Aortic Wall Stress Research Articles

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

BackgroundPrior 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 ResultsWeb 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.ConclusionsBased on limited evidence, this study suggested that PWRI, but not PWS, is greater in ruptured than asymptomatic intact AAAs of similar maximum aortic diameter.

Comparative Study of Aortic Wall Stress According to Geometric Parameters in Abdominal Aortic Aneurysms

In abdominal aortic aneurysm (AAA), the rupture of the aortic tissue is directly related to wall stress. Thus, the investigation of maximum wall stress is a necessary procedure to predict the aortic rupture in AAA. In this study, computational simulations were performed to investigate the correlation between peak wall stress (PWS) and AAA geometry. The Holzapfel model and various orientations of the collagen fibers and thicknesses of the layers of the aorta were employed in the simulation. The material constants used in the Holzapfel model were estimated from the examination and analysis of the biaxial tensile test results of the normal abdominal aorta and AAA. The aneurysm diameter, height, neck angle, and iliac angle were selected as geometric factors affecting the AAA rupture. In addition, a simulation scenario was conceived and created based on the measurement results using the computed tomography data of patients with AAA. Accordingly, the correlation between the PWS and AAA geometry was estimated.

TOWARDS NOVEL CIRCULATING MARKERS FOR ABDOMINAL AORTIC ANEURYSM PROGNOSIS

Objective: Abdominal aortic aneurysm (AAA) is increasing due to aging of the population and is a major cause of death among the elderly. Ultrasound screening programs are useful in early diagnosis but aneurysm size is not always a good predictor of rupture. Thus, there is an urgent need to find new potential prognostic factors. Our aim is to determine whether a battery of immune, inflammatory and oxidative stress markers, previously described to be involved in other cardiovascular diseases, may be used as potential biomarkers to provide personalized prediction of AAA progression for the clinical practice. Design and method: To address this, human abdominal aneurysmatic aortas (N = 80) and blood samples (N = 94) were obtained from patients undergoing open repair or endovascular surgery repair for AAA, whereas healthy aortas (n = 15) and blood samples (n = 46) were obtained from healthy donors. We studied the immune infiltrate in paraffin sections of human aneurysmatic tissue and quantified IgM and IgG circulating levels in our AAA patient cohort. Circulating levels of ROS, CD38, CD36, GDF15 and S100A4 were measured by ELISA and their tissue expression was studied by real Time PCR and by immunostaining. Potential correlations with the aneurysm diameter or with peak wall stress, determined by finite element analysis, were measured by the Pearson product-moment correlation. Results: Our study shows for the first time the alteration of IgM, IgG, ROS, CD38, GDF15 and S100A4 levels in plasma and in aneurysmatic tissue of AAA patients in comparison with controls. After performing the corresponding statistical analysis we could exclude age and sex as confounding factors of our current observations. Circulating levels of IgG, CD38 and GDF15 were positively correlated with abdominal aortic diameter and peak wall stress. Conclusions: Our data indicate that IgG, CD38 and GDF15 may have potential to aid AAA prognosis as indicators of the progression of the aneurysm growth.

Pernicious pregnancy: Type B aortic dissection in pregnant women.

Type B aortic dissection (TBAD) occurs seldomly, particularly in pregnancy, but has disastrous consequences for both mother and fetus. The focus of immediate surgical repair of type A aortic dissection due to higher mortality of patients is less clear in its counterpart, TBAD, in which management is controversial and debated. This article collates knowledge so far on this rare event during pregnancy. A comprehensive literature search was performed in PubMed, Scopus, Google Scholar, Embase, and Medline. Key search terms included "type B aortic dissection," "pregnancy," and corresponding synonyms. Non-English papers were excluded. Risk factors for TBAD includeaortic wall stress due to hypertension, previous cardiac surgery, structural abnormalities (bicuspid aortic valve, aortic coarctation), and connective tissue disorders. In pregnancy, pre-eclampsia is a cause of increased aortic wall stress. Management of this condition is often conservative, but this is dependent on a number of factors, including gestation, cardiovascular stability of the patient, and symptomology. In most cases, a cesarean section before intervention is carried outunless certain indications are present. Due to a scarce number of cases across the decades, it is difficult to determine which management is optimal. The gold-standard management of TBAD has traditionally been the medical treatment for uncomplicated cases and open surgery for those needing urgent intervention, but with the advent of techniques,such as thoracic endovascular aortic repair, the management of these group of patients continues to develop.

Effect of percutaneous aortic valve position on stress map in ascending aorta: A fluid-structure interaction analysis.

Transcatheter aortic valve implantation (TAVI) is an increasingly widespread procedure. Although this intervention is indicated for high and low surgical risk patients, some issues still remain, such as prosthesis positioning optimization in the aortic annulus. Coaxial positioning of the percutaneous prosthesis influences directly on the aortic wall stress map. The determination of the mechanical stress that acts on the vascular endothelium resulting from blood flow can be considered an important task, since TAVI positioning can lead to unfavorable hemodynamic patterns, resulting in changes in parietal stress, such as those found in post-stenotic dilatation region. This research aims to investigate the influence of the prosthetic valve inclination angle in the mechanical stresses acting in the ascending aortic wall. Aortic compliance and blood flow during cardiac cycle were numerically obtained using fluid structure interaction. The aortic model was developed through segmentation of a computed tomography image of a specific patient submitted to TAVI. When compared to standard position (coaxiality match between the prosthesis and the aortic annulus), the inclination of 4° directed to the left main coronary artery decreased the aortic wall area with high values of wall shear stress and pressure. Coaxial positioning optimization of percutaneous aortic prosthesis may decrease the high mechanical stress area. These changes may be important to reduce the aortic remodeling process, vascular calcification or even the prosthesis half-life. Computational fluid dynamics makes room for personalized medicine, with manufactured prosthesis tailored to each patient.

Reproducibility of Thrombus Volume Quantification and Aortic Wall Stress in Abdominal Aortic Aneurysm

Previous studies have suggested that the intra-luminal thrombus volume and aortic wall stress (AWS) can predict abdominal aortic aneurysm (AAA) rupture, however the accuracy and repeatability of these measures are unclear. This study aimed to assess the reproducibility of intra-luminal thrombus volume and AWS in participants with ruptured and asymptomatic intact AAAs.

Can a Biomechanical Measurement From Computed Tomography Predict Abdominal Aortic Aneurysm Rupture?

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 meta-analysis was to compare PWS and PWRI in participants with ruptured and asymptomatic intact AAAs of similar diameter.

Expression of MicroRNA-1281, C-Reactive Protein, and Renal Function in Individuals with Abdominal Aortic Aneurysm and their Clinical Correlation after Endovascular Repair.

Introduction:The treatment of infrarenal aortic aneurysms has changed in the last three decades. Endovascular aneurysm repair (EVAR) has become the primary treatment option in anatomically suitable patients with infrarenal aortic aneurysms. However, there is no serum biomarker to be used in EVAR follow-up.Methods:This is a prospective single-centre study of 30 consecutive patients with abdominal aortic aneurysm (AAA) who underwent EVAR. Serum dosages of micro ribonucleic acid 1281 (miRNA-1281), creatinine, total cholesterol, triglycerides, and C-reactive protein (CRP) were evaluated and angiotomographic evaluations were performed preoperatively and six months after the intervention.Results:There was a hyperexpression of miRNA-1281 in patients with AAA and a significant reduction of it after EVAR, from 1.66-fold before EVAR to 0.27 after the procedure (P<0.0001). MiRNA-1281 expression was not influenced by renal function (creatinine: 1.14±0.29, P=0.68), total cholesterol (179.9±59.9, P=0.22), or CRP (1.17±3.5; P=0.48). There is correlation between AAA size and CRP serum levels, however there was no statically significant reduction of CRP after EVAR.Discussion:MiRNA-1281 expression may be influenced by cholesterol, triglycerides levels, and renal function. We found no difference in these markers before and six months after EVAR. However, miRNA-1281 presents a significant reduction in patients with no follow-up complications. We hypothesize that miRNA-1281 expression may be related to aortic wall stress or flow changes.Conclusion:MiRNA-1281 may contribute as a possible marker of EVAR follow-up.

R41 The Role of Cardiac Magnetic Resonance 4D Flow and Aortic Wall Shear Stress Imaging in Aortic Valve Replacement

Current imaging modalities are limited in assessing aortic valve haemodynamics and wall shear stress (WSS) in patients with severe aortic stenosis (AS). We are using 4D CMR techniques to determine aortic wall stresses to help guide management of AS with transcatheter (TAVR) or surgical (SAVR) aortic valve replacement.

Biomechanical Properties of the Periaortic Abdominal Tissue: It is Not as Fragile as It Seems.

The perivascular adipose tissue has been studied as a critical element that could influence physiological and disease processes of the vessel covered by it. In terms of anatomy, during the abdominal aorta's dissection, it is possible to identify the periaortic adipose tissue and the periaortic parietal peritoneum lying over it, sealing the retroperitoneal space. They seem to be fragile layers, with apparently no biomechanical role in the abdomen. However, it is well known that most cases of ruptured abdominal aortic aneurysms (AAAs) that reach the emergency department still alive present retroperitoneal bleeding contained by the previously mentioned two-layer combination, eventually allowing time for surgical treatment. In previous studies about aortic wall stress, tension, and AAA rupture prediction, only information concerning the vessel wall itself is highlighted. Therefore, the present work aims to study the biomechanical and histological properties of the periaortic tissue, comparing them to the same variables measured in aortic wall samples described in the medical literature. Samples of periaortic tissue were harvested from 27 individuals during necropsy. Smoking status and the presence of AAAs were observed. Biomechanical uniaxial destructive tests were performed up to samples' rupture. Values of failure stress, tension, and strain were obtained. Samples were also harvested for histological analysis. Periaortic tissue presented less amount of collagen in smokers than in nonsmokers (P=0.017). The periaortic tissue seems to be more elastic than aortic walls described in the literature (strain: 0.75±0.37). Analyzing periaortic tissue failure stress (56.8±101.26N/cm2) and tension (7.65±4.99N/cm), it has at least 52% and 55%, respectively, of the stress and tension described in the medical literature for AAA walls. The periaortic tissue presents less collagen fibers in smokers than in nonsmokers. The periaortic tissue seemed very delicate during an autopsy, but the study of its biomechanical properties showed that it presents more than half of the resistance of an AAA wall. This information suggests this tissue might have a mechanical protective role against massive bleeding when it comes to an aortic rupture. Therefore this tissue's biomechanical information should be included in computational models on enlargement and rupture prediction of AAAs.

Epidemiology and management of aortic disease: aortic aneurysms and acute aortic syndromes.

The aorta is the 'greatest artery', through which oxygenated blood is delivered from the left ventricle to end organs with each cardiac cycle (200 million litres of blood transported in an average lifetime). The aorta can be affected by a wide spectrum of acute factors (such as cocaine use, weight lifting and trauma) and chronic acquired and/or genetic conditions (such as systemic arterial hypertension and phaeochromocytoma), which variously lead to increased aortic wall stress. The medial layer of the aorta can also be subject to abnormalities (such as Marfan syndrome, bicuspid aortic valve, inflammatory vasculitis, atherosclerosis and infections). Despite important advances in diagnostic and therapeutic interventions, data derived from registries and population-based studies highlight that the burden of aortic diseases remains high. Therefore, specific resources need to be allocated to design and implement preventive strategies (healthy lifestyles, modifications to cardiovascular risk factors, and educational and screening programmes) at individual and community levels. In this Review, we discuss the epidemiology, management and outcomes of the most common aortic diseases, namely, aortic aneurysms and acute aortic syndromes.

Abstract 16111: Clinical Application of Deep Learning for Stress Analysis of Ascending Thoracic Aortic Aneurysms

Introduction: Current guidelines for elective surgery of ascending thoracic aortic aneurysms (aTAAs) use aneurysm size as primary determinant for risk stratification of adverse events. Biomechanically, dissection may occur when wall stress exceeds wall strength. A widespread method for stress analysis is structural finite-element analysis (FEA). Patient-specific aortic geometries are easily obtainable and stress distributions can potentially predict risk of dissection. However, FEA is a time-consuming and difficult procedure. To bypass this issue, a recent study has developed the first deep learning (DL) approach for a fast and accurate estimation of aortic wall stress distributions. Hypothesis: In this study, we assessed the hypothesis that this deep learning approach can be applied to a large clinical dataset. Model performance was measured by comparing FEA and DL stress predictions in parallel. Methods: Patients with aTAA (n = 169) were studied. Patient-specific aneurysm geometries were obtained from ECG-gated computed tomography. Shapes were represented by hexahedral meshes with 9648 nodes and 6336 solid elements. FEA peak wall stresses and stress distributions were determined using LS-DYNA software with user-defined fiber-embedded material models under systolic pressure. The DL model was implemented in Julia and consisted of unsupervised and supervised learning algorithms. Training was performed on a training set of 152 shapes and testing set of 17 shapes with 10-fold cross-validation. Mean absolute error (MAE) and absolute error of peak stress values (APE) were used to compare DL model predictions with FEA values considered to be ground truth. Results: Average stress values predicted by our DL model were 175.64 ± 4.17 kPa and 95.69 ± 2.15 kPa in the circumferential and longitudinal direction, respectively. We computed a MAE of 5.06 ± 1.08 kPa and APE of 2.58 ± 1.39 kPa in the circumferential direction and MAE of 4.51 ± 0.98 kPa and APE of 2.32 ± 1.84 kPa in the longitudinal direction. Conclusions: DL model trained exclusively on clinical data was able to accurately predict stress distributions on complex aortic geometries. Fast and accurate stress predictions will facilitate real-time clinical applications for the risk assessment of aTAAs.

On the severity of aortic stenosis in ascending aortic aneurysm: A computational tool to examine ventricular-arterial interaction and aortic wall stress

An ascending thoracic aortic aneurysm (ATAA) is a life-threatening cardiovascular consequence of vessel dilatation that portends adverse events and death. From a clinical perspective, ATAA should not be treated as an isolated disease, and surgery is often carried out in the presence of AS, aortic insufficiency or a calcified valve leaflet. Aortic stenosis (AS) is common in ATAAs and leads to both vessel rigidity and left ventricular (LV) impairment. In this study, lumped-parameter modeling and computational analysis were used to assess the change in the wall shear stress (WSS) and intramural wall stress of patient-specific ATAA models with different degrees of AS (i.e., mild to severe). The ATAAs of four patients were reconstructed from imaging data and AS was simulated virtually using the lumped-based CircAdapt tool using clinical and echocardiographic data. Results show that LV work derived from pressure-volume loops increased with the severity of AS. Post-stenotic hemodynamic and structural variables markedly increased with AS severity, with WSS showing a 10-fold increase for the most severe AS model as compared to the baseline model with a well-functioning aortic valve. Most importantly, the increase in WSS and aortic wall stress was associated with pronounced values of valvulo-arterial impedance as an indicator of LV dysfunction. This study provides novel insights into progression of AS in patients with ATAAs at high risk of adverse events, and the potential value of valvulo-arterial impedance to predict changes in hemodynamic and structural parameters with the severity of AS.

Aortic Thickness: A Forgotten Paradigm in Risk Stratification of Aortic Disease.

Background This study aimed at risk-stratifying aortic dilatation using aortic wall thickness (AWT) and comparing methods of AWT assessment. Methods Demographic, epidemiological, and perioperative data on 72 consecutive aortic surgeries (age = 62 years[standard deviation (SD) = 12] years) performed by a single surgeon were collected from hospital database. Aortic thickness was measured on computed tomography scans, as well as intraoperatively in four quadrants, at the level of aortic sinuses, as well as midascending aorta, using calipers. Aortic wall stress was calculated using standard mathematical formulae. Results The ascending aorta was 48.2 (SD = 8) mm and the mean thickness at ascending aorta level was 1.9 (SD = 0.3) mm. There was congruence between imaging and intraoperative measurements of thickness, as well as between the radiologist and surgeon. Preoperatively, 16 patients had multiple imaging studies showing an average rate of growth of 1.2 mm per year without significant difference in thickness. The wider the aorta, the thinner was the lateral or convex wall. Aortic stenosis ( p = 0.01), lateral to medial wall thickness ratio ( p = 0.04), and history of hypertension ( p = 0.00), all had protective effect on aortic root stress. The ascending aortic stress was directly affected by age ( p = 0.03) and inversely related to lateral to medial wall thickness ratio ( p = 0.03). Conclusion Aortic thickness can be measured preoperatively and easily confirmed intraoperatively. Risk stratification based on both aortic thickness and diameter (stress calculations) would better predict acute aortic events in dilated aortas and define aortic resection criteria more objectively.

Intraluminal infusion of Penta-Galloyl Glucose reduces abdominal aortic aneurysm development in the elastase rat model.

An abdominal aortic aneurysm (AAA) is a progressive chronic dilatation of the abdominal aorta with terminally rupture when the aortic wall is so weakened that aortic wall stress exceeds wall strength. No effective medical treatment exists so far. We aimed to test whether intraluminal admission of Penta-Galloyl Glucose (PGG) treatment in a rodent AAA model could hold the potential to inhibit aneurysmal progression. Male Sprague Dawley rats had either intraluminal elastase infused for AAA induction or saline to serve as controls. In two independent experimental series, elastase was used to induce AAA followed by an intraluminal PGG (directly or by a drug eluting balloon) treatment. All rats were followed for 28 days and euthanized. In both series, maximal infrarenal aortic diameter was measured at baseline and at termination as a measure of AAA size. In series 2, maximal internally AAA diameter was followed by ultrasound weekly. AAA tissues were analyzed for elastin integrity by millers stain, collagen deposition by masson trichrome staining. In other AAA tissue samples the mRNA level of CD45, lysyloxidase (LOX), lysyloxidase like protein 1 (LOXL1) were determined by qPCR. Direct administration of PGG significantly reduced AAA expansion when compared to controls. PGG treatment resulted in a higher number and more preserved elastic fibers in the aneurysmal wall, while no significant difference was seen in the levels of CD45 and LOX mRNA levels. The drug eluting balloon (DEB) experiment showed no significant difference in AAA size observed neither macroscopically nor ultrasonically. Also the aneurysmal mRNA levels of CD45, LOX and LOXL1 were unchanged between groups. A significant reduced expansion of AAAs was observed in the PGG group, suggesting PGG as a drug to inhibit aneurysmal progression, while administration through a DEB did not show a promising new way of administration.

Prediction of post-stenting biomechanics in coarcted aortas: A pilot finite element study

Endovascular stenting has recently become a standard treatment for native coarctation of the aorta (CoA) in children and young adults, given the efficacy in relieving vessel obstruction with a low incidence of adverse events. Yet, despite the short-term success of the technique, late hypertension remains an endemic risk. To assess the impact of the percutaneous procedure on the aortic wall biomechanics, we designed a novel finite element (FE) protocol for the simulation of endovascular stenting in three patient-specific CoA anatomies, developing a remeshing procedure that allows for coping with different CoA severities. Our FE protocol was able to yield numerical results on stent distortions and stresses, as well as on changes in aortic wall stresses and distensibility. These results were consistent with intraprocedural in-vivo evidences and with previous findings from the literature, and they suggest that our numerical approach could be used to understand the role of patient specific anatomical features (CoA severity and arch type) on the post-stenting aortic biomechanics. If soundly validated on a vast cohort of patients, our approach could support patient selection for the procedure.

Staged Hybrid Single Lumen Reconstruction (TIGER) in Management of Chronic Symptomatic Complex Type B Aortic Dissection, Techniques, and Literature Review

Endovascular intervention for chronic symptomatic type B aortic dissection (CS-TBAD) induces aortic wall stress with negative hemodynamic cardiovascular consequences. CS-TBAD risks increased morbidity and mortality due to septum maturation with significant impact on false lumen modulation, and partial lumen thrombosis conveying the worst outcome. The aim of the TIGER technique is total aortic remodeling with true lumen expansion, false lumen regression and complete thrombosis, and stabilization of overall aortic diameter. We report 5 cases of aortic dissection with a mean follow-up of 16months (6-28months). All had aneurysmal dilation, with 3 having acute pan aortic dissection and 2 having CS-TBAD. All were managed by sTaged HybrId sinGle lumEn Reconstruction (TIGER). Our first approach was to create one single lumen from the supraceliac, infradiaphragmatic aorta to both common iliac arteries with open surgical patching of the visceral arteries; then, we performed a TEVAR 3 months later. Three patients required a left subclavian artery chimney graft and one required bilateral subclavian to carotid artery transposition. No spinal drainage was required, and all patients had intraoperative transesophageal echo for wire guidance. We had no aortic rupture or retrograde type A dissection, and we experienced no renal, visceral, cardiac, pulmonary, or spinal complications. All patients, but one, went off their antihypertensive medication. All patients had normal estimated glomerular filtration rate postoperatively, and they all demonstrated accelerated aortic modulation. TIGER was not only effective at the semiacute stage to initiate remodeling and prevent malperfusion, it also facilitated a straightforward TEVAR at stage 2, which was made easier by avoiding visceral branch stenting. Moreover, it decreased the length of aortic segment, which was stented, thereby avoiding critical shattering, branch dislodgment, and visceral compromise; spinal ischemia; and negative cardiovascular consequences.

Blockade of angiotensin AT1 receptors prevents arterial remodelling and stiffening in iron-overloaded rats.

Damage to the vasculature caused by chronic iron-overload in both humans and animal models, is characterized by endothelial dysfunction and reduced compliance. In vitro, blockade of the angiotensin II AT1 receptors reversed functional vascular changes induced by chronic iron-overload. In this study, the effect of chronic AT1 receptor blockade on aorta stiffening was assessed in iron-overloaded rats. Male Wistar rats were treated for 15 days with saline as control group, iron dextran 200 mg·kg-1 ·day-1 , 5 days a week (iron-overload group), losartan (20 mg·kg-1 ·day-1 in drinking water), and iron dextran plus losartan. Mechanical properties of the aorta were assessed in vivo. In vitro, aortic geometry and biochemical composition were assessed with morphometric and histological methods. Thoracoabdominal aortic pulse wave velocity (PWV) increased significantly, indicating a decrease in aortic compliance. Co-treatment with losartan prevented changes on PWV, β-index, and elastic modulus in iron-overloaded rats. This iron-related increase in PWV was not related to changes in aortic geometry and wall stress. but to increased elastic modulus/wall stress ratio, suggesting that a change in the composition of the wall was responsible for the stiffness. Losartan treatment also ameliorated the increase in aorta collagen content of the iron-overload group, without affecting circulating iron or vascular deposits. Losartan prevented the structural and functional indices of aortic stiffness in iron-overloaded rats, implying that inhibition of the renin-angiotensin system would limit the vascular remodelling in chronic iron-overload.

Cardiovascular magnetic resonance-derived left ventricular mechanics\u2014strain, cardiac power and end-systolic elastance under various inotropic states in swine

BackgroundCardiovascular magnetic resonance (CMR) strain imaging is an established technique to quantify myocardial deformation. However, to what extent left ventricular (LV) systolic strain, and therefore LV mechanics, reflects classical hemodynamic parameters under various inotropic states is still not completely clear. Therefore, the aim of this study was to investigate the correlation of LV global strain parameters measured via CMR feature tracking (CMR-FT, based on conventional cine balanced steady state free precession (bSSFP) images) with hemodynamic parameters such as cardiac index (CI), cardiac power output (CPO) and end-systolic elastance (Ees) under various inotropic states.Methods Ten anaesthetized, healthy Landrace swine were acutely instrumented closed-chest and transported to the CMR facility for measurements. After baseline measurements, two steps were performed: (1) dobutamine-stress (Dobutamine) and (2) verapamil-induced cardiovascular depression (Verapamil). During each protocol, CMR images were acquired in the short axisand apical 2Ch, 3Ch and 4Ch views. MEDIS software was utilized to analyze global longitudinal (GLS), global circumferential (GCS), and global radial strain (GRS).ResultsDobutamine significantly increased heart rate, CI, CPO and Ees, while Verapamil decreased them. Absolute values of GLS, GCS and GRS accordingly increased during Dobutamine infusion, while GLS and GCS decreased during Verapamil. Linear regression analysis showed a moderate correlation between GLS, GCS and LV hemodynamic parameters, while GRS correlated poorly. Indexing global strain parameters for indirect measures of afterload, such as mean aortic pressure or wall stress, significantly improved these correlations, with GLS indexed for wall stress reflecting LV contractility as the clinically widespread LV ejection fraction.ConclusionGLS and GCS correlate accordingly with LV hemodynamics under various inotropic states in swine. Indexing strain parameters for indirect measures of afterload substantially improves this correlation, with GLS being as good as LV ejection fraction in reflecting LV contractility. CMR-FT-strain imaging may be a quick and promising tool to characterize LV hemodynamics in patients with varying degrees of LV dysfunction.

On the role of material properties in ascending thoracic aortic aneurysms

One of the obstacles standing before the biomechanical analysis of an ascending thoracic aortic aneurysm (ATAA) is the difficulty in obtaining patient-specific material properties. This study aimed to evaluate differences on ATAA-related stress predictions resulting from the elastostatic analysis based on the optimization of arbitrary material properties versus the application of patient-specific material properties determined from ex-vivo biaxial testing. Specifically, the elastostatic analysis relies the on the fact that, if the aortic wall stress does not depend on material properties, the aorta has to be statistically determinate. Finite element analysis (FEA) was applied to a group of nine patients who underwent both angio-CT imaging to reconstruct ATAA anatomies and surgical repair of diseased aorta to collect tissue samples for experimental material testing. Tissue samples cut from excised ATAA rings were tested under equibiaxial loading conditions to obtain experimentally-derived material parameters by fitting stress-strain profiles. FEAs were carried out using both optimized and experimentally-derived material parameters to predict and compare the stress distribution using the mean absolute percentage error (MAPE). Although physiological strains were below yield point (range of 0.08–0.25), elastostatic analysis led to errors on the stress predictions that depended on the type of constitutive model (highest MAPE of 0.7545 for Yeoh model and 0.7683 for Fung model) and ATAA geometry (lowest MAPE of 0.0349 for patient P.7). Elastostatic analysis needs better understanding of its application for determining aneurysm mechanics, and patient-specific material parameters are essential for reliable accurate stress predictions in ATAAs.