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MSCT for noninvasive detection of coronary artery disease

Multislice computed tomography ( MSCT ) provides high accuracy for noninvasive detection of suspected obstructive coronary artery disease, and this technology has potential to complement diagnostic invasive coronary angiography in routine clinical care.

Invasive coronary angiography is currently the diagnostic standard for clinical evaluation of known or suspected coronary artery disease ( CAD ).
The risk of adverse events is small, but serious and potentially life-threatening events may occur, including arrhythmia, stroke, coronary artery dissection, and access site bleeding ( total complication rate, 1.8 percent; death rate, 0.1 percent ). Furthermore, angiography catheterization induces some discomfort and mandates routine follow-up care.
Guidelines recommend that conventional invasive diagnostic angiography be restricted to stringent clinical indications.

A recently developed procedure that may potentially complement invasive coronary angiography is multislice computed tomography, which may achieve a high level of reliability and accuracy in the visualization of the coronary arteries.

MSCT is a sophisticated x-ray imaging technique, in which a CT tube and multiple layered detector rows rotate around the patient, taking numerous images of the body in seconds.
A computer processes the information into three-dimensional images composing volumetric representations of anatomy.
The coronary arteries can be extracted from these images and are presented in arbitrarily oriented sectional cuts.
This procedure eliminates much of the risk and discomfort associated with invasive coronary artery catheterization, although it retains the risks inherent in radiation exposure and use of contrast agents.

Martin H. K. Hoffmann, of University Hospital, Ulm, Germany and colleagues assessed the diagnostic accuracy of 16-slice MSCT scanning vs. invasive coronary angiography in a large group of patients with known or suspected CAD.
The study, which included 103 patients ( average age, 61.5 years ), was conducted from November 2003-August 2004.
The patients underwent both invasive coronary angiography and MSCT using a scanner with 16 detector rows.

The researchers found that compared with invasive coronary angiography for detection of significant lesions ( greater than 50 percent stenosis ), segment-based sensitivity, specificity, and positive and negative predictive values of MSCT were 95 percent, 98 percent, 87 percent, and 99 percent, respectively.
Quantitative comparison of MSCT and invasive coronary angiography showed good correlation, with MSCT systematically measuring greater-percentage stenoses.
Per-patient based analysis indicated high discriminative power to identify patients who might be candidates for revascularization.

“ We found that MSCT shows reasonably high accuracy for detecting significant obstructive CAD when assessed at a patient level. At its current stage of development, it may therefore be used to substantially reduce likelihood of clinically important CAD in patients with suspected disease. The appeal of MSCT compared with conventional coronary angiography is that it is noninvasive, avoiding most catheter-associated risks and discomforts with the exception of exposure to iodinated contrast agents and radiation. With rapidly improving technology, MSCT may well evolve from a useful complement to invasive angiography to a clinically viable alternative,” the authors conclude.

In an accompanying editorial, Mario J. Garcia, of the Cleveland Clinic Foundation, comments on the findings by Hoffmann et al.

“Despite these promising results, several important limitations of MSCT must be considered. First, MSCT requires ionizing radiation,” Garcia writes. “ This dose [ in this study ] is equivalent to 2 to 3 times the dose typically administered during a diagnostic invasive angiogram. Although the long-term risks associated with this level of radiation exposure are relatively low, it raises a concern about repetitive use or use in younger individuals and women of childbearing age. ”
“Second, the extent and severity of coronary calcifications in the population studied by Hoffmann et al is not known definitively.”

“Despite [ these and other limitations ], there is an important segment of the population at risk for heart disease in whom MSCT angiography could provide coronary anatomic information with sufficient diagnostic quality. Indeed, MSCT may offer another advantage over conventional angiography, which is the potential ability to detect and quantify atherosclerotic plaques in the coronary vessel walls. Nevertheless, in the absence of outcome and cost analysis studies, it is not yet clear how MSCT coronary angiography should be integrated in the clinical practice. Should it be used as a first test for the evaluation of chest pain or as a complementary test in patients with equivocal stress test results ? In either case, adequate patient selection will be critically important.”

Source: Journal of the American Medical Association, 2005