Analysis of Cerebral Aneurysm Wall Tension and Enhancement Using Finite Element Analysis and High-Resolution Vessel Wall Imaging

Biomechanical computational simulation of intracranial aneurysms has become a promising method for predicting features of instability leading to aneurysm growth and rupture. Hemodynamic analysis of aneurysm behavior has helped investigate the complex relationship between features of aneurysm shape, morphology, flow patterns, and the proliferation or degradation of the aneurysm wall. Finite element analysis paired with high-resolution vessel wall imaging can provide more insight into how exactly aneurysm morphology relates to wall behavior, and whether wall enhancement can describe this phenomenon. In a retrospective analysis of 23 unruptured aneurysms, finite element analysis was conducted using an isotropic, homogenous third order polynomial material model. Aneurysm wall enhancement was quantified on 2D multiplanar views, with 14 aneurysms classified as enhancing (CRstalk≥0.6) and nine classified as non-enhancing. Enhancing aneurysms had a significantly higher 95th percentile wall tension (μ = 0.77 N/cm) compared to non-enhancing aneurysms (μ = 0.42 N/cm, p < 0.001). Wall enhancement remained a significant predictor of wall tension while accounting for the effects of aneurysm size (p = 0.046). In a qualitative comparison, low wall tension areas concentrated around aneurysm blebs. Aneurysms with irregular morphologies may show increased areas of low wall tension. The biological implications of finite element analysis in intracranial aneurysms are still unclear but may provide further insights into the complex process of bleb formation and aneurysm rupture.

Abstract 1122‐000213: Presence of Blebs Associated with Reduced Aneurysm Wall Tension and Increased Wall Enhancement

Introduction : Aneurysm wall enhancement using high‐resolution vessel wall imaging (HR‐VWI) may provide new surrogate biomarkers for instability. Finite element analysis (FEA) paired with HR‐VWI can provide more insight into complex morphological features that ultimately lead to aneurysm growth and rupture. Methods : Unruptured intracranial aneurysms were reconstructed in 3D from CE‐MRA imaging. Shells were created assuming a uniform wall thickness of 86 μm and FEA was conducted with a 3rd order polynomial material model, assuming the wall to be isotropic, homogenous, and similar between subjects. The 95th percentile wall tension was defined as high wall tension to account for mesh artifacts. Low wall tension was identified from nodal values and verified on contour plots. Regions of high and low wall tension were characterized from contour plots. Aneurysms were measured and classified as enhancing (CR stalk ≥0.6) or non‐enhancing (CR stalk <0.6), using manual ROI measurements from 3T HR‐VWI T1 postcontrast imaging. Results : Of the twenty‐three aneurysms analyzed, fourteen were classified as enhancing (CR stalk ≥0.6) and nine as non‐enhancing. Enhancing aneurysms had a significantly higher 95th percentile wall tension (m = 0.89±0.32 N/cm) compared to non‐enhancing aneurysms (m = 0.48±0.10 N/cm, p<0.001). Wall enhancement remained a significant predictor of wall tension while accounting for the effects of aneurysm size (p = 0.046). High wall tension was consistently concentrated at the neck of the aneurysm, while low wall tension concentrated at the dome. (Figure 1). Aneurysms with blebs (N = 7) had significantly lower minimal wall tension (m = 0.13±0.02 N/cm) than those without (m = 0.21±0.10 N/cm, p = 0.033). Enhancing aneurysms had significantly higher minimal wall tensions (m = 0.23±0.10 N/cm), than non‐enhancing aneurysms (m = 0.13±0.02 N/cm, 0.003). Minimal wall tension was less strongly correlated with diameter and neck size (Spearman’s r = 0.564,0.378 respectively) than 95th percentile wall tension (Spearman’s r = 0.756, 0.541 respectively). Conclusions : Large and irregular aneurysms are subject to complex mechanical loading. The resultant stress concentrators may prompt the histological remodeling response observed in areas of growth, like the aneurysm neck. Low wall tension indicative of wall degradation in areas more prone to rupture colocalized with aneurysm wall enhancement and blebs.

Novel pressure-regulated deployment strategy for improving the safety and efficacy of balloon-expandable transcatheter aortic valves

Background The optimal method for balloon-expandable transcatheter heart valve (THV) deployment remains unknown. Current implantation protocols are volume-dependent and rely on ad-hoc filling of the deployment apparatus without accounting for annular wall tension during prosthesis expansion, predisposing patients to inconsistent clinical outcomes. During THV deployment, the annular wall tension exerted by the expanding prosthesis is determined by prosthesis diameter and balloon pressure (Laplace's Law). Objective We proposed and tested a novel method for balloon-expandable THV deployment, aimed at controlling balloon pressure and the resulting annular wall tension to allow optimal prosthesis-annulus apposition while preventing significant tissue injury. Methods 330 consecutive patients with severe native aortic stenosis who underwent balloon-expandable THV implantation between 2015–2020 were included. 106 patients were considered high-risk for annular rupture. THVs were deployed until reaching a pre-determined balloon pressure; 4–4.5atm in earlier cases to establish experience and safety, later increasing to 5–6.5atm in most cases. Post-dilatation was performed to reduce &gt;mild angiographic regurgitation (PVR). Using a biomechanical model, annular wall stress (tension) was estimated for each case and assessed against recorded rates of post-dilatation, ≥mild paravalvular regurgitation (PVR) on TTE, new PPM or LBBB and annular rupture. Results Patients with wall stress &gt;3MPa (n=184) had reduced post-dilatation rate (p&lt;0.001) and final PVR (≥mild, p=0.014). Annular rupture occurred in 2/3 high-risk cases with wall stress &gt;3.5MPa; no rupture occurred in 102 high-risk cases with wall stress ≤3.5MPa. Based on these results, we defined target deployment wall stress levels (3–3.5MPa) and associated deployment pressure per THV size. Patients within this target range (n=136) had 8.1% new PPM, 12.5% new LBBB, 12.7% mild PVR with no cases of ≥moderate PVR. Importantly, there was an inconsistent relationship between deployment balloon volume and resulting annular wall stress. Conclusion Pressure-regulated THV deployment is a simple, easily reproducible, safe and effective method, regardless of high-risk anatomical complexities. FUNDunding Acknowledgement Type of funding sources: None. Annular wall stress and PVR Model, stress vs volume and new strategy

Needle penetration test - qualifying examination of 3D printable silicones for vascular models in surgical practice

Background During cardiogenic shock blood circulation is minimal in the human body and does not suffice to survive. The extracorporeal life support system (ECLS) acts as a miniature heart-lung-machine that can be temporarily implanted over major vessels e.g. at the groin of the patient to bridge cardiogenic shock. To perform this procedure in an emergency, a proper training model is desirable. Therefore, a 3-dimensional-printable (3D) material must be found that mimics large vessel needle penetration properties. A suitable test bench for material comparison is desirable. Methods A test setup was built, which simulated the clinically relevant wall tension in specimens. The principle was derived from an existing standardized needle penetration test. After design, the setup was fabricated by means of 3D printing and mounted onto an universal testing machine. For testing the setup, a 3D printable polymer with low Shore A hardness and porcine aorta were used. The evaluation was made by comparing the curves of the penetration force to the standardized test considering the expected differences. Results 3D printing proved to be suitable for manufacturing the test setup, which finally was able to mimic wall tension as if under blood pressure and penetration angle. The force displacement diagrams showed the expected curves and allowed a conclusion to the mechanical properties of the materials. Although the materials forces deviated between the porcine aorta and the Agilus30 polymer, the graphs showed similar but still characteristic curves. Conclusions The test bench provided the expected results and was able to show the differences between the two materials. To improve the setup, limitations has been discussed and changes can be implemented without complications.

Polynomial Regression Model Analysis of Abdominal Wall Tension and Intra-abdominal Pressure in Critically ill Patients

BackgroundAbdominal wall tension (AWT) plays an important role in the pathogenesis of abdominal compliance (AC). This study uses a polynomial regression model to analyze the correlation between intra-vesical pressure(IVP) and AWT in critically ill patients and provides new ideas for the diagnosis and treatment of critically ill patients with intra-abdominal hypertension（IAH）.MethodsA retrospective analysis was conducted in critically ill patients who met the inclusion criteria and were admitted to the Department of intensive care unit of Daping Hospital of Army Medical University from March 14, 2019, to May 23, 2020. According to the IVP on the first day of ICU admission and death within 28 days, the patients were divided into the IAH group (IVP ≥12 mmHg), the non-IAH group, the survival group and the nonsurvival group. The demographic and clinical data, prognostic indicators, AWT and IVP on days 1-7 after entering the ICU, IAH risk factors, and 28-day death risk factors were collected.ResultsA total of 100 patients were enrolled, with an average age of 45.59±11.4 years. There were 55 males (55%), 30 patients from departments of internal medicine (30%), 43 patients from surgery departments (43%), and 27 trauma patients (27%). In the IAH group, there were 50 patients (29 males, 58%), with an average age of 45.28±12.27 years; there were 50 patients (26 males, 52%) in the non-IAH group, with an average age of 45.90±10.58 years. The IVP on the 1st day and the average IVP within 7 days of the IAH group was 18.99（17.52，20.77）mmHg and 19.43（16.87，22.25）mmHg, respectively, which was higher than that of the non-IAH group [ 6.14（3.48，8.70）mmHg, 6.66（2.74，9.08）mmHg], p＜0.001. The AWT on the 1st day and the average AWT within 7 days of the IAH group was 2.89±0.32 N/mm and 2.82±0.46 N/mm, respectively, which was higher than that of the non-IAH group [(2.45±0.29)N/mm,(2.43±0.39)N/mm],p＜0.001.The polynomial regression models showed that the average AWT and IVP on the 1st day and within 7 days were AWTday1 = -2.450×10-3IVP2+9.695×10-2 IVP+2.046，r=0.667（p＜0.0001），and AWTmean = -2.293×10-3IVP2+9.273×10-2 IVP+2.081, respectively. The logistic regression analysis showed that AWTday1 of 2.73-2.97 N/mm increased the patient's 28-day mortality risk (OR: 6.834; 95%: 1.105-42.266, p=0.010).ConclusionsThere is a nonlinear correlation between AWT and IVP in critically ill patients, and a high AWT may indicate poor prognosis.

The clinical significance and prognostic value of right ventricular wall tension in moderate or severe tricuspid regurgitation

Background: We aim to explore the determinants of right ventricular wall tension (RV WT [RV base-to-apex length multiplied by systolic pulmonary artery pressure] and association with all-cause mortality in patients with moderate-to-severe tricuspid regurgitation. Materials & methods: Of total, 180 patients (71 ± 15years, 54% females) were included. An increased RV WT was defined as >3300 mmHgxmm. Results: Patients with increased RV WT (n = 85, 47%) were more likely to be male and taller than patients with normal RV WT. In a multivariable-adjusted model, increased RV WT was associated with a 2.6-fold higher risk of all-cause mortality (HR: 2.59, 95% CI: 1.65–4.06). Conclusion: In patients with significant tricuspid regurgitation, an increased RV WT was common, and associated with a 2.6-fold higher risk of all-cause mortality. Male sex was the only independent determinant.