A study of noninvasive fractional flow reserve derived from a simplified method based on coronary computed tomography angiography in suspected coronary artery disease

Abstract

Background: The invasive fractional flow reserve has been considered the gold standard for identifying ischaemia-related stenosis in patients with suspected coronary artery disease. Determining non-invasive FFR based on coronary computed tomographic angiography datasets using computational fluid dynamics tends to be a demanding process. Therefore, the diagnostic performance of a simplified method for the calculation of FFR_CTA requires further evaluation.

Objectives: The aim of this study was to investigate the diagnostic performance of FFR_CTA calculated based on a simplified method by referring to the invasive FFR in patient-specific coronary arteries and clinical decision-making.

Methods: Twenty-nine subjects included in this study underwent CCTA before undergoing clinically indicated invasive coronary angiography for suspected coronary artery disease. Pulsatile flow simulation and a novel boundary condition were used to obtain FFR_CTA based on the CCTA datasets. The Pearson correlation, Bland-Altman plots and the diagnostic performance of FFR_CTA and CCTA stenosis were analyzed by comparison to the invasive FFR reference standard. Ischaemia was defined as an FFR or FFR_CTA ≤0.80, and anatomically obstructive CAD was defined as a CCTA stenosis >50%.

Results: FFR_CTA and invasive FFR were well correlated (r = 0.742, P = 0.001). Slight systematic underestimation was found in FFR_CTA (mean difference 0.03, standard deviation 0.05, P = 0.001). The area under the receiver-operating characteristic curve was 0.93 for FFR_CTA and 0.75 for CCTA on a per-vessel basis. Per-patient accuracy, sensitivity and specificity were 79.3, 93.7 and 61.5%, respectively, for FFR_CTA and 62.1, 87.5 and 30.7%, respectively, for CCTA. Per-vessel accuracy, sensitivity and specificity were 80.6, 94.1 and 68.4%, respectively, for FFR_CTA and 61.6, 88.2 and 36.8%, respectively, for CCTA.

Conclusions: FFR_CTA derived from pulsatile simulation with a simplified novel boundary condition was in good agreement with invasive FFR and showed better diagnostic performance compared to CCTA, suggesting that the simplified method has the potential to be an alternative and accurate way to assess the haemodynamic characteristics for coronary stenosis.

Keywords: CCTA; CFD; FFR; FFRCTA.

Fig. 1

Mesh independent test for the mesh generation procedure. Five densities of meshes were generated for one geometry (coarser, coarse, fine, finer and extra fine) and simulations were performed. The maximum velocity values at the center of the aortic ostium under each density of mesh was recorded for the evaluation of convergence. The test showed that convergence was reached at finer mesh

Fig. 2

The pressure waveform at the aorta and the stenosis from the transient simulation. The pressure dropped due to the stenosis compared to the pressure of the aorta. The FFR_CTA was calculated as the ratio dividing the average pressure at the stenosis in one period of heart cycle by the average pressure at the ostium of the coronary artery in the aorta. The FFR_CTA value presented in the figure was, for example, 0.88

Fig. 3

Comparison among CCTA stenosis, FFR_CTA, FFR_SS and invasive FFR on a per-vessel basis. a Pearson correlation between FFR_CTA and invasive FFR, r was 0.742 with significant difference (P = 0.001). b Bland–Altman plots of FFR_CTA and invasive FFR, mean difference 0.03, standard deviation 0.05. c Pearson correlation between FFR_SS and invasive FFR, r was 0.729 with significant difference (P = 0.001). d Bland–Altman plots of FFR_SS and invasive FFR, mean difference 0.03, standard deviation 0.06. e Pearson correlation between stenosis and invasive FFR, r was −0.409 with significant difference (P = 0.013). f Mean vlaue of FFR, FFR_CTA, FFR_SS and stenosis

Fig. 4

Volume-rendered image (a) and multiplanar reformat (b) of CCTA and FFR_CTA (c) of the left anterior descending artery (LAD). CCTA demonstrates stenosis (80% lumen reduction) of the proximal-portion of LAD (red arrow) and an FFR_CTA value of 0.71. ICA demonstrates a measured FFR value of 0.77

Fig. 5

Volume-rendered image (a) and multiplanar reformat (b) of CCTA and FFR_CTA (c) of the left anterior descending artery (LAD). CCTA demonstrates stenosis (75% lumen reduction) of the mid-portion of LAD (red arrow) and an FFR_CTA value of 0.95. ICA demonstrates a measured FFR value of 0.87

Fig. 6

Area under the receiver-operating characteristic curve (AUC) of FFR_CTA, FFR_SS and CCTA stenosis for discriminating ischemia on a a per-vessel and b per-patient basis separately