For symptomatic patients who undergo cardiac computed tomography angiography to evaluate suspected coronary artery disease, a finding of no CAD conveys an excellent prognosis, according to a meta-analysis of 18 studies of diagnostic cardiac computed tomography angiography (CCTA).
The meta-analysis clearly showed that the low (0.16%) annualized event rate that follows such negative test results is comparable to the background event rate among healthy, low-risk individuals in the general population. It is also comparable to the event rates observed after risk-stratification modalities such as stress echocardiography and myocardial perfusion scanning, said Dr. Edward A. Hulten of the cardiology service at Walter Reed Army Medical Center, Washington, and his associates.
The diagnostic accuracy of CCTA has been reported in more than 50 studies, but the technology's prognostic value has been less well established, the investigators observed. This meta-analysis shows that “the concept that CCTA offers anatomic but not prognostic value compared with widely used functional stress testing is no longer accurate,” they wrote.
Dr. Hulten and his colleagues performed a meta-analysis of prospective and retrospective observational studies in which 9,592 patients suspected of having CAD were evaluated using CCTA and followed for a median of 20 months. Seventeen of these studies were rated as good quality.
For the patients whose CCTA results indicated no CAD, the annualized rate of major adverse cardiovascular events (MACE) was 0.16%. There were no coronary revascularizations, myocardial infarctions, or admissions for unstable angina; the only events were from all-cause mortality.
“Considered in concert with the wealth of data regarding the high anatomic accuracy for CCTA, these results are convincing for CCTA to effectively diagnose CAD and convey risk strata for future adverse cardiovascular events,” the researchers said (J. Am. Coll. Cardiol. 2010;57 [doi:10.1016/jacc.2010.10.011]).
Positive results on CCTA correlated with major adverse cardiovascular events. The average annualized MACE rate for a finding of CAD was 8.8% per year (vs. 0.17% per year for negative findings). Revascularization procedures accounted for most of these events; the annualized rate of death or MI was 3.2% vs. 0.15 for positive vs. negative scans. Moreover, the rate of adverse events increased as the severity of coronary artery disease on CCTA exam increased.
Although a negative CCTA scan can be considered strongly predictive of an excellent outcome, the reverse is not true: A positive CCTA scan cannot be considered strongly predictive of future adverse events. With the annualized MACE rate at only 8.8%, the great majority of patients found on CCTA to have coronary disease also have good outcomes in the 20 months' follow-up, Dr. Hulten and his associates pointed out.
They also noted that many of the authors of studies included in the meta-analysis “reported prognosis based on a relatively simple classification of CAD luminal stenosis, specifically, no CAD, nonobstructive CAD, or potentially obstructive CAD (greater than 50% stenosis).” With studies defining “normal” CCTA in slightly different ways, it was not possible to have stratification details that would be clinically informative, the authors wrote. They also noted that their research included data from “different generations of CT scanning technology” the newer of which are known to have improved image quality and accuracy.
As in many other many studies of noninvasive coronary risk stratification tests, the investigators wrote, a limitation of their study is verification bias: “The observed increase in MACE is driven in part by coronary revascularization, demonstrating evidence of a work-up or verification bias. That is, patients with CCTA evidence of a greater than 50% stenosis are more likely to undergo catheterization and subsequent revascularization.”