A normal coronary CT angiography (CCTA) test conveys an excellent prognosis for symptomatic patients being evaluated for coronary artery disease (CAD), while findings of increasing CAD convey incremental risk, according to a meta-analysis published online Dec. 8 in the Journal of the American College of Cardiology .
The systematic review and meta-analysis is the first comprehensive analysis of multiple recent longitudinal studies describing the prognostic value of CCTA, the authors wrote.
"Small studies have found the diagnostic accuracy of CCTA to be excellent compared with catheter angiography, but there has not been an abundance of clinical outcomes studies. The American College of Cardiology this summer called for increasing research on outcomes data," lead author Edward Hulten, MD, a cardiology fellow at Walter Reed Army Medical Center in Washington, D.C., said in an interview .
"It's important for any cardiovascular test to discriminate whether you send patients to the cath lab for interventions or manage them medically and how they do with their treatment," Hulten said.
In that regard, Hulten and colleagues pooled results from 18 studies with more than 9,500 patients to increase the power to detect clinical events. The median followup was 20 months.
The primary outcome was the negative likelihood ratio (-LR) of MACE (death, MI, unstable angina or revascularization) after normal findings on CCTA. Secondary outcomes included LR of death, MI and revascularization in addition to the sensitivity of CCTA to diagnose patients for the risk of these future events.
They found the event rate for obstructive (greater than 50 percent stenosis) compared with normal CCTA was 8.8 versus 0.17 percent for MACE and 3.2 versus 0.15 percent for death or MI.
When researchers stratified by no CAD, nonobstructive and obstructive CAD, they found an incrementally increasing risk of adverse events.
The authors found that CCTA has a sensitivity of 99 percent and a LR of 0.008 to exclude future coronary clinical events.
"The normal patients on CCTA do very well; the mildly obstructive patients have some events, but they are not at a terribly high risk; and the patients with greater than 50 percent stenosis need to be watched closely, treated aggressively and perhaps revascularized," Hulten said.
"The increase in events seen between groups stratified by CAD severity was also consistent among each of the components of the primary outcome variable: death, MI and coronary revascularization. Therefore, the concept that CCTA offers anatomic but not prognostic value compared with widely used functional stress testing is no longer accurate," the authors wrote.
"The low event rate for normal findings on CCTA of 0.16 percent is comparable to the event rate reported in a previous meta-analysis of patients with normal findings on other noninvasive risk stratification modalities, such as stress echocardiography (0.45 percent) and myocardial perfusion scan (0.54 percent)," according to the study.
The results also were consistent among scanner type: electron-beam (two studies), 16-slice (four) and 64-slice CT.
The researchers did not make any conclusions about whether low- to intermediate-risk patients should be given an initial CT scan over a nuclear test. However, Hulten said, "It most likely won't be a case of CT or SPECT, but rather which test is right for the patient. Each test has advantages and disadvantages. For example, CT offers a considerable reduction in radiation exposure, but it uses contrast dye, so kidney side effects are a concern with CT but not with SPECT. In the future, there will be a role for each test."
The results of this study are similar to those found in the CONFIRM registry, Hulten said.
At the recent American Heart Association (AHA) meeting, James K. Min, MD, a professor of medicine and radiology at Cornell University Medical Center/New York-Presbyterian Hospital in New York City, presented preliminary results from the CONFIRM registry, an international database of more than 27,000 CCTA patients with no known CAD. "The CONFIRM data definitively establish the prognostic value of CT-identified CAD and the risk of death associated with these findings," Min said during AHA10.
Matthew J. Budoff, MD, president of the Society of Cardiovascular CT, said in a statement, "CONFIRM is an important step in the validation of cardiac CT angiography.