In a study of more than 2,000 adults, researchers found that two MRI measurements of the abdominal aorta - the amount of plaque in the vessel and the thickness of its wall - are associated with future cardiovascular events, such as a heart attack or stroke. Results of the study are published online in the journal Radiology.
“This is an important study, because it demonstrates that atherosclerosis in an artery outside the heart is an independent predictor of adverse cardiovascular events,” said the study’s lead author, Christopher D. Maroules, M.D., a radiology resident at the University of Texas Southwestern Medical Center in Dallas and lead author. “MRI is a promising tool for quantifying atherosclerosis through plaque and arterial wall thickness measurements.”
Atherosclerosis is a condition in which fat, cholesterol and other substances collect within the arteries, forming plaque. As plaque accumulates, the artery narrows, limiting blood flow. The condition can occur in any artery, including the cerebral (brain) and coronary (heart) arteries and the aorta, which carries oxygenated blood from the heart through the abdomen to the rest of body. The aorta is the largest artery body.
In the study, researchers analyzed abdominal MR images of 2,122 participants (mean age 44) in the Dallas Heart Study, a multiethnic population-based study of healthy adults from Dallas County, Texas. Two measurements were obtained from the MR images: mean abdominal aortic wall thickness, or the thickness of the vessel wall, and the amount of plaque buildup, referred to as the aortic plaque burden.
Following imaging, study participants were monitored for a period of 7.8 years. During that time, 143 participants experienced an adverse cardiovascular event in which arterial blood flow was obstructed, resulting in death or medical intervention. Researchers categorized the events as related to the heart (cardiac events) or to other arteries (called extra-cardiac vascular events) such as those in the brain or abdomen.
Of the 143 cardiovascular events, 34 were fatal. Seventy-three were non-fatal cardiac events, including heart attack or coronary revascularization, and 46 were non-fatal extra-cardiac vascular events, such as stroke or carotid revascularization.
Using the MRI measurements, the researchers found that increased abdominal aortic wall thickness correlated with a greater risk for all types of cardiovascular events. An increase in both wall thickness and aortic plaque burden was associated with an increased risk for non-fatal extra-cardiac vascular events.
“These MRI measurements may add additional prognostic value to traditional cardiac risk stratification models,” Dr. Maroules said.
Abdominal aortic aneurysm (AAA) rupture has been recognized as a significant cause of mortality for adults aged >60 years in the developed world for some time. AAAs are usually asymptomatic until rupture occurs, and screening programs have been shown to reduce mortality in men aged >65 years. Most AAAs detected by ultrasound are <50 mm in diameter, and there is currently no recognized treatment for these AAAs. Studies aimed at understanding the pathogenesis of AAA are important as they may identify targets for novel therapy.
The mechanisms initiating and stimulating progression of AAA are still poorly understood, with most knowledge coming from cross-sectional association studies in humans and increasingly from investigations in animal models. Such studies suggest the importance of inflammatory pathways, matrix degradation, thrombosis, hemodynamic forces, and a host of associated signaling molecules in AAA pathogenesis. On the basis of the new insights from rodent models, a number of novel strategies are being investigated as potential treatments for small AAA. To date, there have been very few well-designed randomized controlled trials assessing the efficacy of medication in reducing AAA complications in patients.
Patients with AAAs frequently have atherosclerosis, and numerous studies show the association of coronary heart disease and peripheral atherosclerosis with AAA. Whether this association between AAA and atherosclerosis is causal or simply due to common risk factors is unknown. One possibility is that an AAA develops as a pathological response to aortic atherosclerosis, a theory first suggested more than half a century ago, when the term “atherosclerotic aneurysms” was commonly used, but still prevalent today.
MR imaging of the abdominal aorta is less technically challenging than other vascular imaging exams because of the large size of the vessel and its lack of proximity to a moving organ, such as the heart or the lungs. In addition, images of the abdominal aorta are often captured when patients undergo other exams, such as MRI of the spine or abdomen.
“The abdominal aorta is incidentally imaged on a regular basis,” Dr. Maroules said. “Radiologists can infer prognostic information from routine MRI exams that may benefit patients by identifying subclinical disease.”
According to Dr. Maroules, further MRI research will contribute to a better understanding of the progression of atherosclerosis, which scientists believe begins with a remodeling or thickening of the vessel wall prior to the buildup of plaque.
Most aortic aneurysms occur in the part of your aorta that’s in your abdomen. Although the exact cause of abdominal aortic aneurysms is unknown, a number of factors may play a role, including:
Tobacco use. Cigarette smoking and other forms of tobacco use appear to increase your risk of aortic aneurysms. In addition to the damaging effects that smoking causes directly to the arteries, smoking contributes to the buildup of fatty plaques in your arteries (atherosclerosis) and high blood pressure. Smoking can also cause your aneurysm to grow faster by further damaging your aorta.
Hardening of the arteries (atherosclerosis). Atherosclerosis occurs when fat and other substances build up on the lining of a blood vessel, increasing your risk of an aneurysm.
Infection in the aorta (vasculitis). In rare cases, abdominal aortic aneurysm may be caused by an infection or inflammation that weakens a section of the aortic wall.
Aneurysms can develop anywhere along the aorta, but when they occur in the upper part of the aorta, they are called thoracic aortic aneurysms. More commonly, aneurysms form in the lower part of your aorta and are called abdominal aortic aneurysms. These aneurysms may also be referred to as AAA or triple A.
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“Abdominal Aortic Atherosclerosis at MR Imaging Is Associated with Cardiovascular Events: The Dallas Heart Study.” Collaborating with Dr. Maroules were Eric Rosero, M.D., Colby Ayers, M.S., Ronald M. Peshock, M.D., and Amit Khera, M.D., M.Sc.
Radiology is edited by Herbert Y. Kressel, M.D., Harvard Medical School, Boston, Mass., and owned and published by the Radiological Society of North America, Inc.
RSNA is an association of more than 51,000 radiologists, radiation oncologists, medical physicists and related scientists promoting excellence in patient care and health care delivery through education, research and technologic innovation. The Society is based in Oak Brook, Ill. (RSNA.org)
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