AAA Rupture Risk Assessment in the Clinic: Wall Stress or Geometric Characterization?

2013 ◽  
Author(s):  
Ender A. Finol ◽  
Samarth S. Raut ◽  
Kibaek Lee ◽  
Judy Shum ◽  
Satish C. Muluk ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Wall Stress ◽  
Material Model ◽  
Geometric Characterization ◽  
Maximum Diameter ◽  
Controlled Study ◽  
Rupture Risk ◽  
Constitutive Material Model ◽  
Risk Of Rupture ◽  
Peak Wall Stress

The current clinical management of abdominal aortic aneurysm (AAA) disease is based to a great extent on measuring the aneurysm maximum diameter to decide when timely intervention is required. Decades of clinical evidence show that aneurysm diameter is positively associated with the risk of rupture, but other parameters may also play a role in causing or predisposing the AAA to rupture. Geometric factors such as vessel tortuosity, intraluminal thrombus volume, and wall surface area are implicated in the differentiation of ruptured and unruptured AAAs. Biomechanical factors identified by means of computational modeling techniques, such as peak wall stress, have been positively correlated with rupture risk with a higher accuracy and sensitivity than maximum diameter alone. In the present work, we performed a controlled study targeted at evaluating the effect of uncertainty of the constitutive material model used for the vascular wall in the ensuing peak wall stress. Based on the outcome of this study, a second analysis was conducted based on the geometric characterization of surface curvature in two groups of aneurysm geometries, to discern which curvature metric can adequately discriminate ruptured from electively repaired AAA. The outcome of this work provides preliminary evidence on the importance of quantitative geometry characterization for AAA rupture risk assessment in the clinic.

scholarly journals High-frequency murine ultrasound provides enhanced metrics of BAPN-induced AAA growth

2019 ◽  
Vol 317 (5) ◽  
pp. H981-H990 ◽  
Author(s):  
Daniel J. Romary ◽  
Alycia G. Berman ◽  
Craig J. Goergen
Keyword(s):  
Surface Area ◽  
Murine Model ◽  
High Frequency ◽  
Wall Stress ◽  
Growth Patterns ◽  
Aortic Aneurysms ◽  
Maximum Diameter ◽  
Rupture Risk ◽  
Abdominal Aortic ◽  
Peak Wall Stress

An abdominal aortic aneurysm (AAA), defined as a pathological expansion of the largest artery in the abdomen, is a common vascular disease that frequently leads to death if rupture occurs. Once diagnosed, clinicians typically evaluate the rupture risk based on maximum diameter of the aneurysm, a limited metric that is not accurate for all patients. In this study, we worked to evaluate additional distinguishing factors between growing and stable murine aneurysms toward the aim of eventually improving clinical rupture risk assessment. With the use of a relatively new mouse model that combines surgical application of topical elastase to cause initial aortic expansion and a lysyl oxidase inhibitor, β-aminopropionitrile (BAPN), in the drinking water, we were able to create large AAAs that expanded over 28 days. We further sought to develop and demonstrate applications of advanced imaging approaches, including four-dimensional ultrasound (4DUS), to evaluate alternative geometric and biomechanical parameters between 1) growing AAAs, 2) stable AAAs, and 3) nonaneurysmal control mice. Our study confirmed the reproducibility of this murine model and found reduced circumferential strain values, greater tortuosity, and increased elastin degradation in mice with aneurysms. We also found that expanding murine AAAs had increased peak wall stress and surface area per length compared with stable aneurysms. The results from this work provide clear growth patterns associated with BAPN-elastase murine aneurysms and demonstrate the capabilities of high-frequency ultrasound. These data could help lay the groundwork for improving insight into clinical prediction of AAA expansion. NEW & NOTEWORTHY This work characterizes a relatively new murine model of abdominal aortic aneurysms (AAAs) by quantifying vascular strain, stress, and geometry. Furthermore, Green-Lagrange strain was calculated with a novel mapping approach using four-dimensional ultrasound. We also compared growing and stable AAAs, finding peak wall stress and surface area per length to be most indicative of growth. In all AAAs, strain and elastin health declined, whereas tortuosity increased.

Effect of Intraluminal Thrombus on Wall Stress and Growth Rate of Abdominal Aneurysms

2010 ◽  
Author(s):  
Lambert Speelman ◽  
E. Marielle H. Bosboom ◽  
Geert Willem H. Schurink ◽  
Jaap Buth ◽  
Marcel Breeuwer ◽  
...  
Keyword(s):  
Risk Estimation ◽  
Wall Stress ◽  
Aortic Aneurysms ◽  
Maximum Diameter ◽  
Intraluminal Thrombus ◽  
Abdominal Aortic ◽  
Risk Of Rupture ◽  
Peak Wall Stress ◽  
Higher Sensitivity ◽  
Main Factor

In the decision for surgical repair of abdominal aortic aneurysms (AAAs), the risk of rupture is weighed carefully against the risk of the surgical procedure. Currently, AAA diameter is the main factor that determines the decision for surgery. However, in rupture risk estimation AAA wall stress has higher sensitivity and specificity than maximum diameter [1]. Moreover, peak wall stress was higher for ruptured than for non-ruptured or asymptomatic AAAs [2, 3].

Aortic Wall Mechanics: A Geometry-Driven Problem

2011 ◽  
Author(s):  
Samarth S. Raut ◽  
Peng Liu ◽  
Anirban Jana ◽  
Ender A. Finol
Keyword(s):  
Risk Assessment ◽  
Aortic Wall ◽  
Wall Stress ◽  
Aneurysm Rupture ◽  
Intraluminal Pressure ◽  
Wall Material ◽  
Patient Specific ◽  
Rupture Risk ◽  
Constitutive Material Model ◽  
Constitutive Material

Abdominal Aortic Aneurysm (AAA) is a vascular disease that occurs predominantly in people over 60 years of age. The rupture of an AAA is a catastrophic event associated with up to a 90% mortality rate. Hence, it is important for vascular surgeons to justify the risk of repair vis-à-vis the risk of aneurysm rupture. In clinical practice, rupture risk assessment is based on measuring the maximum aneurysm diameter where 5.5 cm is accepted as the critical size for recommending (surgical or endovascular) intervention. However, this criterion is based on an extensive history of evidence-based medicine rather than an individualized assessment of the aneurysm’s potential to rupture. Primary among the biomechanical factors associated with the rupture assessment of an AAA is mechanical wall stress, which is dependent on the accuracy of the geometry reconstruction, intraluminal pressure loading and the constitutive material model used for the aortic wall. We hypothesize that in unruptured, asymptomatic AAA, the wall mechanics is the outcome of primarily the patient specific aneurysm shape and to a lesser extent, the constitutive material property model used to characterize the vascular wall. Evaluating the relative contributions of wall material properties and AAA geometry to wall mechanics estimation will increase our understanding of the factors that influence peak wall stress as an indicator for rupture risk assessment. In the present work, we evaluate the aforementioned hypothesis using a size-matched approach.

scholarly journals WALL STRESS IN ASCENDING AORTA ANEURYSMS AS A PREDICTIVE FACTOR OF BREAKAGE

2021 ◽  
Vol 108 (Supplement_3) ◽  
Author(s):  
R J Burgos Lázaro ◽  
N Burgos Frías ◽  
S Serrano-Fiz García ◽  
V Ospina Mosquera ◽  
F Rojo Pérez ◽  
...  
Keyword(s):  
Aortic Wall ◽  
Wall Stress ◽  
Middle Layer ◽  
Ascending Aorta ◽  
Aortic Aneurysms ◽  
Maximum Diameter ◽  
Resistance Factors ◽  
Risk Of Rupture ◽  
Traction Test

Abstract INTRODUCTION The surgical indication for ascending aortic aneurysms (AAA) is established when the maximum diameter > 50 mm; It responds to Laplace's Law (T wall = P × r / 2e). The aim of the study is to define wall stress in AAA. MATERIAL AND METHODS 218 ascending aortic walls have been studied: 96 from organ donors, and 122 from AAA: Marfán 58 (47.5%), bicuspid aortic valve 26 (21.4%), and atherosclerosis 38 (31.1%). The samples were studied "in vitro", according to the model Young's (relationship between stress and deformed area), by means of the mechanical traction test (Tension = Force / Area). The analysis was performed with the stress-elongation curve (d Tension / d Elongation). RESULTS The stress of the aortic wall, classified from highest to lowest according to pathology and age was: cystic necrosis of the middle layer, arteriosclerosis, age > 60 years, between 35 and 59, and < 34 years. The stress of “control aortas” wall increased directly in relation to the age of the donors. CONCLUSIONS The maximum diameter of the ascending aorta, the patient's type of pathology and age are factors that affect the maximum tension of the aortic wall and resistance, factors that allow differentiation and prediction of the risk of rupture of the AAA. The validation of the results obtained through numerical simulation was significant and the uniaxial analysis has modeled the response of the vessels to their internal pressure.

scholarly journals Biomechanical Rupture Risk Assessment

Aorta ◽  
2016 ◽  
Vol 04 (02) ◽  
pp. 42-60 ◽  
Author(s):  
T. Christian Gasser
Keyword(s):  
Risk Assessment ◽  
Decision Making ◽  
Validation Studies ◽  
Clinical Decision Making ◽  
Clinical Decision ◽  
Patient Treatment ◽  
Maximum Diameter ◽  
Individual Risk ◽  
Rupture Risk ◽  
Aneurysm Wall

AbstractAbdominal aortic aneurysm (AAA) rupture is a local event in the aneurysm wall that naturally demands tools to assess the risk for local wall rupture. Consequently, global parameters like the maximum diameter and its expansion over time can only give very rough risk indications; therefore, they frequently fail to predict individual risk for AAA rupture. In contrast, the Biomechanical Rupture Risk Assessment (BRRA) method investigates the wall’s risk for local rupture by quantitatively integrating many known AAA rupture risk factors like female sex, large relative expansion, intraluminal thrombus-related wall weakening, and high blood pressure. The BRRA method is almost 20 years old and has progressed considerably in recent years, it can now potentially enrich the diameter indication for AAA repair. The present paper reviews the current state of the BRRA method by summarizing its key underlying concepts (i.e., geometry modeling, biomechanical simulation, and result interpretation). Specifically, the validity of the underlying model assumptions is critically disused in relation to the intended simulation objective (i.e., a clinical AAA rupture risk assessment). Next, reported clinical BRRA validation studies are summarized, and their clinical relevance is reviewed. The BRRA method is a generic, biomechanics-based approach that provides several interfaces to incorporate information from different research disciplines. As an example, the final section of this review suggests integrating growth aspects to (potentially) further improve BRRA sensitivity and specificity. Despite the fact that no prospective validation studies are reported, a significant and still growing body of validation evidence suggests integrating the BRRA method into the clinical decision-making process (i.e., enriching diameter-based decision-making in AAA patient treatment).

Abdominal Aortic Aneurysm Growth: The Association of Aortic Wall Mechanics and Geometry

2011 ◽  
Author(s):  
Christopher B. Washington ◽  
Judy Shum ◽  
Satish C. Muluk ◽  
Ender A. Finol
Keyword(s):  
Wall Stress ◽  
Abdominal Ultrasound ◽  
Aneurysm Rupture ◽  
Computational Method ◽  
Maximum Diameter ◽  
Patient Specific ◽  
Element Analysis ◽  
Wall Strength ◽  
Aneurysm Growth ◽  
Peak Wall Stress

In an effort to prevent rupture, patients with known AAA undergo periodic abdominal ultrasound or CT scan surveillance. When the aneurysm grows to a diameter of 5.0–5.5 cm or is shown to expand at a rate greater than 1 cm/yr, elective operative repair is undertaken. While this strategy certainly prevents a number of potentially catastrophic ruptures, AAA rupture can occur at sizes less than 5 cm. From a biomechanical standpoint, aneurysm rupture occurs when wall stress exceeds wall strength. By using non-invasive techniques, such as finite element analysis (FEA), wall stress can be estimated for patient specific AAA models, which can perhaps more carefully predict the rupture potential of a given aneurysm, regardless of size. FEA is a computational method that can be used to evaluate complicated structures such as aneurysms. To this end, it was reported earlier that AAA peak wall stress provides a better assessment of rupture risk than the commonly used maximum diameter criterion [1]. What has yet to be examined, however, is the relationship between wall stress and AAA geometry during aneurysm growth. Such finding has the potential for providing individualized predictions of AAA rupture potential during patient surveillance. The purpose of this study is to estimate peak wall stress for an AAA under surveillance and evaluate its potential correlation with geometric features characteristic of the aneurysm’s morphology.

Risk of Rupture in AAA and Vulnerable Plaques: Patient Based FSI Simulation

2007 ◽  
Author(s):  
Danny Bluestein ◽  
Yared Alemu ◽  
Peter Rissland ◽  
Mikahil Britan ◽  
Idit Avrahami ◽  
...  
Keyword(s):  
Vulnerable Plaque ◽  
Material Model ◽  
Patient Specific ◽  
Rupture Risk ◽  
Fibrous Cap ◽  
Wall Properties ◽  
Aneurysm Wall ◽  
Abdominal Aortic ◽  
Risk Of Rupture ◽  
Failure Location

Two separate fluid structure interaction (FSI) simulations were performed: a patient-specific Abdominal Aortic Aneurysm (AAA) geometry, and an idealized coronary vulnerable plaque (VP) geometry. VP FSI simulations were later performed in patient based geometries reconstructed from intravascular (IVUS) measurements. (AAA): The patient specific AAA FSI simulation was carried out with both isotropic and anisotropic wall properties. An orthotropic material model was used to describe wall properties, closely approximate experimental results [1]. Results show peak wall stresses are dependent on the geometry of the AAA and the region of highest stress corresponds to expected failure location. The ability to quantify stresses developing within the aneurysm wall based on FSI simulations will facilitate clinicians to reach informed decisions in determining rupture risk of AAA and the need for surgical intervention. (Vulnerable Plaque): To study the risk of rupture of a vulnerable plaque in an idealized coronary artery geometry, an FSI simulation was performed. This model of vulnerable plaque includes vessel wall with calcification spot embedded in the fibrous cap, and a lipid core. Identifying rupture risk, regions susceptible to failure and the contribution of the various components were studied. This work led to predicting the rupture risk in patient specific geometries. The results show the upstream side of vulnerable plaque fibrous cap has the highest stresses. The presence of the calcified spot is shown to enhance stresses within the fibrous cap, significantly contributing to its risk of rupture.

Porohyperelastic Simulation of Abdominal Aortic Aneurysms

2008 ◽  
Author(s):  
Avinash Ayyalasomayajula ◽  
Bruce R. Simon ◽  
Jonathan P. Vande Geest
Keyword(s):  
Wall Stress ◽  
Aortic Aneurysms ◽  
Maximum Diameter ◽  
Patient Specific ◽  
Infrarenal Aorta ◽  
Stress Studies ◽  
Abdominal Aortic ◽  
Peak Wall Stress ◽  
Work Done

Abdominal aortic aneurysm (AAA) is a progressive dilation of the infrarenal aorta and results in a significant alteration in local hemodynamic environment [1]. While an aneurysmal diameter of 5.5cm is typically classified as being of high risk, recent studies have demonstrated that maximum wall stress could be a better indicator of an AAA rupture than maximum diameter [2]. The wall stress is greatly influenced by the blood pressure, aneurysm diameter, shape, wall thickness and the presence of thrombus. The work done by Finol et al. suggested that hemodynamic pressure variations have an insignificant effect on AAA wall stress and that primarily the shape of the aneurysm determines the stress distribution. They noted that for peak wall stress studies the static pressure conditions would suffice as the in vivo conditions. Wang et al have developed an isotropic hyperelastic constitutive model for the intraluminal thrombus (ILT). Such models have been used to study the stress distributions in patient specific AAAs [3, 4].

scholarly journals Biomechanical rupture risk assessment of abdominal aortic aneurysms based on a novel probabilistic rupture risk index

2015 ◽  
Vol 12 (113) ◽  
pp. 20150852 ◽  
Author(s):  
Stanislav Polzer ◽  
T. Christian Gasser
Keyword(s):  
Risk Assessment ◽  
Wall Thickness ◽  
Risk Index ◽  
Wall Stress ◽  
Aortic Aneurysms ◽  
Rupture Risk ◽  
Discriminative Power ◽  
Wall Strength ◽  
Abdominal Aortic ◽  
Wide Range

A rupture risk assessment is critical to the clinical treatment of abdominal aortic aneurysm (AAA) patients. The biomechanical AAA rupture risk assessment quantitatively integrates many known AAA rupture risk factors but the variability of risk predictions due to model input uncertainties remains a challenging limitation. This study derives a probabilistic rupture risk index (PRRI). Specifically, the uncertainties in AAA wall thickness and wall strength were considered, and wall stress was predicted with a state-of-the-art deterministic biomechanical model. The discriminative power of PRRI was tested in a diameter-matched cohort of ruptured ( n = 7) and intact ( n = 7) AAAs and compared to alternative risk assessment methods. Computed PRRI at 1.5 mean arterial pressure was significantly ( p = 0.041) higher in ruptured AAAs (20.21(s.d. 14.15%)) than in intact AAAs (3.71(s.d. 5.77)%). PRRI showed a high sensitivity and specificity (discriminative power of 0.837) to discriminate between ruptured and intact AAA cases. The underlying statistical representation of stochastic data of wall thickness, wall strength and peak wall stress had only negligible effects on PRRI computations. Uncertainties in AAA wall stress predictions, the wide range of reported wall strength and the stochastic nature of failure motivate a probabilistic rupture risk assessment. Advanced AAA biomechanical modelling paired with a probabilistic rupture index definition as known from engineering risk assessment seems to be superior to a purely deterministic approach.

scholarly journals Increased Peak Wall Stress, but Not Maximum Diameter, Is Associated with Symptomatic Abdominal Aortic Aneurysm

2017 ◽  
Vol 54 (6) ◽  
pp. 706-711 ◽  
Author(s):  
Begoña Soto ◽  
Luis Vila ◽  
Jaime F. Dilmé ◽  
Jose R. Escudero ◽  
Sergi Bellmunt ◽  
...  
Keyword(s):  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Stress ◽  
Maximum Diameter ◽  
Abdominal Aortic ◽  
Peak Wall Stress
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