Imaging technology could guide therapy designed to prevent heart
attacks
20 April 2005
A catheter-based imaging technology called optical coherence tomography
(OCT) can successfully identify the characteristics of coronary plaques in
patients with various cardiac symptoms. The report from researchers at
Massachusetts General Hospital (MGH) will appear in the journal
Circulation and has received early online release at
http://www.circulationaha.org
"More than 1.2 million people die from coronary artery disease every
year, a quarter of them before or soon after arriving at the hospital," says
Ik-Kyung Jang, MD, PhD, director of cardiovascular clinical research in the
MGH Cardiology Division and lead author of the current study. "The ability
to identify dangerous plaques before they rupture and produce a heart attack
or sudden cardiac death will be crucial to innovative preventive therapies."
Plaques are deposits of fats, cholesterol and other materials that
collect in major arteries, restricting or sometimes blocking blood flow.
While some plaques are relatively stable, others are vulnerable to rupture
and release their contents into the bloodstream, causing a blood clot to
form. Heart attacks and other acute coronary events usually result from the
rupture of high-risk, vulnerable plaques in coronary arteries, and the
characteristics of those plaques have been determined primarily by autopsy
studies.
OCT uses infrared light delivered via fiberoptic catheter to produce
high-resolution, cross-sectional images of blood vessels. Study co-authors
Guillermo Tearney, MD, PhD, of the MGH Pathology Department and the Wellman
Center for Photomedicine at MGH, and Brett Bouma, PhD, also of the Wellman
Center, developed the use of OCT to visualize coronary arteries, including
vulnerable plaques. The technology developed in their laboratory was used
for this first study to examine the structure of plaques in patients with
cardiac disease.
The study enrolled patients scheduled to undergo cardiac catheterization
for whom angiograms or other imaging techniques had identified the arterial
lesion responsible for their symptoms. Participants either had experienced a
recent heart attack or had acute coronary syndrome ( ACS ), a set of
symptoms associated with reduced blood supply to the heart muscle. A third
group had stable angina, chest pain that occurs with physical or mental
stress, which is not usually related to plaque rupture. Clear OCT images of
the suspicious lesions were obtained for 20 heart attack patients, 20 with
ACS and 17 with stable angina.
Vulnerable plaques are believed to have three major characteristics — a
deposit of lipids ( fats ), a thin cap of fibrous material covering the
lipid pool, and infiltration of the immune cells called macrophages. The OCT
images showed that the heart attack and ACS patients had more lipid in their
plaques and significantly thinner fibrous caps than did the stable angina
patients. Overall, vulnerable plaques were identified in 72 percent of the
heart attack patients, 50 percent of those with ACS and only 20 percent of
stable angina patients.
"This is the first technique that allows us to study the structural
changes underlying vulnerable plaques in living patients, and it supports
the conclusions of previously reported postmortem studies," says Jang. "We
still need to gather more data to confirm these characteristics, and our
group will carry out further studies of how plaques develop and rupture.
Someday OCT may provide information that will guide treatments to prevent
plaque rupture and its disastrous consequences." Jang is an associate
professor of Medicine at Harvard Medical School.
Along with the study's senior author Bouma and Tearney, additional
co-authors are Briain MacNeill, MD, Masamichi Takano, MD, and Fabian
Moselewski, of the MGH Cardiology Division; Nicusor Iftima, PhD, and Milen
Shishkov, PhD, of the Wellman Center; Stuart Houser, MD, and Thomas Aretz,
MD, MGH Department of Pathology; and Elkan Halpern, MGH Department of
Radiology. The study was supported by grants from the Center for Integration
of Medicine and Innovative Technology, for development of the imaging system
platform; the National Institutes of Health and Guidant Corporation.
Massachusetts General Hospital website:
www.mgh.harvard.edu
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