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Noninvasive Fractional Flow Reserve Derived From Computed Tomography Angiography for Coronary Lesions of Intermediate Stenosis Severity: Results From the DeFACTO Study
Study Questions:
What is the accuracy of fractional flow reserve (FFR) derived from coronary computed tomography (CT) angiography (FFR-CT) to identify ischemic coronary artery lesions in patients with intermediate coronary artery stenosis?
Methods:
From a total of 252 patients with 407 arteries undergoing standard coronary CT angiography and invasive coronary angiography including FFR, this subgroup analysis from the DeFACTO Study examined 150 arteries in 82 patients with intermediate stenosis by CT (30-69% stenosis). The diagnostic accuracy of FFR-CT was compared to standard coronary CT angiography, using ischemia identified by FFR as the reference standard. Standard coronary CT angiography images were used to derive FFR-CT values. Obstructive stenosis by CT was defined as ≥50% diameter stenosis, and ischemia by FFR and FFR-CT was defined as a value ≤0.80.
Results:
Of the 150 arteries with intermediate stenosis by CT, FFR identified ischemia in 23% (35/150), and FFR-CT reported ischemia in 43% (64/150). For per-artery identification of ischemia on FFR, the sensitivity, specificity, positive predictive values, and negative predictive values for FFR-CT were 74%, 67%, 41%, and 90%; respective values for obstructive stenosis by CT were 34%, 72%, 27%, and 78%. The use of FFR-CT (vs. CT stenosis severity) significantly improved the area under the curve to identify ischemia on FFR both on a per-artery (0.79 vs. 0.53, p < 0.001) and per-patient basis (0.81 vs. 0.50, p < 0.001).
Conclusions:
For detection of ischemia on FFR, the use of FFR-CT had improved diagnostic performance over coronary CT stenosis severity alone.
Perspective:
It is well established that the percentage of diameter stenosis is an unreliable predictor of functional ischemia, and studies have demonstrated that targeted revascularization requiring both an anatomic stenosis and lesion-specific ischemia using FFR improves outcomes. Nevertheless, FFR is an invasive procedure that may be associated with increased cost and procedural time. FFR-CT may permit a noninvasive estimate of FFR, by applying computation fluid dynamics to standard coronary CT images, and modeling the expected effect of lesions on coronary flow using a supercomputer. While alternatives such as stress testing or FFR can also be used to evaluate intermediate lesions for potential ischemia, coronary CT angiography and subsequent modeling using FFR-CT may permit a single test to identify both the presence of anatomic stenoses and potential ischemia. While the diagnostic performance of FFR-CT was markedly improved over CT alone, the overall accuracy was limited, and its relative accuracy in comparison to stress testing remains to be determined.
Keywords: Coronary Angiography, Tomography
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