Computed tomography in the diagnosis of complicated abdominal aortic aneurysms

The paper analyzes the results of computed tomography (CT) conducted in 54 patients with complicated abdominal aortic aneurysms (AAA). Of them, 37 cases were diagnosed as having a complete rupture. There was dissection of the wall of the aneurysmally altered aorta and its slight tear in 11 and 6 cases, respectively. CT has been shown to allow one to diagnose complications due to AAA, their pattern, and site, to identify the factors that increase a risk for rupture, such as a slight tear of the inner layers of the wall of the aneurysmal abdominal aorta and its wall dissection. This all assists in solving a variety of the problems associated with treatment policy and may substantially reduce postoperative morbidity in this group of patients.     

老年Stanford A 型主动脉夹层外科治疗*

目的:总结老年Stanford A型主动脉夹层外科治疗经验,探讨手术方式的选择,以提高手术疗效。方法:2008年9月至2011年5月对31例老年Stanford A型主动脉夹层行手术治疗,根据夹层破口位置、累及范围、主动脉根部病变情况采取相应术式,W-heat手术2例,David+全弓置换+支架象鼻术3例,Bentall+全弓置换+支架象鼻术9例,改良Wheat+全弓置换+支架象鼻术1例,升主动脉+全弓置换+支架象鼻术16例。同时行冠状动脉旁路移植术4例,心包剥脱术1例。结果:全组体外循环(221±43)min,平均心肌阻断(132±41)min,深低温停循环(47±12)min。术后并发症12例(38.7%),其中2例死亡,8例治愈(66.7%),2例术后出现肾功能衰竭家属放弃治疗。全组病人出院前复查主动脉CTA,见升主动脉、弓部人工血管血流通畅,支架位置正常,无明显移位。支架远端降主动脉假腔闭合率87.1%。随访2~35个月,术后近期死亡1例(3.2%),无再次手术者。结论:对老年StanfordA型主动脉夹层这一高危人群,术中根据其病变部位施行最佳的外科手术方式,可明显降低死亡率,改善患者预后。     

Radiation diagnosis of aortic aneurysmal ruptures with formation of anastomoses with the inferior cava and various organs

The results of radiation diagnostic techniques were analyzed in 29 patients with aortic aneurysmal ruptures with formation of aortic anastomoses. The examination and treatment of 362 patients with abdominal aortic aneurysmal ruptures revealed that 23 (6.35%) patients had anastomoses (aortocaval (n = 15), aortoduodenal (n = 6), aortogastric (n = 1), and aortoureteral (n = 1)). Six patients were observed to have secondary aortointestinal anastomoses occurring after reconstructive vascular surgery. In one patient, abdominal aortic aneurysmal rupture first led to the formation of a primary aortoduodenal anastomosis and some time after surgery a secondary aortointestinal fistula emerged. One out of 113 patients with aortic dissecting aortic aneurysms had an aortopulmonary fistula. Ultrasonography, computed tomography, and angiography were performed in 27, 19, and 14 patients, respectively. Radiation diagnostic techniques revealed fistulas in 9 (31%) out of the 29 patients. The diagnosis of aortic anastomoses presents challenges.     

Structural modeling reveals microstructure-strength relationship for human ascending thoracic aorta

High lethality of aortic dissection necessitates accurate predictive metrics for dissection risk assessment. The not infrequent incidence of dissection at aortic diameters <5.5 cm, the current threshold guideline for surgical intervention (Nishimura et al., 2014), indicates an unmet need for improved evidence-based risk stratification metrics. Meeting this need requires a fundamental understanding of the structural mechanisms responsible for dissection evolution within the vessel wall. We present a structural model of the repeating lamellar structure of the aortic media comprised of elastic lamellae and collagen fiber networks, the primary load-bearing components of the vessel wall. This model was used to assess the role of these structural features in determining in-plane tissue strength, which governs dissection initiation from an intimal tear. Ascending aortic tissue specimens from three clinically-relevant patient populations were considered: non-aneurysmal aorta from patients with morphologically normal tricuspid aortic valve (CTRL), aneurysmal aorta from patients with tricuspid aortic valve (TAV), and aneurysmal aorta from patients with bicuspid aortic valve (BAV). Multiphoton imaging derived collagen fiber organization for each patient cohort was explicitly incorporated in our model. Model parameters were calibrated using experimentally-measured uniaxial tensile strength data in the circumferential direction for each cohort, while the model was validated by contrasting simulated tissue strength against experimentally-measured strength in the longitudinal direction. Orientation distribution, controlling the fraction of loaded collagen fibers at a given stretch, was identified as a key feature governing anisotropic tissue strength for all patient cohorts.     

Intraluminal thrombus and risk of rupture in patient specific abdominal aortic aneurysm - FSI modelling

Recent numerical studies of abdominal aortic aneurysm (AAA) suggest that intraluminal thrombus (ILT) may reduce the stress loading on the aneurysmal wall. Detailed fluid structure interaction (FSI) in the presence and absence of ILT may help predict AAA rupture risk better. Two patients, with varied AAA geometries and ILT structures, were studied and compared in detail. The patient specific 3D geometries were reconstructed from CT scans, and uncoupled FSI approach was applied. Complex flow trajectories within the AAA lumen indicated a viable mechanism for the formation and growth of the ILT. The resulting magnitude and location of the peak wall stresses was dependent on the shape of the AAA, and the ILT appeared to reduce wall stresses for both patients. Accordingly, the inclusion of ILT in stress analysis of AAA is of importance and would likely increase the accuracy of predicting AAA risk of rupture.     

Aortic dissection in a gorilla

Autopsy findings in a 39-year-old male gorilla included aortic dissection, internal rupture of the aortic arch with axial direction of the tear, external rupture of the ascending aorta, cardiac tamponade, myocardial hypertrophy, cystic and basophilic degeneration of the aortic media, marked obesity, severe degenerative joint disease, focal glomerulonephritis, and widespread hemosiderosis.     

Mechano-biology in the thoracic aortic aneurysm: a review and case study

An aortic aneurysm is a permanent and localized dilatation of the aorta resulting from an irreversible loss of structural integrity of the aortic wall. The infrarenal segment of the abdominal aorta is the most common site of aneurysms; however, they are also common in the ascending and descending thoracic aorta. Many cases remain undetected because thoracic aortic aneurysms (TAAs) are usually asymptomatic until complications such as aortic dissection or rupture occurs. Clinical estimates of rupture potential and dissection risk, and thus interventional planning for TAAs, are currently based primarily on the maximum diameter and growth rate. The growth rate is calculated from maximum diameter measurements at two subsequent time points; however, this measure cannot reflect the complex changes of vessel wall morphology and local areas of weakening that underline the strong regional heterogeneity of TAA. Due to the high risks associated with both open and endovascular repair, an intervention is only justified if the risk for aortic rupture or dissection exceeds the interventional risks. Consequently, TAAs clinical management remains a challenge, and new methods are needed to better identify patients for elective repair. We reviewed the pathophysiology of TAAs and the role of mechanical stresses and mathematical growth models in TAA management; as a proof of concept, we applied a multiscale biomechanical analysis to a case study of TAA.     

Intraluminal thrombus and risk of rupture in patient specific abdominal aortic aneurysm – FSI modelling

Recent numerical studies of abdominal aortic aneurysm (AAA) suggest that intraluminal thrombus (ILT) may reduce the stress loading on the aneurysmal wall. Detailed fluid structure interaction (FSI) in the presence and absence of ILT may help predict AAA rupture risk better. Two patients, with varied AAA geometries and ILT structures, were studied and compared in detail. The patient specific 3D geometries were reconstructed from CT scans, and uncoupled FSI approach was applied. Complex flow trajectories within the AAA lumen indicated a viable mechanism for the formation and growth of the ILT. The resulting magnitude and location of the peak wall stresses was dependent on the shape of the AAA, and the ILT appeared to reduce wall stresses for both patients. Accordingly, the inclusion of ILT in stress analysis of AAA is of importance and would likely increase the accuracy of predicting AAA risk of rupture.     

经胸超声胸骨右缘切面对Stanford A型主动脉夹层诊断价值的研究

目的:通过经胸超声心动图获取胸骨右缘升主动脉长短轴切面观察Stanford A型主动脉夹层患者的升主动脉结构,探讨对该类患者进行检查时该切面的应用价值。方法:31例经CTA或手术证实为A型主动脉夹层的连续性患者,超声心动图检查除常规通过胸骨左缘切面观察升主动脉结构外,均做胸骨右缘切面以进一步观察升主动脉结构,包括最大内径,有无撕脱内膜及内膜活动情况,同时应用常规胸骨左缘切面和胸骨右缘切面对A型主动脉夹层能够清晰显示出的病例比例加以比较。结果:胸骨左缘切面能够清晰显示升主动脉结构9例,占比例29%。胸骨右缘切面能够清晰显示升主动脉结构20例,比例65%。将两种切面结合能够清晰显示升主动脉结构的比例升高到74%。胸骨右缘肋间切面测得的升主动脉最大径线数值与CTA结果的一致性更好。结论:胸骨右缘肋间切面对A型主动脉夹层显示的清晰度更好,有助于临床诊断,具有重要的参考价值,值得临床广泛推广。     

Patient-specific simulation of stent-graft deployment in type B aortic dissection: model development and validation

Thoracic endovascular aortic repair (TEVAR) has been accepted as the mainstream treatment for type B aortic dissection, but post-TEVAR biomechanical-related complications are still a major drawback. Unfortunately, the stent-graft (SG) configuration after implantation and biomechanical interactions between the SG and local aorta are usually unknown prior to a TEVAR procedure. The ability to obtain such information via personalised computational simulation would greatly assist clinicians in pre-surgical planning. In this study, a virtual SG deployment simulation framework was developed for the treatment for a complicated aortic dissection case. It incorporates patient-specific anatomical information based on pre-TEVAR CT angiographic images, details of the SG design and the mechanical properties of the stent wire, graft and dissected aorta. Hyperelastic material parameters for the aortic wall were determined based on uniaxial tensile testing performed on aortic tissue samples taken from type B aortic dissection patients. Pre-stress conditions of the aortic wall and the action of blood pressure were also accounted for. The simulated post-TEVAR configuration was compared with follow-up CT scans, demonstrating good agreement with mean deviations of 5.8% in local open area and 4.6 mm in stent strut position. Deployment of the SG increased the maximum principal stress by 24.30 kPa in the narrowed true lumen but reduced the stress by 31.38 kPa in the entry tear region where there was an aneurysmal expansion. Comparisons of simulation results with different levels of model complexity suggested that pre-stress of the aortic wall and blood pressure inside the SG should be included in order to accurately predict the deformation of the deployed SG.

     

Hybrid thoracic stent graft repair of a complex type B aortic dissection in a patient who presented three weeks after repair of a type a aortic dissection

Long-term management after repair of a type A aortic dissection includes aggressive medical therapy and routine surveillance with serial imaging to ensure thrombosis of the false lumen. Retained patency of the false lumen can lead to either the development of a false lumen aneurysm with a subsequent rupture or extension of dissection. Typically such events occur late, usually months after repair, and are treated with either a conventional one-stage open thoracoabdominal repair or a two-stage "elephant trunk" procedure. However, most patients who undergo such procedures experience major complications and the procedure-related mortality rate is high. We present a unique case of a 61-year-old woman who presented with a ruptured type B aortic dissection 3 weeks after repair of a type A aortic dissection. She underwent an emergent thoracotomy and primary repair of the ruptured aorta followed by concomitant arch debranching and thoracic stent graft placement. Simultaneous surgical debranching with a median sternotomy and endovascular repair with stent grafts is an attractive hybrid approach in patients who present with an acute rupture of a false lumen aneurysm soon after initial repair of an aortic dissection, a situation in which a conventional repair is not feasible. This report emphasizes that hybrid thoracic stent graft repair should be considered for such high-risk patients in the near future as it offers them relatively lower morbidity and mortality compared with what is seen with conventional repairs.     

RIGHT SINUS OF VALSALVA ANEURYSM RUPTURE INTO THE RIGHT ATRIUM: PRE- AND POSTOPERATIVE ECHOCARDIOGRAPHIC FINDINGS

Echocardiographic features of a patient with sinus of Valsalva aneurysm rupture into the right atrium are discussed. An abnormal echo representing the aneurysmal sac was seen in the anterior aortic root. Other abnormal echoes were demonstrated in the right atrium. Flutter was visible in systole and diastole in the tricuspid area. The pulmonic valve echogram was normal. After surgical repair, the above findings disappeared.     

Biomechanical Characterization of Ascending Aortic Aneurysms

Biomechanics and Modeling in Mechanobiology - Ascending thoracic aortic aneurysms (ATAAs) are a silent disease, ultimately leading to dissection or rupture of the arterial wall. There is a growing...     

Radiation diagnosis of abdominal aortic aneurysms

Four hundred and forty seven patients with aneurysms of the abdominal aorta (AAA), including 238 patients with aneurysmal rupture, were admitted to the Research Institute of Emergency Care in 1990 to 2000. The results of studies in 225 patients (ultrasonography in 197, computed tomography in 59, and angiography in 104), including 155 patients with aneurysmal rupture were analyzed. Computed tomography (CT) has proved to be the most accurate technique in the detection and estimation of the size of aneurysms, as well as in the identification of ruptures (83.9%) and inferior to angiography (AG) in the study of involvement of the branches of the abdominal aorta. Ultrasound study (US) ranks below CT in its accuracy (US detects ruptures in 67.8%); however, US surpasses CT and AS in screening, particularly valuable at an admission unit and an intensive care unit, which permits repeated studies. AG has turned out to be the most valid method in identifying the involvement of renal and iliac arteries in aneurysm and in detecting aortocaval anastomoses; yet it is inferior to US and CT (the former revealed rupture and dissection in 18.6% of cases) in solving other diagnostic tasks. Based on the analysis, the optimal sequence of studies in the patients is US, CT, and AG.     

Identification of regional/layer differences in failure properties and thickness as important biomechanical factors responsible for the initiation of aortic dissections

Thoracic aortic dissections involving the ascending aorta represent one of the most dramatic and lethal emergencies in cardiovascular surgery. It is therefore critical to identify the mechanisms driving them and biomechanical analyses hold great clinical promise, since rupture/dissection occur when aortic wall strength is unable to withstand hemodynamic stresses. Although several studies have been done on the biomechanical properties of thoracic aortic aneurysms, few data are available about thoracic aortic dissections. Detailed mechanical tests with measurement of tissue thickness and failure properties were performed with a tensile-testing device on 445 standardized specimens, corresponding to 19 measurement sites per inner (intima with most of media)/outer layer (leftover media with adventitia); harvested from twelve patients undergoing emergent surgical repair for type A dissection. Our data suggested inherent differences in tissue properties between the origin of dissection and distal locations, i.e. thinner and stiffer inner layers that might render them more vulnerable to tearing despite their increased strength. The strength of tissue circumferentially was greater than that longitudinally, likely determining the direction of tear. The relative strengths of the inner: ∼{65,40}N/cm² and outer layer: ∼{350,270}N/cm² in the two principal directions of dissected tissue were differentiated from the intima: ∼{100,75}N/cm², media: ∼{150,55}N/cm², and adventitia: ∼{270,190}N/cm² of non-dissected ascending aortic aneurysms (Sokolis et al., 2012), in favor of weaker inner and stronger outer layers, allowing an explanation as to why the presently-studied tissue suffered dissection, i.e. tear of the inner layers, and not rupture, i.e. full tearing across the entire wall thickness.     

Stanford B型主动脉夹层撕破口局部计算流体力学研究

目的:探索Stanford B型主动脉夹层局部血流动力学改变对主动脉夹层发生、发展以及临床预后评估的作用,为临床治疗方案选择提供理论依据。方法:通过CT扫描获取临床常见典型形态的Stanford B型主动脉夹层断层序列,重建出三维主动脉夹层计算流体力学分析模型,对主动脉夹层真假腔内血液流场进行数值模拟计算。结果:血液流经Stanford B型主动脉夹层撕破口时会对血管局部壁面产生冲击,造成动脉管壁局部压强升高,此种"冲击效应"不但会出现在近端夹层撕破口附近管腔壁面,也会出现在中间段及远端夹层撕破口附近,当入口血流压强升高时,夹层撕破口附近局部壁面压强差值也会增加。在心动周期内,Stanford B型主动脉夹层壁面剪切应力异常升高区也主要集中在撕破口区附近的动脉壁面上。结论:对于Stanford B型主动脉夹层而言,撕破口的位置相对于撕破口直径而言似乎更有临床意义。对B型夹层患者采用降低血压治疗,可减低局部动脉管壁上的壁面压强差值,但无法消除此壁面压强差,即主动脉夹层管壁上的局部危险区始终存在。此现象揭示主动脉夹层中远端撕破口也可能是造成夹层局部危险因素的原因,采用手术治疗方法封闭撕破口,以消除局部壁面压强增高区,降低破裂风险,可能是更理想的治疗方法。     

A mechanical device for aortic compliance modulation: in vitro simulation of aortic dissection treatment

Stanford type A aortic dissection often rapidly leads to death from aortic rupture. We considered the possibility of introducing a passive counterpulsating damper into the dissected aorta in order to limit the physical stress associated with ventricular ejection and increase the diastolic aorto-ventricular pressure gradient. We conceived a damping device comprising an intravascular balloon connected to an adjustable external reservoir to regulate the air pressure inside the balloon, and performed a simulation study using a mechanical model of the cardiovascular system, mimicking aortic dissection. When the balloon was completely deflated, the behavior of the aortic pressure signal was typical of low-compliance aortic dissection, as characterized by an augmented maximum systolic value, accentuated diastolic decay, and a very low end-diastolic value. Balloon inflation (at incremental steps to 90 mmHg) progressively restored the aorto-ventricular pressure gradient and reduced peak systolic pressure values, leading to progressive improvements in the characteristics of the aortic pressure curve in terms of reduction in the maximum systolic value and slower diastolic decay. The proposed mechanism might exert beneficial effects at two levels: (1) directly, by reducing mechanical stress on the arterial wall; (2) indirectly, by allowing safer use of pharmaceutical agents (beta-blockers etc.). In vivo animal simulation studies are warranted to verify the effects of the device and optimize balloon shape and volume in a realistic pathophysiological setting.     

Surgical treatment of aortic dissection in a patient with metastatic prostate cancer

Acute aortic dissection bears all the stigmata of a true clinical emergency. The natural history of this acute aortic syndrome warrants prompt surgical intervention, with only a few absolute contraindications to this line of treatment. We present a 74-year-old man with documented metastatic prostate cancer who underwent emergent surgery for acute Stanford A aortic dissection. Having acknowledged the relatively favorable evolution of our patient's malignant disease, we were not deterred by its presence from pursuing surgical treatment of his aortic dissection.     

In vitro analysis of localized aneurysm rupture

In this study, bulge inflation tests were used to characterize the failure response of 15 layers of human ascending thoracic aortic aneurysms (ATAA). Full field displacement data were collected during each of the mechanical tests using a digital image stereo-correlation (DIS-C) system. Using the collected displacement data, the local stress fields at burst were derived and the thickness evolution was estimated during the inflation tests. It was shown that rupture of the ATAA does not systematically occur at the location of maximum stress, but in a weakened zone of the tissue where the measured fields show strain localization and localized thinning of the wall. Our results are the first to show the existence of weakened zones in the aneurysmal tissue when rupture is imminent. An understanding these local rupture mechanics is necessary to improve clinical assessments of aneurysm rupture risk. Further studies must be performed to determine if these weakened zones can be detected in vivo using non-invasive techniques.