushing the area with saline. The new system now being tested eliminates this occlusion of the artery.
“The advancement in the technology makes OCT less cumbersome. By reducing the number of steps, OCT technology becomes much more user friendly and the shorter procedure time makes the procedure safer for the patient,” says Dr. Jang.
The domain of previous OCT research has been in the characterization of vulnerable plaques. Dr. Jang’s current study moves the work forward by evaluating its clinical applications. The immediate goal of the research is to establish OCT’s potential roles in improving outcomes of PCI by helping doctors find optimum stent placement in the coronary artery.
“Of course, the long-term, ultimate goal is to identify plaques and prevent sudden cardiac death and heart attacks,” says Dr. Jang.
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