Letter by Mao et al Regarding Article, “Noninvasive Fractional Flow Reserve Derived From Computed Tomography Angiography for Coronary Lesions of Intermediate Stenosis Severity: Results From the DeFACTO Study”

We commend Nakazato et al 1 for their excellent article entitled , " Non-Invasive Fractional Flow Reserve Derived From CT Angiography (FFRCT) for Coronary Lesions of Intermediate Stenosis Severity: Results From the DeFACTO Study. " The well-performed multicenter study concluded that FFR CT possessed higher diagnostic performance for ischemic for coronary lesions of intermediate stenosis severity than CT stenosis. Besides, the high sensitivity and negative predictive values suggested the ability of FFR CT to rule out intermediate lesions effectively that cause ischemia. However, we have some concerns about the study. First, when interpreting FFR CT , 3-dimensional (3D) flow simulations of the coronary arteries were performed, and blood was modeled as a Newtonian fluid to use incompressible Navier–Stokes equations. 1 A method to couple lumped parameter models of the microcircula-tion to the outflow boundaries of the 3D model was used. However, there may be some differences in vivo versus in vitro simulation. For instance, the elasticity of arterial wall may greatly affect the cardiac perfusion pressure in vivo, which was improperly neglected in the computation of FFR CT. 2,3 Second, for lesions of intermediate stenosis severity, FFR CT versus CT stenosis accuracy, sensitivity, specificity, positive predictive value, and negative predictive value was 71% versus 63%, 74% versus 34%, 67% versus 72%, 41% versus 27%, and 90% versus 78%, respectively. 1 Although there was a 2-fold increase in sensitivity and high negative predictive value of FFR CT , we must notice the poor performance of FFR CT in specificity and positive predictive value. The lower specificity and positive predictive value quenched the passion for the costly and complicated method of FFR CT , although it showed a promising role in excluding ischemia with high sensitivity and negative predictive values. 4 Besides, FFR CT is also confined because of the limited indications of CT angiography in the condition of advanced and calcific coronary artery disease and in patients with irregular heart rhythm, tachycardia, or motion artifact. 5 Finally, a recent approach of virtual FFR derived from invasive coronary angiography (ICA) was investigated based on the first-pass analysis and computational fluid dynamics. 5 ICA-derived virtual FFR did not have the limited indications of FFR CT. Moreover, patients who underwent FFR CT will likely require the ICA confirmation because of the poor diagnostic performance of FFR CT in specificity and positive predictive value. 1 Thus, no additional test and cost are needed when virtual …