Intraluminal thrombus predicts rupture of an abdominal aortic aneurysm

The role of long non-coding RNA in abdominal aortic aneurysm

The abdominal aortic aneurysm (AAA) is characterized by segmental expansion of the abdominal aorta and a high mortality rate. The characteristics of AAA suggest that apoptosis of smooth muscle cells, the production of reactive oxygen species, and inflammation are potential pathways for the formation and development of AAA. Long non-coding RNA (lncRNA) is becoming a new and essential regulator of gene expression. Researchers and physicians are focusing on these lncRNAs to use them as clinical biomarkers and new treatment targets for AAAs. LncRNA studies are beginning to emerge, suggesting that they may play a significant but yet unidentified role in vascular physiology and disease. This review examines the role of lncRNA and their target genes in AAA to increase our understanding of the disease’s onset and progression, which is crucial for developing potential AAA therapies.

Shear-driven modelling of thrombus formation in type B aortic dissection

Background: Type B aortic dissection (TBAD) is a dangerous pathological condition with a high mortality rate. TBAD is initiated by an intimal tear that allows blood to flow between the aortic wall layers, causing them to separate. As a result, alongside the original aorta (true lumen), a false lumen (FL) develops. TBAD compromises the whole cardiovascular system, in the worst case resulting in complete aortic rupture. Clinical studies have shown that dilation and rupture of the FL are related to the failure of the FL to thrombose. Complete FL thrombosis has been found to improve the clinical outcomes of patients with chronic TBAD and is the desired outcome of any treatment. Partial FL thrombosis has been associated with late dissection-related deaths and the requirement for re-intervention, thus the level of FL thrombosis is dominant in classifying the risk of TBAD patients. Therefore, it is important to investigate and understand under which conditions complete thrombosis of the FL occurs.

Method: Local FL hemodynamics play an essential role in thrombus formation and growth. In this study, we developed a simplified phenomenological model to predict FL thrombosis in TBAD under physiological flow conditions. Based on an existing shear-driven thrombosis model, a comprehensive model reduction study was performed to improve computational efficiency. The reduced model has been implemented in Ansys CFX and applied to a TBAD case following thoracic endovascular aortic repair (TEVAR) to test the model. Predicted thrombus formation based on post-TEVAR geometry at 1-month was compared to actual thrombus formation observed on a 3-year follow-up CT scan.

Results: The predicted FL status is in excellent agreement with the 3-year follow-up scan, both in terms of thrombus location and total volume, thus validating the new model. The computational cost of the new model is significantly lower than the previous thrombus model, with an approximate 65% reduction in computational time. Such improvement means the new model is a significant step towards clinical applicability.

Conclusion: The thrombosis model developed in this study is accurate and efficient at predicting FL thrombosis based on patient-specific data, and may assist clinicians in choosing individualized treatments in the future.

The role of phosphoinositide 3-kinases in immune-inflammatory responses: potential therapeutic targets for abdominal aortic aneurysm

The pathogenesis of abdominal aortic aneurysm (AAA) includes inflammatory responses, matrix metalloproteinases (MMPs) degradation, VSMC apoptosis, oxidative stress, and angiogenesis, among which the inflammatory response plays a key role. At present, surgery is the only curing treatment, and no effective drug can delay AAA progression in clinical practice. Therefore, searching for a signaling pathway related to the immune-inflammatory response is an essential direction for developing drugs targeting AAA. Recent studies have confirmed that the PI3K family plays an important role in many inflammatory diseases and is involved in regulating various cellular functions, especially in the immune-inflammatory response. This review focuses on the role of each isoform of PI3K in each stage of AAA immune-inflammatory response, making available explorations for a deeper understanding of the mechanism of inflammation and immune response during the formation and development of AAA.

The Detrimental Role of Intraluminal Thrombus Outweighs Protective Advantage in Abdominal Aortic Aneurysm Pathogenesis: The Implications for the Anti-Platelet Therapy

Abdominal aortic aneurysm (AAA) is a common cardiovascular disease resulting in morbidity and mortality in older adults due to rupture. Currently, AAA treatment relies entirely on invasive surgical treatments, including open repair and endovascular, which carry risks for small aneurysms (diameter < 55 mm). There is an increasing need for the development of pharmacological intervention for early AAA. Over the last decade, it has been increasingly recognized that intraluminal thrombus (ILT) is involved in the growth, remodeling, and rupture of AAA. ILT has been described as having both biomechanically protective and biochemically destructive properties. Platelets are the second most abundant cells in blood circulation and play an integral role in the formation, expansion, and proteolytic activity of ILT. However, the role of platelets in the ILT-potentiated AAA progression/rupture remains unclear. Researchers are seeking pharmaceutical treatment strategies (e.g., anti-thrombotic/anti-platelet therapies) to prevent ILT formation or expansion in early AAA. In this review, we mainly focus on the following: (a) the formation/deposition of ILT in the progression of AAA; (b) the dual role of ILT in the progression of AAA (protective or detrimental); (c) the function of platelet activity in ILT formation; (d) the application of anti-platelet drugs in AAA. Herein, we present challenges and future work, which may motivate researchers to better explain the potential role of ILT in the pathogenesis of AAA and develop anti-platelet drugs for early AAA.

Endothelial Dysfunction in the Pathogenesis of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA), defined as a focal dilation of the abdominal aorta beyond 50% of its normal diameter, is a common and potentially life-threatening vascular disease. The molecular and cellular mechanisms underlying AAA pathogenesis remain unclear. Healthy endothelial cells (ECs) play a critical role in maintaining vascular homeostasis by regulating vascular tone and maintaining an anti-inflammatory, anti-thrombotic local environment. Increasing evidence indicates that endothelial dysfunction is an early pathologic event in AAA formation, contributing to both oxidative stress and inflammation in the degenerating arterial wall. Recent studies utilizing single-cell RNA sequencing revealed heterogeneous EC sub-populations, as determined by their transcriptional profiles, in aortic aneurysm tissue. This review summarizes recent findings, including clinical evidence of endothelial dysfunction in AAA, the impact of biomechanical stress on EC in AAA, the role of endothelial nitric oxide synthase (eNOS) uncoupling in AAA, and EC heterogeneity in AAA. These studies help to improve our understanding of AAA pathogenesis and ultimately may lead to the generation of EC-targeted therapeutics to treat or prevent this deadly disease.

The effect of ticagrelor on growth of small abdominal aortic aneurysms-a randomized controlled trial

AIMS

To evaluate if ticagrelor, an effective platelet inhibitor without known non-responders, could inhibit growth of small abdominal aortic aneurysms (AAAs).

METHODS AND RESULTS

In this multi-centre randomized controlled trial, double-blinded for ticagrelor and placebo, acetylic salicylic acid naïve patients with AAA and with a maximum aortic diameter 35-49 mm were included. The primary outcome was mean reduction in log-transformed AAA volume growth rate (%) measured with magnetic resonance imaging (MRI) at 12 months compared with baseline. Secondary outcomes include AAA-diameter growth rate and intraluminal thrombus (ILT) volume enlargement rate. A total of 144 patients from eight Swedish centres were randomized (72 in each group). MRI AAA volume increase was 9.1% for the ticagrelor group and 7.5% for the placebo group (P = 0.205) based on intention-to-treat analysis, and 8.5% vs. 7.4% in a per-protocol analysis (P = 0.372). MRI diameter change was 2.5 mm vs. 1.8 mm (P = 0.113), US diameter change 2.3 mm vs. 2.2 mm (P = 0.778), and ILT volume change 12.9% vs. 10.4% (P = 0.590).

CONCLUSION

In this RCT, platelet inhibition with ticagrelor did not reduce growth of small AAAs. Whether the ILT has an important pathophysiological role for AAA growth cannot be determined based on this study due to the observed lack of thrombus modulating effect of ticagrelor.

TRIAL REGISTRATION

The TicAAA trial is registered at the US National Institutes of Health (ClinicalTrials.gov) #NCT02070653.

Aortic aneurysm screening using duplex ultrasound: Choosing wisely who to examine

The noninvasive vascular laboratory plays a critical role in screening patients at risk for development of abdominal aortic aneurysm (AAA). One-time duplex ultrasound screening reduces aneurysm-related mortality due to rupture and is cost-effective. Population screening based on AAA risk factors is recommended, as it allows for proactive, elective repair of aneurysms at risk for rupture, and surveillance of smaller aneurysms for enlargement. Utilization of societal screening guidelines, such as those published by the Society for Vascular Surgery, can be employed by vascular laboratories to justify individual patient screening, aid primary care physicians to refer patients for testing, and encourage integrated medical health care systems to build prompts in patient electronic health records to ensure compliance with a AAA screening program. Risk factors for developing AAA, that is, age older than 65 years, male sex, family history, and a smoking history of >100 cigarettes, should be used to recommend patient screening, including for women and other elderly (older than 75 years) patients who fall outside of professional societal guidelines.

Antithrombotic therapy in abdominal aortic aneurysm: beneficial or detrimental?

Abdominal aortic aneurysm (AAA) is a degenerative vascular pathology resulting in significant morbidity and mortality in older adults due to rupture and sudden death. Despite 150 000 new cases and nearly 15 000 deaths annually, the only approved treatment of AAA is surgical or endovascular intervention when the risk for aortic rupture is increased. The goal of the scientific community is to develop novel pharmaceutical treatment strategies to reduce the need for surgical intervention. Because most clinically relevant AAAs contain a complex structure of fibrin, inflammatory cells, platelets, and red blood cells in the aneurysmal sac known as an intraluminal thrombus (ILT), antithrombotic therapies have emerged as potential pharmaceutical agents for the treatment of AAA progression. However, the efficacy of these treatments has not been shown, and the effects of shrinking the ILT may be as detrimental as they are beneficial. This review discusses the prospect of anticoagulant and antiplatelet (termed collectively as antithrombotic) therapies in AAA. Herein, we discuss the role of the coagulation cascade and platelet activation in human and animal models of AAA, the composition of ILT in AAA, a possible role of the ILT in aneurysm stabilization, and the implications of antithrombotic drugs in AAA treatment.

Mural destabilization after aneurysm treatment with a flow-diverting device: a report of two cases

BACKGROUND

Flow-diverting stents have demonstrated great promise for the treatment of cerebral aneurysms; however, clinical experience with the devices remains very preliminary. We present two cases of spontaneous delayed complications-one fatal aneurysm rupture and one symptomatic increase in aneurysm volume-following the treatment of intradural aneurysms with the Pipeline Embolization Device (PED).

PRESENTATION/INTERVENTION

Two patients with unruptured, intradural aneurysms of the carotid artery underwent uneventful treatment with the PED (eV3, Irvine, California, USA). One patient, with a giant aneurysm of the carotid terminus, experienced worsening headache 5 days after the procedure and ultimately collapsed and became unresponsive. CT of the head demonstrated acute subarachnoid and intraventricular hemorrhage. The patient died the following day. A second patient with a large left posterior communicating artery aneurysm presented with progressive memory loss 3 months after PED reconstruction of the carotid artery. Although serial CT angiograms showed progressive thrombosis of the aneurysm to near-complete occlusion, MR of the brain demonstrated marked interval growth of the collective aneurysm-intra-aneurysmal thrombus mass with extensive edema throughout the adjacent left temporal lobe.

CONCLUSIONS

Flow-diverting devices have demonstrated tremendous promise for the treatment of complex, unruptured cerebral aneurysms. However, experience with this novel approach to aneurysm treatment is preliminary and the consequences of its application within the cerebrovasculature remain incompletely defined. Mural destabilization resulting in delayed, spontaneous, aneurysm growth and/or rupture may occur in the days to weeks following the application of flow-diverting devices to treat previously unruptured intracranial aneurysms. A better understanding of the incidence and etiology of these complications is essential for this technology to be optimally applied.

FXa inhibition by rivaroxaban modifies mechanisms associated with the pathogenesis of human abdominal aortic aneurysms

AIMS

To evaluate if rivaroxaban, an oral factor Xa (FXa) inhibitor, could modify the expression in vitro of inflammatory and oxidative stress biomarkers in abdominal aortic aneurysmal (AAA) sites showing intraluminal thrombus.

METHODS

AAA sites with intraluminal mural thrombus were obtained from six patients undergoing elective AAA repair. In addition, control abdominal aortic samples were obtained from six organ donors. AAA sites were incubated in the presence and absence of 50 nmol l^-1 rivaroxaban.

RESULTS

AAA sites showing thrombus demonstrated higher content of FXa than control. Interleukin-6 levels released from AAA [Control: median: 23.45 (interquartile range: 16.17-37.15) vs. AAA: median: 153.07 (interquartile range: 100.80-210.69) pg ml^-1  mg tissue^-1 , P < 0.05] and the expression levels of nitric oxide synthase 2 were significantly higher in AAA than in control. The protein expression level of NADPH oxidase subunits gp67-and gp91-phox, but did not gp47-phox, were also significantly higher in the AAA sites than in control. Addition of rivaroxaban to AAA sites explants significantly reduced the release of interleukin-6 [median: 51.61 (interquartile range: 30.87-74.03) pg ml^-1  mg tissue^-1 , P < 0.05 with respect to AAA alone] and the content of nitric oxide synthase 2, gp67 and gp91-phox NADPH subunits. The content of matrix metallopeptidase 9 was significantly higher in the AAA sites as compared to control. Rivaroxaban also reduced matrix metallopeptidase 9 content in AAA sites to similar levels to control.

CONCLUSIONS

FXa inhibition by rivaroxaban exerted anti-inflammatory and antioxidative stress properties in human AAA sites, suggesting a role of FXa in these mechanisms associated with the pathogenesis of AAA.

Rupture After Bypass and Distal Occlusion of Giant Anterior Circulation Aneurysms

BACKGROUND

Giant aneurysms are very high-risk lesions both in terms of natural history and treatment. Bypass with distal occlusion is thought to be a safe treatment option for these aneurysms. Here, we report 2 cases of aneurysm rupture after bypass and distal occlusion, review the literature, and discuss the possible underlying mechanisms, in the hopes of influencing treatment planning and averting such complications in the future.

CASE DESCRIPTION

Two patients successfully underwent surgical treatment of a giant anterior circulation aneurysm via bypass and distal vessel occlusion. In each case, there was sudden thrombosis of the aneurysm without any sign of rupture at the time of surgery. Both patients then experienced delayed postoperative rupture with devastating consequences.

CONCLUSIONS

Aneurysm rupture can occur after bypass and distal occlusion, despite initial appearances of intraoperative stability. We suggest that the mechanisms are not a simple pressure within the dome and may be due to rapid thrombosis with subsequent aneurysm wall destabilization or stretching and capacitance causing persistent filling. When possible, it seems that complete trapping or proximal occlusion may be preferable to distal occlusion for these giant aneurysms. The optimal management of these highly morbid lesions remains to be determined.

Quantitative Aortic Distensibility Measurement Using CT in Patients with Abdominal Aortic Aneurysm: Reproducibility and Clinical Relevance

Purpose. To investigate the reproducibility of aortic distensibility (D) measurement using CT and assess its clinical relevance in patients with infrarenal abdominal aortic aneurysm (AAA). Methods. 54 patients with infrarenal abdominal aortic aneurysm were studied to determine their distensibility by using 64-MDCT. Aortic cross-sectional area changes were determined at two positions of the aorta, immediately below the lowest renal artery (level 1.) and at the level of its maximal diameter (level 2.) by semiautomatic segmentation. Measurement reproducibility was assessed using intraclass correlation coefficient (ICC) and Bland-Altman analyses. Stepwise multiple regression analysis was performed to assess linear associations between aortic D and anthropometric and biochemical parameters. Results. A mean distensibility of D_{level  1.} = (1.05 ± 0.22) × 10⁻⁵  Pa⁻¹ and D_{level  2.} = (0.49 ± 0.18) × 10⁻⁵  Pa⁻¹ was found. ICC proved excellent consistency between readers over two locations: 0.92 for intraobserver and 0.89 for interobserver difference in level 1. and 0.85 and 0.79 in level 2. Multivariate analysis of all these variables showed sac distensibility to be independently related (R² = 0.68) to BMI, diastolic blood pressure, and AAA diameter. Conclusions. Aortic distensibility measurement in patients with AAA demonstrated high inter- and intraobserver agreement and may be valuable when choosing the optimal dimensions graft for AAA before endovascular aneurysm repair.

Intraluminal Thrombus Enhances Proteolysis in Abdominal Aortic Aneurysms

This study examined whether intraluminal thrombus in abdominal aortic aneurysms (AAAs) is a source of fibrinolytic activity and proteolysis that could weaken the aneurysm wall. Plasmin, tissue plasminogen activator (tPA), and urokinase plasminogen activator (uPA) activity, plasminogen activator inhibitor 1 (PAI-1), and α2-antiplasmin (α2AP) antigen were measured in the AAA wall and juxtamural and luminal aspects of intraluminal thrombus in 18 patients. The aneurysm wall contained 100-fold higher tPA activity (1.06 ± 0.34 [standard error of measurement] U/mg soluble protein) compared with juxtamural thrombus (JMT) (0.011 ± 0.001 ) and luminal thrombus (LT) (0.01 ± 0.001) ( p < .00001) and over 6-fold higher uPA activity (29.3 ± 3.4 IU/mg compared with the JMT (4.3 ± 2.4, p = .00024) and LT (7.9 ± 1.76, p = .0005). The LT had significantly lower levels of PAI-1 (1.26 ± 0.34 ng/mg) than the AAA wall (2.08 ± 0.51, p = .04) and the JMT (3.94 ± 0.85, p = .007). The levels of α2AP in the wall (19.4 ± 3.1 ng/mg) were lower than in the JMT or LT (43.0 ± 7.9 ng/mg, p = .013, and 47.6 ± 6.0 ng/mg, p = .002, respectively). There was no significant difference, however, in plasmin activity among the AAA wall, JMT, and LT. There were significant amounts of latent gelatinase B (matrix metalloproteinase [MMP]-9) in the AAA, JMT, and LT. Mean levels of activated MMP-9 activity were similar in the AAA, JMT, and LT. Plasmin activation of MMPs at the interface between intraluminal thrombus and the aneurysm wall may enhance proteolysis and accelerate aneurysm expansion.

The - Not So - Solid 5.5 cm Threshold for Abdominal Aortic Aneurysm Repair: Facts, Misinterpretations, and Future Directions

Abdominal aortic aneurysms (AAAs) represent a focal dilation of the aorta exceeding 1.5 times its normal diameter. It is reported that 4-8% of men and 0.5-1% of women above 50 years of age bear an AAA. Rupture represents the most disastrous complication of aneurysmal disease that is accompanied by an overall mortality of 80%. Autopsy data have shown that nearly 13% of AAAs with a maximum diameter ≤5 cm were ruptured and 60% of the AAAs >5 cm in diameter never ruptured. It is therefore obvious that the "maximum diameter criterion," as a single parameter that fits all patients, is obsolete. Investigators have begun a search for more reliable rupture risk markers for AAA expansion, such as the level and change of peak wall stress or AAA geometry. Furthermore, it is becoming more and more evident that intraluminal thrombus (ILT), which is present in 75% of all AAAs, affects AAA features and promotes their expansion. Though these hemodynamic properties of AAAs are significant and seem to better describe rupture risk, they are in need of specialized equipment and software and demand time for processing making them difficult in use and unattractive to clinicians in everyday practice. In the search for the addition of other risk factors or user-friendly tools, which may predict AAA expansion and rupture, the use of the asymmetrical ILT deposition index seems appealing since it has been reported to identify AAAs that may have an increased or decreased growth rate.

Platelet Inhibitors Reduce Rupture in a Mouse Model of Established Abdominal Aortic Aneurysm

OBJECTIVE

Rupture of abdominal aortic aneurysms causes a high morbidity and mortality in the elderly population. Platelet-rich thrombi form on the surface of aneurysms and may contribute to disease progression. In this study, we used a pharmacological approach to examine a role of platelets in established aneurysms induced by angiotensin II infusion into hypercholesterolemic mice.

APPROACH AND RESULTS

Administration of the platelet inhibitors aspirin or clopidogrel bisulfate to established abdominal aortic aneurysms dramatically reduced rupture. These platelet inhibitors reduced abdominal aortic platelet and macrophage recruitment resulting in decreased active matrix metalloproteinase-2 and matrix metalloproteinase-9. Platelet inhibitors also resulted in reduced plasma concentrations of platelet factor 4, cytokines, and components of the plasminogen activation system in mice. To determine the validity of these findings in human subjects, a cohort of aneurysm patients were retrospectively analyzed using developed and validated algorithms in the electronic medical record database at Vanderbilt University. Similar to mice, administration of aspirin or P2Y12 inhibitors was associated with reduced death among patients with abdominal aortic aneurysm.

CONCLUSIONS

These results suggest that platelets contribute to abdominal aortic aneurysm progression and rupture.

Effect of Intraluminal Thrombus Asymmetrical Deposition on Abdominal Aortic Aneurysm Growth Rate

Purpose: To determine the relationship between asymmetrical intraluminal thrombus (ILT) deposition in abdominal aortic aneurysm (AAA) and growth rate and to explore its biomechanical perspective. Methods: Thirty-four patients with AAA underwent at least 2 computed tomography scans during surveillance. The volumes of the AAA (VAAA) and thrombus (VILT) and the maximum thrombus thickness (ILTthick) were computed. Thrombus distribution was evaluated by introducing the asymmetrical thrombus deposition index (ATDI), with positive and negative values (–1<ATDI<1) associated with anterior and posterior ILT deposition, respectively. Finite element analysis was applied to estimate wall stress. Aneurysms were divided into high and low growth rate groups based on the cohort’s median growth rate, and the abovementioned parameters were compared between groups. Results: Most AAAs had asymmetrical anterior thrombus deposition. The high and low growth rate groups did not present significant differences in maximum diameter, VAAA, VILT, or maximum ILTthick. However, the high growth rate group had significantly higher ATDI (p=0.02). The ATDI<0 group (posterior ILT distribution) presented a significantly lower median growth rate compared to that of ATDI≥0 group (anterior or symmetrical ILT deposition; p=0.029). The specificity of an ATDI<0 criterion for identifying AAAs with a growth rate below the cohort median was 89%. The ATDI<0 group had a significantly lower posterior maximum wall stress compared with that of the ATDI≥0 group (p=0.03). Overall peak wall stress did not differ between groups. Conclusion: Posterior thrombus deposition in AAAs is associated with significantly lower growth rate and lower posterior maximum wall stress compared with that of AAAs with anterior thrombus deposition and could potentially indicate a lower rupture risk.

Finite element analysis in asymptomatic, symptomatic, and ruptured abdominal aortic aneurysms: in search of new rupture risk predictors

OBJECTIVES

To compare biomechanical rupture risk parameters of asymptomatic, symptomatic and ruptured abdominal aortic aneurysms (AAA) using finite element analysis (FEA).

STUDY DESIGN

Retrospective biomechanical single center analysis of asymptomatic, symptomatic, and ruptured AAAs. Comparison of biomechanical parameters from FEA.

MATERIALS AND METHODS

From 2011 to 2013 computed tomography angiography (CTA) data from 30 asymptomatic, 15 symptomatic, and 15 ruptured AAAs were collected consecutively. FEA was performed according to the successive steps of AAA vessel reconstruction, segmentation and finite element computation. Biomechanical parameters Peak Wall Rupture Risk Index (PWRI), Peak Wall Stress (PWS), and Rupture Risk Equivalent Diameter (RRED) were compared among the three subgroups.

RESULTS

PWRI differentiated between asymptomatic and symptomatic AAAs (p < .0004) better than PWS (p < .1453). PWRI-dependent RRED was higher in the symptomatic subgroup compared with the asymptomatic subgroup (p < .0004). Maximum AAA external diameters were comparable between the two groups (p < .1355). Ruptured AAAs showed the highest values for external diameter, total intraluminal thrombus volume, PWS, RRED, and PWRI compared with asymptomatic and symptomatic AAAs. In contrast with symptomatic and ruptured AAAs, none of the asymptomatic patients had a PWRI value >1.0. This threshold value might identify patients at imminent risk of rupture.

CONCLUSIONS

From different FEA derived parameters, PWRI distinguishes most precisely between asymptomatic and symptomatic AAAs. If elevated, this value may represent a negative prognostic factor for asymptomatic AAAs.

Antiphospholipid antibodies predict progression of abdominal aortic aneurysms

Antiphospholipid antibodies (aPLs) frequently occur in autoimmune and cardiovascular diseases and correlate with a worse clinical outcome. In the present study, we evaluated the association between antiphospholipid antibodies (aPLs), markers of inflammation, disease progression and the presence of an intra-aneurysmal thrombus in abdominal aortic aneurysm (AAA) patients.

APLs ELISAs were performed in frozen serum samples of 96 consecutive AAA patients and 48 healthy controls yielding positive test results in 13 patients (13.5%) and 3 controls (6.3%; n.s.). Nine of the 13 aPL-positive AAA patients underwent a second antibody testing >12 weeks apart revealing a positive result in 6 cases. APL-positive patients had increased levels of inflammatory markers compared to aPL-negative patients. Disease progression was defined as an increase of the AAA diameter >0.5 cm/year measured by sonography. Follow-up was performed in 69 patients identifying 41 (59.4%) patients with progressive disease. Performing multipredictor logistic regression analysis adjusting for classical AAA risk factors as confounders, the presence of aPLs at baseline revealed an odds ratio of 9.4 (95% CI 1.0–86.8, p = 0.049) to predict AAA progression. Fifty-five patients underwent a computed tomography in addition to ultrasound assessment indicating intra-aneurysmal thrombus formation in 82.3%. Median thrombus volume was 46.7 cm³ (1.9–377.5). AAA diameter correlated with the size of the intra-aneurysmal thrombus (corr_coeff = 0.721, p<0.001), however neither the presence nor the size of the intra-aneurysmal thrombus were related to the presence of aPLs.

In conclusion, the presence of aPLs is associated with elevated levels of inflammatory markers and is an independent predictor of progressive disease in AAA patients.

Lymphangiogenesis in abdominal aortic aneurysm

Background

Ongoing angiogenesis is implicated in the inflammatory environment that characterizes abdominal aortic aneurysm (AAA). Although lymphangiogenesis has been associated with chronic inflammatory conditions, it has yet to be demonstrated in AAA. The aim was to determine the presence of lymphangiogenesis and to delineate the relationship between inflammation and neovascularization in AAA tissue.

Methods

AAA samples and preoperative computed tomography images were obtained from patients undergoing elective AAA repair. Control samples were age-matched abdominal aortic tissue. Specific immunostains for blood vessels (CD31, CD105), lymphatic vessels (D2-40), vascular endothelial growth factor (VEGF) A and VEGF receptor (VEGFR) 3 allowed characterization and quantitation of vasculature.

Results

The AAA wall contained high levels of inflammatory infiltrate; microvascular densities of blood (P &lt; 0·001) and lymphatic (P = 0·003) vessels were significantly increased in AAA samples compared with controls. Maximal AAA vascularity was observed in inflammatory areas, with vessels that stained positively for CD31 (ρ = 0·625, P = 0·017), CD105 (ρ = 0·692, P = 0·009) and D2-40 (ρ = 0·675, P = 0·008) correlating positively with the extent of inflammation. Increased VEGFR-3 and VEGF-A expression was also evident within inflammatory AAA areas.

Conclusion

These findings demonstrated lymphatic vessel involvement in end-stage AAA disease, which was associated with the degree of inflammation, and confirmed the involvement of neovascularization.

Autologous mesenchymal stem cell endografting in experimental cerebrovascular aneurysms

INTRODUCTION

Coiling is the gold standard for the treatment of intracranial aneurysms. However, some issues associated with endovascular treatment limit its long-term efficiency. Recanalization with coil compaction is certainly the most important. New approaches may be considered to promote thrombus colonization by mesenchymal cells and aneurysm healing. In the present study, we have percutaneously delivered autologous bone marrow mesenchymal stem cells (BMSCs) to an elastase-induced rabbit carotid aneurysm model in vivo.

METHODS

Autologous mesenchymatous stem cells were obtained after femoral puncture and bone marrow aspiration. After 2 weeks of in vitro cell culture, five million BMSCs were grafted in the carotid aneurysm using an endovascular approach.

RESULTS

We demonstrated the feasibility of in vivo percutaneous seeding of autologous BMSCs in the aneurysm by positive Hoechst fluorostaining. Two weeks later, conventional angiography showed an increase in median aneurysmal surface in the sham group, whereas this surface was decreased in the group treated with BMSCs, +28.4 versus -26.4 %, respectively (p = 0.01). BMSC seeding resulted in intimal hyperplasia with cell colonization and disappearance of the thrombus.

CONCLUSION

In conclusion, percutaneous seeding of BMSCs may colonize and heal the arterial wall thus limiting aneurysm expansion.

Clopidogrel, a platelet P2Y12 receptor inhibitor, reduces vascular inflammation and angiotensin II induced-abdominal aortic aneurysm progression

Medial degeneration and inflammation are features of abdominal aortic aneurysms (AAAs). However, the early inflammatory event initiating aneurysm formation remains to be identified. Activated platelets release abundant proinflammatory cytokines and are involved in initial inflammation in various vascular diseases. We investigated the role of platelets in progression of AAA in vivo and in vitro. Histological studies of tissues of patients with AAA revealed that the number of platelets was increased in aneurysm sites along with the increased infiltration of T lymphocytes and augmented angiogenesis. In a murine model of AAA, apolipoprotein E-knockout mice infused with 1,000 ng/kg/min angiotensin II, treatment with clopidogrel, an inhibitor of platelets, significantly suppressed aneurysm formation (47% decrease, P<0.05). The clopidogrel also suppressed changes in aortic expansion, elastic lamina degradation and inflammatory cytokine expression. Moreover, the infiltration of macrophages and production of matrix metalloproteinases (MMPs) were also significantly reduced by clopidogrel treatment. In vitro incubation of macrophages with isolated platelets stimulated MMP activity by 45%. These results demonstrate a critical role for platelets in vascular inflammation and AAA progression.

Intraluminal abdominal aortic aneurysm thrombus is associated with disruption of wall integrity

OBJECTIVE

An association of intraluminal thrombus (ILT) with abdominal aortic aneurysm (AAA) growth has been suggested. Previous in vitro experiments have demonstrated that aneurysm-associated thrombus may secrete proteolytic enzymes and may develop local hypoxia that might lead to the formation of tissue-damaging reactive oxygen species. In this study, we assessed the hypothesis that ventral ILT thickness is associated with markers of proteolysis and with lipid oxidation in the underlying AAA vessel wall.

METHODS

Ventral AAA tissue was collected from asymptomatic patients at the site of maximal diameter during open aneurysm repair. Segments were divided, one part for biochemical measurements and one for histologic analyses. We measured total cathepsin B, cathepsin S levels, and matrix metalloproteinase (MMP)-2 and MMP-9 activity. Myeloperoxidase and thiobarbituric acid reactive substances were determined as measures of lipid oxidation. Histologic segments were analyzed semiquantitatively for the presence of collagen, elastin, vascular smooth muscle cells (VSMCs), and inflammatory cells. Preoperative computed tomography angiography scans of 83 consecutive patients were analyzed. A three-dimensional reconstruction was obtained, and a center lumen line of the aorta was constructed. Ventral ILT thickness was measured in the anteroposterior direction at the level of maximal aneurysm diameter on the orthogonal slices.

RESULTS

Ventral ILT thickness was positively correlated with aortic diameter (r=0.25; P=.02) and with MMP-2 levels (r=0.27; P=.02). No biochemical correlations were observed with MMP-9 activity or cathepsin B and S expression. No correlation between ventral ILT thickness and myeloperoxidase or thiobarbituric acid reactive substances was observed. Ventral ILT thickness was negatively correlated with VSMCs (no staining, 18.5 [interquartile range, 12.0-25.5] mm; minor, 17.6 [10.7-22.1] mm; moderate, 14.5 [4.6-21.7] mm; and heavy, 8.0 [0.0-12.3] mm, respectively; P=.01) and the amount of elastin (no staining, 18.6 [12.2-30.0] mm; minor, 16.5 [9.0-22.1] mm; moderate, 11.7 [2.5-15.3] mm; and heavy 7.7 [0.0-7.7] mm, respectively; P=.01) in the medial aortic layer.

CONCLUSIONS

ILT thickness appeared to be associated with VSMCs apoptosis and elastin degradation and was positively associated with MMP-2 concentrations in the underlying wall. This suggests that ILT thickness affects AAA wall stability and might contribute to AAA growth and rupture. ILT thickness was not correlated with markers of lipid oxidation.

Local inflammation is associated with aortic thrombus formation in abdominal aortic aneurysms. Relationship to clinical risk factors

Intraluminal thrombus formation in aortic abdominal aneurysms (AAA) is associated with adverse clinical prognosis. Interplay between coagulation and inflammation, characterised by leukocyte infiltration and cytokine production, has been implicated in AAA thrombus formation. We studied leukocyte (CD45+) content by flow cytometry in AAA thrombi from 27 patients undergoing surgical repair. Luminal parts of thrombi were leukocyte-rich, while abluminal segments showed low leukocyte content. CD66b+ granulocytes were the most prevalent, but their content was similar to blood. Monocytes (CD14+) and T cells (CD3+) were also abundant, while content of B lymphocytes (CD19+) and NK cells (CD56+CD16+) were low. Thrombi showed comparable content of CD14highCD16- monocytes and lower CD14highCD16+ and CD14dimCD16+, than blood. Monocytes were activated with high CD11b, CD11c and HLA-DR expression. Total T cell content was decreased in AAA thrombus compared to peripheral blood but CD8 and CD3+CD4-CD8- (double negative T cell) contents were increased in thrombi. CD4+ cells were lower but highly activated (high CD69, CD25 and HLA-DR). No differences in T regulatory (CD4+CD25+FoxP3+) cell or pro-atherogenic CD4+CD28null lymphocyte content were observed between thrombi and blood. Thrombus T cells expressed high levels of CCR5 receptor for chemokine RANTES, commonly released from activated platelets. Leukocyte or T cell content in thrombi was not correlated with aneurysm size. However, CD3+ content was significantly associated with smoking in multivariate analysis taking into account major risk factors for atherosclerosis. In conclusion, intraluminal AAA thrombi are highly inflamed, predominantly with granulocytes, CD14highCD16- monocytes and activated T lymphocytes. Smoking is associated with T cell infiltration in AAA intraluminal thrombi.

Investigation on regional variation of intraluminal thrombus: A mechanical and histological study

The abdominal aortic aneurysm is an irreversible dilatation of the artery and when this pathology is localized in the aortic district, the intraluminal thrombus (ILT) is present in approximately 75% of cases. The rupture risk of AAA is thought to be associated with increased levels of wall stress. In recent decades, finite element analysis (FEA) have been used to predict wall stresses in a patient-specific, noninvasive manner. However, FE simulations are mainly based on homogeneous behavior for ILT material. The purpose of this work was to investigate the biomechanical behavior of ILT and to derive an appropriate constitutive relation for ventral and posterior regions. Uniaxial tensile tests were carried out and histological investigations were performed on four fresh thrombi to correlate with the change in the mechanical properties. A second-order polynomial, large-strain, hyperelastic constitutive model was developed and used to fit the uniaxial tensile testing data for determination of the material parameters. Our results indicate that the microstructure of ILT differs between the ventral and dorsal region, with the area region characterized by a nonlinear behavior and the lateral posterior area stiffer than the budge region. The peak stretch values were (mean±SEM) 1·24±0·04 and 1·1±0·09 for the ventral and lateral posterior area of the ILT, respectively. The material models for the thrombi are in excellent agreement with the experimental data.

Intraluminal thrombus has a selective influence on matrix metalloproteinases and their inhibitors (tissue inhibitors of matrix metalloproteinases) in the wall of abdominal aortic aneurysms

BACKGROUND

The influence of intraluminal thrombus (ILT) on the proteolytic environment within the wall of an abdominal aortic aneurysm (AAA) is unknown. This is the first study to examine the correlation between ILT thickness and the levels of matrix metalloproteinases (MMPs) and their natural inhibitors (tissue inhibitors of matrix metalloproteinases [TIMPs]) within the adjacent AAA wall.

METHODS

Thirty-five patients undergoing elective repair of AAAs were studied. A single full-thickness infrarenal aortic sample was obtained uniformly from the arteriotomy site from each patient. All samples were snap frozen and analyzed for total and active MMP 2, 8, and 9 and TIMP 1 and 2. Thrombus thickness at the specimen site was measured on the preoperative contrast computed tomographic angiograms.

RESULTS

There was a statistically significant correlation between ILT thickness, concentration of TIMP 1, and active concentration of MMP 9. MMP 2 (active and total) and TIMP 2 demonstrated a positive correlation with ILT thickness, although not statistically significant.

CONCLUSION

In this novel study, we found a significant positive correlation of ILT thickness with active MMP 9 and TIMP 1 concentration in the adjacent AAA wall, and this may have implications for AAA expansion and eventual rupture.

Delayed spontaneous rupture of a posterior inferior cerebellar artery aneurysm following treatment with flow diversion: a clinicopathologic study

In this report, we present the fatal spontaneous delayed rupture of a previously unruptured large PICA aneurysm following treatment with the PED. Pathology at postmortem examination has supported the theory that intra-aneurysmal thrombus may acutely destabilize the aneurysm wall. Aneurysms with an anatomic arrangement that promote continued flow into the neck may not be optimal candidates for the flow-diversion treatment strategy.

In vitro evaluation of the effects of intraluminal thrombus on abdominal aortic aneurysm wall dynamics

The optimum time to treat abdominal aortic aneurysms (AAAs) still remains an uncertain issue. The decision to intervene does not take in account the effects that wall curvature, intraluminal thrombus (ILT) properties and thickness have on rupture. The role of ILT in aneurysm dynamics and rupture has been controversial. In vitro testing of four silicone AAA models incorporating the ILT and aortic bifurcation was studied under physiological conditions. Pressures (P) and diameters (D) were analysed for models with and without ILT at different locations. The diametral strain, compliance and P/D curves were influenced by the presence, elastic stiffness and thickness of the ILT. In this case, the inclusion of ILT reduced the lumen area by 77% that resulted in a 0.5-81% reduction in compliance depending on ILT properties. With an increase in ILT stiffness from 0.05 to 0.2 MPa, the compliance was reduced by 81%. In the region of maximum diameter, there was a reduction of diametral strain and compliance except for the softer ILT which was more compliant throughout the proximal region. The shifting of the maximum diametral strain and compliance to the proximal neck was pronounced by an increase in ILT stiffness, thus creating a possible rupture site.

Diagnosis and monitoring of abdominal aortic aneurysm: current status and future prospects

Abdominal aortic aneurysm (AAA) remains an important cause of morbidity and mortality in elderly men, and prevalence is predicted to increase in parallel with a global aging population. AAA is commonly asymptomatic, and in the absence of routine screening, diagnosis is usually incidental when imaging to assess unrelated medical complaints. In the absence of approved diagnostic and prognostic markers, AAAs are monitored conservatively via medical imaging until aortic diameter approaches 50-55 mm and surgical repair is performed. There is currently significant interest in identifying molecular markers of diagnostic and prognostic value for AAA. Here we outline the current guidelines for AAA management and discuss modern scientific techniques currently employed to identify improved diagnostic and prognostic markers.

Thrombus volume is associated with cardiovascular events and aneurysm growth in patients who have abdominal aortic aneurysms

BACKGROUND

Patients with abdominal aortic aneurysms (AAA) are predisposed to cardiovascular events and often experience continual expansion of their aneurysm. Cardiovascular events and expansion rates are positively correlated with aneurysm size. AAA is usually associated with intraluminal thrombus, which has previously been implicated in AAA pathogenesis. This study prospectively assessed the association of infrarenal abdominal aortic thrombus volume with cardiovascular events and AAA growth.

METHODS

Ninety-eight patients with AAAs underwent computed tomography angiography (CTA). The volume of infrarenal aorta thrombus was measured by a previously validated technique. Patients were monitored prospectively for a median of 3 years (interquartile range [IQR], 2.0-3.6 years), and cardiovascular events (nonfatal stroke, nonfatal myocardial infarction, coronary revascularization, amputation, and cardiovascular death) were recorded. Of the original patients, 39 underwent repeat CTA a median of 1.5 years (IQR, 1.1-3.3 years) after entry to the study. Kaplan-Meier and Cox proportional analysis were used to examine the association of aortic thrombus with cardiovascular events and average weighted AAA growth.

RESULTS

There were 28 cardiovascular events during follow-up. The incidence of cardiovascular events was 23.4% and 49.2% for patients with small (smaller than the median) and large (median or larger) volumes of aortic thrombus, respectively, at 4 years (P = .040). AAA thrombus volume of median or larger was associated with increased cardiovascular events (relative risk [RR] 2.8, 95% confidence interval [CI], 1.01-5.24) independent of other risk factors, including initial AAA diameter, but was only of borderline significance when patients were censored at the time of AAA repair (RR, 2.35; 95% CI, 0.98-5.63). In the subset of patients with CTA follow-up, the median annual increase in AAA volume was 5.1 cm³ (IQR, 0.8-10.3 cm³). Annual AAA volume increase was positively correlated with initial AAA diameter (r = 0.44, P = .006) and thrombus volume (r = 0.50, P = .001). Median or larger aortic thrombus volume was associated with rapid AAA volume increase (≥ 5 cm/y), independent of initial aortic diameter (RR, 15.0; 95% CI, 1.9-115.7; P = .009).

CONCLUSION

In this small cohort, infrarenal aortic thrombus volume was associated with the incidence of cardiovascular events and AAA progression. These results need to be confirmed and mechanisms underlying the associations clarified in large further studies.

Quantification of particle residence time in abdominal aortic aneurysms using magnetic resonance imaging and computational fluid dynamics

Hemodynamic conditions are hypothesized to affect the initiation, growth, and rupture of abdominal aortic aneurysms (AAAs), a vascular disease characterized by progressive wall degradation and enlargement of the abdominal aorta. This study aims to use magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) to quantify flow stagnation and recirculation in eight AAAs by computing particle residence time (PRT). Specifically, we used gadolinium-enhanced MR angiography to obtain images of the vessel lumens, which were used to generate subject-specific models. We also used phase-contrast MRI to measure blood flow at supraceliac and infrarenal locations to prescribe physiologic boundary conditions. CFD was used to simulate pulsatile flow, and PRT, particle residence index, and particle half-life of PRT in the aneurysms were computed. We observed significant regional differences of PRT in the aneurysms with localized patterns that differed depending on aneurysm geometry and infrarenal flow. A bulbous aneurysm with the lowest mean infrarenal flow demonstrated the slowest particle clearance. In addition, improvements in particle clearance were observed with increase of mean infrarenal flow. We postulate that augmentation of mean infrarenal flow during exercise may reduce chronic flow stasis that may influence mural thrombus burden, degradation of the vessel wall, and aneurysm growth.

Trans-Thrombus Blood Pressure Effects in Abdominal Aortic Aneurysms

How much and how the thrombus supports the wall of an abdominal aortic aneurysm (AAA) is unclear. While some previous studies have indicated that thrombus lacks the mechanical integrity to support much load compared with the aneurysm wall, others have shown that removing thrombus in computational AAA models drastically changes aneurysm wall stress. Histopathological studies have shown that thrombus properties vary through the thickness and it can be porous. The goal of this study is to explore the variations in thrombus properties, including the ability to isolate pressure from the aneurysm wall, incomplete attachment, and their effects on aneurysm wall stress, an important parameter in determining risk for rupture. An analytical model comprised of cylinders and two patient specific models were constructed with pressurization boundary conditions applied at the lumen or the thrombus/aneurysm wall interface (to simulate complete transmission of pressure through porous thrombus). Aneurysm wall stress was also calculated in the absence of thrombus. The potential importance of partial thrombus attachment was also analyzed. Pressurizing at either surface (lumen versus interface) made little difference to mean von Mises aneurysm wall stress values with thrombus completely attached (3.1% analytic, 1.2% patient specific) while thrombus presence reduced mean von Mises stress considerably (79% analytic, 40–46% patient specific) in comparison to models without it. Peak von Mises stresses were similarly influenced with pressurization surface differing slightly (3.1% analytic, 1.4% patient specific) and reductions in stress by thrombus presence (80% analytic, 28–37% patient specific). The case of partial thrombus attachment was investigated using a cylindrical model in which there was no attachment between the thrombus and aneurysm wall in a small area (10 deg). Applying pressure at the lumen resulted in a similar stress field to fully attached thrombus, whereas applying pressure at the interface resulted in a 42% increase in peak aneurysm wall stress. Taken together, these results show that the thrombus can have a wall stress reducing role even if it does not shield the aneurysm wall from direct pressurization—as long as the thrombus is fully attached to the aneurysm wall. Furthermore, the potential for porous thrombus to transmit pressure to the interface can result in a considerable increase in aneurysm wall stress in cases of partial attachment. In the search for models capable of accurately assessing the risk for rupture, the nature of the thrombus and its attachment to the aneurysm wall must be carefully assessed.

Complete abdominal aortic aneurysm thrombosis and obstruction of both common iliac arteries with intrathrombotic pressures demonstrating a continuing risk of rupture: a case report and review of the literature

Introduction

Although mural thrombus in an abdominal aortic aneurysm is frequent and its role has been studied extensively, complete thrombosis of an abdominal aneurysm is extremely rare and its natural history in relation to the risk of rupture is not known. The case of a patient with a completely thrombosed infrarenal aneurysm is presented along with a literature review.

Case presentation

We report the case of a 56-year-old Caucasian man with an infrarenal abdominal aortic aneurysm, presenting at our hospital due to critical ischemia of his right lower limb. Computed tomography and angiography demonstrated complete aneurysm thrombosis and obstruction of both common iliac arteries.

Conclusion

During the operation, systolic and mean intrathrombotic pressures, measured in different levels, constituted 74.5-90.2% and 77.5-92.5% of systolic and mean intraluminal pressure and 73-88.4% and 76.5-91.3% of systemic pressure, respectively. Our findings show that there may be a continuing risk of rupture in cases of a thrombosed abdominal aortic aneurysm.

Three dimensional active contours for the reconstruction of abdominal aortic aneurysms

An aneurysm is a gradual and progressive ballooning of a blood vessel due to wall degeneration. Rupture of abdominal aortic aneurysm (AAA) constitutes a significant portion of deaths in the US. In this study, we describe a technique to reconstruct AAA geometry from CT images in an inexpensive and streamlined fashion. A 3D reconstruction technique was implemented with a GUI interface in MATLAB using the active contours technique. The lumen and the thrombus of the AAA were segmented individually in two separate protocols and were then joined together into a hybrid surface. This surface was then used to obtain the aortic wall. This method can deal with very poor contrast images where the aortic wall is indistinguishable from the surrounding features. Data obtained from the segmentation of image sets were smoothed in 3D using a Support Vector Machine technique. The segmentation method presented in this paper is inexpensive and has minimal user-dependency in reconstructing AAA geometry (lumen and wall) from patient image sets. The AAA model generated using this segmentation algorithm can be used to study a variety of biomechanical issues remaining in AAA biomechanics including stress estimation, endovascular stent-graft performance, and local drug delivery studies.

Mediators of neutrophil recruitment in human abdominal aortic aneurysms

Aims

Neutrophils/platelet interactions are involved in abdominal aortic aneurysm (AAA). The intraluminal thrombus (ILT) is a human model of platelet/neutrophil interactions. The present study focused on mediators involved in neutrophil recruitment in AAA.

Methods and results

Conditioned media from luminal, intermediate, and abluminal layers of 29 human ILTs were analysed for neutrophil markers [elastase/α₁-antitrypsin and MMP9/NGAL complexes, myeloperoxidase (MPO), and α-defensin peptides], RANTES, platelet factor 4 (PF4), and interleukin-8 (IL-8). Their time-dependent release into serum from clots generated in vitro and their plasma concentrations in AAA patients and controls were determined. Immunohistochemistry for neutrophils, platelets, IL-8, PF4, and RANTES on AAA sections was performed; and molecules involved in ILT neutrophil chemotactic function were analysed in vitro. Neutrophils and platelets colocalized in the luminal layer of the thrombus. Consistently, neutrophil markers and platelet-derived RANTES and PF4 were released predominantly by the luminal thrombus pole, where their concentrations were significantly correlated. The luminal ILT layer was also the main source of IL-8, whose immunostaining colocalized with neutrophils. All were also released time dependently from clots and were increased in plasma of AAA patients. Luminal ILT layers displayed potent neutrophil chemotactic activity in vitro, which was inhibited by RANTES- and IL-8-blocking antibodies as well as by reparixin, an antagonist of the IL-8 receptors CXCR1 and CXCR2.

Conclusion

Taken together, these results suggest that platelet-derived RANTES and neutrophil-derived IL-8 are involved in attracting neutrophils to the luminal layer of AAA ILT.