Haemodynamic effects of non-Newtonian fluid blood on the abdominal aorta before and after double tear rupture.

OBJECTIVES: Intimal tears caused by aortic dissection can weaken the arterial wall and lead to aortic aneurysms. However, the effect of different tear states on the blood flow behaviour remains complex. This study uses a novel approach that combines numerical haemodynamic simulation with in vitro experiments to elucidate the effect of arterial dissection rupture on the complex blood flow state within the abdominal aneurysm and the endogenous causes of end-organ malperfusion. MATERIALS AND METHODS: Based on the CT imaging data and clinical physiological parameters, the overall arterial models including aortic dissection and aneurysm with single tear and double tear were established, and the turbulence behaviours and haemodynamic characteristics of arterial dissection and aneurysm under different blood pressures were simulated by using non-Newtonian flow fluids with the pulsatile blood flow rate of the clinical patients as a cycle, and the results of the numerical simulation were verified by in vitro simulation experiments. RESULTS: Hemodynamic simulations revealed that the aneurysm and single-tear false lumen generated a maximum pressure of 320.591 mmHg, 267 % over the 120 mmHg criterion. The pressure differential generates reflux, leading to a WSS of 2247.9 Pa at the TL inlet and blood flow velocities of up to 6.41 m/s inducing extend of the inlet. DTD Medium FL instantaneous WP above 120 mmHg Standard 151 % Additionally, there was 82.5 % higher flow in the right iliac aorta than in the left iliac aorta, which triggered malperfusion. Thrombus was accumulated distal to the tear and turbulence. These results are consistent with the findings of the in vitro experiments. CONCLUSIONS: This study reveals the haemodynamic mechanisms by which aortic dissection induces aortic aneurysms to produce different risk states. This will contribute to in vitro simulation studies as a new fulcrum in the process of moving from numerical simulation to clinical trials.

On the feasibility of ultrasound Doppler-based personalized hemodynamic modeling of the abdominal aorta.

BACKGROUND: Personalized modeling is a promising tool to improve abdominal aortic aneurysm (AAA) rupture risk assessment. Computed tomography (CT) and quantitative flow (Q-flow) magnetic resonance imaging (MRI) are widely regarded as the gold standard for acquiring patient-specific geometry and velocity profiles, respectively. However, their frequent utilization is hindered by various drawbacks. Ultrasound is used extensively in current clinical practice and offers a safe, rapid and cost-effective method to acquire patient-specific geometries and velocity profiles. This study aims to extract and validate patient-specific velocity profiles from Doppler ultrasound and to examine the impact of the velocity profiles on computed hemodynamics. METHODS: Pulsed-wave Doppler (PWD) and color Doppler (CD) data were successfully obtained for six volunteers and seven patients and employed to extract the flow pulse and velocity profile over the cross-section, respectively. The US flow pulses and velocity profiles as well as generic Womersley profiles were compared to the MRI velocities and flows. Additionally, CFD simulations were performed to examine the combined impact of the velocity profile and flow pulse. RESULTS: Large discrepancies were found between the US and MRI velocity profiles over the cross-sections, with differences for US in the same range as for the Womersley profile. Differences in flow pulses revealed that US generally performs best in terms of maximum flow, forward flow and ratios between forward and backward flow, whereas it often overestimates the backward flow. Both spatial patterns and magnitude of the computed hemodynamics were considerably affected by the prescribed velocity boundary conditions. Larger errors and smaller differences between the US and generic CFD cases were observed for patients compared to volunteers. CONCLUSION: These results show that it is feasible to acquire the patient-specific flow pulse from PWD data, provided that the PWD acquisition could be performed proximal to the aneurysm region, and resulted in a triphasic flow pattern. However, obtaining the patient-specific velocity profile over the cross-section using CD data is not reliable. For the volunteers, utilizing the US flow profile instead of the generic flow profile generally resulted in improved performance, whereas this was the case in more than half of the cases for the patients.

The role of asymmetry and volume of thrombotic masses in the formation of local deformation of the aneurysmal-altered vascular wall: An in vivo study and mathematical modeling.

Currently, the primary factor indicating the necessity of an operation for an abdominal aortic aneurysm (AAA) is the diameter at its widest part. However, in practice, a large number of aneurysm ruptures occur before reaching a critical size. This means that the mechanics of aneurysm growth and remodeling have not been fully elucidated. This study presents a novel method for assessing the elastic properties of an aneurysm using an ultrasound technique based on tracking the oscillations of the vascular wall as well as the inner border of the thrombus. Twenty nine patients with AAA and eighteen healthy volunteers were considered. The study presents the stratification of a group of patients according to the elastic properties of the aneurysm, depending on the relative volume of intraluminal thrombus masses. Additionally, the neural network analysis of CT angiography images of these patients shows direct (r = 0.664271) correlation with thrombus volume according to ultrasound data, the reliability of the Spearman correlation is p = 0.000215. The use of finite element numerical analysis made it possible to reveal the mechanism of the negative impact on the AAA integrity of an asymmetrically located intraluminal thrombus. The aneurysm itself is considered as a complex structure consisting of a wall, intraluminal thrombus masses, and areas of calcification. When the thrombus occupies > 70% of the lumen of the aneurysm, the deformations of the outer and inner surfaces of the thrombus have different rates, leading to tensile stresses in the thrombus. This poses a risk of its detachment and subsequent thromboembolism or the rupture of the aneurysm wall. This study is the first to provide a mechanistic explanation for the effects of an asymmetrical intraluminal thrombus in an abdominal aortic aneurysm. The obtained results will help develop more accurate risk criteria for AAA rupture using non-invasive conventional diagnostic methods.

Changes in the Remaining Iliac Artery According to Retrograde Flow after Aorto-Femoral Bypass in Abdominal Aortic Aneurysms.

BACKGROUND: Considering a patient's anatomy and vascular conditions, aorto-femoral bypass is a treatment approach for the open repair of abdominal aortic aneurysms. This study aimed at evaluating changes in the remnant iliac artery and their correlation with the preservation state of retrograde flow from femoral anastomosis. METHODS: Of 221 patients who underwent abdominal aortic aneurysm surgery between 2007 and 2022 in Pusan National University Hospital, 29 patients who underwent aorto-femoral bypass were included in this retrospective cohort study. Of these patients, 21 underwent aortobifemoral bypass and 8 underwent aortoiliac-and-femoral bypass. The change in size of the iliac artery from preoperative to postoperative and whether this difference in size depended on the status of postoperative retrograde flow were investigated. Additionally, factors affecting overall mortality and ischemic complications were identified. RESULTS: The median duration from operation to the last follow-up was 2069.5 days (about 5.7 years). The average age of the patients was 78.1 years, and the proportion of males was 75.9%. In cases of disappearance of postoperative retrograde flow from the femoral anastomosis, the postoperative iliac artery size was significantly reduced compared to its preoperative size (18.4 ± 18.9 mm vs. 13.2 ± 7.9 mm, respectively; P = 0.04). The group with maintained retrograde flow had significantly larger residual common iliac artery size than the group with disappearance of flow. (20.0 ± 28.0 mm vs. 14.6 ± 8.5 mm, respectively; P = 0.02). Disappearance of retrograde flow was a significant factor in the iliac artery size reduction after surgery (odds ratio, 2.5; 95% confidence interval, 1.9-5.3; P = 0.02). Three patients with maintained retrograde flow (18.8%) required intervention owing to an increase in the size of the iliac artery. The factors that significantly influenced overall death as analyzed by Cox proportional hazard regression were chronic obstructive pulmonary disease (hazard ratio, 36.8; 95% confidence interval, 1.6-870.0; P = 0.03), peripheral arterial occlusive disease (hazard ratio, 12.7; 95% confidence interval, 1.4-115.8; P = 0.02), and disappearance of retrograde flow (hazard ratio, 8.7; 95% confidence interval, 1.2-63.9; P = 0.03). CONCLUSIONS: Among the open repair methods for abdominal aortic aneurysms, if retrograde flow was not maintained through femoral anastomosis when aorto-femoral bypass was performed, the size of the remaining iliac artery decreased. However, loss of retrograde flow increased long-term mortality. When aorto-femoral bypass is performed, regular imaging follow-up is necessary at appropriate intervals to check the remnant iliac artery and retrograde flow.

Increased diameter and stiffness of elastic but not muscular arteries in men with abdominal aortic aneurysm.

It has been proposed that formation of abdominal aortic aneurysm (AAA) is part of a systemic arterial dilatative disease. However, arteries in the upper extremities are scarcely studied and it remains unclear whether both muscular and elastic arteries are affected by the proposed systemic arterial dilatation. The aim of this study was to investigate the diameter and stiffness of muscular and elastic arteries in arterial branches originating from the aortic arch. Twenty-six men with AAA (69 ± 4 yr) and 57 men without AAA (70 ± 5 yr) were included in the study. Ultrasound was used to examine the distal and proximal brachial artery, axillary artery, and common carotid artery (CCA), and measurement of diameter and diameter change was performed with wall-tracking software. Blood pressure measurements were used to calculate local arterial wall stiffness indices. The AAA cohort presented larger arterial diameters in the CCA and axillary artery after adjustment for body surface area (P = 0.002, respectively), whereas the brachial artery diameters were unchanged. Indices of increased stiffness in CCA (e.g., lower distensibility, P = 0.003) were seen in subjects with AAA after adjustments for body mass index and mean arterial blood pressure. This study supports the theory of a systemic arterial dilating diathesis in peripheral elastic, but not in muscular, arteries. Peripheral elastic arteries also exhibited increased stiffness, in analogy with findings in the aorta in AAA.NEW & NOTEWORTHY We present data partially supporting the notion of abdominal aortic aneurysm being a systemic vascular disease with focal manifestation in the abdominal aorta, from two well-defined groups recruited from a regional screening program. We show that elastic arteries distal from the aorta exhibit vascular alterations without aneurysmal formation in subjects with AAA compared with controls while muscular arteries seem unaffected.

The potential involvement of glycocalyx disruption in abdominal aortic aneurysm pathogenesis.

BACKGROUND: Abdominal aortic aneurysm is a weakening and expansion of the abdominal aorta. Currently, there is no drug treatment to limit abdominal aortic aneurysm growth. The glycocalyx is the outermost layer of the cell surface, mainly composed of glycosaminoglycans and proteoglycans. OBJECTIVE: The aim of this review was to identify a potential relationship between glycocalyx disruption and abdominal aortic aneurysm pathogenesis. METHODS: A narrative review of relevant published research was conducted. RESULTS: Glycocalyx disruption has been reported to enhance vascular permeability, impair immune responses, dysregulate endothelial function, promote extracellular matrix remodeling and modulate mechanotransduction. All these effects are implicated in abdominal aortic aneurysm pathogenesis. Glycocalyx disruption promotes inflammation through exposure of adhesion molecules and release of proinflammatory mediators. Glycocalyx disruption affects how the endothelium responds to shear stress by reducing nitric oxide availabilty and adversely affecting the storage and release of several antioxidants, growth factors, and antithromotic proteins. These changes exacerbate oxidative stress, stimulate vascular smooth muscle cell dysfunction, and promote thrombosis, all effects implicated in abdominal aortic aneurysm pathogenesis. Deficiency of key component of the glycocalyx, such as syndecan-4, were reported to promote aneurysm formation and rupture in the angiotensin-II and calcium chloride induced mouse models of abdominal aortic aneurysm. CONCLUSION: This review provides a summary of past research which suggests that glycocalyx disruption may play a role in abdominal aortic aneurysm pathogenesis. Further research is needed to establish a causal link between glycocalyx disruption and abdominal aortic aneurysm development.

Evaluation of Hemodynamic Properties After Chimney and Fenestrated Endovascular Aneurysm Repair.

BACKGROUND: Fenestrated (FEVAR) and chimney (ChEVAR) endovascular aortic repair have been applied in anatomically suitable complex aortic aneurysms. However, local hemodynamic changes may occur after repair. This study aimed to compare FEVAR's and ChEVAR's hemodynamic properties, focusing on visceral arteries. METHODS: Preoperative and postoperative computed tomography angiographies have been used to reconstruct patient-based models. Data of 3 patients, for each modality, were analyzed. Following geometric reconstruction, computational fluid dynamics simulations were used to extract near-wall and intravascular hemodynamic indicators, such as pressure drops, velocity, wall shear stress, time averaged wall shear stress, oscillatory shear index, relative residence time, and local normalized helicity. RESULTS: An overall improvement in hemodynamics was detected after repair, with either technique. Preoperatively, a disturbed prothrombotic wall shear stress profile was recorded in several zones of the sac. The local normalized helicity results showed a better organization of the helical structures at postoperative setting, decreasing thrombus formation, with both modalities. Similarly, time averaged wall shear stress increased and oscillatory shear index decreased postoperatively, signaling nondisturbed blood flow. The relative residence time was locally reduced. The flow in visceral arteries tended to be more streamlined in ChEVAR, compared to evident recirculation regions at renal and superior mesenteric artery fenestrations (P = 0.06). CONCLUSIONS: ChEVAR and FEVAR seem to improve hemodynamics toward normal values with a reduction of recirculation zones in the main graft and aortic branches. Visceral artery flow comparison revealed that ChEVAR tended to present lower recirculation regions at parallel grafts' entries while FEVAR showed less intense flow regurgitation in visceral stents.

Arterial Stiffness and Aortic Aneurysmal Disease - A Narrative Review.

It has been documented that large-artery stiffness is independently associated with increased cardiovascular risk and may potentially lead to heart and kidney failure and cerebrovascular disease. A systematic review of studies investigating changes in arterial stiffness in patients undergoing endovascular repair of aortic disease was conducted. In addition, a review of the available literature was performed, analyzing findings from studies using the cardio-ankle vascular index (CAVI) as a marker of arterial stiffness. Overall, 26 studies were included in the present analysis. Our research revealed a high heterogeneity of included studies regarding the techniques used to assess the aortic stiffness. Aortic stiffness was assessed by pulse wave velocity (PWV), elastic modulus (Ep), and augmentation index (AI). Currently a few studies exist investigating the role of CAVI in patients having an aortic aneurysm or undergoing endovascular aortic repair. The majority of studies showed that the treatment of an abdominal aortic aneurysm (AAA) either with open repair (OR) or endovascular aortic repair (EVAR) reduces aortic compliance significantly. Whether EVAR reconstruction might contribute a higher effect on arterial stiffness compared to OR needs further focused research. An increase of arterial stiffness was uniformly observed in studies investigating patients following thoracic endovascular aortic repair (TEVAR), and the effect was more pronounced in young patients. The effects of increased arterial stiffness after EVAR and TEVAR on the heart and the central hemodynamic, and an eventual effect on cardiac systolic function, need to be further investigated and evaluated in large studies and special groups of patients.

Long-term outcomes of staged iliofemoral endoconduits prior to complex endovascular aortic aneurysm repair.

OBJECTIVE: Adverse iliofemoral anatomy may preclude complex endovascular aortic aneurysm repair (EVAR). In our practice, staged iliofemoral endoconduits (ECs) are planned prior to complex EVAR to improve vascular access and decrease operative time while allowing the stented vessel to heal. This study describes the long-term results of iliofemoral ECs prior to complex EVAR. METHODS: Between 2012 and 2023, 59 patients (44% male; median age, 75 ± 6 years) underwent ECs before complex EVAR using self-expanding covered stents (Viabahn). For common femoral artery (CFA) disease, ECs were delivered percutaneously from contralateral femoral access and extended into the CFA to preserve the future access site for stent graft delivery. Internal iliac artery patency was maintained when feasible. During complex EVAR, the EC extended into the CFA was directly accessed and sequentially dilated until it could accommodate the endograft. Technical success was defined as successful access, closure, and delivery of the endograft during complex EVAR. Endpoints were vascular injury or EC disruption, secondary interventions, and EC patency. RESULTS: Unilateral EC was performed in 45 patients (76%). ECs were extended into the CFA in 21 patients (35%). Median diameters of the native common iliac, external iliac, and CFA were 7 mm (interquartile range [IQR], 6-8 mm), 6 mm (IQR, 5-7 mm), and 6 mm (IQR, 6-7 mm), respectively. Internal iliac artery was inadvertently excluded in 10 patients (17%). Six patients (10%) had an intraoperative vascular injury during the EC procedure, and six patients (10%) had EC disruption during complex EVAR, including five EC collapses requiring re-stenting and one EC fracture requiring open cut-down and reconstruction with patch angioplasty. In 23 patients (39%), 22 Fr OD devices were used; 20 Fr were used in 22 patients (37%), and 18 Fr in 14 patients (24%). Technical success for accessing EC was 89%. There was no difference in major adverse events at 30 days between the iliac ECs and iliofemoral ECs. Primary patency by Kaplan-Meier estimates at 1, 3, and 5 years were 97.5%, 89%, and 82%, respectively. There was no difference in primary patency between iliac and iliofemoral ECs. Six secondary interventions (10%) were required. The mean follow-up was 34 ± 27 months; no limb loss or amputations occurred during the follow-up. CONCLUSIONS: ECs improve vascular access, and their use prior to complex EVAR is associated with low rates of vascular injury, high technical success, and optimal long-term patency. Complex EVAR procedures can be performed percutaneously by accessing the EC directly under ultrasound guidance and using sequential dilation to avoid EC disruption.

Reinterventions and sac dynamics after fenestrated endovascular aortic repair with physician-modified endografts for index aneurysm repair and following proximal failure of prior endovascular aortic repair.

OBJECTIVE: The high frequency of reinterventions after fenestrated endovascular aortic repair (FEVAR) with physician-modified endografts (PMEGs) has been well-studied. However, the impact of prior EVAR on reinterventions and sac behavior following these procedures remains unknown. We analyzed 3-year rates of reinterventions and sac dynamics following PMEG for index aneurysm repair compared with PMEG for prior EVAR with loss of proximal seal. METHODS: We performed a retrospective analysis of 122 consecutive FEVARs with PMEGs at a tertiary care center submitted to the United States Food and Drug Administration in support of an investigational device exemption trial. We excluded patients with aortic dissection (n = 5), type I to III thoracoabdominal aneurysms (n = 13), non-elective procedures (n = 4), and prior aortic surgery other than EVAR (n = 8), for a final cohort of 92 patients. Patients were divided into those who underwent PMEG for index aneurysm repair (primary FEVAR) and those who underwent PMEG for rescue of prior EVAR with loss of proximal seal (secondary FEVAR). The primary outcomes were freedom from reintervention and sac dynamics (regression as ≥5 mm decrease, expansion as ≥5 mm increase, and stability as <5 mm increase or decrease) at 3 years. Secondary outcomes were perioperative mortality and 3-year survival. RESULTS: Of the 92 patients included, 56 (61%) underwent primary FEVAR and 36 (39%) underwent secondary FEVAR. Secondary FEVAR patients were older (78 years [interquartile range (IQR), 74.5-83.5 years] vs 73 years [IQR, 69-78.5 years]; P < .001), more frequently male (86% vs 68%; P = .048), and had larger aneurysms (72.5 mm [IQR, 65.5-81 mm] vs 59 mm [IQR, 55-65 mm]; P < .001). Perioperative mortality was 1.8% for primary FEVAR and 2.7% for secondary FEVAR (P = .75). At 3 years, overall survival was 84% for primary FEVAR and 71% for secondary FEVAR (P = .086). Freedom-from reintervention was significantly higher for primary FEVAR than secondary FEVAR, specifically 82% vs 38% at 3 years (P < .001). Primary FEVAR also had more desirable sac dynamics relative to secondary FEVAR at 3 years (primary: 54% stable, 46% regressed, 0% expanded vs secondary: 33% stable, 28% regressed, and 39% expanded; P = .038). CONCLUSIONS: FEVAR for primary aortic repair and FEVAR for rescue of prior EVAR with loss of proximal seal are two distinct entities. Following primary FEVAR, less than a quarter of patients have undergone reintervention at 3 years, and sac expansion was not seen in our cohort. Comparatively, 3 years after secondary FEVAR, over one-half of patients have undergone reintervention and over one-third have had ongoing sac expansion. Vigilant surveillance and a low threshold for further interventions are crucial following secondary FEVAR.

A stable aneurysm sac after endovascular aneurysm repair as a predictor for mortality: An in-depth analysis.

OBJECTIVE: The aim of the present study was to compare the long-term survival of patients with a stable aneurysm sac vs those with aneurysm sac regression after endovascular aneurysm repair (EVAR) and to identify the independent risk factors for aneurysm sac regression and mortality after EVAR. METHODS: We reviewed all the patients who had undergone EVAR from 2005 to 2018 with computed tomography angiography available at 1 year of follow-up. Aneurysm sac regression was defined as a diameter decrease of >10%. We used multivariable regression to identify the independent risk factors for sac regression. Kaplan-Meier analysis and Cox regression were performed to test the differences in 5-year mortality between a stable sac diameter and sac regression. RESULTS: The inclusion criteria were met by 325 patients, with 185 in the sac regression group and 140 in the stable sac group. Multivariable logistic regression analysis showed that treatment of a ruptured aneurysm was an independent risk factor for aneurysm sac regression (hazard ratio [HR], 0.26; 95% confidence interval [CI], 0.07-0.96). Age (HR, 1.05; 95% CI, 1.01-1.09), ischemic heart disease (HR, 1.94; 95% CI, 1.13-3.31), neck thrombus (HR, 2.72; 95% CI, 1.07-6.95), and a type II endoleak (HR, 19.21; 95% CI, 7.32-50.40) were independent risk factors for a stable aneurysm sac diameter. Multivariable Cox regression showed a significantly increased risk of mortality for patients with a stable aneurysm sac after EVAR (odds ratio, 2.25; 95% CI, 1.36-3.72). No significant differences were found in cause of death between the two groups. CONCLUSIONS: A stable aneurysm sac after EVAR was associated with increased mortality. Age, ischemic heart disease, neck thrombus, and a type II endoleak were independent risk factors for a stable aneurysm sac. However, a well-founded explanation for this finding is still lacking. Future research should focus on aggressive treatment of type II endoleaks and inflammatory processes as potential pathophysiologic mechanisms.

Real-Time Evaluation of Blood Flow Patterns Using AneurysmFlow for an in vivo Abdominal Aortic Aneurysm Model.

BACKGROUND: Many new tools for abdominal aortic aneurysm (AAA) rupture risk evaluation have been developed. These new tools need detailed hemodynamic information in AAA. However, hemodynamic data obtained from in vivo research are lacking. Thus, the objective of this study was to analyze blood flow patterns in an in vivo AAA model to acquire real-time hemodynamic information using AneurysmFlow, a novel flow evaluation system. METHODS: Digital subtraction angiography images of patients who underwent endovascular aneurysm repair were analyzed using the visualization function of the AneurysmFlow to classify blood flow patterns as laminar or turbulent flow. The presence of boundary layer separation was also evaluated. The time taken for contrast medium to travel from the infrarenal aortic neck to aortic bifurcation was acquired to calculate the flow velocity. Associations between characteristics of aneurysm including lumen occupying ratio of intraluminal thrombus (ILT) and the hemodynamic flow pattern were evaluated. RESULTS: A total of 37 AAA patients was enrolled. Their blood flow patterns were evaluated using the AneurysmFlow. Logistic regression analyses with lumen occupying ratio of ILT as an independent variable showed that the larger the lumen occupying ratio of ILT, the more likely the aneurysm was to show a laminar pattern (P = 0.03), and the more likely the boundary layer separation would not exist (P = 0.04). The flow velocity from the infrarenal aortic neck to the aortic bifurcation showed a positive association with the lumen occupying ratio of the ILT in linear regression analysis (P < 0.001). CONCLUSIONS: Hemodynamic analysis of AAA with the AneurysmFlow using real-time individual patient models showed different flow patterns and flow velocities depending on ILT. This novel analytic approach using AneurysmFlow has potential to play an important role in obtaining clinically meaningful hemodynamic information of AAA.

The Femoral Venoarterial Perfusion During Open Abdominal Aortic Aneurysm Repair in Patient With Renal Transplant.

We report of a patient with abdominal aortic aneurysm and renal transplant who underwent aneurysm repair. These patients can be treated by eather open or endovascular approach, depending on several factors, including aneurysm morphologic suitability for endovascular tretament, age of patient, and comorbidities.The main challange with open repair approach is to maintain renal transplant perfusion during the aortic cross clamping. Several methods of renal transplant perfusion during aneurysm repair have been described. In this case, we opted for open aneurysm repair beacuse of the age of the patient. The femoral venoarterial perfusion technique using extracorporal circulation machine was employed. We found this technique safe and easy in treating such patients.

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.

Degeneration and Regeneration of Smooth Muscle Cells in Two Different Abdominal Aortic Aneurysm Models in Rabbits.

BACKGROUND: We aimed to investigate the formation and self-healing process of rabbit abdominal aortic aneurysm (AAA) by focus on the degeneration and regeneration of smooth muscle cells (SMCs) in elastase-induced AAA model and enlarging AAA model in rabbits. METHODS: Sixty rabbits were equally divided into 2 aneurysm groups (Group A and Group B). Rabbits received a 10-min incubation of elastase in Group A (10 units/µL) and Group B (1 unit/µL). Rabbits underwent aortic stenosis above the incubated segment in Group B. Aortic diameter was measured and rabbits were sacrificed for histopathological and immunohistochemical studies. RESULTS: The incubated aorta dilated immediately and ran up to maxima by day 21 in Group A. All aneurysms formed by day 21 and enlarged progressively in Group B. SMCs content, elastin content and intima-media thickness decreased significantly by day 0 in Group A. SMCs and elastic fibers were destroyed gradually in Group B, however, SMCs content was significantly lower than Group A by day 70. Intimal thickness increased significantly by day 70 in the Aneurysm groups. MMP2 maintained moderate expression in Group A, which decreased significantly by day 3 in Group B. MMP9 and RAM11 expressions were higher by day 1, but decreased significantly by day 3 in Group B. CONCLUSIONS: Irreversible degeneration of SMCs is critical to a rapid formation of elastase-induced rabbit AAA model, and SMCs excessive regeneration accounts for the selfhealing process. SMCs degradation and regeneration remain relatively stable in an enlarging AAA model. SMCs should be the key target for studying the mechanism of AAA and intervention therapy.

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.

Mid-Term Outcomes of Chimney Endovascular Aortic Aneurysm Repair: A Systematic Review and Meta-analysis.

BACKGROUND: To provide an overview of the literature on the mid-term outcomes of chimney EVAR (ChEVAR) for the treatment of juxtarenal abdominal aortic aneurysms (JAAA). METHODS: Different electronic databases were searched for published articles up to January 2020. The eligibility criteria were studies describing mid- or long-term outcomes of chimney EVAR (mean follow-up at least 1 year) for treatment of JAAA, including more than 10 cases, published in English, and with full text available. The outcomes measure were overall survival rate, target vessel patency, and freedom from reintervention at 3 years. Quality of the included studies was analyzed using the MINORS criteria. Pooled effect estimates were analyzed using random-effect models and heterogeneity was tested using I2 statistics. RESULTS: Thirteen articles met the inclusion criteria. The included studies described 1,019 patients. According to the quality assessment, methodological quality was moderate to poor. The pooled overall survival, freedom from reintervention, and target vessel patency at 3 year was 81.4 % (95%CI 73.8-87.9), 85.7% (95%CI 75.6-93.5), and 95.1% (95%CI 89.3-98.7) respectively. CONCLUSIONS: The results of this review show good to acceptable short and mid-term survival and good mid-term durability, which supports that ChEVAR as a suitable alternative in high-risk JAAA. However, proper patient selection for ChEVAR seems essential to attain good mid-term outcomes, and further large prospective and good quality studies are required to demonstrate its long-term results and enable conclusions on specific determinants for outcome.

Midterm Outcomes of Endovascular Abdominal Aortic Aneurysm Repair with Prevention of type 2 Endoleak by Intraoperative Aortic Side Branch Coil Embolization.

OBJECTIVE: The midterm results of endovascular abdominal aortic aneurysm repair (EVAR) with aortic side branch coil embolization during EVAR was evaluated. METHODS: Our center began coil embolization for all patent inferior mesenteric artery (IMA) and lumbar artery (LA) with an inner diameter more than 2.0 mm during EVAR since June 2015. When four or more LA were patent, coil embolization for LA with inner diameter 2.0 mm or less was done. EVAR without aortic side branches coil embolization was performed for 59 patients prior to June 2015 (control group) and 79 patients underwent EVAR with coil embolization during EVAR (coil group). The success rate of coil embolization for IMA and LA was evaluated in coil group. The frequency of type 2 endoleak (T2EL), freedom from aneurysm sac expansion (5 mm or more) rate and the rate of the aneurysm sac shrinkage (10 mm or more) were compared between the coil and control groups. Additionally, multiple logistic regression analysis for all patients was conducted to analyze whether IMA patency and the number of patent lumbar artery at the end of EVAR were the risk factors of the aneurysm sac expansion of 5 mm or more. RESULTS: The success rate of IMA coil embolization was 96.4% and that of LA was 74.5%. Compared to the control group, the frequency of T2EL was significantly lower in coil group at 7 days (1.3% vs. 60.4%, P <0.0001) and at 6 months (2.1% vs 38.2%, P <0.0001) after EVAR. The freedom from aneurysm sac expansion rate was significantly better in the coil group at 5 years (100% in coil group and 65.2% in control group, P = 0.002). The rate of aneurysm sac shrinkage was significantly better in coil group (15.5% vs. 2.0% at 1 year, 42.8% vs. 6.3% at 2 years and 53.4% vs. 17.8% at 3 years, p = 0.0007). The risk of aneurysm sac expansion of 5 mm or more was estimated to be 11 times greater when the IMA was patent, and 4.9 times greater when 3 or more LAs were patent at the end of EVAR. CONCLUSION: When IMA was occluded and the number of patent LA became 2 or less by aortic side branch coil embolization during EVAR, favorable mid-term results were safely obtained and good long-term result could be expected with EVAR.

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.