Invasive Angio Adds Nothing to CCTA Alone for Risk Prediction: ISCHEMIA

Both invasive coronary angiography and coronary CT angiography (CCTA) add incremental information over baseline characteristics when predicting risk in stable CAD patients, according to an ISCHEMIA analysis. But the data also show that adding invasive angiography on top of CCTA does not provide any more prognostic information over the less invasive imaging test alone.

“The bottom line is that there's modest, if any, incremental risk stratification with catheterization over and above CT,” lead investigator Jonathon Leipsic, MD (University of British Columbia/St. Paul’s Hospital, Canada), told TCTMD.

The results, he added, reaffirm the prognostic usefulness of assessing coronary anatomy with CCTA over invasive angiography and should reassure physicians who are apprehensive about using CT in certain patients, such as those with a high pretest likelihood of CAD.

“Obviously, there's different ways to proceed—you could certainly do a functional test, it wouldn’t be unreasonable—but the traditional reticence to use CT in patients that are deemed to be higher risk is probably overdone at present,” said Leipsic. “With modern CT, with good image quality and experienced readers, we can really do very well, even in complex CAD, and I think this is another example of that. We’re not saying you shouldn't consider other tests in high-risk patients, but you shouldn’t necessarily avoid doing CT because you think it's not going to have value.”

The new study, published as a research letter this week in JACC: Cardiovascular Imaging, builds on prior work from ISCHEMIA that showed CCTA has excellent anatomical agreement with invasive angiography for the identification of angiographically significant CAD. While invasive angiography has been the gold standard for diagnosing coronary disease, CCTA has emerged as a less invasive test with similar diagnostic utility. In the current US chest pain guidelines, CCTA is recommended to diagnose CAD, to aid in risk stratification, and to guide treatment (class 1, level of evidence A) in stable patients at intermediate-to-high risk.

“One of the outstanding questions for some people was whether we still need to do a catheter angiogram to really adjudicate the extent of disease and really make sure we’re clear as far as prognosis goes,” said Leipsic. “We know that CT is really good at ruling out left main disease and identifying a stenosis, but obviously there's more coronary disease than that. So, we really wanted to look at whether there was meaningful prognostic information that was incremental from invasive coronary angiography to CT.”

To date, there have been no head-to-head studies comparing invasive angiography with CCTA for risk stratification, but the ISCHEMIA trial data allowed researchers to assess whether invasive angiography added anything to CCTA when it came to predicting the risk of all-cause mortality and MI.

In total, 1,418 patients (median age 64.2 years; 19.5% female) randomized to the invasive strategy with both an interpretable CCTA and invasive coronary angiogram were included in the analysis. The number of diseased vessels—defined as a stenosis of 50%—on invasive angiography and CCTA added incremental value to risk prediction over baseline characteristics alone. However, the number of diseased vessels on invasive angiography—defined as a stenosis of 50% or 70%—did not add anything to the CCTA data when it came to predicting all-cause mortality or MI.    

Use of the anatomical Duke Jeopardy Score, which assesses both lesion severity and location, did go beyond the CCTA-derived segment stenosis and segment involvement scores.  

“If you look at things like the Duke Jeopardy Score, which is a much more elaborate calculation than what we traditionally do with CT, that is incremental because it starts to integrate the location of the stenosis,” said Leipsic. “If you start doing more elaborate analyses, clearly, you're going to find [better risk stratification].” He imagines that if researchers calculated a more elaborate CT-based score like the Duke Jeopardy Score, it, too, would have similar prognostic utility.