Finite element analysis in asymptomatic, symptomatic, and ruptured abdominal aortic aneurysms: in search of new rupture risk predictors.

OBJECTIVES To compare biomechanical rupture risk parameters of asymptomatic, symptomatic and ruptured abdominal aortic aneurysms (AAA) using finite element analysis (FEA). STUDY DESIGN Retrospective biomechanical single center analysis of asymptomatic, symptomatic, and ruptured AAAs. Comparison of biomechanical parameters from FEA. MATERIALS AND METHODS From 2011 to 2013 computed tomography angiography (CTA) data from 30 asymptomatic, 15 symptomatic, and 15 ruptured AAAs were collected consecutively. FEA was performed according to the successive steps of AAA vessel reconstruction, segmentation and finite element computation. Biomechanical parameters Peak Wall Rupture Risk Index (PWRI), Peak Wall Stress (PWS), and Rupture Risk Equivalent Diameter (RRED) were compared among the three subgroups. RESULTS PWRI differentiated between asymptomatic and symptomatic AAAs (p < .0004) better than PWS (p < .1453). PWRI-dependent RRED was higher in the symptomatic subgroup compared with the asymptomatic subgroup (p < .0004). Maximum AAA external diameters were comparable between the two groups (p < .1355). Ruptured AAAs showed the highest values for external diameter, total intraluminal thrombus volume, PWS, RRED, and PWRI compared with asymptomatic and symptomatic AAAs. In contrast with symptomatic and ruptured AAAs, none of the asymptomatic patients had a PWRI value >1.0. This threshold value might identify patients at imminent risk of rupture. CONCLUSIONS From different FEA derived parameters, PWRI distinguishes most precisely between asymptomatic and symptomatic AAAs. If elevated, this value may represent a negative prognostic factor for asymptomatic AAAs.

Mechanical characterization of aortas using 2D ultrasound elastography

Rupture of aortic aneurysms (AA) is a major cause of death in the Western world. Currently, clinical decision upon surgical intervention is based on the diameter of the aneurysm. However, this method is not fully adequate. Noninvasive assessment of the elastic properties of the arterial wall can be a better predictor for AA growth and rupture risk. The purpose of this study is to estimate mechanical properties of the aortic wall using in vitro inflation testing and 2D ultrasound (US) elastography, and investigate the performance of the proposed methodology for physiological conditions. Two different inflation experiments were performed on twelve porcine aortas: 1) a static experiment for a large pressure range (0 – 140 mmHg); 2) a dynamic experiment closely mimicking the in vivo hemodynamics at physiological pressures (70 – 130 mmHg). 2D raw radiofrequency (RF) US datasets were acquired for one longitudinal and two cross-sectional imaging planes, for both experiments. The RF-data were manually segmented and a 2D vessel wall displacement tracking algorithm was applied to obtain the aortic diameter–time behavior. The shear modulus G was estimated assuming a Neo-Hookean material model. In addition, an incremental study based on the static data was performed to: 1) investigate the changes in G for increasing mean arterial pressure (MAP), for a certain pressure difference (30, 40, 50 and 60 mmHg); 2) compare the results with those from the dynamic experiment, for the same pressure range. The resulting shear modulus G was 94 ± 16 kPa for the static experiment, which is in agreement with literature. A linear dependency on MAP was found for G, yet the effect of the pressure difference was negligible. The dynamic data revealed a G of 250 ± 20 kPa. For the same pressure range, the incremental shear modulus (Ginc) was 240 ± 39 kPa, which is in agreement with the former. In general, for all experiments, no significant differences in the values of G were found between different image planes. This study shows that 2D US elastography of aortas during inflation testing is feasible under controlled and physiological circumstances. In future studies, the in vivo, dynamic experiment should be repeated for a range of MAPs and pathological vessels should be examined. Furthermore, the use of more complex material models needs to be considered to describe the non-linear behavior of the vascular tissue.

Biomechanical wall properties of human intracranial aneurysms resected following surgical clipping (IRRAs Project)

Background and purpose: Individual rupture risk assessment of intracranial aneurysms is a major issue in the clinical management of asymptomatic aneurysms. Aneurysm rupture occurs when wall tension exceeds the strength limit of the wall tissue. At present, aneurysmal wall mechanics are poorly understood and thus, risk assessment involving mechanical properties is inexistent. Aneurysm computational hemodynamics studies make the assumption of rigid walls, an arguable simplification. We therefore aim to assess mechanical properties of ruptured and unruptured intracranial aneurysms in order to provide the foundation for future patient-specific aneurysmal risk assessment. This work also challenges some of the currently held hypotheses in computational flow hemodynamics research. Methods: A specific conservation protocol was applied to aneurysmal tissues following clipping and resection in order to preserve their mechanical properties. Sixteen intracranial aneurysms (11 female, 5 male) underwent mechanical uniaxial stress tests under physiological conditions, temperature, and saline isotonic solution. These represented 11 unruptured and 5 ruptured aneurysms. Stress/strain curves were then obtained for each sample, and a fitting algorithm was applied following a 3-parameter (C(10), C(01), C(11)) Mooney-Rivlin hyperelastic model. Each aneurysm was classified according to its biomechanical properties and (un)rupture status.Results: Tissue testing demonstrated three main tissue classes: Soft, Rigid, and Intermediate. All unruptured aneurysms presented a more Rigid tissue than ruptured or pre-ruptured aneurysms within each gender subgroup. Wall thickness was not correlated to aneurysmal status (ruptured/unruptured). An Intermediate subgroup of unruptured aneurysms with softer tissue characteristic was identified and correlated with multiple documented risk factors of rupture. Conclusion: There is a significant modification in biomechanical properties between ruptured aneurysm, presenting a soft tissue and unruptured aneurysms, presenting a rigid material. This finding strongly supports the idea that a biomechanical risk factor based assessment should be utilized in the to improve the therapeutic decision making.

Morphologic evaluation of ruptured abdominal aortic aneurysm by 3D modeling

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The role of diameter versus volume as the best prognostic measurement of abdominal aortic aneurysms

Accurate measurement of abdominal aortic aneurysms is necessary to predict rupture risk and, more recently, to follow aneurysm sac behavior following endovascular repair. Up until this point, aneurysm diameter has been the most common measurement utilized for these purposes. Although aneurysm diameter is predictive of rupture, accurate measurement is hindered by such factors as aortic tortuosity and interobserver variability, and it does not account for variations in morphology such as saccular aneurysms. Additionally, decreases in aneurysm diameter do not completely describe the somewhat complex remodeling seen following endovascular repair of aortic aneurysms. Measurement of aneurysm volume has the advantage of describing aneurysm morphology in a multidimensional fashion, but it has not been readily available or easily measured until recently. This has changed with the introduction of commercially available software tools that permit quicker and easier to perform volume measurements. Whether it is time for volume to replace, or compliment, diameter is the subject of the current debate.

Automatic generation of models for abdominal aortic aneurysms and intraluminal thrombus based on hexahedral meshes

To propose an automated patient-specific algorithm for the creation of accurate and smooth meshes of the aortic anatomy, to be used for evaluating rupture risk factors of abdominal aortic aneurysms (AAA). Finite element (FE) analyses and simulations require meshes to be smooth and anatomically accurate, capturing both the artery wall and the intraluminal thrombus (ILT). The two main difficulties are the modeling of the arterial bifurcations, and of the ILT, which has an arbitrary shape that is conforming to the aortic wall.

Spontaneous tendon rupture in systemic lupus erythematosus: association with Jaccoud`s arthropathy

Tendon rupture has rarely been described in patients with systemic lupus erythematosus. From observation of three cases of Jaccoud`s arthropathy with tendon rupture, and considering that this arthropathy is more related to an inflammatory process of the tendon sheath than to synovitis per se, the intention of this study was to review the cases of tendon rupture in patients with systemic lupus erythematosus, in the hope of determining the frequency of Jaccoud`s arthropathy associated with this complication. Systematic review using MEDLINE, Scielo and LILACS databases (1966 to 2009) and the following keywords: systemic lupus erythematosus, tendon rupture, Jaccoud`s arthropathy. Secondary references were additionally obtained. Additionally, three Brazilian systemic lupus erythematosus patients who developed tendon rupture are described. Only 40 articles obtained fulfilled the previously established criteria. They were all case reports; the number of cases reported was 52 which, together with the three cases presented herein add up to 55 cases. Forty-six patients were women aged between 19 and 71 years, with a mean age of 40.1 +/- 12.4 years, and the average duration of the disease was 10 years. The most frequently observed rupture sites were the patellar and Achilles` tendons. While almost all patients described were on various doses of corticosteroids, 16 patients concomitantly had Jaccoud`s arthropathy (29%). In conclusion, the association between Jaccoud`s arthropathy and tendon rupture in systemic lupus erythematosus has been underestimated. As almost one-third of the systemic lupus erythematosus patients with tendon rupture also have Jaccoud`s arthropathy, this arthropathy may be recognized as risk marker for tendon rupture. Lupus (2010) 19, 247-254.

Cesarean delivery is associated with an increased risk of obesity in adulthood in a Brazilian birth cohort study

Background: Obesity is epidemic worldwide, and increases in cesarean delivery rates have occurred in parallel. Objective: This study aimed to determine whether cesarean delivery is a risk factor for obesity in adulthood in a birth cohort of Brazilian subjects. Design: We initiated a birth cohort study in Ribeirao Preto, southeastern Brazil, in 1978. A randomly selected sample of 2057 subjects from the original cohort was reassessed in 2002-2004. Type of delivery, birth weight, maternal smoking, and schooling were obtained after birth. The following data from subjects were collected at 23-25 y of age: body mass index (BMI; in kg/m(2)), physical activity, smoking, and income. Obesity was defined as a BMI >= 30. A Poisson multivariable model was performed to determine the association between cesarean delivery and BMI. Results: The obesity rate in adults born by cesarean delivery was 15.2% and in those born by vaginal delivery was 10.4% (P = 0.002). Adults born by cesarean delivery had an increased risk (prevalence ratio: 1.58; 95% CI: 1.23, 2.02) of obesity at adulthood after adjustments. Conclusion: We hypothesize that increasing rates of cesarean delivery may play a role in the obesity epidemic worldwide. Am J Clin Nutr 2011;93:1344-7.

Early Sac Shrinkage Predicts a Low Risk of Late Complications After Endovascular Aortic Aneurysm Repair

BACKGROUND: Aneurysm shrinkage has been proposed as a marker of successful endovascular aneurysm repair (EVAR). Patients with early postoperative shrinkage may experience fewer subsequent complications, and consequently require less intensive surveillance. METHODS: Patients undergoing EVAR from 2000 to 2011 at three vascular centres (in 2 countries), who had two imaging examinations (postoperative and after 6-18 months), were included. Maximum diameter, complications and secondary interventions during follow-up were registered. Patients were categorized according to early sac dynamics. The primary endpoint was freedom from late complications. Secondary endpoints were freedom from secondary intervention, postimplant rupture and direct (type I/III) endoleaks. RESULTS: Some 597 EVARs (71.1 per cent of all EVARs) were included. No shrinkage was observed in 284 patients (47.6 per cent), moderate shrinkage (5-9 mm) in 142 (23.8 per cent) and major shrinkage (at least 10 mm) in 171 patients (28.6 per cent). Four years after the index imaging, the rate of freedom from complications was 84.3 (95 per cent confidence interval 78.7 to 89.8), 88.1 (80.6 to 95.5) and 94.4 (90.1 to 98.7) per cent respectively. No shrinkage was an independent risk factor for late complications compared with major shrinkage (hazard ratio (HR) 3.11; P < 0.001). Moderate compared with major shrinkage (HR 2.10; P = 0.022), early postoperative complications (HR 3.34; P < 0.001) and increasing abdominal aortic aneurysm baseline diameter (HR 1.02; P = 0.001) were also risk factors for late complications. Freedom from secondary interventions and direct endoleaks was greater for patients with major sac shrinkage. CONCLUSION: Early change in aneurysm sac diameter is a strong predictor of late complications after EVAR. Patients with major sac shrinkage have a very low risk of complications for up to 5 years. This parameter may be used to tailor postoperative surveillance.

Unexpected left ventricular free-wall rupture following an aortic catheter-valve implantation.

Our experience with the Sapien trans-apical aortic valve (Edwards Lifesciences Inc., Irvine, CA, USA) has been straightforward without per-procedural mortality except in 1/16 consecutive cases who developed non-apical haemorrhage early after valve implantation. We describe the case of an 84-year-old female carrying a very high operative risk (logistic EuroScore of 44%), who underwent a trans-apical stent-valve implantation for severe and symptomatic aortic valve stenosis (23 mm). Due to massive blood loss, an emergency sternotomy and cannulation for cardiopulmonary bypass resuscitation were necessary to treat (without success) an unusual and unexpected subaortic left ventricular free-wall rupture that occurred few minutes after the stent-valve positioning and implantation. To the best of our knowledge, this is the first described case of a left ventricular free-wall rupture occurring after an otherwise non-complicated standard catheter-based aortic valve replacement.

Identification of biologic markers of the premature rupture of fetal membranes: proteomic approach.

In obstetrics, premature rupture of the membranes (PROM) is a frequent observation which is responsible for many premature deliveries. PROM is also associated with an increased risk of fetal and maternal infections. Early diagnosis is mandatory in order to decrease such complications. Despite that current biological tests allowing the diagnosis of PROM are both sensitive and specific, contamination of the samples by maternal blood can induce false positive results. Therefore, in order to identify new potential markers of PROM (present only in amniotic blood, and absent in maternal blood), proteomic studies were undertaken on samples collected from six women at terms (pairs of maternal plasma and amniotic fluid) as well as on four samples of amniotic fluid collected from other women at the 17(th) week of gestation. All samples (N = 16) were analyzed by two-dimensional (2-D) high-resolution electrophoresis, followed by sensitive silver staining. The gel images were studied using bioinformatic tools. Analyses were focused on regions corresponding to pI between 4.5 and 7 and to molecular masses between 20 and 50 kDa. In this area, 646 +/- 113 spots were detected, and 27 spots appeared to be present on the gels of amniotic fluid, but were absent on those of maternal plasma. Nine out of these 27 spots were also observed on the gels of the four samples of amniotic fluids collected at the 17(th) week of pregnancy. Five of these 9 spots were unambiguously detected on preparative 2-D gels stained by Coomassie blue, and were identified by mass spectrometry analyses. Three spots corresponded to fragments of plasma proteins, and 2 appeared to be fragments of proteins not known to be present in plasma. These 2 proteins were agrin (SWISS-PROT: O00468) and perlecan (SWISS-PROT: P98160). Our results show that proteomics is a valuable approach to identify new potential biological markers for future PROM diagnosis.

Rupture of a concealed aneurysm after intravenous thrombolysis of a thrombus in the parent middle cerebral artery.

BACKGROUND: Management of ischemic stroke in the presence of aneurysmal brain disease is controversial. Recent retrospective evidence suggests that in selected patients, intravenous thrombolysis (IVT) remains a safe approach for reperfusion. METHODS: We document a case of post-thrombolysis aneurysmal rupture. Supported by additional scientific literature we postulate that acute aneurysmal thrombosis leading to stroke in the culprit artery may be an ominous sign of rupture and should be considered separately from fortuitously discovered distant aneurysmal disease. RESULTS: A 71-year-old female presented with an acute right middle cerebral artery stroke syndrome. IVT allowed vessel reperfusion and revealed a previously concealed, juxtaposed non-giant M1 segment saccular aneurysm. Secondary aneurysmal rupture ensued. The aneurysm was secured by surgical clipping. Postoperative course was uneventful. CONCLUSIONS: This case shows that despite reports of thrombolysis safety in the presence of brain aneurysms, thrombolysis remains potentially hazardous and hints toward an increased risk when the stroke arises on the parent vessel itself.

Aortic root rupture: implications of catheter-guided aortic valve replacement.

PURPOSE OF REVIEW: The safety and efficiency of trans catheter aortic valve implantation (TAVI) has been clearly demonstrated. In high-risk patients, the number of procedures is constantly increasing and in western European countries this procedure is employed in more than 30% of isolated aortic valve replacements. The literature, however, focusing on perioperative aortic root (AoR) rupture is rather limited to just a few reports. The aim of this review is to analyze the pathophysiology of AoR rupture during TAVI, stressing the implications of the morphology of the AoR for this devastating complication. RECENT FINDINGS: Currently, perioperative AoR rupture ranges between 0.5 and 1.5% during TAVI, with almost 100% mortality. Recently, valve oversizing and balloon dilatation in a calcified and small AoR were considered as the most important predictive factors for this complication. SUMMARY: The most fragile unit of the AoR is its anchoring substrate to the ostium of the left ventricle. This membranous structure is not involved in the degenerative process leading to aortic valve stenosis. Due to the TAVI and/or balloon dilatation of the calcium stationed on the three leaflets and their attachment, a lesion may result on this structure. And, as a consequence, there is rupture of the AoR.