Prediction of bird-beak configuration in thoracic endovascular aortic repair preoperatively using patient-specific finite element simulations.

Objectives: Formation of bird-beak configuration in thoracic endovascular aortic repair (TEVAR) has been shown to be correlated with the risk of complications such as type Ia endoleaks, stent graft migration, and collapse. The aim of this study was to use patient-specific computational simulations of TEVAR to predict the formation of bird-beak configuration preoperatively. Methods: Patient-specific TEVAR computational simulations are developed using a retrospective cohort of patients treated for thoracic aortic aneurysm. The preoperative computed tomography images were segmented to develop three-dimensional geometry of the thoracic aorta. These geometries were used in finite element simulations of stent graft deployment during TEVAR. Simulated results were compared against the postoperative computed tomography images to assess the accuracy of simulations in predicting the proximal position of a deployed stent graft and presence of bird-beak. In cases with a bird-beak configuration, the length and angle of the bird-beak were measured and compared between the simulated and postoperative results. Results: Twelve TEVAR patient cases were simulated. Computational simulations were able to accurately predict whether the proximal stent graft was fully apposed, proximal bare stents were protruded, or bird-beak configuration was present. In three cases with bird-beak configuration, simulations predicted the length and angle of the bird-beak with less than 10% and 24% error, respectively. Other factors such as a small aortic arch angle, small oversizing value, and landing zones close to the arch apex may have played a role in formation of bird-beak in these patients. Conclusions: Computational simulations of TEVAR accurately predicted the proximal position of a deployed stent graft and the presence of bird-beak preoperatively. The computational models were able to predict the length and angle of bird-beak configurations with good accuracy. These simulations can provide insight into the surgical planning process with the goal of minimizing bird-beak occurrence.

A modeling framework for computational simulations of thoracic endovascular aortic repair.

Thoracic endovascular aortic repair (TEVAR) is a minimally invasive treatment for thoracic aortic conditions including aneurysms and is associated with a number of postoperative stent graft related complications. Computational simulations of TEVAR have the potential to predict surgical outcomes and complications preoperatively. When using simulations for stent graft design and prediction of complications in a population, it is difficult to generalize patient-specific TEVAR computational models due to patient variability. This study proposes a novel modeling framework for creating realistic population-based computational models of TEVAR focused on aneurysms that allow for developing various clinically relevant geometric configurations and scenarios that are not easily attainable with limited patient data. The framework includes a methodology for developing population-based thoracic aortic geometries and defining age-dependent aortic tissue material models, as well as detailed steps and boundary conditions for finite element modeling of stent graft deployment during TEVAR. The simulation framework is illustrated for predicting the formation of a bird-beak configuration, a wedge-shaped gap at the proximal end of the deployed stent graft in TEVAR that leads to incomplete seal. A baseline TEVAR simulation model was developed along with three simulations in which the value of aortic curvature, aortic arch angle, or aortic tissue properties varied from the baseline model. Analyzing the length and angle of the bird-beak configuration in each case shows that the bird-beak size is sensitive to different values of the aortic geometry highlighting the importance of using realistic parameter values.

Identification of geometric and mechanical factors predictive of bird-beak configuration in thoracic endovascular aortic repair using computational models of stent graft deployment.

Objective: Formation of a bird-beak configuration in thoracic endovascular aortic repair (TEVAR) has been shown to be influenced by various factors. However, the main cause of bird-beak formation remains poorly understood. The hypothesis has been that the geometric and mechanical properties of both the aorta and the stent graft contribute to the formation and extent of a bird-beak configuration. The goal of the present study was to use parameter-based computational simulations of TEVAR to predict for bird-beak formation and identify its most significant contributing factors. Methods: In the present study, we considered five parameters for the computational simulations of TEVAR, including aortic curvature, aortic arch angle, age as a surrogate for thoracic aortic tissue properties, TEVAR landing zone, and stent graft oversizing. Using an experimental design approach, computational models for 160 TEVAR scenarios were developed by varying the values of the simulation parameters within clinically relevant ranges. The bird-beak length and angle were used as metrics to evaluate the simulation results. Statistical analysis of the simulation data using a random forest model was conducted to identify significant parameters and interactions. Results: The mean ± standard deviation of the bird-beak length and angle across 160 simulations were 4.32 ± 4.87 mm and 9.16° ± 12.21°, respectively. The largest mean bird-beak length and angle were found in the most distal location in zone 0 (10.04 mm) and zone 2 (21.48°), respectively. An inverse correlation was found between the aortic arch angle and the bird-beak length and angle. In ∼75% of the scenarios, increased stent graft oversizing either fully resolved the presence of the bird-beak configuration or had reduced its size. In the remaining 25%, oversizing minimally changed the bird-beak length and enlarged the bird-beak angle, which mainly occurred in cases with a smaller aortic arch angle and landing zones near the arch apex. This was justified by the mechanism of stent graft bending in the arch angulation. The aortic curvature and tissue properties were shown to be statistically insignificant in relation to bird-beak formation. Conclusions: Significant parameters predictive of a bird-beak configuration in TEVAR were identified, and the trends in which each parameter influenced the bird-beak size were determined. The findings from the present study can inform the surgical planning and device selection process with the goal of minimizing bird-beak formation.