Rationale and design of the DeFACTO ( De termination of F ractional Flow Reserve by A natomic C omputed T omographic Angi O graphy) study

Background Coronary computed tomographic angiography (CTA) allows for noninvasive identification of anatomic coronary artery disease (CAD) severity but does not discriminate whether a stenosis causes ischemia. Computational fluid dynamic techniques applied to CTA images now permit noninvasive computation of fractional flow reserve (FFR), a measure of lesion-specific ischemia, but the diagnostic performance of computed FFR (FFRCT ) as compared with measured FFR at the time of invasive coronary angiography remains unexplored. Objective We determined the diagnostic accuracy of noninvasive FFRCT for the detection and exclusion of ischemia-causing stenoses. Methods DeFACTO (NCT01233518) is a prospective, international, multicenter study of 238 patients designed to evaluate the diagnostic performance of FFRCT for the detection of hemodynamically significant coronary artery stenoses identified by CTA, compared with invasive FFR as a reference standard. FFR values ≤ 0.80 will be considered hemodynamically significant. Patients enrolled in the DeFACTO study will undergo CTA, invasive coronary angiography, and 3-vessel FFR in the left anterior descending artery, left circumflex artery, and right coronary artery distributions. FFRCT will be computed with acquired CTA images, without modification to CTA image acquisition protocols and without additional image acquisition. Blinded core laboratory interpretation will be performed for CTA, invasive coronary angiography, FFR, and FFRCT. Results The primary endpoint of the DeFACTO study is the per-patient diagnostic accuracy of FFRCT for noninvasive assessment of the hemodynamic significance of CAD, compared with FFR during invasive coronary angiography as a reference standard. The secondary endpoints include additional per-patient as well as per-vessel diagnostic performance characteristics, including sensitivity, specificity, positive predictive value, and negative predictive value. Conclusion The DeFACTO study will determine whether the addition of FFRCT to conventional CTA improves the diagnosis of hemodynamically significant CAD.