Emergency Repair of a Ruptured Para-Renal Abdominal Aortic Aneurysm in a Patient with a Functional Renal Graft: A Case Report and Review of the Literature.

INDRODUCTION: Rupture of and abdominal aortic aneurysm (AAA) in a kidney transplant patient is a rare and rarely reported event. Emergent treatment can be challenging and should achieve effective aortic repair while minimizing ischemic damage to the renal graft during aortic cross-clamping. Several renal protective measures have been proposed such as permanent or temporary shunts, renal cold perfusion and general hypothermia. CASE REPORT: We report the effective treatment of a para-renal AAA in a patient with a functional renal allograft. A temporary extra-corporeal axillofemoral shunt was constructed to maintain graft's perfusion during open surgical repair. EVAR was not an option due to a short aortic neck. The postoperative period was complicated by colon ischemia and aortic graft infection. At 3 years follow-up the patient was well and graft's function was unchanged. CONCLUSION: This case is a reminder that renal graft protection must be accounted for when AAA rupture occurs in kidney transplant patients. We reviewed the literature to find previously reported cases and how they were managed.

Stress Analysis in AAA does not Predict Rupture Location Correctly in Patients with Intraluminal Thrombus.

BACKGROUND: A biomechanical approach to the rupture risk of an abdominal aortic aneurysm could be a solution to ensure a personalized estimate of this risk. It is still difficult to know in what conditions, the assumptions made by biomechanics, are valid. The objective of this work was to determine the individual biomechanical rupture threshold and to assess the correlation between their rupture sites and the locations of their maximum stress comparing two computed tomography scan (CT) before and at time of rupture. METHODS: We included 5 patients who had undergone two CT; one within the last 6 months period before rupture and a second CT scan just before the surgical procedure for the rupture. All DICOM data, both pre- and rupture, were processed following the same following steps: generation of a 3D geometry of the abdominal aortic aneurysm, meshing and computational stress analysis using the finite element method. We used two different modelling scenarios to study the distribution of the stresses, a "wall" model without intraluminal thrombus (ILT) and a "thrombus" model with ILT. RESULTS: The average time between the pre-rupture and rupture CT scans was 44 days (22-97). The median of the maximum stresses applied to the wall between the pre-rupture and rupture states were 0.817 MPa (0.555-1.295) and 1.160 MPa (0.633-1.625) for the "wall" model; and 0.365 MPa (0.291-0.753) and 0.390 MPa (0.343-0.819) for the "thrombus" model. There was an agreement between the site of rupture and the location of maximum stress for only 1 patient, who was the only patient without ILT. CONCLUSIONS: We observed a large variability of stress values at rupture sites between patients. The rupture threshold strongly varied between individuals depending on the intraluminal thrombus. The site of rupture did not correlate with the maximum stress except for 1 patient.

Characterizing Tissue Remodeling and Mechanical Heterogeneity in Cerebral Aneurysms.

Accurately assessing the complex tissue mechanics of cerebral aneurysms (CAs) is critical for elucidating how CAs grow and whether that growth will lead to rupture. The factors that have been implicated in CA progression - blood flow dynamics, immune infiltration, and extracellular matrix remodeling - all occur heterogeneously throughout the CA. Thus, it stands to reason that the mechanical properties of CAs are also spatially heterogeneous. Here, we present a new method for characterizing the mechanical heterogeneity of human CAs using generalized anisotropic inverse mechanics, which uses biaxial stretching experiments and inverse analyses to determine the local Kelvin moduli and principal alignments within the tissue. Using this approach, we find that there is significant mechanical heterogeneity within a single acquired human CA. These results were confirmed using second harmonic generation imaging of the CA's fiber architecture and a correlation was observed. This approach provides a single-step method for determining the complex heterogeneous mechanics of CAs, which has important implications for future identification of metrics that can improve accuracy in prediction risk of rupture.

Low Shear Stress at Baseline Predicts Expansion and Aneurysm-Related Events in Patients With Abdominal Aortic Aneurysm.

BACKGROUND: Low shear stress has been implicated in abdominal aortic aneurysm (AAA) expansion and clinical events. We tested the hypothesis that low shear stress in AAA at baseline is a marker of expansion rate and future aneurysm-related events. METHODS: Patients were imaged with computed tomography angiography at baseline and followed up every 6 months >24 months with ultrasound measurements of maximum diameter. From baseline computed tomography angiography, we reconstructed 3-dimensional models for automated computational fluid dynamics simulations and computed luminal shear stress. The primary composite end point was aneurysm repair and/or rupture, and the secondary end point was aneurysm expansion rate. RESULTS: We included 295 patients with median AAA diameter of 49 mm (interquartile range, 43-54 mm) and median follow-up of 914 (interquartile range, 670-1112) days. There were 114 (39%) aneurysm-related events, with 13 AAA ruptures and 98 repairs (one rupture was repaired). Patients with low shear stress (<0.4 Pa) experienced a higher number of aneurysm-related events (44%) compared with medium (0.4-0.6 Pa; 27%) and high (>0.6 Pa; 29%) shear stress groups (P=0.010). This association was independent of known risk factors (adjusted hazard ratio, 1.72 [95% CI, 1.08-2.73]; P=0.023). Low shear stress was also independently associated with AAA expansion rate (ß=+0.28 mm/y [95% CI, 0.02-0.53]; P=0.037). CONCLUSIONS: We show for the first time that low shear stress (<0.4 Pa) at baseline is associated with both AAA expansion and future aneurysm-related events. Aneurysms within the lowest tertile of shear stress, versus those with higher shear stress, were more likely to rupture or reach thresholds for elective repair. Larger prospective validation trials are needed to confirm these findings and translate them into clinical management.

Ruptured sinus of valsalva aneurysm presenting as syncope and hypotension: a case report.

BACKGROUND: Unruptured sinus of valsalva aneurysm (SOVA) are typically asymptomatic, and hence can be easily ignored. Ruptured sinus of valsalva aneurysm (RSOVA) usually protrude into the right atrium or ventricular. However, in this case, the RSOVA protruded into the space between the right atrium and the visceral pericardium leading to compression of the right proximal coronary artery. Very few such cases have been reported till date. CASE PRESENTATION: We describe a case of ruptured right SOVA in a 61-year-old man with syncope and persistent hypotension. At the beginning, considered the markedly elevated troponin, acute myocardial infarction was considered. However, emergency coronary angiography unexpectedly revealed a large external mass compressed right coronary artery (RCA) resulting in severe proximal stenosis. Then, aorta computed tomography angiography (CTA) and urgent surgery confirmed that the ruptured right SOVA led to external compression of the right proximal coronary artery. Finally, ruptured right SOVA repair and RCA reconstruction were successfully performed, and the patient was discharged with no residual symptoms. CONCLUSIONS: It is very important to be vigilant about the existence of SOVA. RSOVA should be suspected in a patient presenting with acute hemodynamic compromise, and echocardiography should be immediately performed. Moreover, it is very important to achieve dynamic monitoring by using cardiac color ultrasound. Definitive diagnosis often requires cardiac catheterization, and an aortogram should be performed unless endocarditis is suspected.

Biomechanical Analysis of Cadaveric Thoracic Aorta Zones: The Isthmus is the Weakest Region.

BACKGROUND: The thoracic aorta is a site of multiple pathological processes, such as aneurysms and dissections. When considering the development of endovascular devices, this vessel has been extensively manipulated because of aortic diseases, as well as to serve as a route for procedures involving the head and neck vessels. Therefore, the aim of the present study was to obtain biomechanical experimental information about the strength and deformability of this vessel. MATERIALS AND METHODS: Thirty-one thoracic aorta specimens were harvested during the autopsy procedure. They were carefully dissected and transversally sectioned according to Criado's aortic arch map landing zones (0 to 4). The supra-aortic trunks were removed, and the aortic rings were opened in their convexity, which resulted in flat tissue segments. Four millimeter-wide strips were prepared from each zone after which they were attached to a clip system connected to the INSTRON SPEC 2200 device, which was responsible for pulling the fragment up to its rupture during the uniaxial tension test. The INSPEC software was used to coordinate the test, and data management was conducted via the SERIES IX software. The biomechanical variables that were measured included failure stress, failure tension, and failure strain. RESULTS: When comparing the five segments from all 31 aortas, three different strength levels were observed. Zones 0 and 1 exhibited the highest failure stress and failure tension values, followed by Zones 2 and 4. Zone 3 (aortic isthmus) was the weakest segment that was tested when compared to the stress and tension of Zones 0 and 1 (P < 0.001), the stress and tension of Zone 2 (P = 0.005 and P = 0.002, respectively) and the stress and tension of Zone 4 (P = 0.023 and P = 0.006, respectively). Among donors > 65 years-old, women presented significantly weaker descending aortas than men in regards to stress (P = 0.049) and tension (P = 0.014). Among male donors, the elderly donors presented significantly stiffer aortic walls and weaker ascending (P = 0.029 for stress) and descending (P = 0.004 for stress; P = 0.031 for tension) aortas than younger men. CONCLUSIONS: Uniaxial tensile strength tests revealed that the thoracic aorta is a very heterogeneous vessel. Isthmus frailty may add to the understanding of the pathophysiology of some aortic diseases that commonly compromise this region. The lower strength that was verifiedin some aortic segments from elderly donors may contribute to the genesis of some thoracic aorta diseases among that group of donors. These data can contribute to the development of new endovascular devices that are specifically designed for this vessel.

Comparison of peak wall stress and peak wall rupture index in ruptured and asymptomatic intact abdominal aortic aneurysms.

BACKGROUND: Previous studies have suggested that finite element analysis (FEA) can estimate the rupture risk of an abdominal aortic aneurysm (AAA); however, the value of biomechanical estimates over measurement of AAA diameter alone remains unclear. This study aimed to compare peak wall stress (PWS) and peak wall rupture index (PWRI) in participants with ruptured and asymptomatic intact AAAs. METHODS: The reproducibility of semiautomated methods for estimating aortic PWS and PWRI from CT images was assessed. PWS and PWRI were estimated in people with ruptured AAAs and those with asymptomatic intact AAAs matched by orthogonal diameter on a 1 : 2 basis. Spearman's correlation coefficient was used to assess the association between PWS or PWRI and AAA diameter. Independent associations between PWS or PWRI and AAA rupture were identified by means of logistic regression analyses. RESULTS: Twenty individuals were included in the analysis of reproducibility. The main analysis included 50 patients with an intact AAA and 25 with a ruptured AAA. Median orthogonal diameter was similar in ruptured and intact AAAs (82·3 (i.q.r. 73·5-92·0) versus 81·0 (73·2-92·4) mm respectively; P = 0·906). Median PWS values were 286·8 (220·2-329·6) and 245·8 (215·2-302·3) kPa respectively (P = 0·192). There was no significant difference in PWRI between the two groups (P = 0·982). PWS and PWRI correlated positively with orthogonal diameter (both P < 0·001). Participants with high PWS, but not PWRI, were more likely to have a ruptured AAA after adjusting for potential confounders (odds ratio 5·84, 95 per cent c.i. 1·22 to 27·95; P = 0·027). This association was not maintained in all sensitivity analyses. CONCLUSION: High aortic PWS had an inconsistent association with greater odds of aneurysm rupture in patients with a large AAA.

Mechanical role of intraluminal thrombus in aneurysm growth: A computational study.

Models that seek to improve our current understanding of biochemical processes and predict disease progression have been increasingly in use over the last decades. Recently, we proposed a finite element implementation of arterial wall growth and remodeling with application to abdominal aortic aneurysms (AAAs). The study focused on changes within the aortic wall and did not include the complex role of intraluminal thrombus (ILT) during the AAA evolution. Thus, in this work, we extend the model with a gradual deposition of ILT and its mechanical influence on AAA growth. Despite neglecting the increased biochemical activity due to the presence of a proteolytically active luminal layer of ILT, and thus underestimating rupture risk potential, we show that ILT helps to slow down the growth of the aneurysm in the axial direction by redirecting blood pressure loading from the axial-radial plane to predominately radial direction. This very likely lowers rupture potential. We also show that the ratio of ILT volume to volume sac is an important factor in AAA stabilization and that fully thrombosed aneurysms could stabilize quicker and at smaller maximum diameters compared to partially thrombosed ones. Furthermore, we show that ILT formation and the associated mural stress decrease negatively impact the wall constituent production and thickness. Although further studies that include increased biochemical degradation of the wall after the formation of ILT and ILT deposition based on hemodynamics are needed, the present findings highlight the dual role an ILT plays during AAA progression.

Preoperative risk score accuracy confirmed in a modern ruptured abdominal aortic aneurysm experience.

OBJECTIVE: Various risk score calculators used to predict 30-day mortality after treatment of ruptured abdominal aortic aneurysms (rAAAs) have produced mixed results regarding their usefulness and reproducibility. We prospectively validated the accuracy of our preoperative scoring system in a modern cohort of patients with rAAAs. METHODS: A retrospective review of all patients wiith rAAAs who had presented to a single academic center from January 2002 to December 2018 was performed. The patients were divided into three cohorts according to when the institutional practice changes had occurred: the pre-endovascular aneurysm repair (EVAR) era (January 2002 to July 2007), the pre-Harbor View risk score era (August 2007 to October 2013), and the modern era (November 2013 to December 2018). The primary outcome measure was 30-day mortality. Our preoperative risk score assigns 1 point for each of the following: age >76 years, pH <7.2, creatinine >2 mg/dL, and any episode of hypotension (systolic blood pressure <70 mm Hg). The previously reported mortality from a retrospective analysis of the first two cohorts was 22% for 1 point, 69% for 2 points, 78% for 3 points, and 100% for 4 points. The goal of the present study was to prospectively validate the Harborview scoring system in the modern era. RESULTS: During the 17-year study period, 417 patients with rAAAs were treated at our institution. Of the 118 patients treated in the modern era, 45 (38.1%) had undergone open aneurysm repair (OAR), 61 (51.7%) had undergone EVAR, and 12 (10.2%) had received comfort measures only. Excluding the 12 patients without aneurysm repair, we found a statistically significant linear trend between the preoperative risk score and subsequent 30-day mortality for all patients combined (P < .0001), for OAR patients alone (P = .0003), and for EVAR patients alone (P < .0001). After adjustment for the Harborview risk score, the 30-day mortality was 41.3% vs 31.6% after OAR vs EVAR, respectively (P = .2). For all repairs, the 30-day mortality was 14.6% for a score of 0, 35.7% for a score of 1, 68.4% for a score of 2, and 100% for a score of 3 or 4. CONCLUSIONS: Our results, representing one of the largest modern series of rAAAs treated at a single institution, have confirmed the accuracy of a simple 4-point preoperative risk score in predicting 30-day mortality in the modern rAAA patient. Such tools should be used when discussing the treatment options with referring physicians, patients, and their family members to help guide transfer and treatment decision-making.

Multiple Chimney Endografts (ChEVAR) for Ruptured Pararenal Aortic Aneurysm.

We present a ruptured pararenal abdominal aortic aneurysm repaired with a complex three-vessel chimney EVAR . This technique allows for rapid sealing of the aneurysm with branch preservation and avoids complex open aortic surgery. This case report highlights techniques and pitfalls from complex three-vessel chimney EVAR repair in the emergency setting.

3D Modeling of Blood Flow in Simulated Abdominal Aortic Aneurysm.

BACKGROUND: Besides biological factors, abdominal aortic aneurysm rupture is also caused by mechanical parameters, which are constantly affecting the wall's tissue due to their abnormal values. The ability to evaluate these parameters could vastly improve the clinical treatment of patients with abdominal aortic aneurysms. The objective of this study was to develop and demonstrate a methodology to analyze the fluid dynamics that cause the wall stress distribution in abdominal aortic aneurysms, using accurate 3D geometry and a realistic, nonlinear, elastic biomechanical model using a computer-aided software. METHODS: The geometry of the abdominal aortic aneurysm; was constructed on a 3D scale using computer-aided software SolidWorks (Dassault Systems SolidWorksCorp., Waltham MA). Due to the complex nature of the abdominal aortic aneurysm geometry, the physiological forces and constraints acting on the abdominal aortic aneurysm wall were measured by using a simulation setup using boundary conditions and initial conditions for different studies such as finite element analysis or computational fluid dynamics. RESULTS: The flow pattern showed an increase velocity at the angular neck, followed by a stagnated flow inside the aneurysm sack. Furthermore, the wall shear stress analysis showed to focalized points of higher stress, the top and bottom of the aneurysm sack, where the flow collides against the wall. An increase of the viscosity showed no significant velocity changed but results in a slight increase in overall pressure and wall shear stress. CONCLUSIONS: Conducting computational fluid dynamics modeling of the abdominal aortic aneurysm using computer-aided software SolidWorks (Dassault Systems SolidWorksCorp., Waltham MA) proves to be an insightful approach for the clinical setting. The careful consideration of the biomechanics of the abdominal aortic aneurysm may lead to an improved, case-specific prediction of the abdominal aortic aneurysm rupture potential, which could significantly improve the clinical management of these patients.

Prediction of Distal Aortic Enlargement after Proximal Repair of Aortic Dissection Using Machine Learning.

OBJECTIVES: This study aimed to construct a risk prediction model for distal aortic enlargement in patients with type B aortic dissection (TBAD) treated with proximal thoracic endovascular aortic repair (TEVAR). METHODS: From June 2010 to June 2016, patients with TBAD who underwent proximal TEVAR were retrospectively analyzed. A total of 38 clinical and imaging variables were collected. Univariable logistic regression was conducted to explore potential risk factors associated with distal aortic enlargement. Elastic net regression was employed to select significantly influential variables. Then, machine learning algorithms (logistic regression (LR), artificial neutral network (ANN), random forest and support vector machine) were applied to build risk prediction models. The area under the receiver operating characteristic curve (AUC), sensitivity and specificity were used to evaluate the performance of these models. RESULTS: A total of 503 patients were enrolled in this study. During the follow-up, 105 (20.9%) patients were identified as having distal aortic enlargement, and 69 (13.7%) patients were found to have distal aortic aneurysm formation. Five patients were identified with aortic rupture. True lumen collapse and multi-false lumens were two potential risk factors for distal aortic enlargement after proximal repair of TBAD. The LR model performed the best in predicting distal aortic enlargement, with the highest sensitivity (96.7%) and an AUC of 0.773. The best model for predicting distal aneurysm formation was the ANN model, which yielded the highest AUC (0.876) and a specificity of 79.1%. CONCLUSIONS: Machine learning approaches can produce accurate predictions of distal aortic enlargement after proximal repair of TBAD, which potentially benefits subsequent management.

Abdominal aortic aneurysms.

Abdominal aortic aneurysms (AAA) are prevalent among older adults and can cause significant morbidity and mortality if not addressed in a timely fashion. Their etiology remains the topic of continued investigation. Known causes include trauma, infection, and inflammatory disorders. Risk factors include cigarette smoking, advanced age, dyslipidemia, hypertension, and coronary artery disease. The pathophysiology of the disease is related to an initial arterial insult causing a cascade of inflammation and extracellular matrix protein breakdown by proteinases leading to arterial wall weakening. When identified early, aneurysms must be monitored for size, growth rate, and other factors which could increase the risk of rupture. Factors predisposing to rupture include size, active smoking, rate of growth, aberrant biomechanical properties of the aneurysmal sac, and female sex. Medical management includes the control of risk factors that may prevent growth, stabilize the aneurysm, and prevent rupture. Surgical management prevents rupture of high risk aneurysms, most commonly predicted by size. Less frequently, surgical management is required when the aneurysm has ruptured. Surgery involves a multidisciplinary approach to evaluate the patient's risk profile and to develop an operative plan involving either an endovascular or an open surgical repair. The patient must be carefully monitored post-operatively for complications and, in the case of endovascular repairs, for endoleaks. AAA management has evolved rapidly in recent years. Technical and technological advances have transformed the diagnosis and treatment of this disease.

Systematic Review and Meta-Analysis of Peak Wall Stress and Peak Wall Rupture Index in Ruptured and Asymptomatic Intact Abdominal Aortic Aneurysms.

Background Prior studies have suggested aortic peak wall stress (PWS) and peak wall rupture index (PWRI) can estimate the rupture risk of an abdominal aortic aneurysm (AAA), but whether these measurements have independent predictive ability over assessing AAA diameter alone is unclear. The aim of this systematic review was to compare PWS and PWRI in participants with ruptured and asymptomatic intact AAAs of similar diameter. Methods and Results Web of Science, Scopus, Medline, and The Cochrane Library were systematically searched to identify studies assessing PWS and PWRI in ruptured and asymptomatic intact AAAs of similar diameter. Random-effects meta-analyses were performed using inverse variance-weighted methods. Leave-one-out sensitivity analyses were conducted to assess the robustness of findings. Risk of bias was assessed using a modification of the Newcastle-Ottawa scale and standard quality assessment criteria for evaluating primary research papers. Seven case-control studies involving 309 participants were included. Meta-analyses suggested that PWRI (standardized mean difference, 0.42; 95% CI, 0.14-0.70; P=0.004) but not PWS (standardized mean difference, 0.13; 95% CI, -0.18 to 0.44; P=0.418) was greater in ruptured than intact AAAs. Sensitivity analyses suggested that the findings were not dependent on the inclusion of any single study. The included studies were assessed to have a medium to high risk of bias. Conclusions Based on limited evidence, this study suggested that PWRI, but not PWS, is greater in ruptured than asymptomatic intact AAAs of similar maximum aortic diameter.

Hemodynamic Changes in an Actively Rupturing Abdominal Aortic Aneurysm.

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

Early and midterm results from a postmarket observational study of Zenith t-Branch thoracoabdominal endovascular graft.

OBJECTIVE: We have reported the short-term outcomes regarding the safety of the off-the-shelf Zenith t-Branch multibranched thoracoabdominal stent-graft (William Cook Europe ApS, Bjaeverskov, Denmark) in a postmarket, multicenter study. METHODS: Patients who had been treated with the t-Branch device from September 2012 to November 2017 at three European centers were either prospectively or retrospectively enrolled in the present study. Device implantation and postprocedural follow-up were performed according to the standard of care at each center. The primary objectives of the present study were to assess the procedure-related mortality and morbidity at 30 days and 1 year and to assess the presence of endoleaks, device integrity, and stent-graft and branch vessel patency. RESULTS: A total of 80 patients were included in the present study (mean age, 71.0 ± 7.4 years; 70.0% male). Most (n = 77) had been treated for thoracoabdominal aortic aneurysms (TAAAs) and the rest for dissection (n = 3). Most TAAAs were stable (72.7%; 56 of 77). The remaining TAAAs were symptomatic (7.8%; 6 of 77) or had a contained rupture (19.5%; 15 of 77). The t-Branch device was successfully deployed in 79 patients. In one patient, the delivery system of the device could not be advanced through the iliac artery. Within 30 days, one patient had died (1.3%). At 1 year, seven patients had died (8.8%), and no aortic rupture or conversion to open surgery had been reported. The 30-day neurologic events included stroke in three patients (3.8%), paraplegia in one (1.3%), and paraparesis in six patients (7.5%). Secondary interventions were required in nine patients (11.3%) during follow-up. Postoperative endoleaks were observed in 37 of 72 patients (51.4%), including type II endoleak in 30, type Ia in 4, and type III endoleak in 6 patients. At 1 year, endoleaks had been reported in 20 patients (16 with type II and 4 with type III). The t-Branch main body graft patency was 100% throughout the 1-year follow-up period. At 30 days after the procedure, all celiac and superior mesenteric artery branches were patent and one left renal and one right renal branch were occluded. At 1 year, occlusion had developed in three bridging stent-grafts for the celiac artery, one for the left renal artery, and two for the right renal artery. CONCLUSIONS: The t-Branch device appears safe, with good 30-day and 1-year mortality and morbidity in the present study, including both stable and symptomatic cases.

Estimating aortic thoracic aneurysm rupture risk using tension-strain data in physiological pressure range: an in vitro study.

Previous studies have shown that the rupture properties of an ascending thoracic aortic aneurysm (ATAA) are strongly correlated with the pre-rupture response features. In this work, we present a two-step machine learning method to predict where the rupture is likely to occur in ATAA and what safety reserve the structure may have. The study was carried out using ATAA specimens from 15 patients who underwent surgical intervention. Through inflation test, full-field deformation data and post-rupture images were collected, from which the wall tension and surface strain distributions were computed. The tension-strain data in the pressure range of 9-18 kPa were fitted to a third-order polynomial to characterize the response properties. It is hypothesized that the region where rupture is prone to initiate is associated with a high level of tension buildup. A machine learning method is devised to predict the peak risk region. The predicted regions were found to match the actual rupture sites in 13 samples out of the total 15. In the second step, another machine learning model is utilized to predict the tissue's rupture strength in the peak risk region. Results suggest that the ATAA rupture risk can be reasonably predicted using tension-strain response in the physiological range. This may open a pathway for evaluating the ATAA rupture propensity using information of in vivo response.

Reasons for and Outcomes of Open Abdominal Aortic Repair in the Endovascular Era.

BACKGROUND: Endovascular aortic aneurysm repair (EVAR) has become the treatment of choice for most patients with abdominal aortic aneurysm (AAA). Open aneurysm repair (OAR) is still being used in a number of patients for specific reasons. The aim of the present study was to investigate the reasons and perioperative outcomes of OAR in a high-volume endovascular center. METHODS: All patients who underwent OAR in a single center institution during the period April 2010 to July 2019 were retrospectively analyzed. RESULTS: During the study period, 222 patients underwent OAR. One hundred and forty-one (63.5%) patients underwent elective surgery, and eighty-one (36.5%) patients were treated acutely. The reasons for the decision to perform OAR instead of EVAR were as follows: anatomical in 89 (40.1%) cases, rupture in unstable patient in 57 (25.7%) cases, AAA with concomitant iliac arterial occlusive disease in 44 (19.8%) cases, previous EVAR with complications in 14 (6.3%) cases, large pararenal aneurysm considered risky to wait for a customized fenestrated stent graft in 7 (3.2%) cases, young patient age in 4 (1.8%) cases, the patient's preference in 3 (1.4%) cases, infected/mycotic AAA in 2 (0.9%) cases, and simultaneous OAR with colon cancer resection (n = 1, 0.5%) and renal transplantation (n = 1, n = 0.5). Thirty-day mortality in elective cases was 5% (7/141) and in acute cases 34.6% (28/81). CONCLUSIONS: This study shows that OAR is still used for selected patients despite improvements in EVAR technology. The most common reason for OAR was an unsuitable anatomy for EVAR. Perioperative mortality of OAR both for acute and elective cases as observed in this study is in line with published outcomes of other centers.