A perspective review on numerical simulations of hemodynamics in aortic dissection

The application of 5E rehabilitation management mode in the nursing of patients with aortic dissection complicated by obstructive sleep apnea

OBJECTIVE

This study was designed to explore the effect of 5E rehabilitation mode (encouragement, education, exercise, employment, and evaluation) in patients with aortic dissection (AD) complicated by obstructive sleep apnea (OSA).

METHODS

Patients with Stanford type B AD (TBAD) complicated by OSA were admitted to Guangdong Provincial People's Hospital from January 2019 to December 2020. They were randomly divided into an experimental group and a control group. After discharge, patients in the control group were given routine nursing and follow-up education, whereas patients in the experimental group were given 5E rehabilitation management mode-based nursing and follow-up education. Upon the nursing intervention, the differences in polysomnography (PSG) parameters, medication adherence, quality of life, blood pressure, and heart rate of patients between the two groups were compared. Logistic regression analysis was performed to evaluate the risk factors for the occurrence of adverse aortic events.

RESULTS

A total of 89 patients were enrolled, 49 in the experimental group and 40 in the control group. After the intervention, the control of heart rate, systolic blood pressure, medication adherence, PSG parameters, and quality of life scores in the experimental group were significantly better than those in the control group (P<0.05). The incidence of adverse aortic events including aortic rupture and progressive aortic dilation in the experimental group was significantly lower than that in the control group (P < 0.05). Logistic regression analysis revealed that acute TBAD [odds ratio (OR) = 15.069; 95%confidence interval (CI), 1.738-130.652; P=0.014], history of chronic kidney disease (OR=10.342; 95%CI, 1.056-101.287; P=0.045), and apnea hypopnea index (AHI) ≥ 30 (OR=2.880; 95%CI, 1.081-9.51; P=0.036) were adverse factors affecting adverse aortic events; while 5E rehabilitation management mode (OR=0.063; 95%CI, 0.008-0.513; P=0.010) was a favorable factor for occurrence of adverse aortic events.

CONCLUSION

The findings suggest that continuous nursing based on information carrier 5E rehabilitation management significantly enhanced medication adherence, improved patients' overall quality of life, and decreased the incidence of adverse aortic events in patients TBAD patients and OSA.

Fluid-structure interaction study for biomechanics and risk factors in Stanford type A aortic dissection

Aortic dissection is a life-threatening condition with a rising prevalence in the elderly population, possibly as a consequence of the increasing population life expectancy. Untreated aortic dissection can lead to myocardial infarction, aortic branch malperfusion or occlusion, rupture, aneurysm formation and death. This study aims to assess the potential of a biomechanical model in predicting the risks of a non-dilated thoracic aorta with Stanford type A dissection. To achieve this, a fully coupled fluid-structure interaction model was developed under realistic blood flow conditions. This model of the aorta was developed by considering three-dimensional artery geometry, multiple artery layers, hyperelastic artery wall, in vivo-based physiological time-varying blood velocity profiles, and non-Newtonian blood behaviours. The results demonstrate that in a thoracic aorta with Stanford type A dissection, the wall shear stress (WSS) is significantly low in the ascending aorta and false lumen, leading to potential aortic dilation and thrombus formation. The results also reveal that the WSS is highly related to blood flow patterns. The aortic arch region near the brachiocephalic and left common carotid artery is prone to rupture, showing a good agreement with the clinical reports. The results have been translated into their potential clinical relevance by revealing the role of the stress state, WSS and flow characteristics as the main parameters affecting lesion progression, including rupture and aneurysm. The developed model can be tailored for patient-specific studies and utilised as a predictive tool to estimate aneurysm growth and initiation of wall rupture inside the human thoracic aorta.

A Bayesian approach to blood rheological uncertainties in aortic hemodynamics

Computational hemodynamics has received increasing attention recently. Patient-specific simulations require questionable model assumptions, for example, for geometry, boundary conditions, and material parameters. Consequently, the credibility of these simulations is much doubted, and rightly so. Yet, the matter may be addressed by a rigorous uncertainty quantification. In this contribution, we investigated the impact of blood rheological models on wall shear stress uncertainties in aortic hemodynamics obtained in numerical simulations. Based on shear-rheometric experiments, we compare the non-Newtonian Carreau model to a simple Newtonian model and a Reynolds number-equivalent Newtonian model. Bayesian Probability Theory treats uncertainties consistently and allows to include elusive assumptions such as the comparability of flow regimes. We overcome the prohibitively high computational cost for the simulation with a surrogate model, and account for the uncertainties of the surrogate model itself, too. We have two main findings: (1) The Newtonian models mostly underestimate the uncertainties as compared to the non-Newtonian model. (2) The wall shear stresses of specific persons cannot be distinguished due to largely overlapping uncertainty bands, implying that a more precise determination of person-specific blood rheological properties is necessary for person-specific simulations. While we refrain from a general recommendation for one rheological model, we have quantified the error of the uncertainty quantification associated with these modeling choices.

An in vitro Assessment of the Haemodynamic Features Occurring Within the True and False Lumens Separated by a Dissection Flap for a Patient-Specific Type B Aortic Dissection

One of the highest mortality rates of cardiovascular diseases is aortic dissections with challenging treatment options. Currently, less study has been conducted in developing in vitro patient-specific Type B aortic dissection models, which mimic physiological flow conditions along the true and false lumens separated by a dissection flap with multiple entry and exit tears. A patient-specific Stanford Type B aortic dissection scan was replicated by an in-house manufactured automatic injection moulding system and a novel modelling technique for creating the ascending aorta, aortic arch, and descending aorta incorporating arterial branching, the true/false lumens, and dissection flap with entry and exit intimal tears. The physiological flowrates and pressure values were monitored, which identified jet stream fluid flows entering and exiting the dissection tears. Pressure in the aorta’s true lumen region was controlled at 125/85 mmHg for systolic and diastolic values. Pressure values were obtained in eight sections along the false lumen using a pressure transducer. The true lumen systolic pressure varied from 122 to 128 mmHg along the length. Flow patterns were monitored by ultrasound along 12 sections. Detailed images obtained from the ultrasound transducer probe showed varied flow patterns with one or multiple jet steam vortices along the aorta model. The dissection flap movement was assessed at four sections of the patient-specific aorta model. The displacement values of the flap varied from 0.5 to 3 mm along the model. This model provides a unique insight into aortic dissection flow patterns and pressure distributions. This dissection phantom model can be used to assess various treatment options based on the surgical, endovascular, or hybrid techniques.

Numerical modeling of residual type B aortic dissection: longitudinal analysis of favorable and unfavorable evolution

Residual type B aortic dissection was numerically investigated to highlight the contribution of biomechanical parameters to the pathology's evolution. Patient-specific geometries from cases involving both favorable and unfavorable evolution were modeled to assess their hemodynamic features. This original approach was supported by a longitudinal study confirming the association between morphological changes, hemodynamic features, adverse clinical outcomes, and CT-angioscan observations on the same patient. Comparing one patient with unfavorable evolution with one with favorable one, we identify potential biomechanical indicators predictive of unfavorable evolution: (i) a patent false lumen with a flow rate above 50% of inlet flow rate; (ii) high wall shear stress above 18 Pa at entry tears, and above 10 Pa at some regions of the false lumen wall; (iii) low time-averaged wall shear stress in distal false lumen below 0.5 Pa; (iv) vortical structure dynamics. Although these comparisons could only be conducted on 2 patients and need to be confirmed by a larger number of cases, our findings point to these hemodynamic markers as possible candidates for early evaluation of the pathology's evolution towards an unfavorable scenario. Graphical Abstract Correlation between hemodynamics index and thrombus initiation for unfavorable case. ET₂ and ET₃ are entry tear numbers 2 and 3 respectively. WSS is wall shear stress. TAWSS is time average shear stress.

Prediction of Stress Map in Ascending Aorta - Optimization of the Coaxial Position in Transcatheter Aortic Valve Replacement

BACKGROUD

Transcatheter aortic valve replacement (TAVR) can reduce mortality among patients with aortic stenosis. Knowledge of pressure distribution and shear stress at the aortic wall may help identify critical regions, where aortic remodeling process may occur. Here a numerical simulation study of the influence of positioning of the prosthetic valve orifice on the flow field is presented.

OBJECTIVE

The present analysis provides a perspective of great variance on flow behavior due only to angle changes.

METHODS

A 3D model was generated from computed tomography angiography of a patient who had undergone a TAVR. Different mass flow rates were imposed at the inlet valve.

RESULTS

Small variations of the tilt angle could modify the nature of the flow, displacing the position of the vortices, and altering the prerssure distribution and the location of high wall shear stress.

CONCLUSION

These hemodynamic features may be relevant in the aortic remodeling process and distribution of the stress mapping and could help, in the near future, the optimization of the percutaneous prosthesis implantation. (Arq Bras Cardiol. 2020; [online].ahead print, PP.0-0).

Fluid-structure interaction simulations of patient-specific aortic dissection

Credible computational fluid dynamic (CFD) simulations of aortic dissection are challenging, because the defining parallel flow channels-the true and the false lumen-are separated from each other by a more or less mobile dissection membrane, which is made up of a delaminated portion of the elastic aortic wall. We present a comprehensive numerical framework for CFD simulations of aortic dissection, which captures the complex interplay between physiologic deformation, flow, pressures, and time-averaged wall shear stress (TAWSS) in a patient-specific model. Our numerical model includes (1) two-way fluid-structure interaction (FSI) to describe the dynamic deformation of the vessel wall and dissection flap; (2) prestress and (3) external tissue support of the structural domain to avoid unphysiologic dilation of the aortic wall and stretching of the dissection flap; (4) tethering of the aorta by intercostal and lumbar arteries to restrict translatory motion of the aorta; and a (5) independently defined elastic modulus for the dissection flap and the outer vessel wall to account for their different material properties. The patient-specific aortic geometry is derived from computed tomography angiography (CTA). Three-dimensional phase contrast magnetic resonance imaging (4D flow MRI) and the patient's blood pressure are used to inform physiologically realistic, patient-specific boundary conditions. Our simulations closely capture the cyclical deformation of the dissection membrane, with flow simulations in good agreement with 4D flow MRI. We demonstrate that decreasing flap stiffness from [Formula: see text] to [Formula: see text] kPa (a) increases the displacement of the dissection flap from 1.4 to 13.4 mm, (b) decreases the surface area of TAWSS by a factor of 2.3, (c) decreases the mean pressure difference between true lumen and false lumen by a factor of 0.63, and (d) decreases the true lumen flow rate by up to 20% in the abdominal aorta. We conclude that the mobility of the dissection flap substantially influences local hemodynamics and therefore needs to be accounted for in patient-specific simulations of aortic dissection. Further research to accurately measure flap stiffness and its local variations could help advance future CFD applications.

The application of computational modeling for risk prediction in type B aortic dissection

OBJECTIVE

New tools are urgently needed to help with surgical decision-making in type B aortic dissection (TBAD) that is uncomplicated at the time of initial presentation. This narrative review aims to answer the clinical question, Can computational modeling be used to predict risk in acute and chronic Stanford TBAD?

METHODS

The review (PROSPERO 2018 CRD42018104472) focused on risk prediction in TBAD. A comprehensive search of the Ovid MEDLINE database, using terms related to computational modeling and aortic dissection, was conducted to find studies of any form published between 1998 and 2018. Cohort studies, case series, and case reports of adults (older than 18 years) with computed tomography or magnetic resonance imaging diagnosis of TBAD were included. Computational modeling was applied in all selected studies.

RESULTS

There were 37 studies about computational modeling of TBAD identified from the search, and the findings were synthesized into a narrative review. Computational modeling can produce numerically calculated values of stresses, pressures, and flow velocities that are difficult to measure in vivo. Hemodynamic parameters-high or low wall shear stress, high pressure gradient between lumens during the cardiac cycle, and high false lumen flow rate-have been linked to the pathogenesis of branch malperfusion and aneurysm formation by numerous studies. Considering the major outcomes of end-organ failure, aortic rupture, and stabilization and remodeling, hypotheses have been generated about inter-relationships of measurable parameters in computational models with observable anatomic and pathologic changes, resulting in specific clinical outcomes.

CONCLUSIONS

There is consistency in study findings about computational modeling in TBAD, although a limited number of patients have been analyzed using various techniques. The mechanistic patterns of association found in this narrative review should be investigated in larger cohort prospective studies to further refine our understanding. It highlights the importance of patient-specific computational hemodynamic parameters in clinical decision-making algorithms. The current challenge is to develop and to test a risk assessment method that can be used by clinicians for TBAD.

Patient-specific Computational Hemodynamic Analysis for Interrupted Aortic Arch in an Adult: Implications for Aortic Dissection Initiation

The guideline for the treatment of interrupted aortic arch (IAA) in adults has not been established although most centers tend to propose surgery. There is no clear evidence for the preferred selection of surgical repair versus conservatively medical treatment for the uncertain effects of both treatments. However, reports of sporadic aortic dissection (AD) of descending aorta (DAo) in IAA in adults before surgery drew our attention. It is quite perplexing because there seems to be no risk factors for the development of AD at DAo such as long-term uncontrolled hypertension, atherosclerosis, aortic aneurysm or genetic disorder. In this paper, we carried out the numerical investigation on the hemodynamics in a patient-specific IAA model, which was reconstructed from computed tomography images. Hemodynamic parameters including the flow pattern, pressure distribution, and wall shear stress (WSS) indicators were obtained. The simulation revealed that the jet flows from the collateral arteries (CAs) induced risk hemodynamic forces on the lumen wall including high time-averaged wall shear stress (TAWSS), high pressure and rapid change of WSS direction throughout the cardiac cycle. Moreover, it is found that only a jet flow which circumferentially washes out the aortic wall might cause tears on the wall. It is concluded that the specific geometrical features of the extensive major CAs might result in the risky hemodynamics leading to the initiation and development of AD in this particular IAA patient. CFD analysis in IAA can provide a clinical reference, and the results should be further studied in depth in the future.

CT patterns of acute type A aortic arch dissection: longer, higher, more anterior

OBJECTIVES

This study analysed CT patterns of the acute dissected aortic arch using original biometric features along with comparison with normal aortas.

METHODS

The diagnostic CT scans of 57 patients (42 males, age (mean ± SD: 64.5 ± 13.8 years) admitted with acute Stanford type A dissection involving the aortic arch were analysed by semi-automatic detection protocol of the true lumen of the dissection. We measured the distances from the apex to the ascending and descending aorta, the curvilinear length of the entire arch and of its segments (especially between the brachiocephalic artery trunk and the left subclavian artery), as well as the surface area, angle, height and shift of the arch. These measurements were compared with results previously obtained in a healthy cohort in an analysis adjusted for age, sex and weight. The surface area and rotation of the false lumen were also analysed.

RESULTS

Compared to normal aortic arches (N), dissected aortic arches (D) were longer (D: 155 ± 26  mm, N: 135 ± 25  mm, p = 0.002), higher (D: 51 ± 10  mm, N: 45 ± 9  mm, p = 0.04), and with a more anterior apex (shift: D: 1.19 ± 0.56, N: 1.40 ± 0.62, p = 0.007). False lumen occupied between 47-65% of the aorta, turned preferentially clockwise and its rotation decreased progressively along the arch.

CONCLUSIONS

The morphology of the dissected aortic arch differs from that of the normal arch. Thus, our compilation of aortic arch measurements may help improve existing endovascular devices and/or design of new endoprostheses. Advances in knowledge: In this article, we provide a comprehensive set of measurements of the dissected aortic arch, and show that dissected aortic arches are longer, higher, and with a more anterior apex than normal arches.

Clinical significance of a false lumen pathway through the arch in acute type A aortic dissection and its influence on cervical branch compromise

OBJECTIVES

Upon onset of acute type A aortic dissection, the aortic true lumen generally becomes fixed around the supra-aortic branches in the greater curvature and Botallo's ligament in the lesser curvature of the aortic arch. Therefore, the pathways of the false lumen through the arch can be categorized as anterior, bilateral and posterior. We investigated the relationship between a false lumen pathway through the arch and cervical branch compromise, stratified by primary tear location.

METHODS

Sixty-four consecutive patients with acute type A aortic dissection underwent emergency surgery at our institution between March 2005 and October 2013. Of these, 40 cases (63%) were DeBakey type I, 15 cases (23%) were type II and 9 cases (14%) were type III-D (retrograde type A). We conducted a retrospective review of preoperative computed tomographic angiography using three-dimensional image post-processing tools for 43 cases, excluding 15 cases with type II and 6 cases with type I for which preoperative digital image data were not available.

RESULTS

Of the 43 cases, 14, 18 and 11 revealed anterior, bilateral and posterior pathways, respectively. Twenty-one cases (49%) showed a primary intimal tear in the ascending aorta (8 anterior, 12 bilateral and 1 posterior), 12 cases (28%) showed a primary intimal tear in the aortic arch (5 anterior, 3 bilateral and 4 posterior) and 10 cases (23%) showed a primary intimal tear in the descending aorta (1 anterior, 3 bilateral and 6 posterior). Twelve of the 14 anterior pathway cases (86%) had a total of 26 supra-aortic branch compromises, 13 of the 18 bilateral pathway cases (72%) had a total of 20 supra-aortic branch compromises, while only 4 of the 11 posterior pathway cases (36%) had a total of four supra-aortic branch compromises. None of the 11 posterior pathway cases had a dissection extending into all 3 supra-aortic branches.

CONCLUSIONS

Posterior pathway cases generally showed primary tear locations in the arch or descending aorta, and cervical branch compromise was rare. Aortic dissections tended to extend into the cervical branches through the anterior side of the aortic arch. A false lumen pathway through the arch was strongly associated with cervical branch compromise in acute type A aortic dissections.