Does the inflow velocity profile influence physiologically relevant flow patterns in computational hemodynamic models of left anterior descending coronary artery?
Introduction
The marked predisposition to develop atherosclerosis makes coronary arteries of paramount clinical relevance. Although atherosclerosis initiation and progression results from the interplay of many systemic factors [1], its development at specific, geometrically predisposed locations such as branching and bifurcations [2] suggested the involvement of local hemodynamics [3,4]. In particular, the role of wall shear stress (WSS) was extensively investigated over the last years [5], [6], [7], [8], while more recently the role of intravascular helical patterns on coronary atherosclerosis initiation and progression was demonstrated [9,10]. In this context, the combined use of medical imaging and computational fluid dynamics (CFD) has proven to be a valuable tool in the study of possible associations between local hemodynamics and coronary artery disease as it makes available highly resolved hemodynamic flow patterns inside anatomically realistic, patient-specific geometries [11], [12], [13]. However, in silico methods require assumptions that introduce uncertainties, weakening CFD findings at a level that could limit their translation to clinics [14], [15], [16], [17], [18], [19], [20]. As recently highlighted, the uncertainties in cardiovascular modelling should not compromise its added value with respect to standard clinical measurement and therefore they should be carefully assessed.
While anatomically realistic geometries can be reconstructed with satisfactory accuracy using in vivo imaging tools, acquiring non-defective patient-specific boundary conditions, as required to perform reliable computational hemodynamics, is not always feasible. This is particularly true for the coronary arteries, for which (1) the measurable (whenever possible) inflow rates can be imposed only in terms of idealized velocity profiles, and (2) the possibility to use realistic three-dimensional (3D) velocity profiles measured directly in vivo as inflow boundary condition is still challenging, due to issues related to resolution and cardiac motion [21]. To be clearer, when only the integral quantity flow rate is available, its translation to inflow Dirichlet boundary condition in terms of 3D velocity profiles in CFD applications necessarily undergoes an idealization process based on a priori hypotheses to fill the gap of information. For these reasons, most of the previous computational studies on coronary arteries, including those accounting for the presence of coronary stents, starting from in vivo flow rate measurements/estimations, prescribed the inflow boundary conditions in terms of flat (e.g. [22], [23], [24], [25]) or fully developed (e.g. [26], [27], [28], [29], [30]) velocity profiles. Such a priori hypotheses on the velocity profiles to be used as conditions at inflow boundaries represent a source of uncertainty in the estimation of helical and WSS patterns [31], potentially masking their relationship with atherosclerosis initiation and progression. Moreover, in vitro and in silico hemodynamic studies revealed the presence of skewed velocity profiles in the left coronary artery [32], [33], [34], with a not negligible presence of secondary flows in the entire coronary tree, as it can be expected by considering the vessel tortuosity and the presence of bifurcations and branching.
In this context, the aim of this study was to evaluate the budget of uncertainty associated with assumptions on the shape of the velocity profiles imposed as inflow boundary conditions in coronary artery CFD models. To this end, a framework was developed enabling the generation of artificial velocity profiles by means of generalized analytical formulations able to (1) generate 3D velocity profiles with secondary flows, and (2) fit the non-circular cross-section of blood vessels. The developed framework was then applied to left anterior descending (LAD) coronary artery models to evaluate the impact that the shape of inflow velocity profiles used as inlet boundary condition has on WSS distribution at the luminal surface and intravascular flow features, focusing on helical flow patterns.
Section snippets
Image data collection and 3D vessel reconstruction
Ten subjects (8 males and 2 females, age = 58.6 ± 6.5) that underwent invasive coronary cineangiography after heart transplant with no sign of atherosclerosis were selected for this study. Clinical images were acquired at Città della Salute e della Scienza hospital (Turin, Italy) with the monoplane X-ray system Allura Xper (Philips Medical Systems, Amsterdam, The Netherlands). Two cranial, end-diastolic angiographic projections, with a minimum angle of 25° between them were used to reconstruct
Near-wall hemodynamics
The impact that the shape of the inflow velocity profile has on WSS was firstly evaluated in terms of AWSS percentage differences with respect to the reference (TP-only parabolic) velocity profile. In the box plot of Fig. 3, the analysis is presented aggregating AWSS data from all the 10 LAD models on the basis of the specific velocity profile used as inflow boundary condition and considering the whole vessel and its division in three segments. Overall, the largest percentage differences from
Discussion
In computational hemodynamics, when dealing with patient-specific models, the imposition of in vivo measured 3D velocity profiles as inflow boundary condition leads to more realistic simulations. However, velocity profiles are often not measurable in vivo, and their idealized versions, based upon assumptions needed to fill a gap of knowledge, are prescribed to model blood flow.
In coronary arteries, blood flow velocity values can be derived in vivo from Doppler flow velocity or thermodilution
Conclusions
In this study, the impact of the shape of blood velocity profiles, prescribed as inflow boundary conditions in image-based computational models of LAD coronary arteries, on local hemodynamics was evaluated. Our findings highlighted that the hemodynamic impact of considering realistic 3D features, such as eccentricity and differently shaped secondary flows, as a part of the inflow velocity profile is limited to the proximal LAD segment. Furthermore, the findings suggested that the problem of the
Declaration of Competing Interest
The authors have no professional or financial conflicts of interest to disclose.
Funding
None.
Ethical approval
The study was approved by the Ethics Committee of the Città della Salute e della Scienza hospital in Turin. Informed consent was obtained from the patients for being included in the study. The Ethical approval was given April 4th, 2019 with protocol number 0036571.
References (61)
- et al.
Coronary Atherosclerosis: pathophysiologic Basis for Diagnosis and Management
Prog Cardiovasc Dis
(2016) - et al.
The impact of helical flow on coronary atherosclerotic plaque development
Atherosclerosis
(2020) - et al.
Uncertainty quantification in coronary blood flow simulations: impact of geometry, boundary conditions and blood viscosity
J Biomech
(2016) - et al.
Impact of uncertainties in outflow boundary conditions on the predictions of hemodynamic simulations of ascending thoracic aortic aneurysms
Comput Fluids
(2018) - et al.
Cardiovascular models for personalised medicine: where now and where next?
Med Eng Phys
(2019) - et al.
Quantifying the effect of side branches in endothelial shear stress estimates
Atherosclerosis
(2016) - et al.
Low Coronary Wall Shear Stress Is Associated With Severe Endothelial Dysfunction in Patients With Nonobstructive Coronary Artery Disease
JACC Cardiovasc Interv
(2018) - et al.
Impact of bifurcation angle and other anatomical characteristics on blood flow - A computational study of non-stented and stented coronary arteries
J Biomech
(2016) - et al.
Link between deviations from Murray’s Law and occurrence of low wall shear stress regions in the left coronary artery
J Theor Biol
(2016) - et al.
Application of an OCT-based 3D reconstruction framework to the hemodynamic assessment of an ulcerated coronary artery plaque
Med Eng Phys
(2020)