Noninvasive Imaging Test Identifies Blocked Blood Vessels as Well as Invasive Coronary Angiography
]]>Coronary angiography]]> is an invasive imaging procedure that is used to detect narrowing of the arteries that supply the heart muscle. Each year, more than two million coronary angiographies are performed in the United States. The procedure is the gold standard for detecting ]]>coronary artery disease]]> (CAD), but it involves the insertion of a wire and catheter into the heart and coronary arteries. This carries with it certain risks, including ]]>arrhythmia]]> and ]]>stroke]]> , both of which could be life-threatening.
Multislice computed tomography (MSCT), a newer noninvasive technology, has been used to complement coronary angiography. MSCT is an x-ray imaging technique in which rows of detectors rotate around a patient, taking multiple images of the body. A computer processes these snapshots into three-dimensional composite images. When focused on the heart, MSCT is capable of producing remarkably detailed pictures of the coronary arteries complete with any obstruction to the flow of blood.
Studies have yet to determine how accurately MSCT can diagnose CAD compared to coronary angiography. In a study published in the May 25, 2005 Journal of the American Medical Association , researchers report that MSCT compared favorably to coronary angiography in detecting the presence and absence of significant blockages of coronary arteries. MSCT also accurately identified patients who, based on their degree of blockage, qualified for a revascularization procedure, such as angioplasty, to restore blood flow.
About the Study
Researchers enrolled 103 patients (averaging 61.5 years old) suspected of having CAD. All patients underwent both coronary angiography and MSCT. The MSCT was performed using a scanner with 16 detector rows.
The scientists compared the accuracy of MSCT and coronary angiography in detecting the presence and absence of coronary arteries that were significantly (more than 50%) blocked. They also observed how accurately MSCT identified patients who were appropriate for a resvascularization procedure, based on the degree of blockage.
Compared to coronary angiography, MSCT correctly identified the presence of significant vessel blockage 95% (test sensitivity) of the time and correctly identified the absence of significant blockage 98% (test specificity) of the time.
MSCT had a positive predictive value of 87% compared to coronary angiography. In other words, 87% of patients who actually had a significant blockage were correctly identified by MSCT. On the other hand, MSCT had a negative predictive value of 99% compared to coronary angiography, meaning that 99% of patients without a significant blockage were correctly identified.
MSCT also did well at identifying patients who would benefit from surgery to restore blood flow to blocked blood vessels, based on criteria defined by the researchers.
All participants in this study were referred for coronary angiography, which indicates that they were all at moderate to high risk for CAD. As a result, the findings from this study cannot be applied to patients at low risk for CAD.
How Does This Affect You?
This study found that multislice computed tomography can identify the presence or absence of coronary artery blockages almost as well as coronary angiography, which is today’s standard diagnostic test.
Although MSCT does not have the same risks associated with an invasive procedure, it is not risk-free. MSCT exposes patients to higher levels of radiation than angiography does. Another disadvantage of MSCT is that if a significant blockage is identified, an invasive procedure may still be necessary to treat it.
The newest generation of scanners has 64 detection rows, compared to the 16-row scanner used for this study. As imaging technology continues to rapidly evolve, image quality will likely get better and better increasing the possibility that MSCT will be advocated as a replacement for coronary angiography. Despite the favorable results of this study, however, it is still too early to know the exact role MSCT should play in the management of CAD. If one day MSCT followed by coronary angiography when necessary proves to be more cost-effective than coronary angiography alone, MSCT could become the standard of care for most CAD patients.
National Heart, Lung, and Blood Institute
National Institutes of Health
Radiological Society of North America
Garcia MJ. Noninvasive coronary angiography: hype or new paradigm? [Editorial.] JAMA . 2005; 293(20):2531-2533.
Hoffmann MHK et al. Noninvasive coronary angiography with multislice computed tomography. JAMA . 2005; 293(20):2471-2478.
Last reviewed May 27, 2005 by ]]>Richard Glickman-Simon, MD]]>
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