Clinical usefulness of cardiac CT scan for detecting blockages in coronary arteries is limited

Use of the 16-row multidetector computed tomography ( CT ) scan to detect narrowing of coronary arteries may result in a high number of cases in which the diagnosis cannot be determined, limiting the clinical usefulness of the test.
However, the heart CT test may be useful in excluding coronary disease in selected patients.

Coronary artery disease is a leading cause of death and health care expenditure in Western countries. Establishing its anatomic diagnosis requires coronary angiography, a procedure that is costly and carries risks and discomfort.
Recent technical advances with the non-invasive multidetector computed tomography ( MDCT ) have allowed for excellent visualization of the coronary arteries.
MDCT is a form of diagnostic imaging in which a two-dimensional array of detector elements acquire images of multiple slices or sections of an artery or organ simultaneously. With a 16-row MDCT, 16 images are captured per rotation of the machine. Some previous studies have indicated promising results for this technology, but it remains uncertain whether their findings may be replicated in clinical centers with different levels of expertise.

Mario J. Garcia, of the Cleveland Clinic Foundation, and colleagues investigated the diagnostic accuracy of 16-row MDCT for the detection of obstructive coronary disease in a multicenter study.

The study included 238 patients who were clinically referred for nonemergency coronary angiography from June 2004 through March 2005 at 11 participating sites. A total of 187 patients underwent contrast-enhanced MDCT and also had conventional angiography performed one to 14 days after MDCT. The results of these two tests were compared.

Of 1,629 nonstented coronary artery segments larger than 2 mm in diameter, there were 89 ( 5.5 percent ) in 59 ( 32 percent ) of 187 patients with stenosis of more than 50 percent by conventional angiography. Of 1,629 segments, 71 percent were evaluable on MDCT. The sensitivity ( positive findings on MDCT and narrowed artery on angiogram ) ranged from 89 percent to 94 percent, whereas the specificity ( negative findings on MDCT and no narrowing on angiogram ) ranged from 51 percent to 67 percent, in analyses that were based on vessel segments or based on individual patients.
The researchers write: " The results of this multicenter study demonstrate a higher number of false-positive and nonevaluable segments than previously reported with MDCT coronary angiography. Because the prevalence of obstructive coronary artery disease was significant ( 38 percent ) in patients with nonevaluable segments, these patients would need to proceed to conventional angiography or additional noninvasive testing in clinical practice. " If all nonevaluable MDCT segments were excluded ( or considered negative ), 15 patients with stenosis of more than 50 percent would have been missed.

" Multidetector CT coronary angiography may be useful to exclude coronary artery disease in selected patients in whom a false-positive stress test result is suspected. Our results indicate that a negative MDCT coronary angiogram could have a significant discriminative power to exclude significant stenosis in patients with intermediate probability in the absence of nonevaluable segments," the researchers write.

In this study population, if clinically implemented, a negative evaluable MDCT study may have avoided conventional angiography in 69 ( 37 percent ) of 187 patients, while missing only 1 patient with single vessel obstructive disease ( 0.4 percent ).

" In summary, the results of our study indicate that use of MDCT coronary angiography performed with 16-row scanners is limited by a high number of nondiagnostic cases. Thus, routine implementation of MDCT angiography as a primary diagnostic test to evaluate patients with suspected coronary artery disease would lead to an excessive use of conventional angiography, additional confirmatory noninvasive testing, or both. Nevertheless, the high sensitivity and negative predictive value of this test suggests that if selectively applied, MDCT may be a useful alternative to conventional angiography in selected patients with undetermined or suspected false-positive stress test results. Further studies are needed to determine if MDCT coronary angiography performed with newer 64-slice scanners provides improved performance characteristics that could justify routine clinical application as a primary diagnostic test."

"… stress testing should remain as the primary diagnostic modality for this purpose until further data obtained with newer generation MDCT technology demonstrates improved performance characteristics," the authors conclude."

Source: Journal of American Medical Association, 2006


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