Ulm, Germany - Multislice computed tomography (MSCT) provides high accuracy for detecting coronary artery disease (CAD) and may represent a useful adjunct to conventional coronary angiography, according to a new German study [1].

Radiologist Dr Martin HK Hoffmann (University Hospital, Ulm, Germany) and colleagues compared the diagnostic accuracy of 16-slice MSCT scanning with invasive coronary angiography in a large group of patients with known or suspected CAD. They report their findings the May 25, 2005 issue of the Journal of the American Medical Association.

People want to challenge angiography directly or replace it—I don't think we are ready for this yet.

Hoffmann told heartwire that the study "shows that the best place for MSCT right now is as a gatekeeper for coronary angiography. People want to challenge angiography directly or replace it—I don't think we are ready for this yet."

In an accompanying editorial, Dr Mario J Garcia (Cleveland Clinic Foundation, OH) says the study provides "promising results" but several important limitations of MSCT must be considered [2]. And in the absence of outcome and cost-analysis studies, "it is not yet clear how MSCT coronary angiography should be integrated into clinical practice," he concludes.

Hoffman et al enrolled 103 consecutive patients (average age 61.5 years) primarily with suspected CAD who underwent both invasive coronary angiography and 16-slice MSCT. The study was conducted from November 2003 through August 2004.

Compared with invasive coronary angiography for detection of significant lesions (>50% stenosis), segment-based sensitivity, specificity, and positive and negative predictive values of MSCT were 95%, 98%, 87%, and 99%, respectively.

Hoffman told heartwire that these results "were more or less a repetition of what we have seen in other published studies" but that the strength and novelty of this study is in the robustness of the data.

"The robustness is demonstrated in the quantification techniques that we employed that allowed us to perform, for example, a ROC [receiver operating characteristic] analysis," he explained. "Nobody else has founded study decisions on quantification."

[With MSCT] we could sort out the patients with mid-range to significant disease and send them to the cath lab.

This quantitative comparison of MSCT and angiography showed "reasonably good correlation (r=0.87; p<0.001)," says Hoffman, with MSCT systematically measuring greater-percentage stenoses.

Per-patient-based analysis indicated high discriminative power to identify patients who might be candidates for revascularization, he added. "We could sort out the patients with mid-range to significant disease and send them to the cath lab."

"The diagnostic accuracy is there today—you get it with 16-slice. But we have already replaced the 16-slice machine—which you could now consider ancient technology—with a 40-slice machine, and the robustness will only improve as more sophisticated machinery is employed," Hoffman adds.

For example, he explains, with the 16-slice MSCT, about 20% of patients had incomplete coronary coverage: "You might get beautiful images on the left but not so good on the right." With 64-slice MSCT, "We would expect to see less than 10% of patients with image artifacts," he predicts.

"In conclusion, 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 the 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."

In his editorial, Garcia says the reported per-segment sensitivity and specificity "are noteworthy, particularly when . . . compared with those of other indirect methods used for the detection of obstructive CAD."

The fact that the authors report diagnostic characteristics according to a per-patient-based analysis "is critically important," he says "since the implications of detecting or missing the presence or absence of any significant coronary obstruction are more clinically relevant from the perspective of the individual patient. In this patient population, MSCT is a robust test for establishing the diagnosis of obstructive CAD," he states.

Undoubtedly, if these results could be replicated in clinical practice, the clinical and economic implications could be substantial.

"If MSCT would have been used as an initial diagnostic test [in their study population], more than 40% of the patients in this group could have avoided unnecessary invasive angiography and only two patients (2%) having significant disease would have been missed. Undoubtedly, if these results could be replicated in clinical practice, the clinical and economic implications could be substantial."

Nevertheless, says Garcia, several important limitations must be considered. The extent and severity of coronary calcification in the population studied was not known definitively, he says, since the diagnostic accuracy of MSCT is reduced in those with calcifications. In-stent visualization with MSCT is not feasible or accurate in most cases, and the MSCT technology is currently limited to those with stable regular heart rates, although "it is likely that this will rapidly improve with technological advances."

Another potential problem is that image resolution may be compromised in morbidly obese subjects, says Garcia, and finally MSCT requires ionizing radiation. "The dose [in this study] is equivalent to two to three 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," he notes.

"The growing enthusiasm for MSCT in the community must be matched with adequate training, proper credentialing, and, above all, appropriate utilization," Garcia concludes.

Hoffman told heartwire: "I have read the editorial and disagree only with the comments on radiation-dose exposure. Garcia points out that the radiation dose used during a cardiac CT examination would equal two to three times the dose necessary for an invasive diagnostic study. This comparison factor is much too high and founded on very low doses reported for cath procedures. The realistic comparison would be in the range of 1.5 to two times the dose of cath necessary for noninvasive CT cardiac imaging.

"Other than this minor issue I fully agree with the statements of Garcia and especially appreciate that he outlines the multiple restrictions that currently apply to the modality."