含血栓静脉管壁病理形态学特征的比较性研究

目的 探讨含血栓的静脉管壁病理形态学特征及管腔内径变化.方法 收集含血栓的曲张大隐静脉主干标本18例(血栓组),单纯曲张大隐静脉主干标本18例(曲张组),另设正常大隐静脉主干标本12例(对照组).采用苏木精-伊红和Masson染色法,观察管壁组织结构,测量血管壁内径与内膜、中膜、外膜厚度.结果 血栓组管壁全层及血栓内见大量炎细胞浸润,血栓附着处内皮细胞缺失,大量增生的胶原纤维自破裂内膜处延伸至血栓内致部分血栓机化.曲张组管壁全层偶见炎细胞,内膜增厚,中膜平滑肌细胞不规则增生,排列紊乱,胶原纤维增生.对照组管壁内膜薄,中膜平滑肌束排列规则.血栓组管腔内径、内膜厚度、中膜厚度和外膜厚度与曲张组、对照组比较差异均有统计学意义(P＜0.05),曲张组管腔内径和内膜厚度与对照组比较差异有统计学意义(P＜0.05).结论 含血栓的曲张静脉管腔增大、管壁增厚是病理形态学改变的主要特征.     

腔内血栓降低大鼠腹主动脉瘤壁残余应力对瘤壁保护作用的评价

目的：用测量张开角的方法研究大鼠单纯腹主动脉瘤（AAA）和腔内血栓AAA模型的应力分布，对比两种模型瘤壁的顺就生，评估腔内血栓对瘤壁的保护作用。方法：用猪弹力蛋白酶灌注Wistar大鼠腹主动脉建立梭形肾下AAA模型，相似的方法并机械破坏内腹建立腔内血栓AAA模型，测量并对比单纯AAA和腔内血栓AAA动脉环的蠕变速度，残余应力，对比两组AAA同一瘤体不同部位的残余应力，动脉环内径和瘤壁厚度。结果：单纯AAA模型建立的成功率90%，腔内血栓AAA模型建立的成功率为60%，单纯AAA动脉环蠕变速度较腔内血栓AAA慢，单纯AAA入口和出口的残余应力值最大，内径和瘤壁厚度最小；腔内血栓AAA的残余应力分布规律相似，但总体残余应力较低。结论：残余应力量化反映AAA瘤壁的顺应性，腔内血栓AAA较单纯AAA的顺应性大；单纯AAA和腔内血栓AAA入口和出口附近应力最大，腔内血栓通过降低血管的残余应力对AAA起保护作用。     

改良腹主动脉瘤大鼠模型的制作方法

目的 介绍一种改良腹主动脉腔内灌注猪胰蛋白酶（PPE）制作腹主动脉瘤（AAA）大鼠模型的方法。方法 将20只SD大鼠随机为两组,分别是改良腹主动脉腔内灌注PPE组和传统腹主动脉腔内灌注PPE组,每组10只。通过超声测量腹主动脉直径,比较两组大鼠的手术相关指标,大鼠存活率,术后7、14d的AAA成瘤率和腹主动脉扩张率。通过弹性纤维染色和免疫组织化学染色（IHC）染色法观察腹主动脉弹性纤维情况和炎性细胞浸润情况。结果 改良腹主动脉腔内灌注PPE组的手术时间明显短于传统腹主动脉腔内灌注PPE组,每只大鼠的PPE用量明显少于传统腹主动脉腔内灌注PPE组,差异均有统计学意义（P﹤0.01）。术后14 d,两组的大鼠存活率比较,差异无统计学意义（P﹥0.05）。术后7 d,改良腹主动脉腔内灌注PPE组的腹主动脉扩张率、AAA成瘤率均高于传统腹主动脉腔内灌注PPE组,差异均有统计学意义（P﹤0.05）;术后14 d,改良腹主动脉腔内灌注PPE组的腹主动脉扩张率明显高于传统腹主动脉腔内灌注PPE组,差异有统计学意义（P﹤0.01）,但两组的AAA成瘤率比较,差异无统计学意义（P﹥0.05）。改良腹主动...     

如何做好腹主动脉瘤腔内修复术

腹主动脉瘤（abdominal aortic aneurysm,AAA）为血管外科临床重要疾病之一,随瘤体增大,其增长速度加快,破裂风险增加,破裂AAA的病死率高。多数AAA患者因高龄或伴有其他严重内科疾病而不适于行开放手术。1991年,阿根廷Parodi等首次报道用支架型人工血管（后简称“支架”）成功治愈AAA,开创了AAA腔内修复治疗（endovascular aneurysm repair,EVAR）的新时代。以下将就如何做好AAA的EVAR的相关问题作一探讨。     

腹主动脉瘤腔内修复术后内漏的诊断与治疗

腹主动脉瘤（AAA）腔内修复术（EVAR）是目前大动脉病变腔内治疗最成熟的技术之一。AAA EVAR术后内漏指支架型血管置入后，在支架型血管腔外、被旷置的瘤体及邻近血管腔内出现持续性血流的现象。内漏是AAA EVAR术后最为常见、对疗效影响很大的并发症，其发生率大约15％～50％。内漏可导致瘤体进一步增大甚至破裂。目前，内漏的机理尚不完全明确，诊断与治疗方面也存在争议。现根据我院临床经验，结合近年来相关文献报道探讨AAA EVAR术后内漏的诊治。     

腹主动脉瘤腔内修复术后Ⅱ型内漏的影响因素分析和预测模型构建

目的 探讨腹主动脉瘤（AAA）腔内修复术（EVAR）后发生Ⅱ型内漏的影响因素并构建预测模型。方法收集2018年1月至2022年9月于山东第一医科大学附属省立医院进行EVAR治疗的286例AAA患者的临床资料,根据术后随访期间是否发生Ⅱ型内漏将患者分为对照组（n=210）和Ⅱ型内漏组（n=76）。比较两组患者的临床特征、血液指标、AAA解剖情况及手术情况。分析AAA患者EVAR术后发生Ⅱ型内漏的影响因素,构建预测模型,绘制列线图,构建评分系统,并绘制模型的校准曲线,计算一致性指数（C-index）,绘制受试者工作特征（ROC）曲线和临床决策曲线,验证预测模型的准确性和临床有效性。结果 两组患者的吸烟史比例、肠系膜下动脉（IMA）开口直径、腰动脉（LA）数量和IMA通畅情况比较,差异均有统计学意义（P<0.05）。多因素分析结果显示,吸烟史是AAA患者EVAR术后发生Ⅱ型内漏的保护因素,IMA通畅情况、IMA开口直径和LA数量均是AAA患者EVAR术后发生Ⅱ型内漏的独立危险因素（P<0.05）。预测模型的C-index为0.824(95%CI:0.718～0.930),校准后的...     

复杂解剖结构腹主动脉瘤腔内修复术后主要并发症的影响因素分析

目的 探讨复杂解剖结构的腹主动脉瘤（AAA）腔内修复术（EVAR）后发生并发症的影响因素。方法 收集2007年8月至2022年6月于内蒙古医科大学附属医院行EVAR治疗的162例AAA患者的临床资料,根据EVAR术后是否发生并发症将其分为并发症组（n=42）和无并发症组（n=120）。记录患者的一般情况、实验室检查指标、腹主动脉瘤解剖形态信息、术中指标,统计术后1个月病死率及并发症发生情况,分析EVAR术后发生并发症的影响因素。结果 两组患者血清白蛋白水平、老年营养风险指数（GNRI）、髂动脉狭窄/闭塞、短瘤颈、大成角、瘤颈血栓比较,差异均有统计学意义（P﹤0.05）。多因素分析结果显示,GNRI﹤82、瘤颈血栓、髂动脉狭窄/闭塞均是复杂解剖结构AAA患者EVAR术后发生并发症的独立危险因素（P﹤0.05）。结论 GNRI﹤82、髂动脉狭窄/闭塞及瘤颈血栓可提示行EVAR的复杂解剖结构的AAA患者术后并发症发生风险增高。     

超声检测老年人真性腹主动脉瘤附壁血栓

目的探讨超声成像检测老年人腹主动脉瘤（AAA）附壁血栓的临床价值。方法采用二维及彩色多普勒超声检测51例AAA患者,观察有无附壁血栓及其分布,分析血栓与AAA瘤径大小及其内血流变化的关系。结果51例AAA患者中,37例（72.55%）伴附壁血栓形成,多为弧形、环形或新月形和不规则形。AAA瘤腔增大,层流范围缩小,湍流范围加大,附壁血栓发生率及厚度增加（P〈0.05）。结论超声检测附壁血栓对判断病情发展、治疗和预后具有一定价值。血栓形成及其厚度与AAA瘤径相关,瘤体内血流变化是附壁血栓形成的重要因素。     

“ENGAGE”治疗腹主动脉瘤8年随访数据解读及展望

腹主动脉瘤（AAA）是一种永久且不可逆的腹主动脉局部扩张性病变，其破裂病死率高达60%~70%。AAA腔内修复术凭借其临床安全性和有效性已经成为AAA的一线治疗方法，但其长期随访中的支架移位、内漏等并发症仍值得关注。“ENGAGE”是迄今最大的AAA腔内治疗的长期注册研究，笔者基于“ENGAGE”研究8年随访结果和相应的文献分析，系统介绍AAA腔内治疗现状及前景。     

HMGB1和MMP-9在腹主动脉瘤组织中的表达及临床意义

目的：通过检测高迁移率族蛋白B1（HMGB1）和基质金属蛋白酶-9（MMP-9）在非破裂腹主动脉瘤（AAA）及破裂腹主动脉瘤（RAAA）组织中的定位表达,探讨HMGB1和MMP-9在腹主动脉瘤发病机制中的作用及临床意义。方法：应用免疫组织化学技术,分别检测HMGB1和MMP-9在30例非破裂AAA（包括9例小AAA：横径〈5.0 cm,15例中AAA：横径5.0～7.0 cm,6例大AAA：横径≥7.0 cm）、12例RAAA中的定位表达,并与10例正常腹主动脉组织中HMGB1和MMP-9表达进行对照研究。结果：在非破裂AAA和RAAA组织中HMGB1与MMP-9的表达均明显高于正常腹主动脉（P〈0.05）。在RAAA组织中MMP-9的表达明显高于非破裂AAA（P=0.045）;MMP-9在大AAA和RAAA组织中的表达阳性率明显高于中、小AAA（P=0.010）,而HMGB1在不同大小AAA组织中的表达无差异（P=0.602）。MMP-9在发生心脑血管意外患者中的表达明显高于未发生者（P=0.027）。HMGB1与MMP-9在非破裂AAA组织中的表达无相关性（P=0.767）,在RAAA组织中的表达呈正相关（P=0.016）。结论：MMP-9在AAA扩张甚至破裂中发挥重要作用;HMGB1与MMP-9在RAAA组织中发挥正协同作用;HMGB1和MMP-9在AAA的发病机制中有重要作用。     

Impact of calcification and intraluminal thrombus on the computed wall stresses of abdominal aortic aneurysm

BACKGROUND: Increased biomechanical stresses within the abdominal aortic aneurysm (AAA) wall contribute to its rupture. Calcification and intraluminal thrombus can be commonly found in AAAs, but the relationship between calcification/intraluminal thrombus and AAA wall stress is not completely described. METHODS: Patient-specific three-dimensional AAA geometries were reconstructed from computed tomographic images of 20 patients. Structural analysis was performed to calculate the wall stresses of the 20 AAA models and their altered models when calcification or intraluminal thrombus was not considered. A nonlinear large-strain finite element method was used to compute the wall stress distribution. The relationships between wall stresses and volumes of calcification and intraluminal thrombus were sought. RESULTS: Maximum stress was not correlated with the percentage of calcification, and was negatively correlated with the percentage of intraluminal thrombus (r = -0.56; P = .011). Exclusion of calcification from analysis led to a significant decrease in maximum stress by a median of 14% (range, 2%-27%; P < .01). When intraluminal thrombus was eliminated, maximum stress increased significantly by a median of 24% (range, 5%-43%; P < .01). CONCLUSION: The presence of calcification increases AAA peak wall stress, suggesting that calcification decrease the biomechanical stability of AAA. In contrast, intraluminal thrombus reduces the maximum stress in AAA. Calcification and intraluminal thrombus should both be considered in the evaluation of wall stress for risk assessment of AAA rupture.     

Size and location of thrombus in intact and ruptured abdominal aortic aneurysms

PURPOSE: This study compared the volume and morphology of intraluminal thrombus (ILT) in intact and ruptured abdominal aortic aneurysms (AAAs). METHODS: ILT volume in 67 intact AAAs and in 31 ruptured AAAs was assessed by using computed tomography (CT) angiography to measure the major and minor diameter of the outer wall and lumen of AAA as outlined by contrast at multiple sites. ILT thrombus morphology was recorded by AutoCAD 2000 software. Four equidistant images traced from the CT scan were recorded along the length of AAA. Thrombus volume was categorized as anterior-eccentric if the calculated area of thrombus was greater anteriorly, posterior-eccentric if greater posteriorly, eccentric-equal if the difference between the anterior and posterior thrombus was 相似文献   

Association of intraluminal thrombus in abdominal aortic aneurysm with local hypoxia and wall weakening

PURPOSE: Our previous computer models suggested that intraluminal thrombus (ILT) within an abdominal aortic aneurysm (AAA) attenuates oxygen diffusion to the AAA wall, possibly causing localized hypoxia and contributing to wall weakening. The purpose of this work was to investigate this possibility. METHODS: In one arm of this study, patients with AAA were placed in one of two groups: (1) those with an ILT of 4-mm or greater thickness on the anterior surface or (2) those with little (< 4 mm) or no ILT at this site. During surgical resection but before aortic cross-clamping, a needle-type polarographic partial pressure of oxygen (PO2) electrode was inserted into the wall of the exposed AAA, and the PO2 was measured. The probe was advanced, and measurements were made midway through the thrombus and in the lumen. Mural and mid-ILT PO2 measurements were normalized by the intraluminal PO2 measurement to account for patient variability. In the second arm of this study, two AAA wall specimens were obtained from two different sites of the same aneurysm at the time of surgical resection: group I specimens had thick adherent ILT, and group II specimens had thinner or no adherent ILT. Nonaneurysmal tissue was also obtained from the infrarenal aorta of organ donors. Specimens were subjected to histologic, immunohistochemical, and tensile strength analyses to provide data on degree of inflammation (% area inflammatory cells), neovascularization (number of capillaries per high-power field), and tensile strength (peak attainable load). Additional specimens were subjected to Western blotting and immunohistochemistry for qualitative evaluation of expression of the cellular hypoxia marker oxygen-regulated protein. RESULTS: The PO2 measured within the AAA wall in group I (n = 4) and group II (n = 7) patients was 18% +/- 9% luminal value versus 60% +/- 6% (mean +/- SEM; P <.01). The normalized PO2 within the ILT of group I patients was 39% +/- 10% (P =.08 with respect to the group I wall value). Group I tissue specimens showed greater inflammation (P <.05) compared with both group II specimens and nonaneurysmal tissue: 2.9% +/- 0.6% area (n = 7) versus 1.7% +/- 0.3% area (n = 7) versus 0.2% +/- 0.1% area (n = 3), respectively. We found similar differences for neovascularization (number of vessels/high-power field), but only group I versus control was significantly different (P <.05): 16.9 +/- 1.6 (n = 7) vs 13.0 +/- 2.3 (n = 7) vs 8.7 +/- 2.0 (n = 3), respectively. Both Western blotting and immunohistochemistry results suggest that oxygen-regulated protein is more abundantly expressed in group I versus group II specimens. Tensile strength of group I specimens was significantly less (P <.05) than that for group II specimens: 138 +/- 19 N/cm2 (n = 7) versus 216 +/- 34 N/cm2 (n = 7), respectively. CONCLUSION: Our results suggest that localized hypoxia occurs in regions of thicker ILT in AAA. This may lead to increased, localized mural neovascularization and inflammation, as well as regional wall weakening. We conclude that ILT may play an important role in the pathology and natural history of AAA.     

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 alpha2-antiplasmin (alpha2AP) 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 alpha2AP 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.     

Influence of intraluminal thrombus on structural and cellular composition of abdominal aortic aneurysm wall

INTRODUCTION: It has been suggested that the intraluminal thrombus of abdominal aortic aneurysm (AAA) affects the underlying vessel wall. Aneurysm enlargement has been associated with growth of thrombus, and rupture has been proposed to occur after bleeding into the thrombus. To examine how thrombus affects the vessel wall, we compared the morphology of aneurysm wall covered with thrombus with wall segments exposed to flowing blood.Material and methods Sixteen patients (14 men, 2 women; age range, 56-79 years) undergoing elective repair of AAA, where computed tomography scans showed thrombus and segments of the aneurysm wall exposed to flowing blood, were included in the study. Specimens from the aneurysm were taken for light and electron microscopy. Masson trichrome staining was performed for wall thickness determination and demonstration of collagen, and Weigert-van Gieson staining for elastin. The cellular composition was analyzed by immunohistochemistry with antibodies against CD3 for T cells, CD4 for T helper cells, CD8 for T cytotoxic cells, CD20 for B cells, CD68 for macrophages, and smooth muscle alpha-actin for smooth muscle cells (SMCs). Caspase-3 staining and TUNEL analysis were performed to evaluate apoptosis. RESULTS: The aneurysm wall covered with thrombus was thinner and contained fewer elastin fibers, and the few that were found were often fragmented. This part of the wall also contained fewer SMCs and more apoptotic nuclei than the wall exposed to flowing blood. Clusters of inflammatory cells were detected in the media of the aneurysm wall and in higher numbers in the parts covered with thrombus. Electron microscopy showed that the aneurysm wall without thrombus contained a dense collagenous matrix with differentiated SMCs. In the segment covered with thrombus, SMCs were more dedifferentiated (synthetic) and apoptotic or necrotic. There were also an increased number of inflammatory cells located in close contact with SMCs in various stages of apoptosis. CONCLUSION: The aneurysm wall covered with thrombus is thinner and shows more frequent signs of inflammation, apoptosis of SMCs, and degraded extracellular matrix. These findings suggest that thrombus formation and accumulation of inflammatory cells may perturb the structural integrity and stability of the vessel wall and thereby increase the risk for aneurysm rupture.     

A systematic review summarizing local vascular characteristics of aneurysm wall to predict for progression and rupture risk of abdominal aortic aneurysms

ObjectiveAt present, the rupture risk prediction of abdominal aortic aneurysms (AAAs) and, hence, the clinical decision making regarding the need for surgery, is determined by the AAA diameter and growth rate. However, these measures provide limited predictive information. In the present study, we have summarized the measures of local vascular characteristics of the aneurysm wall that, independently of AAA size, could predict for AAA progression and rupture.MethodsWe systematically searched PubMed and Web of Science up to September 13, 2021 to identify relevant studies investigating the relationship between local vascular characteristics of the aneurysm wall and AAA growth or rupture in humans. A quality assessment was performed using the ROBINS-I (risk of bias in nonrandomized studies of interventions) tool. All included studies were divided by four types of measures of arterial wall characteristics: metabolism, calcification, intraluminal thrombus, and compliance.ResultsA total of 20 studies were included. Metabolism of the aneurysm wall, especially when measured by ultra-small superparamagnetic iron oxide uptake, and calcification were significantly related to AAA growth. A higher intraluminal thrombus volume and thickness had correlated positively with the AAA growth in one study but in another study had correlated negatively. AAA compliance demonstrated no correlation with AAA growth and rupture. The aneurysmal wall characteristics showed no association with AAA rupture. However, the metabolism, measured via ultra-small superparamagnetic iron oxide uptake, but none of the other measures, showed a trend toward a relationship with AAA rupture, although the difference was not statistically significant.ConclusionsThe current measures of aortic wall characteristics have the potential to predict for AAA growth, especially the measures of metabolism and calcification. Evidence regarding AAA rupture is scarce, and, although more work is needed, aortic wall metabolism could potentially be related to AAA rupture. This highlights the role of aortic wall characteristics in the progression of AAA but also has the potential to improve the prediction of AAA growth and rupture.     

Filling of the aneurysmal sac with DEAC-glucosamine in an animal model of abdominal aortic aneurysm following stent-graft repair

AIM: The aim of this study was to present the preliminary results of a technique of abdominal aortic aneurysm (AAA) sac filling in an attempt to obliterate the sac in a swine AAA model, using deacetylated-poly-N-acetyl glucosamine (DEAC-poly-N-acetyl glucosamine). METHODS: Eleven Yucatan pigs, 6 months of age, 40 kg -60 kg, were used to create an AAA with a Dacron pouch implanted surgically and left to mature for 2 weeks. One animal was used to establish the AAA creation procedures. Eight animals were used for AAA sac filling; of the 8 subjects 2 were used for acute studies, and 6 for longer-term studies. Two additional animals were used as controls without polymer sac filling. Two weeks after the AAA creation, a 13 mmx5.5 cm straight tube AneuRx stent-graft was placed to exclude the aneurysm. The aneurysmal sac was filled with a polymer, DEAC-poly-N-acetyl glucosamine at 1.5%, 70% deacetylated, mixed with iohexol. There was filling of a lumbar artery by the polymer in 2 animals. Endpoints were at 1, 2, 4, 6, 12 and 24 weeks, in the chronic study animals and 6 and 12 weeks in the control subjects, procedures consisting of aortography followed by necropsy and pathologic examination. RESULTS: The AAA creation and aneurysm sac filling was successful in all animals. An organized thrombus layer of about 2 mm in thickness was observed in all subjects along the Dacron aneurysm wall. All aneurysms were angiographically patent at the time of treatment, but fresher thrombus within the sac was seen in 4 subjects before the polymer injection. The stent-graft placement excluded the AAA sac and the polymer injection filled all AAA sacs. The AAA sac had acquired a firm rubbery consistency at the time of necropsy. There was mild inflammatory reaction to the Dacron material in the surrounding tissues and within the sac, to a lesser extent. Two animals developed paralysis of the hind limbs following treatment, most likely related to spinal ischemia, and were used as acute subjects. There was no recanalization of the aneurysm sac, during the follow-up time, ranging from 1 to 24 weeks in the treatment or control subjects. There was a 25% shrinkage of the AAA sac at 6th, 40% at 12th week and 75% by the 24th week. The 2 control subjects showed shrinkage of less than 25% at 6 and 12 weeks. There was replacement of the polymer/thrombus complex by connective tissue, fat tissue with capillary neovascularization in the treated subjects. Fibrosis and calcifications were also detected within the sac, mostly around the stent-graft and in contact with the aortic wall starting at 4 weeks. Control subjects did not show replacement of the thrombus by connective tissue or neovascularization. CONCLUSION: The results of this preliminary study support the aneurysm sac filling as a potential tool to exclude the aneurismal sac, promoting shrinkage of the AAA. DEAC -poly-N-acetyl glucosamine promotes clotting within the AAA sac with progressive replacement by connective tissue and neovascularization and may have a potential to prevent endoleaks. The polymer is easy to use, and it seems to have adequate gradual long-term replacement properties, preventing aneurysm sac recanalization.     

Effect of thrombus on abdominal aortic aneurysm wall dilation and stress

AIM: Our goal is to understand how a mural thrombus may influence the pressure transmitted to and the dilation experienced by the abdominal aortic aneurysm (AAA) wall. METHODS: Two intact AAAs with mural thrombus were removed from patients and pressurized to 100 mmHg. The pressure was measured using a micro-tip needle transducer inserted in the aneurysm wall and advanced through the thrombus. In 1 patient with AAA, similar measurements were made in vivo. Also, in vitro, in the two aneurysms the dilation as a function of pressure was measured using the markers on the surface before and after the thrombus was removed. RESULTS: Both, in vitro and in vivo, in the presence of the thrombus the pressure transmitted to the aneurysm wall was 91+/-10% of luminal pressure and at 6 mm from the wall it was 96+/-5%. The aneurysm dilated more in the pressure range of 0-40 mmHg (2-8%) than in the range of 40-100 mmHg (0.4-1.8%). Upon removal of the thrombus these dilations increased significantly to 4-15% and 0.9-3.3%, respectively. Overall, the strains (dilation) in the circumferential and longitudinal directions were similar before the thrombus was removed. CONCLUSIONS: Even though the thrombus allows the transmission of luminal pressure to the aneurysm wall, it may prevent the aneurysm from rupture by diminishing the strain on the wall. Consistent with this, a mechanical model of the thrombus proposed is "a thrombus as a fibrous network adherent to the aneurysm wall".     

Biomechanical factors in abdominal aortic aneurysm rupture

Hitherto the size of abdominal aortic aneurysms (AAA) has been considered the most important factor in determining the risk of rupture. For this reason most interest had been devoted to physical, echographic and tomographic analyses of the shape of AAA. However, its is known that rupture can also occur in small AAA. Other factors must be considered to have an important role in the natural history of aneurysms. The aim of t his study was to characterise the mechanical stress in the wall of an AAA due to pressure in the presence of atherosclerosis, intraluminal thrombus and anatomical restraints. The Finite Elements Method (FEM) was used to determine wall stress distribution. Due to the simplicity of the AAA structure an axisymmetric model has been built. The results of the structural analysis confirms that maximum stress increases with diameter. These effects may be reduced by the presence of intraluminal thrombus, which in the models reduces maximum stress by up to 30%; however this is not the case for dissecting thrombus. On the other hand atherosclerotic plaques cause stress concentration and a significant increase in maximum wall stress. The risk of rupture can increase by about 200%. Finally the investigation shows the FEM is a versatile tool for studying the mechanics of vascular structures. It enables the influence of various parameters on wall stress to be quantified in diagnostic settings, and so could be useful for predicting the rupture of AAA, although at present such predictions are limited by data leakage and by the approximations used in the model.