Multicentre Evaluation of an Extra Low Dose Protocol to Reduce Radiation Exposure in Superior Mesenteric Artery Stenting.

OBJECTIVE: Radiation dose in mesenteric stenting (MS) remains under evaluated. Yet, MS can lead to high levels of radiation mainly because lateral angulation is needed. The aim of this study was to evaluate the efficacy of an extra low dose protocol (ELDP) to reduce radiation exposure in MS. METHODS: From November 2017 to November 2019, all patients presenting with either acute or chronic atherosclerotic mesenteric ischaemia treated by antegrade MS using either fixed or mobile imaging systems in three university hospitals were included. In November 2018, an ELDP including ≤3 frames/s fluoroscopy and digital subtraction angiography (DSA) was introduced. Prospectively enrolled ELDP patients (Nov 2018-Nov 2019) were compared with retrospectively captured patients (Historical group, Nov 2017-Nov 2018). Radiation data including dose area product (DAP), cumulative air kerma (CAK), and fluoroscopy time (FT) were analysed. RESULTS: Overall, 46 patients (median age 73 years [63-72], 59% males) were included (ELDP group, n = 21; Historical group, n = 25). Thirty-three patients (72%) underwent MS in a hybrid room. Median DAP (ELDP group, 10 [4.7-26] Gy.cm2vs. Historical group, 45 [24-88] Gy.cm2, p = .002), median CAK (ELDP group, 170 [58-260] vs. Historical group, 262 [152-460], p = .037), and median number of DSA runs (ELDP group, 4 [1.5-5] vs. Historical group, 5.5 [3.7-5], p = .030) were statistically significantly lower in patients receiving the ELDP, whereas median FT (ELDP group, 16 min [11-23] vs. Historical group, 14 min [9-25], p = .71) and technical success (ELDP group, 95%; Historical group, 92%, p = .65) were not statistically significantly different between groups. CONCLUSION: MS exposes both patients and physicians to a high ionising radiation dose. Awareness of radiation safety and seeking dose reduction is paramount in these highly irradiating procedures. The use of ELDP significantly reduces radiation without compromising technical success.

Comparison of Cryopreserved Arterial Allografts Versus Heparin-bonded Vascular Grafts in Infragenicular Bypass for Chronic Limb Threatening Ischemia.

BACKGROUND: The purpose of this study was to compare cryopreserved arterial allograft (CAA) to heparin-bonded prosthesis (HBP) in infragenicular bypasses for patients with chronic limb-threatening ischemia (CLTI). METHODS: This retrospective study took place in 2 university hospitals and included 41 consecutive patients treated for CLTI. In the absence of a suitable saphenous vein, an infragenicular bypass was performed using either CAA (24 cases) or HBP (17 cases). Kaplan-Meyer analysis compared primary and secondary patency and amputation-free survival rates. Binomial logistic regression analyzed risk factors for major amputation and thrombosis. RESULTS: The mean followup was 18.5 months (±14.3) in the CAA group, 17.6 (±6.1) in the HBP group. In the CAA group, primary and secondary patency rates at 12 months were 52% (±10.6) and 61% (±10.3), compared to 88% (±7.8) and 94% (±5.7) in the HBP group, respectively. The difference in patency rates was not statistically different (P = 0.27 and P = 0.28, respectively). The statistically significant factors of graft thrombosis were, a stage 4 from the WIfI classification (Wound Ischemia foot Infection) with a 6 times higher risk (P = 0.04), and a distal anastomosis on a leg artery with a 9 times higher risk of thrombosis (P = 0.03). Amputation-free survival rates at 18 months were similar between the groups (CCA: 75% (±9) versus HBP: 94% (±6), P = 0.11). Patients classified as WIfI stage 4 had 13 times higher odds to undergo major amputation than patients with WIfI stage 2 or 3 (95% CI, 1.16-160.93; P = 0.04). The intervention was longer in the CCA group of 74 min (278 min ± 86) compared to the HBP group (203 min ± 69). This difference was statistically significant (95% CI, 17.86-132.98), t(35) = 2.671, P = 0.01. CONCLUSIONS: CCA is not superior to HBP in infragenicular bypasses for CLTI, and may not be worth the extra cost and the longer operative duration.

Lower Rate of Restenosis and Reinterventions With Covered vs Bare Metal Stents Following Innominate Artery Stenting.

PURPOSE: To determine any difference between bare metal stents (BMS) and balloon-expandable covered stents in the treatment of innominate artery atheromatous lesions. MATERIALS AND METHODS: A multicenter retrospective study involving 13 university hospitals in France collected 93 patients (mean age 63.2±11.1 years; 57 men) treated over a 10-year period. All patients had systolic blood pressure asymmetry >15 mm Hg and were either asymptomatic (39, 42%) or had carotid (20, 22%), vertebrobasilar (24, 26%), and/or brachial (20, 22%) symptoms. Innominate artery stenosis ranged from 50% to 70% in 4 (4%) symptomatic cases and between 70% and 90% in 52 (56%) cases; 28 (30%) lesions were preocclusive and 8 (9%) were occluded. One (1%) severely symptomatic patient had a <50% stenosis. Demographic characteristics, operative indications, and procedure details were compared between the covered (36, 39%) and BMS (57, 61%) groups. Multivariate analysis was performed to determine relative risks of restenosis and reinterventions [reported with 95% confidence intervals (CI)]. RESULTS: The endovascular procedures were performed mainly via retrograde carotid access (75, 81%). Perioperative strokes occurred in 4 (4.3%) patients. During the mean 34.5±31.2-month follow-up, 30 (32%) restenoses were detected and 13 (20%) reinterventions were performed. Relative risks were 6.9 (95% CI 2.2 to 22.2, p=0.001) for restenosis and 14.6 (95% CI 1.8 to 120.8, p=0.004) for reinterventions between BMS and covered stents. The severity of the treated lesions had no influence on the results. CONCLUSION: Patients treated with BMS for innominate artery stenosis have more frequent restenoses and reinterventions than patients treated with covered stents.

Treatment of Complex Aortic Aneurysms Using Combination of Renal and Visceral Bypass and Fenestrated/Branched Stent Grafts.

BACKGROUND: The purpose of this study was to report our experience of treatment of aortic aneurysms using combination of renal and visceral arteries bypasses and fenestrated/branched stent graft in various complex anatomical situations. METHODS: Between November 2005 and March 2017, 10 patients underwent a hybrid strategy combining bypasses for renal and/or visceral arteries and custom-made fenestrated/branched stent grafts. Two patients had abdominal aortic aneurysm (1 juxtarenal and 1 suprarenal), and 8 patients had thoracoabdominal aortic aneurysm (1 type I, 2 type II including one dissection, 2 type III, 1 type IV, and 2 type V). In total, 37 renal and visceral arteries were targeted, of which 23 were treated using fenestrated or branched stent graft and 14 were treated by bypass (11 to renal artery and 3 to celiac trunk). RESULTS: Technical success was 100%, and no patient died during a mean follow-up of 24.3 ± 21 months. Six patients had 7 postoperative complications after bypass surgery, and 3 patients had 3 complications after fenestrated or branched endovascular aneurysm repair (FEVAR/BEVAR) procedure. Seven reinterventions were performed in 3 patients. No occlusion of target vessels occurred. Renal function was stable during follow-up in all patients except one who developed end-stage renal failure requiring permanent dialysis. On the last follow-up computed tomography scan, aneurysm diameter decreased for 6 patients, was stable for 3 patients, and increased for one patient, in which persistent type II endoleak was observed. Aneurysm exclusion was complete in the remaining 9 patients. CONCLUSIONS: Combination of FEVAR/BEVAR procedures with renal and/or visceral artery bypass in patients with complex aortic aneurysms is feasible with acceptable results. Morbidity associated with bypass surgery has to be carefully balanced with the risk of catheterization difficulties in the setting of adverse anatomical features of the visceral/renal arteries or the aorta.

Cryopreserved arterial allografts for in situ reconstruction of abdominal aortic native or secondary graft infection.

OBJECTIVE: The objective of this study was to evaluate the early and long-term outcome of cryopreserved arterial allografts (CAAs) used for in situ reconstruction of abdominal aortic native or secondary graft infection and to identify predictors of mortality. METHODS: We retrospectively included 71 patients (mean age, 65.2 years [range, 41-84 years]; men, 91.5%) treated for abdominal aortic native or secondary graft infection (65 prosthetic graft infections; 16 of them had secondary aortoenteric fistula, 2 venous graft infections, and 4 mycotic aneurysms) by in situ reconstruction with CAA in the university hospitals of Clermont-Ferrand and Saint-Etienne from 2000 to 2016. The cryopreservation protocol was identical in both centers (-140°C). Early (<30 days) and late (>30 days) mortality and morbidity, reinfection, and CAA patency were assessed. Computed tomography was performed in all survivors. Survival was analyzed with the Kaplan-Meier method. Univariate analyses were performed with the log-rank test and multivariate analysis with the Cox regression model. RESULTS: Mean follow-up was 45 months (0-196 months). Early postoperative mortality rate was 16.9% (11/71). Early postoperative CAA-related mortality rate was 2.8% (2/71); both patients died of proximal anastomotic rupture on postoperative days 4 and 15. Early CAA-related reintervention rate was 5.6% (4/71); all had an anastomotic rupture, and two were lethal. Early postoperative reintervention rate was 15.5% (11/71). Intraoperative bacteriologic samples were positive in 56.3%, and 31% had a sole microorganism. Escherichia coli was more frequently identified in the secondary aortoenteric fistula and Staphylococcus epidermidis in the infected prosthesis. Late CAA-related mortality rate was 2.8%: septic shock at 2 months in one patient and proximal anastomosis rupture at 1 year in one patient. Survival at 1 year, 3 years, and 5 years was 75%, 64%, and 54%, respectively. Multivariate analysis identified type 1 diabetes (hazard ratio, 2.49; 95% confidence interval, 1.05-5.88; P = .04) and American Society of Anesthesiologists class 4 (hazard ratio, 2.65; 95% confidence interval, 1.07-6.53; P = .035) as predictors of mortality after in situ CAA reconstruction. Reinfection rate was 4% (3/71). Late CAA-related reintervention rate was 12.7% (9/71): proximal anastomotic rupture in one, CAA branch stenosis/thrombosis in five, ureteral-CAA branch fistula in one, and distal anastomosis false aneurysm in two. Primary patency at 1 year, 3 years, and 5 years was 100%, 93%, and 93%, respectively. Assisted primary patency at 1 year, 3 years, and 5 years was 100%, 96%, and 96%, respectively. No aneurysm or dilation was observed. CONCLUSIONS: The prognosis of native or secondary aortic graft infections is poor. Aortic in situ reconstruction with CAA offers acceptable early and late results. Patients with type 1 diabetes and American Society of Anesthesiologists class 4 are at higher risk of mortality.

Endovascular Repair of a Short Neck Abdominal Aortic Aneurysm with a Physician-Modified Vascutek Anaconda Stent Graft.

An 81-year-old woman was referred for the treatment of a 79-mm-diameter short neck abdominal aortic aneurysm with highly tortuous iliac arteries. She was considered at high risk for open repair and not suitable for standard endovascular repair given the short length of the proximal neck. Delay for a manufactured custom-made fenestrated stent graft was too long given the diameter of the aneurysm. A flexible stent graft was preferred because of severe iliac tortuosity. Endovascular repair was performed using a physician-modified Anaconda stent graft with 1 fenestration for the left renal artery. The technique for device modification and implantation is described. Postoperative course was uneventful and 1-year computed tomography scan showed complete exclusion of the aneurysm sac and patent left renal artery.

Prognostic Value of Aortoiliac Calcification Score in Kidney Transplantation Recipients.

BACKGROUND: Kidney recipients are increasingly older with arterial disease and extended arterial calcifications. In a kidney transplantation population, the prognosis value of aortic and iliac calcifications remains poorly explored. We aimed to assess the impact of pretransplantation aortoiliac vascular calcifications on patients, grafts survival, and cardiovascular events. METHODS: This retrospective study included kidney transplantation patients from 2006 to 2012 for whom we had available presurgery abdominal computed tomography results (n = 100). We designed a score to quantify aortoiliac calcifications. Primary end points were patient and graft survival. Secondary end points were renal function and cardiovascular morbidity. Predictive performances of calcification score were assessed using area under receiver-operating characteristic curves. Patients were classified in quartiles depending on global calcium score value. RESULTS: The cumulated rate of death and graft loss was 13% with no significant differences for survival between quartiles. No significant difference was observed in renal function (P = 0.4). Seventeen cardiovascular events were registered with a significant correlation between calcium score elevation and need of cardiovascular surgery during the follow-up (P = 0.01). Global calcium score had a predictive value of 74.5% (95% confidence interval 0.62-0.87) with 71% sensitivity and 73% specificity. CONCLUSIONS: Aortoiliac calcifications do not decrease patient and graft survival. High calcium score predict cardiovascular events and procedures during the follow-up.

Renovascular hypertension: results in adulthood of renal autotransplantation performed in children.

BACKGROUND: This study describes the long-term results of renal autotransplantation for renovascular hypertension performed in children who are now 21 years of age or older. METHODS: Sixteen children (4 boys, 12 girls) with a mean age of 11.2 years at the time of the procedure underwent ex-vivo surgery at the university hospital of Saint-Etienne between 1992 and 2008. Acetylsalicylic acid was used for antiplatelet therapy in the postoperative period, without routine anticoagulation. The mean follow-up period was 15 years. The clinical course of these patients was retrospectively reviewed in adulthood and the results analyzed. RESULTS: The children were treated with a mean of 2.37 drugs per patient, and the mean preoperative blood pressure of the entire patient population was 151/89 mmHg. Mean preoperative creatinine clearance was 80 ml/min/1.73 m2. There was no postoperative death. One patient experienced a thrombosis immediately after the surgery, leading to a redo surgery. In this patient diuresis was restarted, but without efficient concentration and filtration, ultimately leading the patient to have a renal transplant after 1 year. At the end of the follow-up period, eight of the 16 patients (50%) were cured and the others were improved. At the last follow-up the mean blood pressure was 127/70 mmHg, and the mean number of drugs per patient was 0.68. The mean creatinine clearance at last follow-up was 104.3 ml/min/1.73 m2. Three patients had secondary procedures, with two undergoing percutaneous angioplasty (at postoperative months 9 and 12, respectively) and one having an hepatorenal bypass at postoperative year 4. Primary patency was 12/16 (75%); primary assisted patency was 15/16 (94%); secondary patency was 16/16 (100%). CONCLUSION: This study shows that renal autotransplantation has good and stable long-term results and is an effective conservative strategy for treating renovascular hypertension in children, thus avoiding nephrectomy.

Renal Function after Fenestrated or Branched Endovascular Aortic Repair: The Early Impairment Predictive Factors.

BACKGROUND: The purpose of this study was to define predictive factors of early renal impairment after fenestrated or branched endovascular aortic repair (FEVAR or BEVAR) for aortic aneurysm. METHODS: Eighty-two patients underwent FEVAR or BEVAR for aortic aneurysm from January 2008 to December 2014. The primary end point was postoperative renal impairment on day 15 (D15). Renal impairment was defined as a 25% decrease in the glomerular filtration rate (GFR) and a GFR < 60 mL/min/1.73 m2 according to the Risk Injury Failure Loss and End-Stage criteria. Univariate and multivariate analyses were used to determine variables associated with early postoperative renal impairment. RESULTS: Seventy-seven of the 82 patients had a creatinine level on D15 and were included in this study, including a total of 145 target renal arteries. A preoperative GFR < 60 mL/min/1.73 m2 was present in 16 (20.8%) patients. On D15, 8 (10.4%) patients had an early postoperative renal impairment and 21 (27.3%) patients had a GFR < 60 mL/min/1.73 m2. A single patient had immediate postoperative dialysis for 10 days. "Perirenal hematoma" and "preoperative renal length under 100 mm" were significantly associated with the occurrence of the renal impairment after mutual adjustment in multivariate analysis (P < 0.001 and P = 0.01). No significant association was found between preoperative renal insufficiency combining all stages or with a GFR < 60 mL/min/1.73 m2 and early renal impairment after surgery (P = 0.096 and P = 0.263). CONCLUSION: The presence of a reduced preoperative renal length and the postoperative occurrence of a perirenal hematoma are predictive factors of renal impairment on D15 for patients treated with FEVAR or BEVAR.

Characteristics of thoracic aortic aneurysm rupture in vitro.

UNLABELLED: Ascending thoracic aortic aneurysms (ATAAs) are focal dilatations in the aorta that are prone to rupture or dissection. To accurately evaluate the rupture risk, one must know the local mechanical conditions at the rupture site and understand how rupture is triggered in a layered fibrous media. A challenge facing experimental studies of ATAA rupture is that the ATAA tissue is highly heterogeneous; experimental protocols that operate under the premise of tissue homogeneity will have difficulty delineating the location conditions. In this work, we employed a previously established pointwise identification method to characterize wall stress, strain, and property distributions to a sub-millimeter resolution. Based on the acquired field data, we obtained the local mechanical properties at the rupture site in nine ATAA tissue samples. The rupture stress, ultimate strain, energy density, and the toughness of the tested samples were also reported. Our results show that the direction of the rupture is aligned with the direction of maximum stiffness, indicating that higher stiffness is not always related to higher strength. It was also found that the rupture generally occurs at a location of highest stored energy. As a higher stiffness and higher strain energy indicate a larger recruitment of collagen fibers in the tissue at the location and along the direction of rupture, the recruitment of collagen fibers in the deformation of the tissue is probably essential in ATAA rupture. STATEMENT OF SIGNIFICANCE: A major challenge in the experimental study of aneurysm properties is that the tissues are heterogeneous. When the specimens are not reasonably homogeneous, traditional tests that work under the premise of tissue homogeneity cannot reliably delineate the local conditions at the rupture site. In this work, we investigated the local characteristics of rupture of human ascending aortic aneurysm tissue. We identified the stress, strain, and elastic properties to a submillimeter resolution. Based on the field values, we determined the local conditions - elastic properties, direction of maximum stiffness, stress, strain, energy consumption - at the rupture site. It was found that the tissues consistently cleave in the direction of the maximum stiffness, and generally occurs at the location of highest energy. Since a higher stiffness and higher strain energy indicate a larger recruitment of collagen fibers in the tissue at the location and along the direction of rupture, the work suggests that the recruitment of collagen fibers in the deformation of the tissue is probably essential in aneurysm rupture.

Biaxial rupture properties of ascending thoracic aortic aneurysms.

UNLABELLED: Although hundreds of samples obtained from ascending thoracic aortic aneurysms (ATAA) of patients undergoing elective surgical repair have already been characterized biomechanically, their rupture properties were always derived from uniaxial tensile tests. Due to their bulge shape, ATAAs are stretched biaxially in vivo. In order to understand the biaxial rupture of ATAAs, our group developed a novel methodology based on bulge inflation and full-field optical measurements. The objective of the current paper is threefold. Firstly, we will review the failure properties (maximum stress, maximum stretch) obtained by bulge inflation testing on a cohort of 31 patients and compare them with failure properties obtained by uniaxial tension in a previously published study. Secondly, we will investigate the relationship between the failure properties and the age of patients, showing that patients below 55years of age display significantly higher strength. Thirdly, we will define a rupture risk based on the extensibility of the tissue and we will show that this rupture risk is strongly correlated with the physiological elastic modulus of the tissue independently of the age, ATAA diameter or the aortic valve phenotype of the patient. STATEMENT OF SIGNIFICANCE: Despite their medical importance, rupture properties of ascending thoracic aortic aneurysms (ATAA) subjected to biaxial tension were inexistent in the literature. In order to address this lack, our group developed a novel methodology based on bulge inflation and full-field optical measurements. Here we report rupture properties obtained with this methodology on 31 patients. It is shown for the first time that rupture occurs when the stretch applied to ATAAs reaches the maximum extensibility of the tissue and that this maximum extensibility correlates strongly with the elastic properties. The outcome is a better detection of at-risk individuals for elective surgical repair.

Unusual complication during a percutaneous coronary intervention for a bifurcation lesion using T and Protrusion technique.

Our case reports the first migration of a stent already deployed at high pressure in the main vessel during a 2-stent strategy for a bifurcation lesion using T and protrusion technique. The Kissing balloon was not optimal and could have led to an insufficient strut/cell opening and then to LAD stent pulled back into the artery tree. This case report highlights the importance of an optimal Kissing Balloon in two stent bifurcation technique.

Local mechanical properties of human ascending thoracic aneurysms.

Ascending thoracic aortic aneurysms (ATAAs) are focal, asymmetric dilatations of the aortic wall which are prone to rupture. To identify potential rupture locations in advance, it is necessary to consider the inhomogeneity of the ATAA at the millimeter scale. Towards this end, we have developed a combined experimental and computational approach using bulge inflation tests, digital image correlation (DIC), and an inverse membrane approach to characterize the pointwise stress, strain, and hyperelastic properties of the ATAA. Using this approach, the pointwise hyperelastic material properties were identified on 10 human ATAA samples collected from patients undergoing elective surgery to replace their ATAAs with a graft. Our method was able to capture the varying levels of heterogeneity in the ATAA from regional to local. It was shown for the first time that the material properties in the ATAA are unmistakably heterogeneous at length scales between 1mm and 1cm, which are length scales where vascular tissue is typically treated as homogeneous. The distributions of the material properties for each patient were also examined to study the inter- and intra-patient variability. Large inter-subject variability was observed in the elastic properties.

Predictive Models with Patient Specific Material Properties for the Biomechanical Behavior of Ascending Thoracic Aneurysms.

The aim of this study is to identify the patient-specific material properties of ascending thoracic aortic aneurysms (ATAA) using preoperative dynamic gated computed tomography (CT) scans. The identification is based on the simultaneous minimization of two cost functions, which define the difference between model predictions and gated CT measurements of the aneurysm volume at respectively systole and cardiac mid-cycle. The method is applied on five patients who underwent surgical repair of their ATAA at the University Hospital Center of St. Etienne. For these patients, the aneurysms were collected and tested mechanically using an in vitro bench. For the sake of validation, the mechanical properties found using the in vivo approach and the in vitro bench were compared. We eventually performed finite-element stress analyses based on each set of material properties. Rupture risk indexes were estimated and compared, showing promising results of the patient-specific identification method based on gated CT.

Patient specific stress and rupture analysis of ascending thoracic aneurysms.

An ascending thoracic aortic aneurysm (ATAA) is a serious medical condition which, more often than not, requires surgery. Aneurysm diameter is the primary clinical criterion for determining when surgical intervention is necessary but, biomechanical studies have suggested that the diameter criterion is insufficient. This manuscript presents a method for obtaining the patient specific wall stress distribution of the ATAA and the retrospective rupture risk for each patient. Five human ATAAs and the preoperative dynamic CT scans were obtained during elective surgeries to replace each patient's aneurysm with a synthetic graft. The material properties and rupture stress for each tissue sample were identified using bulge inflation tests. The dynamic CT scans were used to generate patient specific geometries for a finite element (FE) model of each patient's aneurysm. The material properties from the bulge inflation tests were implemented in the FE model and the wall stress distribution at four different pressures was estimated. Three different rupture risk assessments were compared: the maximum diameter, the rupture risk index, and the overpressure index. The peak wall stress values for the patients ranged from 28% to 94% of the ATAA's failure stress. The rupture risk and overpressure indices were both only weakly correlated with diameter (ρ=-0.29, both cases). In the future, we plan to conduct a large experimental and computational study that includes asymptomatic patients under surveillance, patients undergoing elective surgery, and patients who have experienced rupture or dissection to determine if the rupture risk index or maximum diameter can meaningfully differentiate between the groups.

Endovascular repair of mitroaortic intervalvular fibrosa aneurysm after bentall surgery.

We report the first case of a successful transapical transcatheter treatment of a giant pseudoaneurysm originating from a rupture of the mitroaortic fibrosa that occurred 3 months after a Bentall procedure in a 81-year-old male patient. Because of the age of the patient and the location of the leak at the mitroaortic fibrosa, the risk of a conventional ascending aorta reoperation was considered too high, and a transcatheter approach was chosen. A transapical puncture was performed with a left minithoracotomy followed by a catheterization of the pseudoaneurysm neck and an 8-mm Amplatzer (St. Jude Medical, Saint Paul, MN, USA) device was delivered, resulting in a successful complete endovascular exclusion of the pseudo-aneurysmal sac.

Pointwise characterization of the elastic properties of planar soft tissues: application to ascending thoracic aneurysms.

In this manuscript, we present a combined experimental and computational technique that can identify the heterogeneous elastic properties of planar soft tissues. By combining inverse membrane analysis, digital image correlation, and bulge inflation tests, we are able to identify a tissue's mechanical properties locally. To show how the proposed method could be implemented, we quantified the heterogeneous material properties of a human ascending thoracic aortic aneurysm (ATAA). The ATAA was inflated at a constant rate using a bulge inflation device until it ruptured. Every 3 kPa images were taken using a stereo digital image correlation system. From the images, the three-dimensional displacement of the sample surface was determined. A deforming NURBS mesh was derived from the displacement data, and the local strains were computed. The wall stresses at each pressure increment were determined using inverse membrane analysis. The local material properties of the ATAA were then identified using the pointwise stress and strain data. To show that it is necessary to consider the heterogeneous distribution of the mechanical properties in the ATAA, three different forward finite element simulations using pointwise, elementwise, and homogeneous material properties were compared. The forward finite element predictions revealed that heterogeneous nature of the ATAA must be accounted for to accurately reproduce the stress-strain response.

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.