Computational Analysis of Stresses Acting on Intermodular Junctions in Thoracic Aortic Endografts

Abstract

¤ ¤Purpose: To evaluate the biomechanical and hemodynamic forces acting on the intermodular junctions of a multi-component thoracic endograft and elucidate their influence on the development of type III endoleak due to disconnection of stent-graft segments.Methods: Three-dimensional computer models of the thoracic aorta and a 4-component thoracic endograft were constructed using postoperative (baseline) and follow-up computed tomography (CT) data from a 69-year-old patient who developed type III endoleak 4 years after stent-graft placement. Computational fluid dynamics (CFD) techniques were used to quantitate the displacement forces acting on the device. The contact stresses between the different modules of the graft were then quantified using computational solid mechanics (CSM) techniques. Lastly, the intermodular junction frictional stability was evaluated using a Coulomb model. Results:The CFD analysis revealed that curvature and length are key determinants of the displacement forces experienced by each endograft and that the first 2 modules were exposed to displacement forces acting in opposite directions in both the lateral and longitudinal axes. The CSM analysis revealed that the highest concentration of stresses occurred at the junction between the first and second modules of the device. Furthermore, the frictional analysis demonstrated that most of the surface area (53%) of this junction had unstable contact. The predicted critical zone of intermodular stress concentration and frictional instability matched the location of the type III endoleak observed in the 4-year follow-up CT image. Conclusion:The region of larger intermodular stresses and highest frictional instability correlated with the zone where a type III endoleak developed 4 years after thoracic stentgraft placement. Computational techniques can be helpful in evaluating the risk of endograft migration and potential for modular disconnection and may be useful in improving device placement strategies and endograft design.

Group-wise construction of reduced models for understanding and characterization of pulmonary blood flows from medical images

“…Conversely, pathology developments can depend on abnormal hemodynamics, such as in the absence of a functioning valve, as will be the case in this work. Computer hemodynamic simulations provide a tool to predict hemodynamic changes due to surgical repair (Vignon-Clementel et al, 2010b), explore different scenarios for treatment (see, e.g., (Hsia et al, 2011;Yang et al, 2011)), non-invasively compute indices that are otherwise invasively measured such as fractional flow reserve (FFR) (Koo et al, 2011), and design artificial devices or conduits that are subject to blood flow (see, e.g., (Prasad et al, 2011;Pant et al, 2011)). …”

Delayed Graft Dislocation After Thoracic Aortic Endovascular Repair

“…Briefly, EG migration has been defined for proximal or distal movements >10 mm relative to anatomical landmarks or any movement event leading to symptoms or requiring reintervention. 6 Collapse was described as the radiologic detection of a wedge-shaped gap between the undersurface or the infolding of the EG with/without lost of apposition of the EG to the aortic wall along the lesser curve. …”

“…4,5 Endograft migration has been defined as the loss of positional stability resulting from the pulsatile forces of blood flow. 6 Late migration of the EG has been reported to occur in a wide range of 0% to 30% of patients, and was more frequently associated with first-generation devices, even or not in association with neck dilatation and device kinking. [4][5][6][7] Currently, different U.S. pivotal trials have tested the presence of an endoleak, type of sac reperfusion, aneurysm expansion, and endoleak intervention.…”

“…6 Late migration of the EG has been reported to occur in a wide range of 0% to 30% of patients, and was more frequently associated with first-generation devices, even or not in association with neck dilatation and device kinking. [4][5][6][7] Currently, different U.S. pivotal trials have tested the presence of an endoleak, type of sac reperfusion, aneurysm expansion, and endoleak intervention. The CT-A examinations were evaluated on workstations by a team of a vascular surgeon and an interventional radiologist, using multiplanar reformatting capabilities and MIP/ MPR/3D reconstruction to identify and classify the type of complication.…”

Blood Flow Simulations for the Design of Stented Valve Reducer in Enlarged Ventricular Outflow Tracts

“…14 Stent fracture in PPVI, without reducer, has been investigated based on patient-specific solid mechanics simulations. 29 Connected computational blood flow simulations describe the fluid mechanics due to replacement of other types of valves (typically mechanical aortic valves, e.g., 39 ) or on the hemodynamic forces that can explain the direction of stented graft migration in other arteries (e.g., the aorta 26 ). Previous hemodynamics modeling works after ToF repair studied pulmonary regurgitation with 0D 20 or 3D simulations, 12,19 but none of these have been performed yet in the context of this percutaneous pulmonary valve reducer (PPVR).…”