Yingguang Li

In Vivo Flow Simulation at Coronary Bifurcation Reconstructed by Fusion of 3-Dimensional X-ray Angiography and Optical Coherence Tomography

High-quality reconstruction of coronary bifurcations is crucial in the evaluation of lesions, dedicated bifurcation stents, and stent techniques. Although 3-dimensional (3D) X-ray angiography restores natural bending of vascular structures, optical coherence tomography (OCT) provides an ultra–high resolution of the vessel wall morphology and stents at baseline and follow-up. We present a new method for 3D fusion of the 2 imaging modalities combined with flow simulation at the target bifurcation. A 63-year-old woman was admitted for percutaneous coronary intervention attributable to severe stenosis (Figure 1A) in the left anterior descending artery (LAD) at the bifurcation of the first diagonal branch (D1). The target bifurcation was reconstructed in 3D (Figure 1B) using a dedicated 3D QCA software package (QAngio XA 3D Research Edition 1.0, Medis Specials, Leiden, The Netherlands).1 Fusion of the 2 OCT pullbacks acquired in the LAD and in the D1 with the 3D QCA (Figure 1D and Video I in the online-only Data Supplement) was performed using QAngioOCT Advanced Edition (Medis Specials).2 The entire fusion procedure can be summarized in a few major steps as follows: (1) isocenter offset in the angiographic acquisition was corrected; (2) lumen edges at the bifurcation were automatically detected in the 2 angiographic projections; (3) automated reconstruction and modeling techniques were performed, resulting in a 3D lumen surface and a so-called reference surface, ie, the normal lumen as if the disease was not present; (4) the spatial correspondence, including alignment and angulation, of the OCT images with respect to the 3D angiographic reconstruction was determined based on the common carina position and the segmented OCT contours; (5) the OCT pullbacks were transformed and fused with the 3D angiographic reconstruction using …

Fractional Flow Reserve and Coronary Bifurcation Anatomy : A Novel Quantitative Model to Assess and Report the Stenosis Severity of Bifurcation Lesions

OBJECTIVES The aim of this study was to develop a new model for assessment of stenosis severity in a bifurcation lesion including its core. The diagnostic performance of this model, powered by 3-dimensional quantitative coronary angiography to predict the functional significance of obstructive bifurcation stenoses, was evaluated using fractional flow reserve (FFR) as the reference standard. BACKGROUND Development of advanced quantitative models might help to establish a relationship between bifurcation anatomy and FFR. METHODS Patients who had undergone coronary angiography and interventions in 5 European cardiology centers were randomly selected and analyzed. Different bifurcation fractal laws, including Murray, Finet, and HK laws, were implemented in the bifurcation model, resulting in different degrees of stenosis severity. RESULTS A total of 78 bifurcation lesions in 73 patients were analyzed. In 51 (65%) bifurcations, FFR was measured in the main vessel. A total of 34 (43.6%) interrogated vessels had an FFR≤0.80. Correlation between FFR and diameter stenosis was poor by conventional straight analysis (ρ=-0.23, p<0.001) but significantly improved by bifurcation analyses: the highest by the HK law (ρ=-0.50, p<0.001), followed by the Finet law (ρ=-0.49, p<0.001), and the Murray law (ρ=-0.41, p<0.001). The area under the receiver-operating characteristics curve for predicting FFR≤0.80 was significantly higher by bifurcation analysis compared with straight analysis: 0.72 (95% confidence interval: 0.61 to 0.82) versus 0.60 (95% confidence interval: 0.49 to 0.71; p=0.001). Applying a threshold of ≥50% diameter stenosis, as assessed by the bifurcation model, to predict FFR≤0.80 resulted in 23 true positives, 27 true negatives, 17 false positives, and 11 false negatives. CONCLUSIONS The new bifurcation model provides a comprehensive assessment of bifurcation anatomy. Compared with straight analysis, identification of lesions with preserved FFR values in obstructive bifurcation stenoses was improved. Nevertheless, accuracy was limited by using solely anatomical parameters.

Assessment of endothelial shear stress in patients with mild or intermediate coronary stenoses using coronary computed tomography angiography: comparison with invasive coronary angiography.

Characterization of endothelial shear stress (ESS) may allow for prediction of the progression of atherosclerosis. The aim of this investigation was to develop a non-invasive approach for in vivo assessment of ESS by coronary computed tomography angiography (CTA) and to compare it with ESS derived from invasive coronary angiography (ICA). A total of 41 patients with mild or intermediate coronary stenoses who underwent both CTA and ICA were included in the analysis. Two geometrical models of the interrogated vessels were reconstructed separately from CTA and ICA images. Subsequently, computational fluid dynamics were applied to calculate the ESS, from which ESSCTA and ESSICA were derived, respectively. Comparisons between ESSCTA and ESSICA were performed on 163 segments of 57 vessels in the CTA and ICA models. ESSCTA and ESSICA were similar: mean ESS: 4.97 (4.37–5.57) Pascal versus 4.86 (4.27–5.44) Pascal, p = 0.58; minimal ESS: 0.86 (0.67–1.05) Pascal versus 0.79 (0.63–0.95) Pascal, p = 0.37; and maximal ESS: 14.50 (12.62–16.38) Pascal versus 13.76 (11.44–16.08) Pascal, p = 0.44. Good correlations between the ESSCTA and the ESSICA were observed for the mean (r = 0.75, p < 0.001), minimal (r = 0.61, p < 0.001), and maximal (r = 0.62, p < 0.001) ESS values. In conclusion, geometrical reconstruction by CTA yields similar results to ICA in terms of segment-based ESS calculation in patients with low and intermediate stenoses. Thus, it has the potential of allowing combined local hemodynamic and plaque morphologic information for risk stratification in patients with coronary artery disease.

Numerical and experimental investigations of the flow–pressure relation in multiple sequential stenoses coronary artery

Virtual fractional flow reserve (vFFR) has been evaluated as an adjunct to invasive fractional flow reserve (FFR) in the light of its operational and economic benefits. The accuracy of vFFR and the complexity of hyperemic flow simulation are still not clearly understood. This study investigates the flow–pressure relation in an idealised multiple sequential stenoses coronary artery model via numerical and experimental approaches. Pressure drop is linearly correlated with flow rate irrespective of the number of stenosis. Computational fluid dynamics results are in good agreement with the experimental data, demonstrating reasonable accuracy of vFFR. It was also found that the difference between data obtained with steady and pulsatile flows is negligible, indicating the steady flow may be used instead of pulsatile flow conditions in vFFR computation. This study adds to the current understanding of vFFR and may improve its clinical applicability as an adjunct to invasively determined FFR.

Assessment of superficial coronary vessel wall deformation and stress : validation of in silico models and human coronary arteries in vivo

Cyclic biomechanical stress at the lumen-intima interface plays a crucial role in the rupture of coronary plaque. We performed a comprehensive assessment of a novel angiography-based method for four-dimensional (4D) dynamic assessment of superficial wall stress (SWS) and deformation with a total of 32 analyses in virtual stenosis models with equal lumen dimensions and 16 analyses in human coronary arteries in vivo. The in silico model analyses demonstrated that the SWS, derived by the proposed global displacement method without knowledge of plaque components or blood pressure, was comparable with the result calculated by traditional finite element method. Cardiac contraction-induced vessel deformation increased SWS. Softer plaque and positive arterial remodeling, associated with a greater plaque burden, showed more variation in mean lumen diameter within the cardiac cycle and resulted in higher SWS. In vivo patient analyses confirmed the accuracy of computed superficial wall deformation. The centerlines predicted by our method at random selected time instant matched well with the actual one in angiograms by Procrustes analysis (scaling: 0.995 ± 0.018; dissimilarity: 0.007 ± 0.014). Over 50% of the maximum SWS occurred at proximal plaque shoulders. This novel 4D approach could be successfully to predict superficial wall deformation of coronary artery in vivo. The dynamic SWS might be more realistic to evaluate the risk of plaque rupture.

In vivo reconstruction of coronary artery and bioresorbable stents from intracoronary optical coherence tomography.

The implantation of bioresorbable scaffolds (BRS) alters the local hemodynamic environment. Computational fluid dynamics (CFD) allows evaluation of local flow pattern, shear stress (SS) and Pressure_distal/ Pressure_approximal (Pd/Pa). The accuracy of CFD results relies to a great extent on the reconstruction of the 3D geometrical model. The aim of this study was to develop a new approach for in vivo reconstruction of coronary tree and BRS by fusion of Optical Coherence Tomography (OCT) and X-ray angiography. Ten patients enrolled in the BIFSORB pilot study with BRS implanted in coronary bifurcations were included for analysis. All patients underwent OCT of the target vessel after BRS implantation in the main vessel. Coronary 3D reconstruction was performed creating two geometrical models: one was angiography model and the other was OCT model with the implanted BRS. CFD analysis was performed separately on these two models. The main vessel was divided into portions of 0.15 mm length and 0.15mm arc width for point-perpoint comparison of SS between the two models. Reconstruction of the implanted BRS in naturally bent shape was successful in all cases. SS was compared in the matched 205463 portions of the two models. The divergence of shear stress was higher in the OCT model (mean±SD: 2.27 ± 3.95 Pa, maximum: 142.48 Pa) than that in the angiography model (mean±SD: 2.05 ± 3.12 Pa, maximum: 83.63 Pa). Pd/Pa values were lower in the OCT model than in the angiography model for both main vessels and side branches (mean±SD: 0.979 ± 0.009 versus 0.984 ± 0.011, and 0.951 ± 0.068 versus 0.966 ± 0.051). Reconstruction of BRS in naturally bent shape after implantation is feasible. It allows detailed analysis of local flow pattern, including shear stress and Pd/Pa in vivo.

Local Flow Patterns After Implantation of Bioresorbable Vascular Scaffold in Coronary Bifurcations ― Novel Findings by Computational Fluid Dynamics ―

BACKGROUND Development of methods for accurate reconstruction of bioresorbable scaffolds (BRS) and assessing local hemodynamics is crucial for investigation of vascular healing after BRS implantation.Methods and Results:Patients with BRS that crossed over in a coronary bifurcation were included for analysis. Reconstructions of the coronary lumen and BRS were performed by fusion of optical coherence tomography and coronary angiography generating a tree model (TM) and a hybrid model with BRS (TM-BRS). A virtual BRS model with thinner struts was created and all 3 models were analyzed using computational fluid dynamics to derive: (1) time-average shear stress (TASS), (2) TASS gradient (TASSG), which represents SS heterogeneity, and (3) fractional flow reserve (FFR). Reconstruction of the BRS was successful in all 10 patients. TASS and TASSG were both higher by TM-BRS than by TM in main vessels (difference 0.27±4.30 Pa and 10.18±27.28 Pa/mm, P<0.001), with a remarkable difference at side branch ostia (difference 13.51±17.40 Pa and 81.65±105.19 Pa/mm, P<0.001). With thinner struts, TASS was lower on the strut surface but higher at the inter-strut zones, whereas TASSG was lower in both regions (P<0.001 for all). Computational FFR was lower by TM-BRS than by TM for both main vessels and side branches (P<0.001). CONCLUSIONS Neglecting BRS reconstruction leads to significantly lower SS and SS heterogeneity, which is most pronounced at side branch ostia. Thinner struts can marginally reduce SS heterogeneity.

TCT-567 In Vivo Reconstruction of Bioresorbable Stents and Its Impact on Computation of Shear Stress

The implantation of bioresorbable stents (BVS) alters the local hemodynamic environment. Computational fluid dynamics (CFD) allows evaluation of local flow pattern and shear stress (SS). The aim of this study was to develop a new approach for in vivo reconstruction of BVS after implantation and to