Diagnostic Accuracy of Fractional Flow Reserve From Anatomic CT Angiography

Study Questions:

What is the diagnostic performance of noninvasive fractional flow reserve (FFR) obtained by coronary computed tomography (FFRCT) plus CT for detecting hemodynamically significant coronary stenosis?


DeFACTO (Determination of Fractional Flow Reserve by Anatomic Computed Tomographic Angiography), a multicenter diagnostic performance study involving 252 stable patients with suspected or known coronary artery disease (CAD), was conducted in 17 centers in 5 countries. The patients underwent CT, invasive coronary angiography (ICA), FFR, and FFRCT between October 2010 and October 2011. CT, ICA, FFR, and FFRCT were interpreted in blinded fashion by independent core laboratories. Accuracy of FFRCT and CT for diagnosis of ischemia was compared with an invasive FFR reference standard. Ischemia was defined by an FFR or FFRCT of 0.80 or less, while anatomically obstructive CAD was defined by a stenosis of 50% or larger on CT and ICA. The primary study endpoint was FFRCT plus CT for diagnosis of per-patient ischemia with the prespecified endpoint >70% of the lower bound of the 95% confidence interval (CI) compared with an FFR reference standard.


Mean age was 63 years, 71% were male, 80% had stable angina, and in 17%, it was worsening. Among study participants, 137 (54.4%) had an abnormal FFR. On a per-patient basis, diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of FFRCT were 73% (95% CI, 67%-78%), 90% (95% CI, 84%-95%), 54% (95% CI, 46%-83%), 67% (95% CI, 60%-74%), and 84% (95% CI, 74%-90%), respectively. The overall accuracy for patients with intermediate CT stenosis (30%-70%) for FFRCT ≤0.80 was 71%, and for CT stenosis >50% was 57%. Compared with obstructive CAD diagnosed by CT alone (area under the receiver operating characteristic curve [AUC], 0.68; 95% CI, 0.62-0.74), FFRCT was associated with improved discrimination (AUC, 0.81; 95% CI, 0.75-0.86; p < 0.001).


Although the study did not achieve its prespecified primary outcome goal for the level of per-patient diagnostic accuracy, use of noninvasive FFRCT plus CT among stable patients with suspected or known CAD was associated with improved diagnostic accuracy and discrimination compared to CT alone for the diagnosis of hemodynamically significant CAD.


FFRCT can add discriminatory power to identify and exclude ischemia in patients with suspected CAD. Whether it will be useful clinically as has been shown for invasive FFR will depend on results of similar observational outcome studies. I would like to see the utility of FFRCT and CT compared to nuclear stress imaging assessment of flow reserve.

Clinical Topics: Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Atherosclerotic Disease (CAD/PAD), Interventions and Coronary Artery Disease, Interventions and Imaging, Angiography, Nuclear Imaging

Keywords: Outcome Assessment, Health Care, Coronary Artery Disease, Coronary Stenosis, Coronary Angiography, Tomography, Cardiology, Coronary Circulation, Angioplasty, Hemodynamics

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