Computational Assessment of Hemodynamic Significance in Patients With Intramural Anomalous Aortic Origin of the Coronary Artery Using Virtually Derived Fractional Flow Reserve and Downstream Microvascular Resistance

Influence of boundary conditions and blood rheology on indices of wall shear stress from IVUS-based patient-specific stented coronary artery simulations

The long-term clinical efficacy of coronary stents is limited by restenosis. Coronary stenting results in altered arterial geometry, local blood flow patterns, and wall shear stress (WSS), all of which can influence restenosis. Computational fluid dynamics (CFD) simulations employ assumptions about blood properties and boundary conditions, which also influence WSS alterations from stenting. Our objective was to evaluate three common assumptions applied with stented coronary artery CFD simulations (inlet velocity profile, outlet boundary conditions, and viscosity) to provide insight for future studies. A patient-specific right coronary artery was reconstructed from intravascular ultrasound and computed tomography imaging. Time-averaged WSS (TAWSS) and oscillatory shear index (OSI) were compared for CFD simulations using parabolic and Womersley (α = 2.5) velocity profiles and Newtonian versus non-Newtonian (Carreau-Yasuda) viscosity. TAWSS and OSI differences were quantified for 5-element lumped parameter network (LPN) outlet boundary conditions as compared to a 3-element Windkessel approach previously applied by neglecting ventricular contraction. Differences in velocity profiles were negligible beyond two diameters from the inlet. Differences between Womersley inlet 3-element and 5-element LPNs were ~ 5% for TAWSS and ~ 200% for OSI, and most pronounced near stent struts. OSI differences were due to pressure differences between outlet boundary conditions inducing different near-wall velocity gradients. TAWSS differences between viscosity models were greatest near struts (~ 100%). Collectively these results suggest certain assumptions commonly applied for simulations of stented coronary arteries have a greater impact on TAWSS and OSI than others, with outlet boundary conditions being paramount, followed by viscosity model and inlet velocity profile.

Hemodynamic Evaluation of Norwood Aortic Arch Geometry Compared to Native Arch Controls

The Norwood procedure creates a reconstructed neo-aorta to provide unobstructed systemic cardiac output for hypoplastic left heart syndrome patients. We used patient-specific computational fluid dynamics (CFD) simulations incorporating physiologic boundary conditions to quantify hemodynamics for reconstructed aortic arch geometries versus native aortic arches from a control group of single ventricle patients. We hypothesized that reconstructed arches from Norwood patients (n = 5) would experience significant differences in time-averaged wall shear stress normalized to body surface area (TAWSSnBSA), oscillatory shear index (OSI), energy efficiency (Eeff), and energy loss (EL) versus controls (n = 3). CFD simulations were conducted using 3 T cardiac magnetic resonance imaging, blood flow, and pressure data. Simulations incorporated downstream vascular resistance and compliance to replicate patient physiology. TAWSSnBSA and OSI were quantified axially and circumferentially. Global differences in Eeff and EL were compared. Significance was assessed by Mann-Whitney U test. Norwood patients had higher TAWSSnBSA distal to the transverse arch at locations of residual narrowing presenting following coarctation correction, as well as higher OSI within ascending aorta and transverse arch regions (p < 0.05). EL correlated with patient features including cardiac output (r = 0.9) and BT-shunt resistance (r = -0.63) but did not correlate with arch measurements or morphology. These results indicate reconstructed arches from Norwood patients are exposed to altered wall shear stress and energy indices linked to cellular proliferation and inefficiency in prior studies. These results may help clinicians further understand what constitutes an optimally reconstructed arch after confirmation in larger studies.

Fluid-structure interaction simulations for the prediction of fractional flow reserve in pediatric patients with anomalous aortic origin of a coronary artery

Computer simulations of blood flow in patients with anomalous aortic origin of a coronary artery (AAOCA) have the promise to provide insight into this complex disease. They provide an in silico experimental platform to explore possible mechanisms of myocardial ischemia, a potentially deadly complication for patients with this defect. This paper focuses on the question of model calibration for fluid-structure interaction models of pediatric AAOCA patients. Imaging and cardiac catheterization data provide partial information for model construction and calibration. However, parameters for downstream boundary conditions needed for these models are difficult to estimate. Further, important model predictions, like fractional flow reserve (FFR), are sensitive to these parameters. We describe an approach to calibrate downstream boundary condition parameters to clinical measurements of resting FFR. The calibrated models are then used to predict FFR at stress, an invasively measured quantity that can be used in the clinical evaluation of these patients. We find reasonable agreement between the model predicted and clinically measured FFR at stress, indicating the credibility of this modeling framework for predicting hemodynamics of pediatric AAOCA patients. This approach could lead to important clinical applications since it may serve as a tool for risk stratifying children with AAOCA.

Anomalous Aortic Origin of a Coronary Artery in Pediatric Patients

Purpose of Review

We present a contemporary approach to risk assessment and management of patients with anomalous aortic origin of a coronary artery (AAOCA).

Recent Findings

Anomalous left coronary artery from the right aortic sinus (L-AAOCA) with interarterial course carries a high risk of sudden cardiac death (SCD); therefore, current guidelines recommend exercise restriction and surgical intervention. Recent data in intraseptal and juxtacommissural L-AAOCA showed inducible perfusion abnormalities, leading to consideration of surgical intervention. Anomalous right coronary artery from the left aortic sinus (R-AAOCA) carries a much lower risk and stress perfusion imaging is helpful in identifying patients with inducible ischemia. Perfusion abnormalities resolve following successful surgical intervention of AAOCA. Computational modeling techniques identifying risk features shows promise in the evaluation of AAOCA.

Summary

Stress perfusion imaging is helpful in assessing AAOCA upon presentation and following surgical intervention. Computational modeling has potential in bridging knowledge gaps in AAOCA.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40124-024-00317-7.

Numerical vs analytical comparison with experimental fractional flow reserve values of right coronary artery stenosis

BACKGROUND: The fractional flow reserve (FFR) index has been widely accepted as a standard diagnostic method for identifying functional relevance of coronary stenosis. Since the invasive techniques used for its determination are associated with a certain risk of vascular injury, as well as with an increased cost, several non-invasive procedures have been developed. OBJECTIVE: The aim of this study was to compare FFR values for the coronary artery obtained by computational fluid dynamics (CFD) and coronary computed tomography angiography (CCTA). METHODS: Computation of FFR has been performed using both numerical and the analytical method. The numerical method employs CFD to solve the governing equations which relate to mass and momentum conservation (the continuity equation and the Navier-Stokes equations) as well as CCTA to generate the three-dimensional computational domain. After imposing the appropriate boundary conditions, the values of the pressure change are calculated and the FFR index is determined. Based on Bernoulli’s law, the analytical method calculates the overall pressure drop across the stenosis in the coronary artery, enabling FFR determination. RESULTS: The clinical data for twenty patients who underwent invasive coronary angiography are used to validate the results obtained by using CFD (together with CCTA) simulation and analytical solution. The medically measured FFR compared to the analytical one differs by about 4%, while, the difference is about 2.6% when compared to the numerical FFR. For FFR values below 0.8 (which are considered to be associated with myocardial ischemia) the standard error has a value of 0.01201, while the standard deviation is 0.02081. For FFR values above 0.80, these values are slightly higher. Bland-Altman analysis showed that medical measurement and numerical FFR were in good agreement (SD = 0.0292, p< 0.0001). CONCLUSIONS: The analytically calculated FFR has a slightly lower coefficient of determination than the numerically computed FFR when compared with experimental one. However, it can still give a reliable answer to the question of whether patients need a stent, bypass surgery or only drug treatment and it requires a significantly lower computation time.

Characterization of hemodynamics in anomalous aortic origin of coronary arteries using patient-specific modeling

The anomalous aortic origin of coronary arteries (AAOCA) is a congenital disease that can lead to sudden cardiac death (SCD) during strenuous physical activity. Despite AAOCA being the second leading cause of SCD among young athletes, the mechanism behind sudden cardiac death remains mostly unknown. Computational fluid dynamics provides a powerful tool for studying how pathologic anatomy can affect different hemodynamic states. The present study investigates the effect of AAOCA on patient hemodynamics. We performed patient-specific hemodynamic simulations of interarterial AAOCA at baseline and in the exercise state using our massively parallel flow solver. Additionally, we investigate how surgical correction via coronary unroofing impacts patient blood flow. Results show that patient-specific AAOCA models exhibited higher interarterial time-averaged wall shear stress (TAWSS) values compared to the control patients. The oscillatory shear index had no impact on AAOCA. Finally, the coronary unroofing procedure normalized the elevated TAWSS by decreasing TAWSS in the postoperative patient. The present study provides a proof of concept for the potential hemodynamic factors underlying coronary ischemia in AAOCA during exercise state.

Patient-Specific Fluid-Structure Simulations of Anomalous Aortic Origin of Right Coronary Arteries

Objectives

Anomalous aortic origin of the right coronary artery (AAORCA) may cause ischemia and sudden death. However, the specific anatomic indications for surgery are unclear, so dobutamine-stress instantaneous wave-free ratio (iFR) is increasingly used. Meanwhile, advances in fluid–structure interaction (FSI) modeling can simulate the pulsatile hemodynamics and tissue deformation. We sought to evaluate the feasibility of simulating the resting and dobutamine-stress iFR in AAORCA using patient-specific FSI models and to visualize the mechanism of ischemia within the intramural geometry and associated lumen narrowing.

Methods

We developed 6 patient-specific FSI models of AAORCA using SimVascular software. Three-dimensional geometries were segmented from coronary computed tomography angiography. Vascular outlets were coupled to lumped-parameter networks that included dynamic compression of the coronary microvasculature and were tuned to each patient's vitals and cardiac output.

Results

All cases were interarterial, and 5 of 6 had an intramural course. Measured iFRs ranged from 0.95 to 0.98 at rest and 0.80 to 0.95 under dobutamine stress. After we tuned the distal coronary resistances to achieve a stress flow rate triple that at rest, the simulations adequately matched the measured iFRs (r = 0.85, root-mean-square error = 0.04). The intramural lumen remained narrowed with simulated stress and resulted in lower iFRs without needing external compression from the pulmonary root.

Conclusions

Patient-specific FSI modeling of AAORCA is a promising, noninvasive method to assess the iFR reduction caused by intramural geometries and inform surgical intervention. However, the models’ sensitivity to distal coronary resistance suggests that quantitative stress-perfusion imaging may augment virtual and invasive iFR studies.