Diagnostic accuracy of fractional flow reserve from anatomic CT angiography

Abstract

Context: Coronary computed tomographic (CT) angiography is a noninvasive anatomic test for diagnosis of coronary stenosis that does not determine whether a stenosis causes ischemia. In contrast, fractional flow reserve (FFR) is a physiologic measure of coronary stenosis expressing the amount of coronary flow still attainable despite the presence of a stenosis, but it requires an invasive procedure. Noninvasive FFR computed from CT (FFR(CT)) is a novel method for determining the physiologic significance of coronary artery disease (CAD), but its ability to identify ischemia has not been adequately examined to date.

Objective: To assess the diagnostic performance of FFR(CT) plus CT for diagnosis of hemodynamically significant coronary stenosis.

Design, setting, and patients: Multicenter diagnostic performance study involving 252 stable patients with suspected or known CAD from 17 centers in 5 countries who underwent CT, invasive coronary angiography (ICA), FFR, and FFR(CT) between October 2010 and October 2011. Computed tomography, ICA, FFR, and FFR(CT) were interpreted in blinded fashion by independent core laboratories. Accuracy of FFR(CT) plus CT for diagnosis of ischemia was compared with an invasive FFR reference standard. Ischemia was defined by an FFR or FFR(CT) of 0.80 or less, while anatomically obstructive CAD was defined by a stenosis of 50% or larger on CT and ICA.

Main outcome measures: The primary study outcome assessed whether FFR(CT) plus CT could improve the per-patient diagnostic accuracy such that the lower boundary of the 1-sided 95% confidence interval of this estimate exceeded 70%.

Results: Among study participants, 137 (54.4%) had an abnormal FFR determined by ICA. On a per-patient basis, diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of FFR(CT) plus CT 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. Compared with obstructive CAD diagnosed by CT alone (area under the receiver operating characteristic curve [AUC], 0.68; 95% CI, 0.62-0.74), FFR(CT) was associated with improved discrimination (AUC, 0.81; 95% CI, 0.75-0.86; P < .001).

Conclusion: Although the study did not achieve its prespecified primary outcome goal for the level of per-patient diagnostic accuracy, use of noninvasive FFR(CT) plus CT among stable patients with suspected or known CAD was associated with improved diagnostic accuracy and discrimination vs CT alone for the diagnosis of hemodynamically significant CAD when FFR determined at the time of ICA was the reference standard.

Conflict of interest statement

Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Min reports research support from GE Healthcare and Philips Medical. Dr Leipsic reports research support from GE Healthcare and serving as a consultant to Edwards Life-sciences. Dr Pencina reports consulting fees from Heart-Flow to his institution. Dr Berman reports research support from Siemens Medical Systems and Lantheus Medical Imaging and stock options in Spectrum Dynamics. Dr Budoff reports research support from GE Healthcare and grants to his institution from Roche and Pfizer. Dr Cole reports grant for research support from HeartFlow. Dr Jaffer reports serving as consultant to Boston Scientific, Siemens, and Merck and receiving nonfinancial research support from Abbott Vascular. Dr Mancini reports a grant to his institution from HeartFlow. Dr Mauri reports serving as a consultant to Medtronic and Cordis and receiving research support from Medtronic, Cordis, Abbott, Boston Scientific, Eli Lilly, Daiichi Sankyo, Bristol-Myers Squibb, and sanofiaventis; she also reports grants and consulting fees paid to her institution from HeartFlow. No other disclosures were reported.

Figures

Figure 1

Study Enrollment CT indicates computed tomographic angiography; FFR, fractional flow reserve; FFRCT, fractional flow reserve calculated from CT; ICA, invasive coronary angiography.

Figure 2

Representative Examples of 2 Patients From the DeFACTO Study Although both patients have obstructive coronary artery disease by computed tomographic angiography (CT), one patient (A) has ischemia and the other patient (B) does not have ischemia. A, Multiplanar reformat of a CT angiogram demonstrating obstructive stenosis of the proximal portion of the left anterior descending artery (LAD) and a computed fractional flow reserve (FFRCT) value of 0.62, indicating vessel ischemia. Invasive coronary angiogram demonstrates obstructive stenosis of the proximal portion of the LAD and measured fractional flow reserve (FFR) values of 0.65, indicating vessel ischemia. B, CT angiogram demonstrating obstructive stenosis of the mid portion of the right coronary artery (RCA) and an FFRCT value of 0.87, indicating no vessel ischemia. Invasive coronary angiogram demonstrates obstructive stenosis of the mid portion of the RCA and a measured FFR value of 0.88, indicating no vessel ischemia.

Figure 3

Areas Under the Receiver Operating Characteristic Curve of Per-Patient and Per-Vessel Performance of FFRCT ≤0.80 and CT Stenosis ≥50% Compared With Invasive FFR for Diagnosis of Ischemia FFR indicates fractional flow reserve; CT, computed tomographic angiography; FFRCT, fractional flow reserve calculated from CT.