Multislice Spiral CT Detects Dysfunctional Coronary Bypass Grafts

Noninvasive coronary imaging using 16-detector row multislice spiral computed tomography (MSCT) is feasible for visualization of coronary bypass grafts and coronary artery lesions, two research teams in Germany report.

Conventional invasive coronary angiography, the standard in following patients with coronary artery bypass grafts, is risky and costly, point out Dr. Jorg Barkhausen and colleagues at University Hospital in Essen. Recent studies have shown that a new generation of multislice spiral CT scanners could be a viable alternative for detecting obstructive coronary artery disease (see Reuters Health report, September 30, 2002).

In the September 15th issue of the Journal of the American College of Cardiology, Dr. Barkhausen’s team note that they compared invasive angiography with CT angiography in 48 patients. All bypass grafts and 74% of distal bypass anastomoses could be visualized by CTA. It detected 21 bypass graft occlusions and one significant stenosis, plus five false positive and one false negative finding. Thus the sensitivity was 96% and specificity was 95%.

Dr. Barkhausen and his associates observe that “the 16-detector row MSCT allows for a reliable differentiation between patent and occluded arterial and venous bypass grafts.”

Compared with the older four-slice MSCT, the 16-row scanner is associated with fewer respiratory and cardiac motion artifacts, and better spatial resolution, they say. Drawbacks include the necessity for contrast injection, the use of beta-blockers to control heart rate, and radiation exposure.

In the same issue of the Journal, Dr. Axel Kuettner and colleagues at Eberhard-Karls-Univeristy of Tuebingen, describe their comparison of MCST with conventional angiography in 60 patients. They were able to obtain a diagnostic contrast-enhanced scan for 58.

Of 763 coronary segments examined, conventional testing detected 75 lesions of 50% or higher. The MSCT correctly assessed 54. There were 21 false-positives and 21 false negatives, so sensitivity was estimated to be 72% and specificity 97%.

When analysis was restricted to those patients with “non-excessive” calcium deposition, MSCT correctly detected 39 of 40 lesions. There were 10 false-positives and one false-negative, yielding a sensitivity and specificity each of 98%.

Overall, 58 patients were considered to be correctly diagnosed. This is the case, the authors say, if diagnosis is considered correct if any significant lesions greater than 50% could be ruled out or at least one such lesion could be detected and confirmed by conventional angiography.

Current limitations seem to involve severe calcifications and smaller vessels, the team points out. They suggest that MSCT not be considered a replacement for coronary angiography, but rather a means of ruling out significant lesions in patients with a low pretest probability.

In an accompanying editorial, Drs. P. J. de Feyter and K. Nieman, from Erasmus Medical Center in Rotterdam, The Netherlands, comment that MSCT is not yet ready for clinical practice.

Future trials, they conclude, are needed to evaluate “whether MSCT is useful as a screening method in a selected patient population, as an alternative to exercise testing, myocardial perfusion, or dobutamine stress testing, or as an alternative to conventional angiography in patients with favorable characteristics.”