MSCT a Safe Rule-Out Test for CAD, Follow-Up Study Suggests

August 21, 2007 — A study tracking rates of mid-term clinical events following a multislice computed tomography (MSCT) test indicates that the technology can safely rule out suspected coronary artery disease (CAD) without putting patients at risk of subsequent events. Other studies have suggested that MSCT has high sensitivity and negative predictive value when compared against conventional coronary angiography (CAG) — the gold standard — but few studies have linked negatives tests with subsequent events.
The study appears in the August 13/27 issue of the Archives of Internal Medicine.[1]
Dr Martine Gilard (Brest University Hospital, France) and colleagues initially tested 200 patients using MSCT instead of the conventional coronary angiogram for which they had originally been scheduled. If MSCT showed a lot of calcium in the arterial tree, or if the scan was noninterpretable, patients were sent on for conventional angiography. MSCT ruled out a diagnosis of CAD in 141 patients and these were subsequently followed over a mean of 14.7 months during which time no patients died, and rates of subsequent CAG and myocardial infarction (MI) were low. These outcomes were comparable to those of patients who had been diagnosed as normal by standard CAG.
"These results confirm that MSCT-CAG is useful in the diagnostic workup of patients with suspected significant CAD and can, when the result is normal, safely rule out this diagnosis," the authors concluded. As a result, a significant proportion of patients can safely avoid an invasive conventional coronary angiogram, and its potential complications, without facing a higher risk of subsequent events down the road, they say.
How Normal Is "Normal"
Commenting on the study for heartwire, Dr Paul Schoenhagen (Cleveland Clinic, OH) pointed out that the definition of "normal" in the study was defined as < 50% luminal narrowing by MSCT.
"Although calcium scoring and contrast-enhanced coronary CT angiography [CTA] was performed, the specific MSCT findings are not described in the manuscript," he said. "It remains unclear, how many of the 141 patients had a negative calcium score, non-calcified, mixed, and predominantly calcified plaque."
That's problematic, Schoenhagen says, because the calcium scoring literature as well as recent MSCT studies suggest that these sub-categories have prognostic significance. "We do not know how 'normal' these CT [computed tomographic] scans were. For example, it is possible that all these patient did not have any evidence of disease — no calcification, no plaque at all — which would define a low-risk group. On the other hand it is possible that these patients had calcified and non-calcified plaque but less than 50% stenosis, which would likely define a higher risk of future events, based on calcium scoring literature and emerging CTA data. Without knowing the distribution of these CT findings in the reported population, application to clinical practice is very limited."
Schoenhagen also took issue with the lack of information included in the paper on patients who did go on to have conventional coronary angiograms. "The pre-test probability of CAD in the study population remains incompletely defined and there is no information about the outcome of those patients with positive coronary CT," he said. "Future studies in well-defined intermediate risk populations, correlating specific MSCT findings with clinical outcome, will be critical to understand the potential clinical role of CTA."
Source
Martine Gilard M, Le Gal G, Cornily JC, et al. Coronary artery disease and normal multislice computed tomographic findings. A prospective management outcome study. Arch Intern Med 2007;165:1686-1689.