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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.

One particular complexity of coronary artery is the natural tapering of the vessel with proximal segments having larger caliber and distal tapering as the vessel get smaller. The natural tapering of a coronary artery often leads to proximal incomplete stent apposition (ISA). ISA alters coronary hemodynamics and creates pathological path to develop complications such as in-stent restenosis, and more worryingly, stent thrombosis (ST). By employing state-of-the-art computer-aided design software, generic stent hoops were virtually deployed in an idealized tapered coronary artery with decreasing malapposition distance. Pulsatile blood flow simulations were carried out using computational fluid dynamics (CFD) on these computer-aided design models. CFD results reveal unprecedented details in both spatial and temporal development of microrecirculation environments throughout the cardiac cycle (CC). Arterial tapering also introduces secondary microrecirculation. These primary and secondary microrecirculations provoke significant fluctuations in arterial wall shear stress (WSS). There has been a direct correlation with changes in WSS and the development of atherosclerosis. Further, the presence of these microrecirculations influence strongly on the local levels of blood viscosity in the vicinity of the malapposed stent struts. The observation of secondary microrecirculations and changes in blood rheology is believed to complement the wall (-based) shear stress, perhaps providing additional physical explanations for tissue accumulation near ISA detected from high resolution optical coherence tomography (OCT).

With the goal of reducing vessel injury, the conventional approach to stent design has prioritized flexibility and conformability to the vessel wall. This strategy has contributed to several immensely successful devices, among them the platinum-chromium everolimus-eluting stents. This chapter begins with a brief discussion of the platinum-chromium alloy and then examines the role of stent architecture in the risk for longitudinal deformation. It presents technical aspects of the platinum-chromium everolimus-eluting stents and several landmark trials evaluating their clinical performance. As with cobalt-chromium (CoCr) alloys, development of the platinum- chromium (PtCr) alloy was driven by the clinical need for stronger and denser materials than stainless steel. Stent corrosion and metal ion release into vascular tissues are increasingly viewed as contributors to vascular inflammation and perhaps even thrombosis. Longitudinal stent deformation (LSD) refers to the elongation or shortening of a stent after deployment.

Underexpansion and overexpansion have been incriminated as causative factors of adverse cardiac events. However, dynamic biological interaction between vessel wall and scaffold may attenuate the adverse haemodynamic impact of overexpansion or underexpansion.

Coronary plaque rupture is the most common cause of vessel thrombosis and acute coronary syndrome. The accurate early detection of plaques prone to rupture may allow prospective, preventative treatment; however, current diagnostic methods remain inadequate to detect these lesions. Established imaging features indicating vulnerability do not confer adequate specificity for symptomatic rupture. Similarly, even though experimental and computational studies have underscored the importance of endothelial shear stress in progressive atherosclerosis, the ability of shear stress to predict plaque progression remains incremental. This review examines recent advances in image-based computational modelling that have elucidated possible mechanisms of plaque progression and rupture, and potentially novel features of plaques most prone to symptomatic rupture. With further study and clinical validation, these markers and techniques may improve the specificity of future culprit plaque detection.

Coronary optical coherence tomography (OCT) is now an established imaging technique in many catheterization laboratories worldwide. With its near-histological view of the vessel wall and lumen interface, it offers unprecedented imaging quality to improve our understanding of the pathophysiology of atherosclerosis, plaque vulnerability, and vascular biology. Not only is OCT used to accurately detect atherosclerotic plaque and optimize stent position, but it can further characterize plaque composition, quantify stent apposition, and assess stent tissue coverage. Given that its resolution of 15 μm is well above that of angiography and intravascular ultrasound, OCT has become the invasive imaging method of choice to examine the interaction between stents and the vessel wall. This review focuses on the application of OCT to examine coronary stents, the mechanisms of stent complications, and future directions of OCT-guided intervention.

A 3.0 × 18 mm Absorb bioresorbable vascular scaffold (Abbott Vascular, Santa Clara, California) was implanted in the midsegment of the left anterior descending coronary artery of a patient with stable angina pectoris. Optical coherence tomography was performed following scaffold implantation (

Incomplete stent apposition (ISA) is sometimes found in stent deployment at complex lesions, and it is considered to be one of the causes of post-stenting complications, such as late stent thrombosis and restenosis. The presence of ISA leads to large recirculation bubbles behind the stent struts, which can reduce shear stress at the arterial wall that retards neointimal formation process and thus lead to complications. Computational fluid dynamics (CFD) simulations are performed on simplified two-dimensional axisymmetric arterial models with stents struts of square and circular cross-sectional shapes at a malapposition distance of 120 μm from the arterial wall. To investigate the effects of pulsatile flow period on the dynamics of the recirculation bubbles, high fidelity simulations are carried out with pulsatile flows of period 0.4 s and 0.8 s. Under the condition of the same flow rate, both square and circular strut cases show that shorter period provides greater flow deceleration, leading to the formation of a larger recirculation bubble. With the same thickness, circular strut has a significant improvement over the square strut in terms of the size of the recirculation bubble, and therefore less likely to lead to complications.

A 3.0 × 18 mm Absorb bioresorbable vascular scaffold (Abbott Vascular, Santa Clara, CA, USA) was implanted in the left circumflex coronary artery of patient with stable angina pectoris. Optical coherence tomography (OCT) revealed a well-expanded and apposed scaffold (pullback speed: 18 mm/s, acquisition rate: 180 frames/s). A patient-specific 3D geometry of the scaffolded lumen was generated by fusing OCT with coronary angiography. Pulsatile computational fluid dynamic (CFD) simulations were carried out by solving the Navier–Stokes equations. Blood was modelled as non-Newtonian fluid. Endothelial shear stress (ESS) at lumen and scaffold surfaces was calculated as product of local blood viscosity and near-wall velocity gradient. During low-coronary flow in systole, low-ESS predominates (PanelsA and C) whereas at peak diastolic flow the vessel is exposed to high-ESS (PanelsB and D). Irrespective of systolic or diastolic phase, the post-implantation vessel appears highly corrugated with an alternans of high-ESS on top of the struts and low-ESS between struts (PanelsA and B), that has been associated with blood micro-recirculation, fibrin deposition, and platelet aggregation. By 5 years, heterogeneity in ESS has largely dissipated (PanelsC and D, see Supplementary data online, Videos S1) while ESS distribution narrows and becomes more homogenous in both systole and diastole (PanelE). Histograms depicting the overall percent area of the simulated vessel exposed to varying levels of ESS during each of the studied flow conditions and time-points (PanelE) demonstrate that vessel exposure to very low and very high ESS decreases, leading to an overall increase in mid-range values of ESS generally considered to be more physiologic.

Fractional flow reserve (FFR) is a useful tool for the evaluation of coronary bifurcation lesions. FFR can guide treatment strategy, simplify the procedure and reduce unnecessary complex interventions. However, the application of FFR to complex bifurcation lesions requires a comprehensive understanding of its roles and potential pitfalls. Furthermore, FFR should be interpreted in the context of complex bifurcation anatomy and physiology rather than as a simple number. Finally, it should be recalled that the ischaemic burden is more important than the presence of ischaemia, and the risk/benefit of a complex intervention should be incorporated into the treatment decision after FFR measurement.