FFRCT Provides Superior Functional Assessment of Coronary Stenosis When Compared With Traditional Functional Imaging Techniques

A study published in JACC reported that fractional flow reserve (FFR) computation from coronary computed tomography angiography (CTA) datasets (FFRCT) had higher diagnostic performance as compared with standard coronary CTA, SPECT, and PET for vessel-specific ischemia, provided coronary CTA images were evaluable by FFRCT, whereas PET had a favorable performance in per-patient and intention-to-diagnose analysis. The investigators also stressed that in patients in whom 3-vessel FFRCT could be analyzed, FFRCT held the clinical potential to provide anatomic and hemodynamic significance of coronary lesions.

FFRCT has recently emerged as a promising non-invasive test to assess the hemodynamic severity of coronary disease (CAD) but has not yet been compared with traditional functional imaging. Keeping this in mind, the purpose of this study was to evaluate how the diagnostic accuracy of fractional flow reserve (FFR) computation from coronary computed tomography angiography (CTA) datasets (FFR_CT) compared to that of CTA, single-photon emission CT (SPECT), and positron emission tomography (PET) myocardial perfusion imaging (MPI).

The authors conducted a non–prespecified secondary analysis of 208 patients with suspected stable CAD enrolled in the prospective PACIFIC trial. Coronary CTA scans were sent for quantification of FFR_CT and this was compared with blinded interpretations of coronary CTA alone, SPECT MPI, and PET MPI for diagnosis of FFR ≤0.80. Importantly, although the FFR_CT core lab was blinded to FFR values, they were not blinded to the location of measured FFR. For the primary analysis, datasets not evaluable by FFR_CT were excluded, although a secondary intention-to-diagnose analysis of all datasets was performed. The results of the study showed that 505 of 612 (83%) vessels could be evaluated with FFRCT. Moreover, FFRCT showed a diagnostic accuracy, sensitivity, and specificity of 87%, 90%, and 86% on a per-vessel basis and 78%, 96%, and 63% on a per-patient basis, respectively. Area under the receiver-operating characteristic curve (AUC) for identification of ischemia-causing lesions was significantly greater for FFRCT (0.94 and 0.92) in comparison with coronary CTA (0.83 and 0.81; p < 0.01 for both) and SPECT (0.70 and 0.75; p < 0.01 for both), on a per-vessel and -patient level, respectively. FFRCT also outperformed PET on a per-vessel basis (AUC 0.87; p < 0.01), but not on a per-patient basis (AUC 0.91; p ¼ 0.56). Finally, in the intention-to diagnose analysis, PET showed the highest per-patient and -vessel AUC followed by FFRCT (0.86 vs. 0.83; p ¼ 0.157; and 0.90 vs. 0.79; p ¼ 0.005, respectively). Although one in four coronary CTA scans was unevaluable for FFR_CT, this method could have slightly higher diagnostic accuracy compared to coronary CTA and SPECT, but not compared to PET. Importantly, this analysis was fully blinded for CTA, SPECT, and PET, but only partly blinded for FFR_CT.

Summarizing the study findings, Dr. Paul Knaapen, Department of Cardiology, VU University Medical Center, Netherlands stated, “In this head-to-head comparative study, FFRCT showed the highest diagnostic performance for vessel-specific ischemia, provided coronary CTA images were evaluable by FFRCT. On an intention-to-diagnose basis, however, PET displays the highest diagnostic performance due to the relatively high rejection rate of FFRCT. Further improvements in CT acquisition and reconstruction are needed to improve the evaluability rate of FFRCT so the diagnostic performance could be similar to PET. Still, FFRCT would be of value in clinical practice for the noninvasive evaluation of CAD, providing not only anatomic but also the hemodynamic significance of coronary lesions.”

The authors stressed that in the present PACIFIC substudy of patients with suspected stable CAD, FFRCT values strongly correlated with invasively derived FFR, which resulted in high diagnostic performance even though, in line with previous reports, measured FFRCT values were systematically lower than invasive FFR values. When images were of sufficient quality to analyze FFRCT, it showed an improved per-vessel and -patient diagnostic discriminative ability compared with coronary CTA, SPECT, and PET in terms of AUC, except for per-patient analysis with PET. However,intention-to-diagnose analysis, including coronary CTA images non-evaluable for FFRCT, diluted the incremental value of FFRCT resulting in a lower per-patient AUC than PET. Emphasizing the importance of these findings, corresponding author Dr. Roel S. Driessen remarked, “The current results represent the first true head-to-head comparison of the functional FFRCT assessment derived from standard coronary CTA against more traditional functional imaging with SPECT and PET. Our findings support the use of FFRCT in clinical practice, taking into account an anticipated increase of FFRCT analyzability, whereas current multisociety guidelines do not advocate the use of any specific imaging modality.” It is clear that future studies should focus on enhancing CT image acquisition and reconstruction to improve the applicability of FFRCT in clinical practice.”