Abdominal Aortic Aneurysm Rupture Risk Research Articles

MicroRNAs in abdominal aortic aneurysms

The abdominal aortic aneurysm (AAA), representing 70% to 90% of all aortic aneurysms, is characterized by a widening of the diameter due to an irreversible weakening of the vascular walls. Risk factors include advanced age, male sex, smoking, hypertension, atherosclerosis, and genetic predisposition. From a pathophysiological point of view, AAA involves alterations in connective tissue proteins, chronic inflammation with the release of cytokines and matrix metalloproteinases, as well as changes in the extracellular matrix. MicroRNAs (miRNAs) have emerged as promising biomarkers and therapeutic targets in the regulation of gene expression and different specific signaling pathways in vascular pathologies. Among which some miRNAs have been highlighted such as: miR-29 and miR-27b-3p, involved in the degradation of the extracellular matrix and inflammatory processes during the progression of AAA. Some diagnostic methods such as computed tomography play a fundamental role, while some innovative therapeutic strategies, such as the inhibition of miRNAs, represent a leading role as possible diagnostic and therapeutic targets. A comprehensive approach includes surveillance and surgical treatment strategies to mitigate the progression and risk of AAA rupture, thus highlighting the relevance of miRNAs in the diagnosis and treatment of this pathology.

Dual-Drug Nanomedicine Assembly with Synergistic Anti-Aneurysmal Effects via Inflammation Suppression and Extracellular Matrix Stabilization.

Abdominal aortic aneurysm (AAA) represents a critical cardiovascular condition characterized by localized dilation of the abdominal aorta, carrying a significant risk of rupture and mortality. Current treatment options are limited, necessitating novel therapeutic approaches. This study investigates the potential of a pioneering nanodrug delivery system, RAP@PFB, in mitigating AAA progression. RAP@PFB integrates pentagalloyl glucose (PGG) and rapamycin (RAP) within a metal-organic-framework (MOF) structure through a facile assembly process, ensuring remarkable drug loading capacity and colloidal stability. The synergistic effects of PGG, a polyphenolic antioxidant, and RAP, an mTOR inhibitor, collectively regulate key players in AAA pathogenesis, such as macrophages and smooth muscle cells (SMCs). In macrophages, RAP@PFB efficiently scavenges various free radicals, suppresses inflammation, and promotes M1-to-M2 phenotype repolarization. In SMCs, it inhibits apoptosis and calcification, thereby stabilizing the extracellular matrix and reducing the risk of AAA rupture. Administered intravenously, RAP@PFB exhibits effective accumulation at the AAA site, demonstrating robust efficacy in reducing AAA progression through multiple mechanisms. Moreover, RAP@PFB demonstrates favorable biosafety profiles, supporting its potential translation into clinical applications for AAA therapy.

Simultaneous Transcatheter Aortic Valve Implantation and Endovascular Aneurysm Repair for Severe Aortic Stenosis and Symptomatic Abdominal Aortic Aneurysm: Mini Review.

Background: The treatment of patients with severe aortic stenosis (SAS) who concomitantly present with abdominal aortic aneurysm (AAA) is not defined. Aortic valve replacement surgery, performed alone, increases the risk of AAA rupture. Transcatheter aortic valve replacement (TAVR) and endovascular abdominal aortic aneurysm repair (EVAR) in the same intervention, especially in high-risk patients, is a safe alternative. Purpose: We report a case of simultaneous endovascular treatment of SAS and AAA and a mini literature review of nineteen cases with similar characteristics. Research design: Case report and literature review. Data Collection: An electronic search of PubMed and Scopus was performed from inception to December 2023. Results: Nineteen case reports of simultaneous transcatheter aortic valve repair and endovascular aneurysm repair for SAS and symptomatic AAA were identified published in the literature. Conclusions: We regard the simultaneous endovascular approach to both pathologies as a promising treatment alternative for selected patients with severe aortic stenosis and abdominal aortic aneurysm. We highlight the need to conduct randomized clinical trials in this patient population.

Effects of preoperative aortic tortuosity and postoperative hypertension on patient-specific hemodynamics of abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a serious dilated vascular disease. The risk factors of aneurysm rupture and postoperative blood pressure are the major clinical concerns. The purpose of this work is to analyze the hemodynamic difference between preoperative and postoperative AAA using patient-specific boundary conditions and explore the rupture risk of AAA with different torsion and to simulate the blood flow of different degrees of hypertension. A three-element Windkessel model is utilized as the outlet boundary condition. 20-sim software and self-developed user-defined functions are used to calibrate the parameters. To analyze the influence of aortic tortuosity on hemodynamics, five AAA geometries with different torsion degrees are modified and obtained. We also grade the hypertension and explore the effect of hypertension after operation. The analysis results are consistent with the patient-specific situation. The results show that stent implantation for aneurysms reduces the pressure at the lesion site and increase the speed and wall shear stress. Vessels with high torsion have lower time-averaged wall shear stress (TAWSS), higher oscillatory shear stress index (OSI) and relative retention time, and more disordered blood flow. After stent implantation, with the increase in blood pressure, TAWSS and OSI continue to increase, and the blood flow speed is also faster. AAA with high torsion is more likely to rupture. In clinical practice, attention should be paid to the degree of torsion of the lesion site. Furthermore, blood pressure should be monitored and controlled in time to prevent postoperative complications.

Suppression of Inflammation-induced Abdominal Aortic Aneurysm Formation by Induction of Elastin Tolerance

Abdominal aortic aneurysm (AAA) is a vascular disease process whereby the aorta expands to apoint where rupture may occur. This serious condition is diagnosed in approximately 200,000 people in the United States per year and accounts for over 15,000 deaths annually. The only medical intervention proven to reduce the risk of AAA rupture is surgical repair; however, such repair is associated with high risk of death, reduced quality of life, and high expense. AAA is caused by the weakening of the artery wall due to inflammation-induced destruction of its structural components. Our clinical data shows increased levels of circulating elastin degradation products in patients with AAA, especially smokers, compared to risk factor matched controls. This observation led us to hypothesize that an immune reaction to elastin fragments initiates the inflammatory cascade in the aorta that leads to AAA formation. To test this hypothesis, C57BL/6 mice were injected with poly(lactide-co-glycolide) nanoparticle-encapsulated IL-10 to induce immune tolerance or nanoparticle-encapsulated control ovalbumin. Injection of elastin fragments was performed 7 days later to induce an immune response. AAA of the infrarenal aorta was induced by topical application of elastase during laparotomy procedure 14 days after nanoparticle injection. Aorta diameter was measured 16 days post-operatively with Microfil. Immunologic changes were evaluated by cytokine analysis, Tr1/Th17 cell ratio inperipheral blood, and splenic Th17 and Tr1 response to elastin. Based on prior work, we expect that induction of elastin tolerance using poly(lactide-co-glycolide) nanoparticle-encapsulated IL-10 will suppress abdominal aortic aneurysm expansion and promote an anti-inflammatoryenvironment characterized by increased Tr1/Th17 cell ratio, increased levels of anti-inflammatory cytokines, and decreased pro-inflammatory cytokine expression.

Biomechanics of abdominal aortic aneurysm in the framework of Windkessel effect and fully-developed inflow velocity via two-way non-linear FSI

Abdominal aortic aneurysm (AAA) is a pathological condition characterised by localised dilation of the infrarenal aorta, which can be fatal if rupture occurs. Current diagnostic criteria for repair are not patient-specific, but computational modelling may help to predict the potential growth and risk of AAA rupture accurately. This paper highlights how important using the Windkessel effect and fully-developed inflow velocity framework for the biomechanical analysis of AAA is; in other words, this research investigates how different boundary conditions in modelling methods affect the ability to correctly represent the biomechanics of AAA with complex non-linear parameters using a two-way fluid–structure interaction (FSI) technique. Time-averaged wall shear stress (TAWSS) is highly sensitive to boundary conditions, so unrealistic or simplified boundary conditions can lead to very different TAWSS results. This study also revealed that the use of outflow 3-element Windkessel boundary conditions on pulsatile pressure affects the flow pattern and increases the flow recirculation period. By accounting for the Windkessel effect and preventing backflow in numerical studies of AAA, the maximum displacement found in the distal branches can also be reduced. Models assuming plug velocity profiles overestimate peak wall stress by approximately 20% compared with models using fully developed parabolic inlet velocity profiles. This study incorporated a three-layer anisotropic material model and non-Newtonian fluid properties into the simulation, providing a more realistic representation of the effect of boundary condition selection on AAA mechanics. The results summarised from the parametric study could contribute to better prediction of AAA growth and rupture risk, and have important implications for the development of improved treatment strategies for AAA patients.

Prevalence of risk factors associated with rupture of abdominal aortic aneurysm (AAA): a single center retrospective study.

Abdominal aortic aneurysm (AAA) is a severe cardiovascular disease. The mortality rate for an AAA rupture is very high. Understanding the risk factors for AAA rupture would help AAA management, but little is known about these risk factors in the Chinese population. This retrospective study included patients that were diagnosed with AAA during the last 5 years in a large national hospital in southern China. AAA patients were divided into a rupture and non-rupture group. Clinical data were extracted from the hospital medical record system. Clinical features were compared between the rupture and non-rupture groups. The associations between potential risk factors and rupture risk were evaluated using a multivariate logistic regression analysis. A total of 337 AAA patients were included for analysis in the present study. AAA diameter was significantly larger, and high-sensitivity C-reactive protein (hs-CRP) and serum creatinine levels were both significantly higher in AAA rupture patients. High-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and total cholesterol (TC) levels were significantly lower in AAA rupture patients. After adjustment, the multivariate logistic analysis found that AAA diameter and hs-CRP were independently positively associated with AAA rupture, and HDL-C level was adversely associated with AAA rupture. Our data suggests that larger AAA diameter and higher hs-CRP level are associated with a higher risk of AAA rupture, and higher HDL-C level is associated with a lower risk of AAA rupture. The results of this study may be helpful for the management of AAA patients in southern China.

Computational modelling to evaluate abdominal aortic aneurysm rupture risk: state-of-the-art, pitfalls and scientific impact

Computational modelling to evaluate abdominal aortic aneurysm rupture risk: state-of-the-art, pitfalls and scientific impact

Type III endoleaks after endovascular aneurysm repair for abdominal aortic aneurysm: a case series

Background: Owing to the increased number of endovascular aneurysm repairs (EVAR) for abdominal aortic aneurysms (AAA), the number of patients requiring reinterventions for type III endoleaks is also growing.Objective: To analyze our experience in treatment of type IIIa and IIIb endoleaks after EVAR.Methods: Of 457 patients treated by EVAR between 2010 and 2019, type IIIa and IIIb endoleaks were detected in 5 (1.1%) patients: 4 men and 1 woman. Their mean age was 67.2 years.Results: Type IIIa and IIIb endoleaks were found in an average of 77.4 months after EVAR. The incidence of type III endoleaks was 1.1%. Type IIIb and IIIa endoleaks were observed in 1 and 4 cases, respectively. In one case, type IIIa endoleak resulted in a ruptured AAA. The main treatment methods were relining (n = 1), stent graft implantation (n = 4), implantation of a bifurcated stent graft into a stent graft. No intraoperative complications or perioperative mortality were reported. 100% of the interventions were successful. In the long-term follow-up period, 2 patients had reinterventions. One patient required an intervention for type IIIa endoleak on the contralateral side, and the other patient was diagnosed with type Ia endoleak after type IIIb endoleak treatment. In the long-term follow-up period, no ruptured aneurysms or deaths were reported.Conclusion: Type III endoleaks are associated with a risk of AAA rupture and require treatment. Endovascular treatment of endoleaks demonstrated good immediate results; however, due to the high risk of endoleaks requiring reintervention, further long-term follow-up is needed. Received 18 November 2022. Revised 15 December 2022. Accepted 19 December 2022. Informed consent: The patient’s informed consent to use the records for medical purposes is obtained. Funding: The study did not have sponsorship. Conflict of interest: The authors declare no conflict of interest. Contribution of the authors: The authors contributed equally to this article.

Sex difference in early mortality after abdominal aortic aneurysm repair

ObjectiveAlthough female patients have a lower prevalence of abdominal aortic aneurysm (AAA), they seem to have a worse treatment outcome compared with male patients. Both maximum aneurysm diameter and aortic size index (ASI) are important indicators of the risk of AAA rupture, among which ASI has been shown capable of equalizing sex-related anatomical differences. Our study aimed to investigate whether sex is an independent risk factor for early postoperative mortality and how the diameter or ASI affects the association between sex and mortality. MethodsWe performed a retrospective analysis of patients who enrolled in the AAA registry of the German Society of Vascular Surgery from 2013 to 2019. The patients were treated by either open surgical repair (OSR) or endovascular aneurysm repair (EVAR). The association between sex and 30-day mortality was investigated using logistic regression analysis. The interaction and mediating effects of maximum aneurysm diameter and ASI were investigated to verify their roles in the effect of sex on mortality. The relationships between the diameter (or ASI) and the risk of 30-day mortality in different sexes were demonstrated by the restricted cubic spline. ResultsOverall, 23,275 cases were included in our analysis, with 20,130 male (86.5%) and 3139 female (13.5%) patients. Female patients had a smaller maximum aneurysm diameter (OSR, 55.23 ± 10.29 mm vs 58.05 ± 11.28 mm [P < .001]; EVAR, 54.06 ± 9.08 mm vs 56.11 ± 9.38 mm [P < .001]), but a higher ASI (OSR, 3.16 ± 0.71 vs 2.92 ± 0.69 [P < .001]; EVAR, 3.05 ± 0.66 vs 2.80 ± 0.59 [P < .001]) compared with male patients. The 30-day mortality rate was higher for female patients in both OSR (6.6% vs 4.2%; P = .002) and EVAR groups (1.8% vs 0.8%; P < .001). Logistic regression confirmed a significantly higher risk of 30-day mortality for female patients compared with male patients (odds ratio, 1.55; 95% confidence interval, 1.21-1.99; P = .001). No interaction was found between sex and diameter or ASI, but there were mediating effects for diameter and ASI in the effect of sex on 30-day mortality. For female patients, the risk of 30-day mortality linearly increased with the increase of diameter (PNonlinear = .089) or ASI (PNonlinear = .888), whereas the risk for male patients was U-shaped (for diameter, PNonlinear < .001; for ASI, PNonlinear = .020). ConclusionsSex is an independent risk factor for 30-day mortality after AAA repair. Both diameter and ASI are mediating factors for the effect of sex on 30-day mortality. The relationship between diameter or ASI and the risk of 30-day mortality is different for male and female patients.

Anticoagulants and reduced thrombus load in abdominal aortic aneurysms assessed with three-dimensional contrast-enhanced ultrasound examination.

The relationship between intraluminal thrombus (ILT) and abdominal aortic aneurysm (AAA) growth and rupture risk remains ambiguous. Studies have shown a limited effect of antiplatelet therapy on ILT size, whereas the impact of anticoagulant therapy on ILT is unresolved. This study aims to evaluate an association between antithrombotic therapy and ILT size assessed with three-dimensional contrast-enhanced ultrasound (3D-CEUS) examination in a cohort of patients with AAA. In a cross-sectional study, 309 patients with small AAAs were examined with 3D-CEUS. Patients were divided into three groups based on prescribed antithrombotic therapy: anticoagulant (n= 36), antiplatelet (n= 222), and no antithrombotic therapy (n= 51). Patient ILT size was calculated in volume and thickness and compared between the three groups. Patients on anticoagulants had a significantly lower estimated marginal mean ILT volume of 16mL (standard error [SE],±3.2) compared with 28mL (SE,±2.7) in the no antithrombotic group and 30mL (SE,±1.3) in the antiplatelet group when adjusting for AAA volume (P< .001) and comorbidities (P< .001). In addition, patients on anticoagulant therapy had significantly lower estimated marginal mean ILT thickness of 10mm (SE,±1.1) compared with 13mm (SE,±0.9) in the no antithrombotic group of and 13mm (SE,±0.4) in the antiplatelet group when adjusting for AAA diameter (P= .03) and comorbidities (P= .035). A 3D-CEUS examination is applicable for ILT assessment and demonstrates that patients with AAA on anticoagulant therapy have lower ILT thickness and volume than patients with AAA on antiplatelet therapy and those without antithrombotic therapy. Causality between anticoagulants and ILT size, and extrapolation to AAA growth and rupture risk, is unknown and merits further investigations, to further nuance US-based AAA surveillance strategy.

An abdominal aortic aneurysm rupture risk score: a pilot study for combining precise aortic measurements and clinical factors

ObjectiveCurrent screening and management for abdominal aortic aneurysms (AAAs) are based on maximal aortic diameter criteria. This study sought to compare anatomic and clinical factors between ruptured and intact AAAs to identify predictors of rupture. MethodsPatients treated for AAAs at Thomas Jefferson University Hospital from 2010 to 2021 were reviewed from intact AAAs (iAAAs), ruptured AAAs (rAAAs), and no aortic pathology (NP) groups. Preoperative computed tomography angiography (CTA) studies were retrospectively measured with Aquarius iNtuition (TeraRecon Inc). Maximal diameter, length, mural thrombus volume (MTV), and calcification volume were measured from the lowest renal artery to the femoral artery. A rupture risk score was calculated using AAA diameter (1 point), percent ≥MTV 50% (1 point), number of antihypertensive agents <2 (1 point), not on cholesterol-lowering medication (1 point), and active smoking (1 point) for a 5-point total score. ResultsCTAs from 48 patients (age, 69.5 ± 8.1 years; 87.5% male) were measured (23 iAAAs, 15 rAAAs, and 10 controls). When compared with iAAAs, the maximal AAA diameter (rAAA, 7.71 cm; iAAA, 6.02 cm; P = .005) and %MTV (rAAA, 66.1%; iAAA, 45.3%; P = .0001) were greater in patients with rAAAs. Mean AAA rupture risk score was greater in patients with rAAAs than those with iAAAs (rAAA, 3.40 ± 1.12; iAAA, 1.78 ± 1.44; P < .001) with 100% of rAAAs and 47.8% of iAAAs having a score 2 or greater. ConclusionsThis study demonstrates that AAA diameter, percent MTV, blood pressure control, and active smoking are significant risk factors for AAA rupture. Patients with multiple risk factors (risk score ≥2) were more likely to rupture and should be considered high risk.

Biomechanical Rupture Risk Assessment in Management of Patients with Abdominal Aortic Aneurysm in COVID-19 Pandemic.

Background: The acute phase of the COVID-19 pandemic requires a redefinition of healthcare system to increase the number of available intensive care units for COVID-19 patients. This leads to the postponement of elective surgeries including the treatment of abdominal aortic aneurysm (AAA). The probabilistic rupture risk index (PRRI) recently showed its advantage over the diameter criterion in AAA rupture risk assessment. Its major improvement is in increased specificity and yet has the same sensitivity as the maximal diameter criterion. The objective of this study was to test the clinical applicability of the PRRI method in a quasi-prospective patient cohort study. Methods: Nineteen patients (fourteen males, five females) with intact AAA who were postponed due to COVID-19 pandemic were included in this study. The PRRI was calculated at the baseline via finite element method models. If a case was diagnosed as high risk (PRRI > 3%), the patient was offered priority in AAA intervention. Cases were followed until 10 September 2021 and a number of false positive and false negative cases were recorded. Results: Each case was assessed within 3 days. Priority in intervention was offered to two patients with high PRRI. There were four false positive cases and no false negative cases classified by PRRI. In three cases, the follow-up was very short to reach any conclusion. Conclusions: Integrating PRRI into clinical workflow is possible. Longitudinal validation of PRRI did not fail and may significantly decrease the false positive rate in AAA treatment.

Association Between Blood Flow Pattern and Rupture Risk of Abdominal Aortic Aneurysm Based on Computational Fluid Dynamics

This study aimed to derive a novel classification of blood flow pattern in abdominal aortic aneurysms (AAA) based on computational fluid dynamics (CFDs), and to determine the predictive value of flow patterns in AAA rupture. This was an age and sex matched case control study. Cases were identified as patients who underwent emergency endovascular or open repair due to ruptured or AAA at risk of impending rupture. Controls were age and sex matched with patients with an AAA who were asymptomatic and had a confirmed unruptured AAA from computed tomography angiography images from the same period. Classification of blood flow pattern (type I: non-helical main flow channel with multiple vortices; type II: non-helical main flow channel with single vortices; and type III, helical main flow channel with helical vortices) and haemodynamic parameters (areas of low wall shear stress [AlowWSS], aneurysm pressure drop [Δ pressure], etc) were derived from CFD analyses. Multivariable regression was used to determine independent AAA rupture risk factors. The incremental discriminant and reclassification abilities for AAA rupture were compared among different models. Fifty-three ruptured and 53 intact AAA patients were included. Ruptured AAA showed a higher prevalence of type III flow pattern than intact AAA (60.4% vs. 15.1%; p < .001). Type III flow pattern was associated with a significantly increased risk of aneurysm rupture (odds ratio 10.22, 95% confidence interval 3.43 – 30.49). Among all predicting models, the combination of AAA diameter, haemodynamic parameters (AlowWSS or Δ pressure), and flow pattern showed highest discriminant abilities in both the overall population (c-index = 0.862) and subgroup patients with AAAs < 55 mm (c-index = 0.972). Compared with AAA diameter, adding the flow pattern could significantly improve the reclassification abilities in both the overall population (net reclassification index [NRI] = 0.321; p < .001) and the subgroup of AAAs < 55 mm (NRI = 0.732; p < .001). Type III flow pattern was associated with a significantly increased risk of AAA rupture. The integration of blood flow pattern may improve the identification of high risk aneurysms in both overall population and in those with AAAs < 55 mm.

Flow Behaviour and Wall Shear Stress Derivatives in Abdominal Aortic Aneurysm Models: A Detailed CFD Analysis into Asymmetry Effect

Assessing the risk of rupture is extremely important to reduce the mortality of the abdominal aortic aneurysm (AAA). Current clinical guidelines suggest considering the maximum diameter as a criterion for planning and surgical intervention; however, this approach is too simplistic and overlooks other morphological parameters that are associated with the risk of rupture. The aim of this paper is to study the thrombogenicity and to predict the risk of AAA rupture by taking into consideration the geometrical asymmetry of the aneurysm, studying its effect on blood flow behaviour and vortical structure, spatiotemporal distribution of wall shear stresses (WSS), and their related parameters. To show the effect of asymmetry on blood flow dynamics and hemodynamic forces, five virtual models were constructed using five values of geometrical asymmetry ratio β ranging from β=0.2 (asymmetric model; AM) to β=1 (symmetric model; SM). Simulations were run for each geometry under transient physiological flow conditions using finite volume discretization. Resting flow rate was investigated in these models and our results demonstrate that the asymmetry of the aneurysm has a clear effect on the flow behaviour, and consequently on WSS distribution, oscillatory shear index (OSI) and time averaged wall shear stress (TAWSS). Furthermore, these preliminary findings suggest that thrombus formation and rupture risk are more probable in an asymmetric abdominal aortic aneurysm.

Prediction of abdominal aortic aneurysm growth by artificial intelligence taking into account clinical, biologic, morphologic, and biomechanical variables.

To develop a prediction model that could risk stratify abdominal aortic aneurysms (AAAs) into high and low growth rate groups, using machine learning algorithms based on variables from different pathophysiological fields. A cohort of 40patients with small AAAs (maximum diameter 32-53mm) who had at least an initial and a follow-up CT scan (median follow-up 12months, range 3-36months) were included. 29 input variables from clinical, biological, morphometric, and biomechanical pathophysiological aspects extracted for predictive modeling. Collected data were used to build two supervised machine learning models. A gradient boosting (XGboost) and a support vector machines (SVM) algorithm were trained with 60% and tested with 40% of the data to predict which AAA would achieve a growth rate higher than the median of our study cohort. Receiver operating characteristics (ROC) curves and areas under the curve (AUC) were used for the evaluation of the developed algorithms. XGboost achieved the highest AUC in predicting high compared to low AAA growth rate with an AUC of 81.2% (95% CI from 61.1 to 100%). SVM achieved the second highest performance with an AUC of 68.8% (95% CI from 46.5 to 91%). Based on the best performing algorithm, variable importance was estimated. Diameter-diameter ratio (maximum diameter/neck diameter), Tortuosity from Renal arteries to aortic bifurcation, and maximum thickness of the intraluminal thrombus were found to be the most important factors for model predictions. Other factors were also found to play a significant but less important role. A prediction model that can risk stratify AAAs into high and low growth rate groups could be developed by analyzing several factors implicated in the multifactorial pathophysiology of this disease, with the use of machine learning algorithms. Future studies including larger patient cohorts and implementing additional risk markers may aid in the establishment of such methodology during AAA rupture risk estimation.

Association Between Blood Flow Pattern and Rupture Risk of Abdominal Aortic Aneurysm Based on Computational Fluid Dynamics

This study aimed to derive a novel classification of blood flow pattern in abdominal aortic aneurysms (AAA) based on computational fluid dynamics (CFDs), and to determine the predictive value of flow patterns in AAA rupture. This was an age and sex matched case control study. Cases were identified as patients who underwent emergency endovascular or open repair due to ruptured or AAA at risk of impending rupture. Controls were age and sex matched with patients with an AAA who were asymptomatic and had a confirmed unruptured AAA from computed tomography angiography images from the same period. Classification of blood flow pattern (type I: non-helical main flow channel with multiple vortices; type II: non-helical main flow channel with single vortices; and type III, helical main flow channel with helical vortices) and haemodynamic parameters (areas of low wall shear stress [AlowWSS], aneurysm pressure drop [Δ pressure], etc) were derived from CFD analyses. Multivariable regression was used to determine independent AAA rupture risk factors. The incremental discriminant and reclassification abilities for AAA rupture were compared among different models. Fifty-three ruptured and 53 intact AAA patients were included. Ruptured AAA showed a higher prevalence of type III flow pattern than intact AAA (60.4% vs. 15.1%; p < .001). Type III flow pattern was associated with a significantly increased risk of aneurysm rupture (odds ratio 10.22, 95% confidence interval 3.43 - 30.49). Among all predicting models, the combination of AAA diameter, haemodynamic parameters (AlowWSS or Δ pressure), and flow pattern showed highest discriminant abilities in both the overall population (c-index= 0.862) and subgroup patients with AAAs < 55 mm (c-index= 0.972). Compared with AAA diameter, adding the flow pattern could significantly improve the reclassification abilities in both the overall population (net reclassification index [NRI]= 0.321; p < .001) and the subgroup of AAAs < 55 mm (NRI= 0.732; p < .001). Type III flow pattern was associated with a significantly increased risk of AAA rupture. The integration of blood flow pattern may improve the identification of high risk aneurysms in both overall population and in those with AAAs < 55 mm.

Abdominal Aortic Aneurysm Rupture Risk Assessment Using Machine Learning to Integrate Biomechanical, Geometrical, and Patient Characteristics

Introduction: The correlation between maximum diameter and rupture in abdominal aortic aneurysm (AAA) has been studied extensively, and a maximum AAA diameter of 55 mm in men or a diameter growth of more than 10 mm per year are accepted to indicate AAA repair. However, the maximum diameter criterion fails to describe AAA rupture risk in a patient specific manner and should therefore not directly be applied to individual patients. The poor sensitivity of diameter has been known for a long time and has stimulated the search for more patient specific risk indicators.

Convolutional Neural Network based Segmentation of Abdominal Aortic Aneurysms.

Abdominal aortic aneurysms (AAAs) are balloonlike dilations in the descending aorta associated with high mortality rates. Between 2009 and 2019, reported ruptured AAAs resulted in ~28,000 deaths while reported unruptured AAAs led to ~15,000 deaths. Automating identification of the presence, 3D geometric structure, and precise location of AAAs can inform clinical risk of AAA rupture and timely interventions. We investigate the feasibility of automatic segmentation of AAAs, inclusive of the aorta, aneurysm sac, intra-luminal thrombus, and surrounding calcifications, using 30 patient-specific computed tomography angiograms (CTAs). Binary masks of the AAA and their corresponding CTA images were used to train and test a 3D U-Net - a convolutional neural network (CNN) - model to automate AAA detection. We also studied model-specific convergence and overall segmentation accuracy via a loss-function developed based on the Dice Similarity Coefficient (DSC) for overlap between the predicted and actual segmentation masks. Further, we determined optimum probability thresholds (OPTs) for voxel-level probability outputs of a given model to optimize the DSC in our training set, and utilized 3D volume rendering with the visualization tool kit (VTK) to validate the same and inform the parameter optimization exercise. We examined model-specific consistency with regard to improving accuracy by training the CNN with incrementally increasing training samples and examining trends in DSC and corresponding OPTs that determine AAA segmentations. Our final trained models consistently produced automatic segmentations that were visually accurate with train and test set losses in inference converging as our training sample size increased. Transfer learning led to improvements in DSC loss in inference, with the median OPT of both the training segmentations and testing segmentations approaching 0.5, as more training samples were utilized.

TP5.2.13 Perceived risk of pre-operative abdominal aortic aneurysm rupture due to pulmonary function testing: all blown out of proportion?

Abstract Aim Though contraindicated in some respiratory laboratories due to a perceived increased risk of aneurysm rupture, pulmonary function tests (PFT) and cardiopulmonary exercise tests (CPET) are used commonly in preoperative assessment of patients with abdominal aortic aneurysm (AAA) considered for elective repair. We examine whether preoperative PFT/CPET are associated with increased AAA rupture risk. Methods A retrospective analysis of a prospective database of patients with AAA ≥50mm who had PFT/CPET/both as part of their preoperative assessment from November 2012 to December 2020 in a single vascular hub before elective AAA repair (open/endovascular). Patients with AAA &amp;lt;50mm, or those who did not have PFT/CPET preoperatively were excluded from analysis. Baseline demographics, AAA size, type of repair, time from PFT/CPET to repair, rupture rate and 30-day post-operative mortality are presented. Results A total of 410 patients (mean age 74 ± 8 years, 361 (88%) male) were included in the analysis. The mean AAA size was 63 ±11mm. 350 (85%) patients underwent endovascular repair. 220 (53%) patients had PFT, 69 (17%) had CPET and the remaining 121 (30%) had both PFT/CPET preoperatively. The median time from PFT/CPET to repair was 36 days (IQR 48 days), with no preoperative AAA rupture in this cohort. 30-day post-operative mortality was 3%. Conclusions This study strongly suggests that PFT and CPET are not associated with increased risk of AAA rupture and are therefore safe for assessing respiratory function in patients considered for AAA repair without adding to pre-operative rupture risk.