A Review of Biological Factors Implicated in Abdominal Aortic Aneurysm Rupture

The Implications of Oxygen-Dependent Chronic Obstructive Pulmonary Disease on Sac Growth and Mortality Following Endovascular Aneurysm Repair

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a known risk factor for abdominal aortic aneurysm (AAA) growth and rupture. The impact of COPD on AAA sac behavior following endovascular aneurysm repair (EVAR) is poorly understood. This study aimed to determine the association between COPD and sac remodeling after EVAR.

METHODS

We identified all EVAR patients (2010-2021) in the Society for Vascular Surgery-Vascular Quality Initiative database. COPD severity (none, medication-treated, oxygen (O2)-dependent) was the primary exposure variable. The primary end point was 1-year sac growth post-EVAR. Mixed effects linear and logistic regression were used to assess the effects of COPD severity on sac remodeling, controlling for covariates. Cox proportional hazards regression and competing risks regression identified predictors of mortality and reintervention.

RESULTS

30,686 patients met inclusion criteria. COPD was present in 24% of patients (no COPD, 75.8% [n = 23,260], medication-treated COPD, 19.7% [n = 6,057], O2-dependent COPD, 4.5% [n = 1,369]). O2-dependent COPD was associated with persistent sac growth (mean difference: +0.55 mm, 95% confidence interval [CI] [0.05-1.05], P = 0.03) following EVAR implantation; however, medication-treated COPD was not (mean difference: -0.06 mm, 95% CI [-0.32 to 0.19]; P = 0.64). O2-dependent COPD patients did not experience increased reintervention rates (hazard ratio [HR] 0.82, 95% CI [0.65-1.02], P = 0.07) but were identified to have significantly increased mortality (HR 1.8, 95% CI [1.52-2.22], P < 0.0001).

CONCLUSION

O2-dependent COPD was significantly associated with increased sac growth after EVAR. O2-dependent COPD did not correlate with increased reintervention, likely due to the disproportionately elevated mortality rates in this group. These findings highlight that patients with O2-dependent COPD have limited life expectancy and potentially less favorable sac remodeling, and elective EVAR should thus be reserved for only those at greatest risk for AAA-related mortality.

Computational analysis to assess hemodynamic forces in descending thoracic aortic aneurysms

Descending thoracic aortic aneurysm (DTAA) is a life-threatening disorder, defined as a localized enlargement of the descending portion of the thoracic aorta. In this context, we develop a fluid-structure interaction (FSI) computational framework, with the inclusion of a turbulence model and different material properties for the healthy and the aneurysmatic portions of the vessel, to study the hemodynamics and its relationship with DTAA. We first provide an analysis on nine ideal scenarios, accounting for different aortic arch types and DTAA ubications, to study changes in blood pressure, flow patterns, turbulence, wall shear stress, drag forces and internal wall stresses. Our findings demonstrate that the hemodynamics in DTAA is profoundly disturbed, with the presence of flow re-circulation, formation of vortices and transition to turbulence. In particular, configurations with a steeper aortic arch exhibit a more chaotic hemodynamics. We notice also an increase in pressure values for configurations with less steep aortic arch and in drag forces for configurations with distal DTAA. Second, we replicate our analysis for three patient-specific cases (one for type of arch) obtaining comforting results in terms of accordance with the ideal scenarios. Finally, in a very preliminary way, we try to relate our findings to possible stent-graft migrations after TEVAR procedure to provide predictions on the postoperative state. KEY POINTS: This study employs computational methods to assess hemodynamic forces in descending thoracic aortic aneurysms. We consider ideal cases by varying aortic arch type and aneurysm location. Our results show: chaotic hemodynamics for steep aortic arches; increase in pressure values for less steep aortic arches; high risk of plaque deposition in the aneurysmal sac for proximal aneurysms and near the neck for distal aneurysms. We also analyse three patient-specific cases, confirming the major outcomes found for the ideal cases. We try to suggest how our preoperative findings may correlate to assess the risk of stent-graft migration of a possible TEVAR procedure.

Predictive ability of red blood cell distribution width for negative remodeling of type B aortic dissection

OBJECTIVE

To investigate the correlation between red blood cell distribution width (RDW) and negative remodeling (NR) in type B aortic dissection (TBAD).

METHODS

This study involved the retrospective analysis of clinical data of 264 patients with nonsurgical TBAD admitted to our hospital between September 2015 and September 2022. Patients underwent regular follow-up after discharge, including periodic chest and abdominal aortic computed tomography angiography. Aortic dissection false lumen expansion was evaluated based on computed tomography angiography images taken at the final follow-up. Patients were divided into two groups based on the occurrence of NR in aortic dissection: NR and non-NR groups.

RESULTS

A total of 264 patients with an average age of 60 years (63.6% male), with a mean follow-up duration of 53.5 months and a survival rate of 87.9% (232/264 patients), were enrolled. During the follow-up period, 87 patients (33.0%) developed NR of the aortic dissection (NR group). Twenty-four patients in the NR group underwent surgery, which was significantly higher than the number of patients in the non-NR group (27.6% vs 16.9%). One patient in each group died of aortic rupture. RDW levels were significantly higher in the NR than the non-NR group (13.7 ± 1.2 vs 12.7 ± 1.0; P < .001). Spearman's correlation analysis identified a positive correlation between RDW and NR (r = 0.368; P < .001). Multivariate logistic regression analysis identified elevated RDW (odds ratio, 3.910; P < .001) as an independent risk factor for NR. The receiver operating characteristic curve indicated that a cutoff point of RDW >13.7% achieved an area under the curve for prediction of 0.770, sensitivity of 75.1%, and specificity of 93.2% (95% confidence interval, 0.722-0.818; P < .001).

CONCLUSIONS

RDW is a simple, inexpensive, and effective predictive marker of NR in TBAD. Herein, we identified that an RDW of >13.7% is a risk factor for NR in patients with nonsurgical TBAD during follow-up. This limit may provide a reliable basis for assessing the need for surgical intervention, optimizing prognosis evaluation, and making clinical decisions, ultimately improving the long-term survival and quality of life of patients.

Evaluating the Stress State and the Load-Bearing Fraction as Predicted by an In Vivo Parameter Identification Method for the Abdominal Aorta

Background: Arterial mechanics are crucial to cardiovascular functionality. The pressure-strain elastic modulus often delineates mechanical properties. Emerging methods use non-linear continuum mechanics and non-convex minimization to identify tissue-specific parameters in vivo. Reliability of these methods, particularly their accuracy in representing the in vivo stress state, is a significant concern. This study aims to compare the predicted stress state and the collagen-attributed load-bearing fraction with the stress state from in silico experiments. Methods: Our team has evaluated an in vivo parameter identification method through in silico experiments involving finite element models and demonstrated good agreement with the parameters of a healthy abdominal aorta. Results: The findings suggest that the circumferential stress state is well represented for an abdominal aorta with a low transmural stress gradient. Larger discrepancies are observed in the axial direction. The agreement deteriorates in both directions with an increasing transmural stress gradient, attributed to the membrane model's inability to capture transmural gradients. The collagen-attributed load-bearing fraction is well predicted, particularly in the circumferential direction. Conclusions: These findings underscore the importance of investigating both isotropic and anisotropic aspects of the vessel wall. This evaluation advances the parameter identification method towards clinical application as a potential tool for assessing arterial mechanics.

A 20-Year Analysis of Ruptured Abdominal Aortic Aneurysm Outcomes and Associated Factors in Korea

BACKGROUND

Unlike western countries, which have reported distinct decreases in incidence of ruptured abdominal aortic aneurysm (rAAA) over the last few decades, epidemiologic studies in Korea have not shown significant changes in incidence or mortality of rAAA. The purpose of this study was to analyze the changes in rAAA treatment outcomes and various associated risk factors over the past 2 decades.

METHODS

A 20-year retrospective multicenter review for rAAA cases from the period of January 2000 to December 2020 was undertaken. Preoperative, intraoperative and postoperative clinical data were extracted for patients diagnosed with rAAA. For analysis, outcomes from the early era, defined as patients treated between January 1, 2000, and December 31, 2010, were compared with outcomes from the late era, defined as patients treated between January 1, 2011, and December 31, 2020.

RESULTS

The total in-hospital mortality was 34.1% in the early era compared to 44.8% in the late era. Patients in the late era were older than those in the early era (75.2 ± 10.3 years vs. 70.3 ± 8.9 years; P = 0.009). Treatment with rAAA endovascular aneurysm repair increased from 2.3% in early to 13.8% in late era (P = 0.031). In the early era, more patients were operated by experienced surgeons than the late era (78.1% vs. 45.9%; P = 0.002). The emergency room to operating room time did not show improvement over the 20 years.

CONCLUSIONS

The results indicate that mortality rate of rAAA in Korea has not changed over the last 2 decades. The study suggests the need for national preventive strategies, improved systemic coordination, and potential centralization of vascular services to enhance survival rates for rAAA.

Rolipram impacts on redox homeostasis and cellular signaling in an experimental model of abdominal aortic aneurysm

INTRODUCTION

Cyclic nucleotide phosphodiesterases (PDEs) of the PDE4 subfamily are responsible for the hydrolysis and subcellular compartmentalization of cAMP, a second messenger that modulates vascular functionality. We had shown that PDE4B is induced in abdominal aortic aneurysms (AAA) and that PDE4 inhibition by rolipram limits experimental aneurysms. In this study we have delved into the mechanisms underlying the beneficial effect of rolipram on AAA.

METHODS

AAA were induced in ApoE-/- mice by angiotensin II (Ang II) infusion. Aneurysm formation was evaluated by ultrasonography. The expression of enzymes involved in rédox homeostasis was analyzed by real-time RT-PCR and the activation of signaling pathways by Western blot.

RESULTS

Induction of PDE4B in human AAA has been confirmed in a second cohort of patients. In Ang II-infused ApoE-/- mice, rolipram increased the percentage of animals free of aneurysms without affecting the percentage of aortic ruptures. Quantitative analyses determined that this drug significantly attenuated aortic collagen deposition. Additionally, rolipram reduced the increased Nox2 expression triggered by Ang II, exacerbated Sod1 induction, and normalized Sod3 expression. Likewise, PDE4 inhibition decreased the activation of both ERK1/2 and the canonical Wnt pathway, while AKT activity was not altered.

CONCLUSIONS

The inhibition of PDE4 activity modulates the expression of enzymes involved in rédox homeostasis and affects cell signaling pathways involved in the development of AAA.

Systematic literature review and critical analysis of RDW in patients with aortic pathologies

Diseases of the aorta, such as aortic aneurysm, dissection, and rupture, account for a large proportion of acute clinical emergencies. The red blood cell distribution width (RDW), which directly reflects anisocytosis (i.e., the heterogeneity of erythrocyte volumes), has emerged as a promising biomarker for many cardiovascular pathologies. Thus, we aimed to explore the implication of RDW in aortic pathologies. We searched Scopus and PubMed using the keywords "RDW" OR "red blood cell distribution width" AND "aortic aneurysm" OR "aortic dilatation" OR "aortic dissection" for identifying studies in which RDW values were measured in patients with these aortic diseases. Ten observational studies were finally included. In all studies, RDW value was increased in patients with aortic diseases. In the four studies in which sufficient RDW data were available for pooling, the weighted mean difference (WMD) of RDW in patients with or without complicated aortic pathologies was 0.575 (95 %CI, 0.254-0.896). RDW may be a valuable diagnostic and prognostic biomarker in patients with aortic pathologies.

Effect of Ultraviolet Radiation on the Enzymolytic and Biomechanical Profiles of Abdominal Aortic Adventitia Tissue

BACKGROUND

The abdominal aortic aneurysm (AAA) is defined as an increase in aortic diameter by more than 50% and is associated with a high risk of rupture and mortality without treatment. The aim of this study is to analyze the role of aortic adventitial collagen photocrosslinking by UV-A irradiation on the biomechanical profile of the aortic wall.

METHODS

This experimental study is structured in two parts: the first part includes in vitro uniaxial biomechanical evaluation of porcine adventitial tissue subjected to either short-term elastolysis or long-term collagenolysis in an attempt to duplicate two extreme situations as putative stages of aneurysmal degeneration. In the second part, we included biaxial biomechanical evaluation of in vitro human abdominal aortic adventitia and human AAA adventitia specimens. Biomechanical profiles were examined for porcine and human aortic tissue before and after irradiation with UV-A light (365 nm wavelength).

RESULTS

On the porcine aortic sample, the enhancing effect of irradiation was evident both on the tissue subjected to elastolysis, which had a high collagen-to-elastin ratio, and on the tissue subjected to prolonged collagenolysis despite being considerably depleted in collagen. Further, the effect of irradiation was conclusively demonstrated in the human adventitia samples, where significant post-irradiation increases in Cauchy stress (longitudinal axis: p = 0.001, circumferential axis: p = 0.004) and Young's modulus (longitudinal axis: p = 0.03, circumferential axis: p = 0.004) were recorded. Moreover, we have a stronger increase in the strengthening of the AAA adventitia samples following the exposure to UV-A irradiation (p = 0.007) and a statistically significant but not very important increase (p = 0.021) regarding the stiffness in the circumferential axis.

CONCLUSIONS

The favorable effect of UV irradiation on the strength and stiffness of degraded aortic adventitia in experimental situations mimicking early and later stages of aneurysmal degeneration is essential for the development and potential success of procedures to prevent aneurysmal ruptures. The experiments on human normal and aneurysmal adventitial tissue confirmed the validity and potential success of a procedure based on exposure to UV-A radiation.

Integrated particle image velocimetry and fluid-structure interaction analysis for patient-specific abdominal aortic aneurysm studies

BACKGROUND

Understanding the hemodynamics of an abdominal aortic aneurysm (AAA) is crucial for risk assessment and treatment planning. This study introduces a low-cost, patient-specific in vitro AAA model to investigate hemodynamics using particle image velocimetry (PIV) and flow-simulating circuit, validated through fluid-structure interaction (FSI) simulations.

METHODS

In this study, 3D printing was employed to manufacture a flexible patient-specific AAA phantom using a lost-core casting technique. A pulsatile flow circuit was constructed using off-the-shelf components. A particle image velocimetry (PIV) setup was built using an affordable laser source and global shutter camera, and finally, the flow field inside the AAA was analyzed using open-source software. Fluid-structure interaction (FSI) simulations were performed to enhance our understanding of the flow field, and the results were validated by PIV analysis. Both steady-state and transient flow conditions were investigated.

RESULTS

Our experimental setup replicated physiological conditions, analyzing arterial wall deformations and flow characteristics within the aneurysm. Under constant flow, peak wall deformations and flow velocities showed deviations within - 12% to + 27% and - 7% to + 5%, respectively, compared to FSI simulations. Pulsatile flow conditions further demonstrated a strong correlation (Pearson coefficient 0.85) in flow velocities and vectors throughout the cardiac cycle. Transient phenomena, particularly the formation and progression of vortex structures during systole, were consistently depicted between experimental and numerical models.

CONCLUSIONS

By bridging high-fidelity experimental observations with comprehensive computational analyses, this study underscores the potential of integrated methodologies in enhancing our understanding of AAA pathophysiology. The convergence of realistic AAA phantoms, precise PIV measurements at affordable cost point, and validated FSI models heralds a new paradigm in vascular research, with significant implications for personalized medicine and bioengineering innovations.

Quantitative Magnetic Resonance Imaging to Assess Progression and Rupture Risk of Aortic Aneurysms: A Scoping Review

PURPOSE

In current practice, the diameter of an aortic aneurysm is utilized to estimate the rupture risk and decide upon timing of elective repair, although it is known to be imprecise and not patient-specific. Quantitative magnetic resonance imaging (MRI) enables the visualization of several biomarkers that provide information about processes within the aneurysm and may therefore facilitate patient-specific risk stratification. We performed a scoping review of the literature on quantitative MRI techniques to assess aortic aneurysm progression and rupture risk, summarized these findings, and identified knowledge gaps.

METHODS

Literature concerning primary research was of interest and the medical databases PubMed, Scopus, Embase, and Cochrane were systematically searched. This study used the PRISMA protocol extension for scoping reviews. Articles published between January 2010 and February 2023 involving animals and/or humans were included. Data were extracted by 2 authors using a predefined charting method.

RESULTS

A total of 1641 articles were identified, of which 21 were included in the scoping review. Quantitative MRI-derived biomarkers were categorized into hemodynamic (8 studies), wall (5 studies) and molecular biomarkers (8 studies). Fifteen studies included patients and/or healthy human subjects. Animal models were investigated in the other 6 studies. A cross-sectional study design was the most common, whereas 5 animal studies had a longitudinal component and 2 studies including patients had a prospective design. A promising hemodynamic biomarker is wall shear stress (WSS), which is estimated based on 4D-flow MRI. Molecular biomarkers enable the assessment of inflammatory and wall deterioration processes. The ADAMTS4-specific molecular magnetic resonance (MR) probe showed potential to predict abdominal aortic aneurysm (AAA) formation and rupture in a murine model. Wall biomarkers assessed using dynamic contrast-enhanced (DCE) MRI showed great potential for assessing AAA progression independent of the maximum diameter.

CONCLUSION

This scoping review provides an overview of quantitative MRI techniques studied and the biomarkers derived from them to assess aortic aneurysm progression and rupture risk. Longitudinal studies are needed to validate the causal relationships between the identified biomarkers and aneurysm growth, rupture, or repair. In the future, quantitative MRI could play an important role in the personalized risk assessment of aortic aneurysm rupture.

CLINICAL IMPACT

The currently used maximum aneurysm diameter fails to accurately assess the multifactorial pathology of an aortic aneurysm and precisely predicts rupture in a patient-specific manner. Quantitative magnetic resonance imaging (MRI) enables the detection of various quantitative parameters involved in aneurysm progression and subsequent rupture. This scoping review provides an overview of the studied quantitative MRI techniques, the biomarkers derived from them, and recommendations for future research needed for the implementation of these biomarkers. Ultimately, quantitative MRI could facilitate personalized risk assessment for patients with aortic aneurysms, thereby reducing untimely repairs and improving rupture prevention.

A review on the biomechanical behaviour of the aorta

Large aortic aneurysm and acute and chronic aortic dissection are pathologies of the aorta requiring surgery. Recent advances in medical intervention have improved patient outcomes; however, a clear understanding of the mechanisms leading to aortic failure and, hence, a better understanding of failure risk, is still missing. Biomechanical analysis of the aorta could provide insights into the development and progression of aortic abnormalities, giving clinicians a powerful tool in risk stratification. The complexity of the aortic system presents significant challenges for a biomechanical study and requires various approaches to analyse the aorta. To address this, here we present a holistic review of the biomechanical studies of the aorta by categorising articles into four broad approaches, namely theoretical, in vivo, experimental and combined investigations. Experimental studies that focus on identifying mechanical properties of the aortic tissue are also included. By reviewing the literature and discussing drawbacks, limitations and future challenges in each area, we hope to present a more complete picture of the state-of-the-art of aortic biomechanics to stimulate research on critical topics. Combining experimental modalities and computational approaches could lead to more comprehensive results in risk prediction for the aortic system.

A quarter of a century biomechanical rupture risk assessment of abdominal aortic aneurysms. Achievements, clinical relevance, and ongoing developments

Abdominal aortic aneurysm (AAA) disease, the local enlargement of the infrarenal aorta, is a serious condition that causes many deaths, especially in men exceeding 65 years of age. Over the past quarter of a century, computational biomechanical models have been developed towards the assessment of AAA risk of rupture, technology that is now on the verge of being integrated within the clinical decision-making process. The modeling of AAA requires a holistic understanding of the clinical problem, in order to set appropriate modeling assumptions and to draw sound conclusions from the simulation results. In this article we summarize and critically discuss the proposed modeling approaches and report the outcome of clinical validation studies for a number of biomechanics-based rupture risk indices. Whilst most of the aspects concerning computational mechanics have already been settled, it is the exploration of the failure properties of the AAA wall and the acquisition of robust input data for simulations that has the greatest potential for the further improvement of this technology.

The immunomodulatory role of matrix metalloproteinases in colitis-associated cancer

Matrix metalloproteinases (MMPs) are an important class of enzymes in the body that function through the extracellular matrix (ECM). They are involved in diverse pathophysiological processes, such as tumor invasion and metastasis, cardiovascular diseases, arthritis, periodontal disease, osteogenesis imperfecta, and diseases of the central nervous system. MMPs participate in the occurrence and development of numerous cancers and are closely related to immunity. In the present study, we review the immunomodulatory role of MMPs in colitis-associated cancer (CAC) and discuss relevant clinical applications. We analyze more than 300 pharmacological studies retrieved from PubMed and the Web of Science, related to MMPs, cancer, colitis, CAC, and immunomodulation. Key MMPs that interfere with pathological processes in CAC such as MMP-2, MMP-3, MMP-7, MMP-9, MMP-10, MMP-12, and MMP-13, as well as their corresponding mechanisms are elaborated. MMPs are involved in cell proliferation, cell differentiation, angiogenesis, ECM remodeling, and the inflammatory response in CAC. They also affect the immune system by modulating differentiation and immune activity of immune cells, recruitment of macrophages, and recruitment of neutrophils. Herein we describe the immunomodulatory role of MMPs in CAC to facilitate treatment of this special type of colon cancer, which is preceded by detectable inflammatory bowel disease in clinical populations.

Changes in aortic diameter induced by weight loss: The HELENA trial- whole-body MR imaging in a dietary intervention trial

Obesity-related metabolic disorders such as hypertension, hyperlipidemia and chronic inflammation have been associated with aortic dilatation and resulting in aortic aneurysms in many cases. Whether weight loss may reduce the risk of aortic dilatation is not clear. In this study, the diameter of the descending thoracic aorta, infrarenal abdominal aorta and aortic bifurcation of 144 overweight or obese non-smoking adults were measured by MR-imaging, at baseline, and 12 and 50 weeks after weight loss by calorie restriction. Changes in aortic diameter, anthropometric measures and body composition and metabolic markers were evaluated using linear mixed models. The association of the aortic diameters with the aforementioned clinical parameters was analyzed using Spearman`s correlation. Weight loss was associated with a reduction in the thoracic and abdominal aortic diameters 12 weeks after weight loss (predicted relative differences for Quartile 4: 2.5% ± 0.5 and -2.2% ± 0.8, p < 0.031; respectively). Furthermore, there was a nominal reduction in aortic diameters during the 50-weeks follow-up period. Aortic diameters were positively associated with weight, visceral adipose tissue, glucose, HbA1c and with both systolic and diastolic blood pressure. Weight loss induced by calorie restriction may reduce aortic diameters. Future studies are needed to investigate, whether the reduction of aortic diameters via calorie restriction may help to prevent aortic aneurysms.

The Ratio of the Size of the Abdominal Aortic Aneurysm to That of the Unchanged Aorta as a Risk Factor for Its Rupture

Background: A ruptured abdominal aortic aneurysm is a severe condition associated with high mortality. Currently, the most important criterion used to estimate the risk of its rupture is the size of the aneurysm, but due to patients’ anatomical variability, many aneurysms have a high risk of rupture with a small aneurysm size. We asked ourselves whether individual differences in anatomy could be taken into account when assessing the risk of rupture. Methods: Based on the CT scan image, aneurysm and normal aorta diameters were collected from 186 individuals and compared in patients with ruptured and unruptured aneurysms. To take into account anatomical differences between patients, diameter ratios were calculated by dividing the aneurysm diameter by the diameter of the normal aorta at various heights, and then further comparisons were made. Results: It was found that the calculated ratios differ between patients with ruptured and unruptured aneurysms. This observation is also present in patients with small aneurysms, with its maximal size below the level that indicates the need for surgical treatment. For small aneurysms, the ratios help us to estimate the risk of rupture better than the maximum sac size (AUC: 0.783 vs. 0.650). Conclusions: The calculated ratios appear to be a valuable feature to indicate which of the small aneurysms have a high risk of rupture. The obtained results suggest the need for further confirmation of their usefulness in subsequent groups of patients.

Micromechanical and Ultrastructural Properties of Abdominal Aortic Aneurysms

Abdominal aortic aneurysms are a common condition of uncertain pathogenesis that can rupture if left untreated. Current recommended thresholds for planned repair are empirical and based entirely on diameter. It has been observed that some aneurysms rupture before reaching the threshold for repair whilst other larger aneurysms do not rupture. It is likely that geometry is not the only factor influencing rupture risk. Biomechanical indices aiming to improve and personalise rupture risk prediction require, amongst other things, knowledge of the material properties of the tissue and realistic constitutive models. These depend on the composition and organisation of the vessel wall which has been shown to undergo drastic changes with aneurysmal degeneration, with loss of elastin, smooth muscle cells, and an accumulation of isotropically arranged collagen. Most aneurysms are lined with intraluminal thrombus, which has an uncertain effect on the underlying vessel wall, with some authors demonstrating a reduction in wall stress and others a reduction in wall strength. The majority of studies investigating biomechanical properties of ex vivo abdominal aortic aneurysm tissues have used low-resolution techniques, such as tensile testing, able to measure the global material properties at the macroscale. High-resolution engineering techniques such as nanoindentation and atomic force microscopy have been modified for use in soft biological tissues and applied to vascular tissues with promising results. These techniques have the potential to advance the understanding and improve the management of abdominal aortic aneurysmal disease.

Association of High-Sensitivity C-Reactive Protein With Aneurysm Sac Shrinkage in Patients Undergoing Endovascular Abdominal Aneurysm Repair

PURPOSE

The factors associated with aneurysm sac shrinkage after endovascular aneurysm repair (EVAR) are not well established. As inflammation is implicated in aneurysm pathophysiology, we hypothesized that high-sensitivity C-reactive protein (hsCRP) was associated with aneurysm sac shrinkage after EVAR and compared the preoperative level of hsCRP between patients with and without postoperative aneurysm sac shrinkage after EVAR.

METHODS

From November 2013 to April 2019, 143 patients undergoing EVAR using Gore C3 Excluder (W. L. Gore & Associates, Inc, Flagstaff, Arizona) at our university hospital were included in this study. Aneurysm sac size was compared between that on baseline preoperative computed tomography (CT) and that on postoperative CT scans. A change in aneurysm sac size ≥5 mm was considered to be significant, whether due to enlargement or shrinkage.

RESULTS

Aneurysm sac size showed a significant decrease from 50.6 ± 9.8 mm to 47.1 ± 10.3 mm at 1 year. At 1 year postoperatively, aneurysm sac shrinkage (≥5 mm) was observed in 48 patients (34%), a stable aneurysm sac was noted in 93 patients (65%), and aneurysm sac enlargement was noted in 2 patients (1.4%). The mean preoperative hsCRP was 0.33 ± 0.54 mg/dL. Univariable analysis showed that preoperative hsCRP (p=0.029) and the presence of a renal cyst (p=0.002) were associated with aneurysm sac shrinkage. Multivariable analysis showed that preoperative hsCRP [>0.19mg/dL] (odds ratio [OR] = 0.22; 95% confidence interval [CI] = 0.05-0.96; p=0.042), and the presence of a renal cyst (OR = 0.31; 95% CI = 0.15-0.67; p=0.002) were independent risk factors for aneurysm sac shrinkage after EVAR.

CONCLUSIONS

The level of preoperative hsCRP was independently associated with aneurysm sac shrinkage after EVAR in patients with abdominal aortic aneurysms. These data suggest that the high level of hsCRP can be a negative predictor for aneurysm sac shrinkage after EVAR.

Biomechanical consequences of compromised elastic fiber integrity and matrix cross-linking on abdominal aortic aneurysmal enlargement

Abdominal aortic aneurysms (AAAs) are characterized histopathologically by compromised elastic fiber integrity, lost smooth muscle cells or their function, and remodeled collagen. We used a recently introduced mouse model of AAAs that combines enzymatic degradation of elastic fibers and blocking of lysyl oxidase, and thus matrix cross-linking, to study progressive dilatation of the infrarenal abdominal aorta, including development of intraluminal thrombus. We quantified changes in biomaterial properties and biomechanical functionality within the aneurysmal segment as a function of time of enlargement and degree of thrombosis. Towards this end, we combined multi-modality imaging with state-of-the art biomechanical testing and histology to quantify regional heterogeneities for the first time and we used a computational model of arterial growth and remodeling to test multiple hypotheses, suggested by the data, regarding the degree of lost elastin, accumulation of glycosaminoglycans, and rates of collagen turnover. We found that standard histopathological findings can be misleading, while combining advanced experimental and computational methods revealed that glycosaminoglycan accumulation is pathologic, not adaptive, and that heightened collagen deposition is ineffective if not cross-linked. In conclusion, loss of elastic fiber integrity can be a strong initiator of aortic aneurysms, but it is the rate and effectiveness of fibrillar collagen remodeling that dictates enlargement. STATEMENT OF SIGNIFICANCE: Precise mechanisms by which abdominal aortic aneurysms enlarge remain unclear, but a recent elastase plus β-aminopropionitrile mouse model provides new insight into disease progression. As in the human condition, the aortic degeneration and adverse remodeling are highly heterogeneous in this model. Our multi-modality experiments quantify and contrast the heterogeneities in geometry and biomaterial properties, and our computational modeling shows that standard histopathology can be misleading. Neither accumulating glycosaminoglycans nor frustrated collagen synthesis slow disease progression, thus highlighting the importance of stimulating adaptive collagen remodeling to limit lesion enlargement.

Vascular Mechanobiology: Homeostasis, Adaptation, and Disease

Cells of the vascular wall are exquisitely sensitive to changes in their mechanical environment. In healthy vessels, mechanical forces regulate signaling and gene expression to direct the remodeling needed for the vessel wall to maintain optimal function. Major diseases of arteries involve maladaptive remodeling with compromised or lost homeostatic mechanisms. Whereas homeostasis invokes negative feedback loops at multiple scales to mediate mechanobiological stability, disease progression often occurs via positive feedback that generates mechanobiological instabilities. In this review, we focus on the cell biology, wall mechanics, and regulatory pathways associated with arterial health and how changes in these processes lead to disease. We discuss how positive feedback loops arise via biomechanical and biochemical means. We conclude that inflammation plays a central role in overriding homeostatic pathways and suggest future directions for addressing therapeutic needs.

Galectin-3 as a Biomarker for Stratifying Abdominal Aortic Aneurysm Size in a Taiwanese Population

Abdominal aortic aneurysm (AAA) ruptures are unpredictable and lethal. A biomarker predicting AAA rupture risk could help identify patients with small, screen-detected AAAs. Galectin-3 (Gal-3), a β-galactosidase–binding lectin, is involved in inflammatory processes and may be associated with AAA incidence. We investigated whether Gal-3 can be used as a biomarker of AAA size. Plasma Gal-3 protein concentrations were examined in patients with AAA (n = 151) and control patients (n = 195) using Human ProcartaPlex multiplex and simplex kits. Circulating Gal-3 levels were significantly higher in patients with AAA than in control patients. The area under the receiver operating characteristic curve for Gal-3 was 0.91. Multivariate logistic regression analysis revealed a significant association between Gal-3 level and the presence of AAA. Circulating Gal-3 levels were significantly correlated with aortic diameter in a concentration-dependent manner. In conclusion, higher plasma Gal-3 concentrations may be a useful biomarker of AAA progression.

Intraluminal thrombus: Innocent bystander or factor in abdominal aortic aneurysm pathogenesis?

BACKGROUND

Abdominal aortic aneurysms (AAAs) represent a complex multifactorial hemodynamic, thrombotic, and inflammatory process that can ultimately result in aortic rupture and death. Despite improved screening and surgical management of AAAs, the mortality rates have remained high after rupture, and little progress has occurred in the development of nonoperative treatments. Intraluminal thrombus (ILT) is present in most AAAs and might be involved in AAA pathogenesis. The present review examined the latest clinical and experimental evidence for possible involvement of the ILT in AAA growth and rupture.

METHODS

A literature review was performed after a search of the PubMed database from 2012 to June 2020 using the terms "abdominal aortic aneurysm" and "intraluminal thrombus."

RESULTS

The structure, composition, and hemodynamics of ILT formation and propagation were reviewed in relation to the hemostatic and proteolytic factors favoring ILT deposition. The potential effects of the ILT on AAA wall degeneration and rupture, including a review of the current controversies regarding the position, thickness, and composition of ILT, are presented. Although initially potentially protective against increased wall stress, increasing evidence has shown that an increased volume and greater age of the ILT have direct detrimental effects on aortic wall integrity, which might predispose to an increased rupture risk.

CONCLUSIONS

ILT does not appear to be an innocent bystander in AAA pathophysiology. However, its exact role remains elusive and controversial. Despite computational evidence of a possible protective role of the ILT in reducing wall stress, increasing evidence has shown that the ILT promotes AAA wall degeneration in humans and in animal models. Further research, with large animal models and with more chronic ILT is crucial for a better understanding of the role of the ILT in AAAs and for the potential development of targeted therapies to slow or halt AAA progression.

Abdominal aortic aneurysm and acute appendicitis: a case report and review of the literature

Background

Abdominal aortic aneurysm and acute appendicitis occur relatively frequently in elderly patients. However, the co-occurrence of the two pathologies is very rare and serious.

Case presentation

We present the case of an elderly Caucasian patient who was aware of having an abdominal aortic aneurysm but refused treatment and was subsequently admitted to the hospital’s emergency department with acute abdominal symptoms. A computed tomography scan raised the possibility of complication due to the characteristics of the aneurysm. The patient then agreed to emergency surgery. Laparotomy revealed the existence of an acute perforated appendicitis with a significant abscess in the right iliac fossa and an uncomplicated aneurysm. Appendectomy was performed and the abscess drained. The postoperative period passed without complications, and the patient again refused surgery for the aneurysm, which due to its anatomical characteristics was not a candidate for standard endovascular treatment.

Conclusions

In light of this experience, we review the literature about the relationship between abdominal aortic aneurysm and acute appendicitis.

Hemodynamic Changes in an Actively Rupturing Abdominal Aortic Aneurysm

Computational fluid dynamics were used to assess hemodynamic changes in an actively rupturing abdominal aortic aneurysm (AAA) over a 9-day period. Active migration of contrast from the lumen into the thickest region of intraluminal thrombus (ILT) was demonstrated until it ultimately breached the adventitial layer. Four days after symptom onset, there was a discrete disruption of adventitial calcium with bleb formation at the site of future rupture. Rupture occurred in a region of low wall shear stress and was associated with a marked increase in AAA diameter from 6.6 to 8.4 cm. The cross-sectional area of the flow lumen increased across all time points from 6.28 to 12.08 cm2. The increase in luminal area preceded the increase in AAA diameter and was characterized by an overall deceleration in recirculation flow velocity with a coinciding increase in flow velocity penetrating the ILT. We show that there are significant hemodynamic and structural changes in the AAA flow lumen in advance of any appreciable increase in aortic diameter or rupture. The significant increase in AAA diameter with rupture suggests that AAA may actually rupture at smaller sizes than those measured on day of rupture. These findings have implications for algorithms the predict AAA rupture risk.

Methodology for Estimation of Annual Risk of Rupture for Abdominal Aortic Aneurysm

BACKGROUND AND OBJECTIVE

Estimating patient specific annual risk of rupture of abdominal aortic aneurysm (AAA) is currently based only on population. More accurate knowledge based on patient specific data would allow surgical treatment of only those AAAs with significant risk of rupture. This would be beneficial for both patients and health care system.

METHODS

A methodology for estimating annual risk of rupture (EARR) of abdominal aortic aneurysms (AAA) that utilizes Bayesian statistics, mechanics and patient-specific blood pressure monitoring data is proposed. EARR estimation takes into consideration, peak wall stress in AAA computed by patient-specific finite element modeling, the probability distributions of wall thickness, wall strength, systolic blood pressure and the period of time that the patient is known to have already survived with the intact AAA. Initial testing of proposed approach was performed on fifteen patients with intact AAA (mean maximal diameter 51mm±8mm). They were equipped with a pressure holter and their blood pressure was recorded over 24 hours. Then, we calculated EARR values for four possible scenarios - without considering any days of survival prior identification of AAA at computed tomography scans (EARR_0), considering past survival of 30 (EARR_30), 90 (EARR_90) and 180 days (EARR_180). Finally, effect of patient-specific blood pressure variability was analyzed.

RESULTS

Consideration of past survival does indeed significantly improve predictions of future risk: EARR_30 (1.04%± 0.87%), EARR_90 (0.67%± 0.56%) and EARR_180 (0.47%± 0.39%) which are unrealistically high otherwise (EARR_0 5.02%± 5.24%). Finally, EARR values were observed to vary by an order as a consequence of blood pressure variability and by factor of two as a consequence of neglected growth.

CONCLUSIONS

Methodology for computing annual risk of rupture of AAA was developed for the first time. Sensitivity analyses showed respecting patient specific blood pressure is important factor and should be included in the AAA rupture risk assessment. Obtained EARR values were generally low and in good agreement with confirmed survival time of investigated patients so proposed method should be further clinically validated.

A REVIEW OF THE MECHANICAL STRESSES PREDISPOSING ABDOMINAL AORTIC ANEURYSMAL RUPTURE: UNIAXIAL EXPERIMENTAL APPROACH

In this paper, problems concerning the uniaxial experimental investigation of the human abdominal aortic aneurysm (AAA) biomechanical characteristics, concomitant values of the associated Cauchy stress, failure (ultimate) stress in AAA, and the constitutive modeling of AAA are considered. The aim of this paper is to review and compare the disposable experimental data, to reveal the reasons for the high dissipation of the results between studies, and to propound some unification criteria. We examined 22 literature sources published between 1994 and 2017 and compared their results, including our own results. The experiments in the reviewed literature have been designed to obtain the stress–strain characteristics and the failure (ultimate) stress and strain of the aneurysmal tissue. A variety of forms of the strain–energy function (SEF) have been applied in the considered studies to model the biomechanical behavior of the aneurysmal wall. The specimen condition and physical parameters, the experimental protocols, the failure stress and strain, and SEFs differ between studies, contributing to the differences between the final results. We propound some criteria and suggestions for the unification of the experiments leading to the comparable results.

Detection of Macrophage Localization in the Abdominal Aortic Aneurysm Wall Using Ex Vivo Superparamagnetic Iron Oxide-Enhanced Magnetic Resonance Imaging

BACKGROUND

Macrophages in the aneurysmal wall play an important role in the pathogenesis of abdominal aortic aneurysms (AAAs). Superparamagnetic iron oxide (SPIO) is a macrophage-specific contrast agent that results in negative enhancement on magnetic resonance imaging (MRI). SPIO-enhanced MRI targeting the intraluminal thrombus of AAAs has been previously reported. However, macrophages in the media and adventitia of AAA wall have not been investigated in detail. This study aimed to evaluate macrophage localization using SPIO-enhanced MRI in the media and adventitia of AAA wall, as macrophages play a crucial role in AAA pathogenesis.

METHODS

Here, we included study and control patients planning to undergo open surgery for AAA. The study patients received SPIO injection 2 days preoperatively (the SPIO group, n = 7), whereas the control patients did not receive this injection (the control group). Ex vivo MRI was performed on the harvested AAA wall in the SPIO group during the surgery. The concordance between the number of macrophages and berlin blue (BB)-stained areas was histologically evaluated in both groups. Moreover, the concordance between regions of interest in MR images and BB-stained areas was evaluated.

RESULTS

The proportion of BB-stained macrophages was higher in the SPIO group (0.93; interquartile range [IQR], 0.83-0.95) than in the control group (0.03; IQR, 0.026-0.11) (P < 0.05), indicating uptake of SPIO by macrophages in the AAA wall. A significant positive correlation was found between the number of BB-stained macrophages and BB-stained areas using Kendall rank correlation coefficient in the SPIO group (τ = 0.58; P < 0.05). Significant correlations were found in the distributions of the region of interest of SPIO-enhanced MRI and BB-stained areas in the media and adventitia in 5 of 7 patients.

CONCLUSIONS

Macrophages present in the media and adventitia of the AAA wall showed an uptake of the SPIO contrast agent injected 2 days prior, which were then detected by ex vivo MRI. This suggests that SPIO-enhanced MR images help detect the localization of macrophages on the AAA wall, indicating its potential to serve as a novel index for AAA pathogenesis.

Evaluation of a smart activatable MRI nanoprobe to target matrix metalloproteinases in the early-stages of abdominal aortic aneurysms

Matrix metalloproteinases (MMPs) activation contributes to abdominal aortic aneurysm (AAA) growth and rupture. The study was to evaluate the ability of a novel activatable magnetic resonance imaging (MRI) nanoprobe, to target MMPs in an Angiotensin II (ANG II)-induced AAA model. The activatable nanoprobe is composed of a hydrophilic polyethylene glycol coating layer immobilized on the external surface of core/shell Fe/iron oxide nanoparticles; between them, there was grafted the MMP peptide substrate. In the ANG II infusion mice model of AAAs, MRI was performed to characterize the progression of model. The contrast-to-noise ratio was lower in the aneurysm of the mice injected with activatable nanoprobe. Histological studies revealed the presence of MMPs and iron-oxide in regions of MR signal decrease. MRI combined with nanoprobe allows the detection of MMP activity within the wall of AAA, thus representing a potential noninvasive method to predict the rupture risk of AAA.

In vitro histomechanical effects of enzymatic degradation in carotid arteries during inflation tests with pulsatile loading

In this paper, the objective is to assess the histomechanical effects of collagen proteolysis in arteries under loading conditions reproducing in vivo environment. Thirteen segments of common porcine carotid arteries (8 proximal and 5 distal) were immersed in a bath of bacterial collagenase and tested with a pulsatile tension/inflation machine. Diameter, pressure and axial load were monitored throughout the tests and used to derive the stress-stretch curves and to determine the secant circumferential stiffness. Results were analysed separately for proximal and distal segments, before and after 1, 2 and 3 h of enzymatic degradation. A histological analysis was performed to relate the arterial microstructure to its mechanical behavior under collagen proteolysis. Control (before enzymatic degradation) and treated populations (after 1, 2 or 3 h of enzymatic degradation) were found statistically incomparable, and histology confirmed the alteration of the fibrous structure of collagen bundles induced by the collagenase treatment. A decrease of the secant circumferential stiffness of the arterial wall was noticed mostly at the beginning of the treatment, and was less pronounced after 1 h. These results constitute an important set of enzymatically damaged arteries that can be used to validate biomechanical computational models correlating structure and properties of blood vessels.

High-performance detection of an abdominal aortic aneurysm biomarker by immunosensing

Abdominal aortic aneurysm (AAA) is a serious, life-threatening vascular disease that presents as an enlarged area of the aorta, which is the main artery that carries blood away from the heart. AAA may occur at any location in the aorta, but it is mainly found in the abdominal region. A ruptured AAA causes serious health issues, including death. Traditional imaging techniques, such as computed tomography angiogram, magnetic resonance imaging, and ultrasound sonography, have been used to identify AAAs. Circulating biomarkers have recently become attractive for diagnosing AAAs due to their cost-effectiveness compared to imaging. Insulin-like growth factor 1 (IGF-1), a secreted hormone vital for human atherosclerotic plaque stability, has been found to be an efficient biomarker for AAA identification. In this report, immunosensing was performed by using an InterDigitated electrode (IDE) sensor to detect circulating levels of IGF-1. The detection limit of IGF-1 was found to be 100 fM with this sensor. Moreover, related protein controls (IGF-2 and IGFBP3) were not detected with the same antibody, indicating selective IGF-1 detection. Thus, immunosensing by using an IDE sensor may help to effectively diagnose AAAs and represents a basic platform for further development.

Endothelium in Aortic Aneurysm Disease: New Insights

Inflammation is recognized as a fundamental element in the development and growth of aortic aneurysms. Aortic aneurysm is correlated with aortic wall deformities and injury, as a result of inflammation, matrix metalloproteinases activation, oxidative stress, and apoptosis of vascular smooth muscle cells. The endothelial wall has a critical part in the inflammation of the aorta and endothelial heterogeneity has proven to be significant for modeling aneurysm formation. Endothelial shear stress and blood flow affect the aortic wall through hindrance of cytokines and adhesion molecules excreted by endothelial cells, causing reduction of the inflammation process in the media and adventitia. This pathophysiological process results in the disruption of elastic fibers, degradation of collagen fibers, and destruction of vascular smooth muscle cells. Consequently, the aortic wall is impaired due to reduced thickness, decreased mechanical function, and cannot tolerate the impact of blood flow leading to aortic expansion. Surgery is still considered the mainstay therapy for large aortic aneurysms. The prevention of aortic dilation, though, is based on the hinderance of endothelial dysregulation with drugs, the reduction of reactive oxygen and nitrogen species, and also the reduction of pro-inflammatory molecules and metalloproteinases. Further investigations are required to enlighten the emerging role of endothelial cells in aortic disease.

Mechanical Weakness of Thoracic Aorta Related to Aging or Dissection Predicted by Speed of Sound with Collagenase

Scanning acoustic microscopy reveals information on histology and speed of sound (SOS) through tissues. Slower SOS corresponds to lower stiffness. The aim of the present study was to investigate whether SOS values reflect the degree of degeneration with aging or dissection and whether enzymatic digestion susceptibility is distinct. The SOSs of media other than the atheromatous areas of normal and surgical dissections were measured and compared using medial degeneration grade (MDG) scores. To evaluate the damage rate, SOS was assessed after collagenase digestion. SOS scores negatively correlated with aging and MDG scores. Dissected aortas had higher SOS and MDG scores without age correlation. Collagenase digestion was present in all aortas, but older aortas were more injured than younger aortas. Dissected aortas were more vulnerable to collagenase. Older and dissected aortas expressed specific extracellular matrix components to compensate for mechanical weakness. The present method can evaluate mechanical weakness corresponding to histology to investigate the cause of rupture.

Feasibility of Assessing Inflammation in Asymptomatic Abdominal Aortic Aneurysms With Integrated 18F-Fluorodeoxyglucose Positron Emission Tomography/Magnetic Resonance Imaging

OBJECTIVE

This study aimed to evaluate the feasibility of 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) combined with contrast enhanced magnetic resonance imaging (MRI) to identify inflammation in asymptomatic abdominal aortic aneurysms (AAA).

METHODS

FDG PET/MRI was performed on 15 patients with asymptomatic infrarenal AAAs >45 mm diameter. Prevalence of FDG uptake and MRI findings of inflammatory changes (oedema, wall thickening, and late gadolinium enhancement [LGE]) in the aortic wall were investigated at three levels: suprarenal aorta; non-aneurysmal aortic neck; and AAA.

RESULTS

The median diameter of the AAAs was 54 mm (range 47-65 mm) and the median expansion rate in the last 12 months was 3 mm (range 1-13 mm). The standard uptake value (SUV) of FDG in the aneurysmal wall (SUVmax 2.5) was higher than the blood pool (SUVmax 1.0; p < .001). The maximum target to background ratio was higher in the suprarenal aorta (mean ± SD; 3.1 ± 0.6) and aortic neck (2.7 ± 0.5) than in the aneurysmal aorta (2.5 ± 0.5; p < .001). Thirty-six FDG hotspots were observed in the aneurysmal wall of 13 patients. Wall thickening and LGE were identified in eight patients. The number of FDG hotspots correlated with recent AAA growth (r = 0.62, p = .01). The recent aneurysm expansion rate was higher in aneurysms with LGE than in those without (7 mm vs. 2 mm; p = .03). MRI inflammatory changes were observed in nine of 36 hot spots (25%) and in three of 13 patients with focal FDG uptake.

CONCLUSION

Fully integrated FDG PET/MRI can be used to study inflammation in asymptomatic AAAs. Heterogenous uptake of FDG in the aneurysmal wall indicates increased glucose metabolism, suggesting an ongoing inflammation. However, these FDG hotspots rarely correspond to MRI findings of inflammation, raising the question of which type of cellular activity is present in these areas. The presence of LGE and FDG hotspots both correlated to recent aneurysm growth, and their usefulness as clinical markers of aneurysm growth warrant additional investigation.

Alterations in phenotype and gene expression of adult human aneurysmal smooth muscle cells by exogenous nitric oxide

Abdominal aortic aneurysms (AAA) are characterized by matrix remodeling, elastin degradation, absence of nitric oxide (NO) signaling, and inflammation, influencing smooth muscle cell (SMC) phenotype and gene expression. Little is known about the biomolecular release and intrinsic biomechanics of human AAA-SMCs. NO delivery could be an attractive therapeutic strategy to restore lost functionality of AAA-SMCs by inhibiting inflammation and cell stiffening. We aim to establish the differences in phenotype and gene expression of adult human AAA-SMCs from healthy SMCs. Based on our previous study which showed benefits of optimal NO dosage delivered via S-Nitrosoglutathione (GSNO) to healthy aortic SMCs, we tested whether such benefits would occur in AAA-SMCs. The mRNA expression of three genes involved in matrix degradation (ACE, ADAMTS5 and ADAMTS8) was significantly downregulated in AAA-SMCs. Total protein and glycosaminoglycans synthesis were higher in AAA-SMCs than healthy-SMCs (p < 0.05 for AAA-vs. healthy- SMC cultures) and was enhanced by GSNO and 3D cultures (p < 0.05 for 3D vs. 2D cultures; p < 0.05 for GSNO vs. non-GSNO cases). Elastin gene expression, synthesis and deposition, desmosine crosslinker levels, and lysyl oxidase (LOX) functional activity were lower, while cell proliferation, iNOS, LOX and fibrillin-1 gene expressions were higher in AAA-SMCs (p < 0.05 between respective cases), with differential benefits from GSNO exposure. GSNO and 3D cultures reduced MMPs -2, -9, and increased TIMP-1 release in AAA-SMC cultures (p < 0.05 for GSNO vs. non-GSNO cultures). AAA-SMCs were inherently stiffer and had smoother surface than healthy SMCs (p < 0.01 in both cases), but GSNO reduced stiffness (~25%; p < 0.01) and increased roughness (p < 0.05) of both cell types. In conclusion, exogenously-delivered NO offers an attractive strategy by providing therapeutic benefits to AAA-SMCs.

Systems Approach to Study Associations between OxLDL and Abdominal Aortic Aneurysms

Although abdominal aortic aneurysm (AAA) is a common vascular disease and is associated with high mortality, the full pathogenesis of AAA remains unknown to researchers. Abdominal aortic aneurysms and atherosclerosis are strongly related. Currently, it is more often suggested that development of AAA is not a result of atherosclerosis, however, individual factors can act independently or synergistically with atherosclerosis. One of such factors is low-density lipoprotein (LDL) and its oxidized form (oxLDL). It is known that oxLDL plays an important role in the pathogenesis of atherosclerosis, thus, we decided to examine oxLDL impact on the development of AAA by creating two models using Petri-nets. The first, full model, contains subprocess of LDL oxidation and all subprocesses in which it participates, while the second, reduced model, does not contain them. The analysis of such models can be based on t-invariants. They correspond to subprocesses which do not change the state of the modeled system. Moreover, the knockout analysis has been used to estimate how crucial a selected transition (representing elementary subprocess) is, based on the number of excluded subprocesses as a result of its knockout. The results of the analysis of our models show that oxLDL affects 55.84% of subprocesses related to AAA development, but the analysis of the nets based on knockouts and simulation has shown that the influence of oxLDL on enlargement and rupture of AAA is negligible.

Hemodynamic Simulation of Pancreaticoduodenal Artery Aneurysm Formation Using an Electronic Circuit Model and a Case Series Analysis

Objective: To assess mechanisms underlying aneurysm formation using a simple electronic circuit model.

Materials and Methods: We created a simple circuit model connecting the celiac artery (CA) to the superior mesenteric artery via the pancreaticoduodenal arcade. We retrospectively reviewed 12 patients with true pancreaticoduodenal artery aneurysms (PDAAs) who received open or endovascular treatment between 2004 and 2017. We set the resistance of each artery and organ voltage and calculated flow volume and rate in response to degrees of simulated CA stenosis from 0% to 99.9%.

Results: Flow volume rates of the anterior pancreaticoduodenal artery and posterior pancreaticoduodenal artery decreased to zero when CA stenosis increased from 0% to 50% and then increased drastically, at which point flow direction reverted and the flow was up to three times the initial rate. The gastroduodenal artery (GDA) also showed reversed flow with severe CA stenosis. In 12 patients with PDAA, eight presented with a CA lesion, and the other patients presented with comorbidities causing the arteries to be pathologically fragile, such as Marfan syndrome, Behçet’s disease, and segmental arterial mediolysis. All four GDA aneurysms were not accompanied by CA lesions.

Conclusion: The mechanism underlying CA-lesion-associated PDAA formation may be partially explained using our model.

Role of Vascular Smooth Muscle Cell Phenotypic Switching and Calcification in Aortic Aneurysm Formation

Aortic aneurysm is a vascular disease whereby the ECM (extracellular matrix) of a blood vessel degenerates, leading to dilation and eventually vessel wall rupture. Recently, it was shown that calcification of the vessel wall is involved in both the initiation and progression of aneurysms. Changes in aortic wall structure that lead to aneurysm formation and vascular calcification are actively mediated by vascular smooth muscle cells. Vascular smooth muscle cells in a healthy vessel wall are termed contractile as they maintain vascular tone and remain quiescent. However, in pathological conditions they can dedifferentiate into a synthetic phenotype, whereby they secrete extracellular vesicles, proliferate, and migrate to repair injury. This process is called phenotypic switching and is often the first step in vascular pathology. Additionally, healthy vascular smooth muscle cells synthesize VKDPs (vitamin K-dependent proteins), which are involved in inhibition of vascular calcification. The metabolism of these proteins is known to be disrupted in vascular pathologies. In this review, we summarize the current literature on vascular smooth muscle cell phenotypic switching and vascular calcification in relation to aneurysm. Moreover, we address the role of vitamin K and VKDPs that are involved in vascular calcification and aneurysm. Visual Overview- An online visual overview is available for this article.

Strain Mapping From Four-Dimensional Ultrasound Reveals Complex Remodeling in Dissecting Murine Abdominal Aortic Aneurysms

Current in vivo abdominal aortic aneurysm (AAA) imaging approaches tend to focus on maximum diameter but do not measure three-dimensional (3D) vascular deformation or strain. Complex vessel geometries, heterogeneous wall compositions, and surrounding structures can all influence aortic strain. Improved understanding of complex aortic kinematics has the potential to increase our ability to predict aneurysm expansion and eventual rupture. Here, we describe a method that combines four-dimensional (4D) ultrasound and direct deformation estimation to compute in vivo 3D Green-Lagrange strain in murine angiotensin II-induced suprarenal dissecting aortic aneurysms, a commonly used small animal model. We compared heterogeneous patterns of the maximum, first-component 3D Green-Lagrange strain with vessel composition from mice with varying AAA morphologies. Intramural thrombus and focal breakage in the medial elastin significantly reduced aortic strain. Interestingly, a dissection that was not detected with high-frequency ultrasound also experienced reduced strain, suggesting medial elastin breakage that was later confirmed via histology. These results suggest that in vivo measurements of 3D strain can provide improved insight into aneurysm disease progression. While further work is needed with both preclinical animal models and human imaging studies, this initial murine study indicates that vessel strain should be considered when developing an improved metric for predicting aneurysm growth and rupture.

Identification of Potential Plasma Biomarkers for Abdominal Aortic Aneurysm Using Tandem Mass Tag Quantitative Proteomics

Plasma biomarkers that identify abdominal aortic aneurysm (AAA) rupture risk would greatly assist in stratifying patients with small aneurysms. Identification of such biomarkers has hitherto been unsuccessful over a range of studies using different methods. The present study used an alternative proteomic approach to find new, potential plasma AAA biomarker candidates. Pre-fractionated plasma samples from twelve patients with AAA and eight matched controls without aneurysm were analyzed by mass spectrometry applying a tandem mass tag (TMT) technique. Eight proteins were differentially regulated in patients compared to controls, including decreased levels of the enzyme bleomycin hydrolase. The down-regulation of this enzyme was confirmed in an extended validation study using an enzyme-linked immunosorbent assay (ELISA). The TMT-based proteomic approach thus identified novel potential plasma biomarkers for AAA.

Intraluminal Thrombus Deposition Is Reduced in Ruptured Compared to Diameter-matched Intact Abdominal Aortic Aneurysms

BACKGROUND

The aim of this study is to compare the pattern of intraluminal thrombus (ILT) deposition in diameter-matched ruptured and nonruptured abdominal aortic aneurysms (AAAs).

METHODS

We performed a single-center, retrospective study. Ruptured AAAs were collected during 24 months. Diameter-matched intact lesions were randomly selected in a 2:1 ratio and served as controls. ILT cross-sectional area, relative area, maximum thickness, and asymmetric distribution were recorded at the site of maximum aneurysm size and compared between groups. Moreover, additional comparisons were performed inside the group of ruptured AAAs, between the site of maximum size and the site of rupture.

RESULTS

Fifteen ruptured cases were compared with 30 nonruptured cases. ILT relative area (37.5% vs. 73.5%, P = 0.004) and maximum thickness (14.5 vs. 28 mm, P= 0.0017) were significantly reduced among ruptured compared to intact AAAs. The latter group presented mostly an anterior eccentric ILT deposition, while the former presented a more symmetrical pattern. The site of rupture was located at the site of maximum size in only 2 cases. In general, ILT was reduced at the site of rupture compared to the site of maximum aneurysm size in ruptured cases but differences did not reach statistical significance.

CONCLUSIONS

In similar sized AAAs, ILT is reduced in ruptured compared to nonruptured cases.

Diabetes mellitus and abdominal aortic aneurysms: A review of the mechanisms underlying the negative relationship

INTRODUCTION

Diabetes mellitus appears to be negatively associated with abdominal aortic aneurysm; however, the mechanisms underlying this relationship remain poorly understood. The aim of this article is to provide a comprehensive review of the currently understood biological pathways underlying this relationship.

METHODS

A review of the literature ('diabetes' OR 'hyperglycaemia' AND 'aneurysm') was performed and relevant studies grouped into biological pathways.

RESULTS

This review identified a number of biological pathways through which diabetes mellitus may limit the presence, growth and rupture of abdominal aortic aneurysms. These include those influencing extracellular matrix volume, extracellular matrix glycation, the formation of advanced glycation end-products, inflammation, oxidative stress and intraluminal thrombus biology. In addition, there is an increasing evidence to suggest that the medications used to treat diabetes can also limit the development and progression of abdominal aortic aneurysms.

CONCLUSION

The negative association between diabetes and abdominal aortic aneurysm is robust. Future studies should attempt to target the pathways identified in this review to develop novel therapeutic agents aimed at slowing or even halting aneurysm progression.

Geometric surrogates of abdominal aortic aneurysm wall mechanics

The maximum diameter criterion is the most important factor in the clinical management of abdominal aortic aneurysms (AAA). Consequently, interventional repair is recommended when an aneurysm reaches a critical diameter, typically 5.0 cm in the United States. Nevertheless, biomechanical measures of the aneurysmal abdominal aorta have long been implicated in AAA risk of rupture. The purpose of this study is to assess whether other geometric characteristics, in addition to maximum diameter, may be highly correlated with the AAA peak wall stress (PWS). Using in-house segmentation and meshing algorithms, 30 patient-specific AAA models were generated for finite element analysis using an isotropic constitutive material for the AAA wall. PWS, evaluated as the spatial maximum of the first principal stress, was calculated at a systolic pressure of 120 mmHg. The models were also used to calculate 47 geometric indices characteristic of the aneurysm geometry. Statistical analyses were conducted using a feature reduction algorithm in which the 47 indices were reduced to 11 based on their statistical significance in differentiating the models in the population (p < 0.05). A subsequent discriminant analysis was performed and 7 of these indices were identified as having no error in discriminating the AAA models with a significant nonlinear regression correlation with PWS. These indices were: D_max (maximum diameter), T (tortuosity), DDr (maximum diameter to neck diameter ratio), S (wall surface area), K_median (median of the Gaussian surface curvature), C_max (maximum lumen compactness), and M_mode (mode of the Mean surface curvature). Therefore, these characteristics of an individual AAA geometry are the highest correlated with the most clinically relevant biomechanical parameter for rupture risk assessment. We conclude that the indices can serve as surrogates of PWS in lieu of a finite element modeling approach for AAA biomechanical evaluation.

Case Study: Intra-Patient Heterogeneity of Aneurysmal Tissue Properties

Introduction: Current recommendations for surgical treatment of abdominal aortic aneurysms (AAAs) rely on the assessment of aortic diameter as a marker for risk of rupture. The use of aortic size alone may overlook the role that vessel heterogeneity plays in aneurysmal progression and rupture risk. The aim of the current study was to investigate intra-patient heterogeneity of mechanical and fluid mechanical stresses on the aortic wall and wall tissue histopathology from tissue collected at the time of surgical repair. Methods: Finite element analysis (FEA) and computational fluid dynamics (CFD) simulations were used to predict the mechanical wall stress and the wall shear stress fields for a non-ruptured aneurysm 2 weeks prior to scheduled surgery. During open repair surgery one specimen partitioned into different regions was collected from the patient's diseased aorta according to a pre-operative map. Histological analysis and mechanical testing were performed on the aortic samples and the results were compared with the predicted stresses. Results: The preoperative simulations highlighted the presence of altered local hemodynamics particularly at the proximal segment of the left anterior area of the aneurysm. Results from the post-operative assessment on the surgical samples revealed a considerable heterogeneity throughout the aortic wall. There was a positive correlation between elastin fragmentation and collagen content in the media. The tensile tests demonstrated a good prediction of the locally varying constitutive model properties predicted using geometrical variables, i.e., wall thickness and thrombus thickness. Conclusions: The observed large regional differences highlight the local response of the tissue to both mechanical and biological factors. Aortic size alone appears to be insufficient to characterize the large degree of heterogeneity in the aneurysmal wall. Local assessment of wall vulnerability may provide better risk of rupture predictions.

Geometric analysis of ruptured and nonruptured abdominal aortic aneurysms

OBJECTIVE

The objective of this study was to use parameters to determine the geometric differences between ruptured abdominal aortic aneurysms (AAAs) and nonruptured AAAs.

METHODS

Computed tomography data of 38 ruptured AAAs and 215 electively repaired (nonruptured) AAAs were collected from multiple institutes. We compared the ruptured AAA group and nonruptured AAA group with 1:1 matching by using the Mahalanobis distance, which was calculated using the patient's age, sex, and AAA diameter. We selected the longitudinal AAA image in multiplanar reconstruction view, placed a hypothetical ellipse on the aneurysm's protruded curve, and placed a circle on the portion connecting the aneurysm and the aorta. We then measured the aspect ratio (the vertical diameter divided by the horizontal diameter) and fillet radius (the radius of arc).

RESULTS

The aspect ratio was significantly lower in the ruptured group than in the nonruptured group (2.02 ± 0.53 vs 2.60 ± 1.02; P = .002), as was the fillet radius (0.28 ± 0.18 vs 0.81 ± 0.44; P < .001). Receiver operating characteristic analysis revealed that the area under the curve of the aspect ratio was 0.688, and the optimal cutoff point was 2.23, with sensitivity and specificity of 0.55 and 0.76, respectively. The area under the curve of the fillet radius was 0.933, and the optimal cutoff was 0.347, with sensitivity and specificity of 0.97 and 0.87, respectively.

CONCLUSIONS

The geometric analysis performed in this study revealed that ruptured AAAs had a smaller fillet radius and smaller aspect ratio than nonruptured AAAs did.

Cilostazol Attenuates Angiotensin II-Induced Abdominal Aortic Aneurysms but Not Atherosclerosis in Apolipoprotein E-Deficient Mice

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a permanent dilation of the abdominal aorta associated with rupture, which frequently results in fatal consequences. AAA tissue is commonly characterized by localized structural deterioration accompanied with inflammation and profound accumulation of leukocytes, although the specific function of these cells is unknown. Cilostazol, a phosphodiesterase III inhibitor, is commonly used for patients with peripheral vascular disease or stroke because of its anti-platelet aggregation effect and anti-inflammatory effect, which is vasoprotective effect. In this study, we evaluated the effects of cilostazol on angiotensin II-induced AAA formation.

APPROACH AND RESULTS

Male apolipoprotein E-deficient mice were fed either normal diet or a diet containing cilostazol (0.1% wt/wt). After 1 week of diet consumption, mice were infused with angiotensin II (1000 ng/kg per minute) for 4 weeks. Angiotensin II infusion increased maximal diameters of abdominal aortas, whereas cilostazol administration significantly attenuated dilatation of abdominal aortas, thereby, reducing AAA incidence. Cilostazol also reduced macrophage accumulation, matrix metalloproteinases activation, and inflammatory gene expression in the aortic media. In cultured vascular endothelial cells, cilostazol reduced expression of inflammatory cytokines and adhesive molecules through activation of the cAMP-PKA (protein kinase A) pathway.

CONCLUSIONS

Cilostazol attenuated angiotensin II-induced AAA formation by its anti-inflammatory effect through phosphodiesterase III inhibition in the aortic wall. Cilostazol may be a promising new therapeutic option for AAAs.

Inflammatory Mechanisms of Cardiovascular Remodeling

Inflammation and fibrosis play an important role in the development and progression of cardiovascular diseases. Acute coronary syndrome (ACS) is caused by rupture of inflamed atherosclerotic plaque and subsequent atherothrombosis. Recent studies have shown that inflammatory markers such as C-reactive protein (CRP) can predict ACS development and have demonstrated the effectiveness of new therapeutic approaches targeting inflammation. Studies have also shown that an enhanced inflammatory response after myocardial infarction (MI) is associated with cardiac rupture, ventricular aneurysm formation, and exacerbation of left ventricular (LV) remodeling. Inflammation is a physiological reaction in which fibrosis is induced to facilitate the healing of tissue damage. However, when an excessive inflammatory response consisting mainly of monocytes/macrophages is induced by various factors, impaired reparative fibrosis and resulting pathological remodeling processes may occur. A similar phenomenon is observed in abdominal aortic aneurysm (AAA) expansion. In contrast, myocardial diseases such as inflammatory dilated cardiomyopathy (DCMI) and valvular diseases such as aortic valve stenosis (AS) are characterized by chronic inflammation mediated mainly by T lymphocytes and the associated enhancement of reactive fibrosis. Thus, inflammation can take 2 paths (the inhibition or promotion of fibrosis), depending on the phase of inflammation, inducing pathological cardiovascular remodeling. Elucidation of the regulatory mechanisms of inflammation and fibrosis will contribute to the development of new therapeutic approaches for cardiovascular diseases.