Global and local stiffening of ex vivo-perfused stented human thoracic aortas: A mock circulation study

Mechanisms of aortic dissection: From pathological changes to experimental and in silico models

Aortic dissection continues to be responsible for significant morbidity and mortality, although recent advances in medical data assimilation and in experimental and in silico models have improved our understanding of the initiation and progression of the accumulation of blood within the aortic wall. Hence, there remains a pressing necessity for innovative and enhanced models to more accurately characterize the associated pathological changes. Early on, experimental models were employed to uncover mechanisms in aortic dissection, such as hemodynamic changes and alterations in wall microstructure, and to assess the efficacy of medical implants. While experimental models were once the only option available, more recently they are also being used to validate in silico models. Based on an improved understanding of the deteriorated microstructure of the aortic wall, numerous multiscale material models have been proposed in recent decades to study the state of stress in dissected aortas, including the changes associated with damage and failure. Furthermore, when integrated with accessible patient-derived medical data, in silico models prove to be an invaluable tool for identifying correlations between hemodynamics, wall stresses, or thrombus formation in the deteriorated aortic wall. They are also advantageous for model-guided design of medical implants with the aim of evaluating the deployment and migration of implants in patients. Nonetheless, the utility of in silico models depends largely on patient-derived medical data, such as chosen boundary conditions or tissue properties. In this review article, our objective is to provide a thorough summary of medical data elucidating the pathological alterations associated with this disease. Concurrently, we aim to assess experimental models, as well as multiscale material and patient data-informed in silico models, that investigate various aspects of aortic dissection. In conclusion, we present a discourse on future perspectives, encompassing aspects of disease modeling, numerical challenges, and clinical applications, with a particular focus on aortic dissection. The aspiration is to inspire future studies, deepen our comprehension of the disease, and ultimately shape clinical care and treatment decisions.

Cardiac remodeling and antihypertensive medication changes after thoracic endovascular aortic repair vs open surgical repair

OBJECTIVE

Cardiovascular complications remain one of the major all-cause mortalities among patients who receive either thoracic endovascular aortic repair (TEVAR) or open surgical repair (OSR). Increased aortic stiffness after endograft deployment has been shown to induce left ventricular hypertrophy, diastolic dysfunction, and reduced coronary flow reserve. However, there is limited data on the hemodynamic effects after OSR. The purpose of this study is to compare the cardiovascular and hemodynamic changes after TEVAR and OSR.

METHODS

A retrospective analysis of 100 patients with thoracic aortic aneurysm or dissection who underwent open (n = 50) or endovascular repair (n = 50) was conducted. Information on demographics, medical and surgical history, and clinical outcomes were retrieved. Transthoracic echocardiographic imaging results were collected to assess cardiac function. Changes to antihypertensive medication dosage and number were used as surrogate markers for hemodynamic changes and aortic stiffness.

RESULTS

No statistically significant differences were observed in antihypertensive medication number or dosage between the TEVAR and OSR group at 12 months, 24 months, and 36 months post-surgery. When adjusting for patient demographic factors of age, sex, and body surface area in a multivariable generalized estimating equation model, patients who underwent TEVAR had a higher likelihood of receiving more antihypertensive medications (incidence rate ratio [IRR], 1.131; P = .044). Patient characteristics such as body surface area (IRR, 1.266; P = .001), hypertension (IRR, 2.070; P ≤ .001), diabetes mellitus (IRR, 1.474; P ≤ .001), and end-stage renal disease (IRR, 1.304; P = .011) were also associated with a higher number of antihypertensive medications. A significant increase in beta-blockers (P ≤ .001) and diuretics (P = .046) intake was observed post-TEVAR and post-OSR. No significant differences in left ventricular ejection fraction and left ventricular hypertrophy were observed between the two groups.

CONCLUSIONS

We observed a greater likelihood of antihypertensive medications escalation following TEVAR, suggesting an increase in aortic stiffness postoperatively. No significant differences in cardiac remodeling were observed between the two groups. Our findings emphasize the need for an improved postoperative cardiac surveillance program in patients undergoing both TEVAR and OSR. Furthermore, additional innovation is needed to create aortic grafts that are more compatible with the native aorta to reduce long-term cardiovascular complications.

TEVAR versus open aortic arch replacement in ex vivo perfused human thoracic aortas

This study aims to assess the outcomes of therapeutic options for aortic arch pathologies by comparing thoracic endovascular aortic repair (TEVAR) with open arch replacement (OAR) using woven polyester grafts from a mechanical and biomechanical perspective, with emphasis on ex vivo perfused human thoracic aortas reproducing heart rate and stroke volume conditions. Eleven non-diseased thoracic aortas from human cadavers were divided into TEVAR (n=5) and OAR (n=6) and tested using a custom-built mock circulation loop. Pressure, diameter, and stroke volume were monitored during perfusion before and after the intervention. Samples undergoing TEVAR showed a higher ascending systolic pressure post-intervention than OAR (TEVAR: 137±9mmHg vs OAR: 126±6mmHg, p=0.017). After the intervention, a significant discrepancy in the mean pressure differences between the ascending and descending aorta ΔP was observed (TEVAR: 9±3mmHg vs OAR: 1±2mmHg, p=0.004). Input impedance at zero frequency, approximating Windkessel resistance, was higher for TEVAR than for OAR (TEVAR: 1.78±0.04 vs OAR: 1.66±0.03mmHgs/ml, p=0.004). A correlation was found between the resistance and the negative peak of the time-normalized wave intensity analysis (Kendall's coefficient τ=-0.35 and p=0.023). Another correlation was observed between resistance and ΔP (τ=0.51, p=0.001). Looking at the replication of heart rate and stroke volume over the course of the study, the observed differences can largely be attributed to the type of intervention. The results suggest that TEVAR has adverse effects compared to OAR, particularly with regard to left ventricular afterload. Clinicians should consider the possibility of increased afterload and altered wave dynamics when deciding on TEVAR, particularly in patients with pre-existing impaired cardiovascular conditions.

Type B Aortic Dissection CTA Collection with True and False Lumen Expert Annotations for the Development of AI-based Algorithms

Aortic dissections (ADs) are serious conditions of the main artery of the human body, where a tear in the inner layer of the aortic wall leads to the formation of a new blood flow channel, named false lumen. ADs affecting the aorta distally to the left subclavian artery are classified as a Stanford type B aortic dissection (type B AD). This is linked to substantial morbidity and mortality, however, the course of the disease for the individual case is often unpredictable. Computed tomography angiography (CTA) is the gold standard for the diagnosis of type B AD. To advance the tools available for the analysis of CTA scans, we provide a CTA collection of 40 type B AD cases from clinical routine with corresponding expert segmentations of the true and false lumina. Segmented CTA scans might aid clinicians in decision making, especially if it is possible to fully automate the process. Therefore, the data collection is meant to be used to develop, train and test algorithms.

Review of Systemic Mock Circulation Loops for Evaluation of Implantable Cardiovascular Devices and Biological Tissues

CLINICAL IMPACT

On needs-based ex vivo monitoring of implantable devices or tissues/organs in cardiovascular simulators provides new insights and paves new paths for device prototypes. The insights gained could not only support the needs of patients, but also inform engineers, scientists and clinicians about undiscovered aspects of diseases (during routine monitoring). We analyze seminal and current work and highlight a variety of opportunities for developing preclinical tools that would improve strategies for future implantable devices. Holistically, mock circulation loop studies can bridge the gap between in vivo and in vitro approaches, as well as clinical and laboratory settings, in a mutually beneficial manner.

Towards biomechanics-based pre-procedural planning for thoracic endovascular aortic repair of aortic dissection

BACKGROUND AND OBJECTIVE

Although thoracic aortic endovascular repair (TEVAR) has shown promising outcomes in the treatment of patients with complicated type B aortic dissection, complications still occur after TEVAR that can lead to catastrophic events. Biomechanical interactions between the stent-graft (SG) and the local aortic tissue play a critical role in determining the outcome of TEVAR. Different SG design may cause different biomechanical responses in the treated aorta, but such information is not known at the time of pre-procedural planning. By developing patient-specific virtual stent-graft deployment tools, it is possible to analyse and compare the biomechanical impact of different SGs on the local aorta for individual patients.

METHODS

A finite element based virtual SG deployment model was employed in this study. Computational simulations were performed on a patient-specific model of type B aortic dissection, accounting for details of the SG design and the hyperelastic behaviour of the aortic wall. Based on the geometry reconstructed from the pre-TEVAR CTA scan, the patient-specific aortic dissection model was created and pre-stressed. Parametric models of three different SG products (SG1, SG2 and SG3) were built with two different lengths for each design. The SG models incorporated different stent and graft materials, stent strut patterns, and assembly approaches. Using our validated SG deployment simulation framework, virtual trials were performed on the patient-specific aortic dissection model using different SG products and varying SG lengths.

CONCLUSION

Simulation results for different SG products suggest that SG3 with a longer length (SG3-long) would be the most appropriate device for the individual patient. Compared to SG1-short (the SG deployed in the patient), SG3-long followed the true lumen tortuosity closely, resulted in a more uniform true lumen expansion and a significant reduction in peak stress in the distal landing zone. These simulation results are promising and demonstrate the feasibility of using the virtual SG deployment model to assist clinicians in pre-procedural planning.

Design and computational optimization of compliance-matching aortic grafts

Introduction: Synthetic vascular grafts have been widely used in clinical practice for aortic replacement surgery. Despite their high rates of surgical success, they remain significantly less compliant than the native aorta, resulting in a phenomenon called compliance mismatch. This incompatibility of elastic properties may cause serious post-operative complications, including hypertension and myocardial hypertrophy. Methods: To mitigate the risk for these complications, we designed a multi-layer compliance-matching stent-graft, that we optimized computationally using finite element analysis, and subsequently evaluated in vitro. Results: We found that our compliance-matching grafts attained the distensibility of healthy human aortas, including those of young adults, thereby significantly exceeding the distensibility of gold-standard grafts. The compliant grafts maintained their properties in a wide range of conditions that are expected after the implantation. Furthermore, the computational model predicted the graft radius with enough accuracy to allow computational optimization to be performed effectively. Conclusion: Compliance-matching grafts may offer a valuable improvement over existing prostheses and they could potentially mitigate the risk for post-operative complications attributed to excessive graft stiffness.