New research explores limits of non-invasive coronary imaging tests

Study examines whether multi-slice computed tomography detects more than just plaque build-up in patients with moderate risk of coronary artery disease

If multi-slice computed tomography (MSCT) shows that a patient has plaque build-up in the artery walls, does it also mean that there is actual reduced blood flow in the artery" New research shows that more often than not, the plaque in coronary artery walls does not necessarily harm blood flow to the heart. Two distinct non-invasive imaging tests were used to examine complimentary characteristics of coronary artery disease (CAD) – plaque build-up and artery blockage. The research, led by Jeroen J. Bax, MD, PhD, Department of Cardiology at the Leiden University Medical Center in the Netherlands, appears in the Dec. 19 edition of the Journal of the American College of Cardiology.

In a quest to find new, non-invasive ways to detect the blockage of coronary arteries, researchers sought to determine whether MSCT, a promising non-invasive imaging technique that detects narrowing of the coronary arteries due to plaque build-up (atherosclerosis), can also accurately identify reduced blood flow in the arteries due to the blockage (ischemia).

The study compared MSCT to another non-invasive imaging technique, myocardial perfusion imaging (MPI) with single-photon emission computed tomography (SPECT), among patients with a moderate risk of CAD to find the answer. CAD occurs when a buildup of plaque in the arteries prevents oxygen-rich blood from nourishing the heart muscle.

Results of the study show that only 45 percent of patients who were shown to have atherosclerosis through the use of MCST were also found to have ischemia through the use of MPI. In fact, only half of the patients who were shown to have obstructive CAD -- defined as having fifty percent or more narrowing of the coronary arteries -- through the use of MSCT were shown to have ischemia, based on the results of the MPI test. In other words, the narrowing of the coronary arteries (stenosis) wasn’t harming the blood flow to the heart.

"The study shows that there’s a big discrepancy between atherosclerosis and ischemia," said Dr. Bax. "These two different types of coronary imaging tests are clearly looking at different, yet complimentary aspects of CAD. MSCT detects atherosclerosis, while MPI identifies ischemia."

MSCT shows the anatomy of the coronary arteries, whereas MPI shows its function. MSCT is a rapid CT scan that provides a series of pictures to show how much plaque is in the coronary arteries. MPI with SPECT uses radionuclide imaging to examine the myocardial blood flow at rest and following stress, making diagnosis of ischemia possible.

"This is the first time that that MSCT was used in patients with a moderate risk of CAD," said Bax. "Findings show that it has a high accuracy of detecting CAD in this population."

However, there are some disadvantages to using MSCT. In order to provide high resolution "still" images, patients are exposed to a significant amount of radiation. Newer technology, however, will most likely result in significant reductions in radiation dose in the near future.

The study involved 114 patients who had chest pain and/or risk factors for CAD, but no prior history of CAD. Patients underwent both noninvasive imaging procedures within 30 days of each other. The MSCT was performed using 16- and 64-slice CT in 28 and 86 patients, respectively. The MPI was performed using either physical exercise or pharmacological stress combined with a Tc-99m imaging agent. Invasive coronary angiography was also performed in a subset of 58 patients, confirming previous studies that the agreement between MSCT and invasive coronary angiography was excellent.

"This study has major implications in the management of patients in clinical practice," said Dr. Bax. "One possibility is to use MCST to identify the presence and extent of plaques in the arteries and if (considerable) atherosclerosis is shown to be present, then clinicians may proceed to use SPECT imaging to evaluate if the patient has ischemia."

"Future studies are needed on how to apply both techniques in the clinical setting in patients with intermediate likelihood of CAD," he added.

Sharmila Dorbala, MD, Divisions of Nuclear Medicine/PET and Cardiovascular Imaging, Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School in Boston was not connected with the research but agreed that MSCT deserves further study. Dr. Dorbala wrote an editorial that will accompany publication of the new research.

"How this new test, MSCT fits into our existing clinical paradigm is not completely known," said Dr. Dorbala. "The findings of this study are important and add to the growing evidence that MSCT detects coronary plaque but not ischemia. Thus, relying on this test alone for making decisions about coronary revascularization (improving blood flow to the heart muscle with balloon angioplasty, stents or coronary artery bypass surgery) could result in unnecessary revascularization procedures and higher costs without clear benefits to patients. The results of this and other similar studies will be important in guiding our decisions about management of patients with intermediate likelihood of CAD."

"In the future, it will be of interest to find out whether specific characteristics of plaque or in specific patient groups, MSCT stenosis would better indicate flow limitation," adds Dr. Dorbala. "Until then, the findings of this study reiterate the need to base decisions about coronary revascularization in conjunction with objective evidence of the degree of ischemia and symptoms," said Dorbala, "but not solely on the severity of coronary stenosis seen on MSCT."

Dr. Bax reports no disclosures with this research. Financial support was provided by the Netherlands Heart Foundation, the Hague, the Netherlands.

Also in this issue of JACC

Nicotine can cause the growth of new blood vessels. A new study in the Dec. 19 issue of the Journal of the American College of Cardiology shows that nicotine can activate endothelial precursor cells, a form of adult stem cells, to grow new blood vessels in animals. The growth of blood vessels can play a role in tobacco-related diseases, such as tumor, plaque, and eye disease.

Researchers at Stanford and in Frankfurt, Germany sought to determine whether nicotine can cause the bone marrow to release a form of adult stem cells into the blood to help form new blood vessels. The study was an extension of their previous research, which found that nicotine has an angiogenic effect; that is, it causes blood vessels to grow.

In the study, nicotine was administered in mice to see if new blood vessels could form around a blockage of a blood vessel in the hind leg. A portion of these new blood vessels were composed of cells from the bone marrow. Understanding the mechanism of this surprising finding may yield new therapies for diseases of abnormal or insufficient vessel growth.

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The American College of Cardiology is leading the way to optimal cardiovascular care and disease prevention. The College is a 34,000-member nonprofit medical society and bestows the credential Fellow of the American College of Cardiology upon physicians who meet its stringent qualifications. The College is a leader in the formulation of health policy, standards and guidelines, and is a staunch supporter of cardiovascular research. The ACC provides professional education and operates national registries for the measurement and improvement of quality care. More information about the association is available online at www.acc.org .

The American College of Cardiology (ACC) provides these news reports of clinical studies published in the Journal of the American College of Cardiology as a service to physicians, the media, the public and other interested parties. However, statements or opinions expressed in these reports reflect the view of the author(s) and do not represent official policy of the ACC unless stated so.


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