PSI - Issue 49

Kevin Bates et al. / Procedia Structural Integrity 49 (2023) 23–29 Kevin Bates / Structural Integrity Procedia 00 (2023) 000 – 000

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Typically, SVASD were repaired by cardiac surgery, however in recent years, a novel procedure involving a covered stent placed from the superior vena cava (SVC) to an anchor point in the right atrium has been studied to percutaneously close SVASD in some patients with success (Hansen et al. 2020). This covered stent directs flow from the SVC to the right atrium, closing the defect and redirecting pulmonary venous flow towards the left atrium, stopping blood shunting from left to right. This is a complex procedure; clinicians must thoroughly understand the surrounding anatomy. It is critical that the stent does not migrate after deployment, and it must be ensured that the pulmonary vein draining into the left atrium does not get occluded. Brancato et al. and Hansen et al. used 3D reconstructions and 3D printed models to evaluate patients for this procedure. They used the models to determine optimal stent sizing, anchor points and anchor methods (Brancato et al. 2021; Hansen et al. 2020). The case being studied in this paper is that of a 76 year-old patient with right heart failure and a large sinus venosus atrial septal defect. Due to their many comorbidities, the patient was at a high surgical risk. A percutaneous approach using the covered stent method was therefore investigated as a better treatment option. 3D reconstructions and physical representations of the heart using 3D printing were used to guide the medical team. 2. Methods 2.1. 3D model creation Evaluation of the patient for a covered stent defect closure required the evaluation of the defect itself, the right and left atria, the SVC, the pulmonary veins, as well as the sinus venosus, a small vein draining into the SVC just above the right atrium. The clinical team needed to determine: 1. Whether a covered stent procedure was feasible given the internal heart geometry; 2. How much would the stent need to be expanded to seal the defect and 3. Would doing so occlude the right pulmonary vein draining into the left atrium? 3D reconstruction of the heart’s four chambers was performed with the SVC and proximal ends of the pulmonary veins. This provided a global view of the heart, and the model could be sectioned later to omit certain structures if required. The aorta was neglected from the reconstruction to provide a better visualization of the SVC and atria. 3D image segmentation was performed using ITK-SNAP (Yushkevich et al. 2006). An MRI image sequence with 4mm slices was used for the reconstruction. A higher resolution CT scan was not available due to the patient’s precarious renal situation. Following this, the virtual model was sectioned to show the internal features of the heart and provide easy visualization of the SVASD. 2.2. Virtual stent placement To aid the clinical team in evaluating the required stent expansion for defect closure while not occluding the pulmonary vein, the covered stent was idealized as a varying diameter cylinder and modeled using Autodesk Fusion 360®. The model was juxtaposed within the SVC volume to show a simplification of the procedure. The 3D virtual model was extensively studied through virtual meetings. The cardiac team met with the engineering team multiple times to discuss the case. These meetings led to studying different views and sections of the heart to determine how some aspects of the procedure would be tackled. Throughout these meetings, stent landing zones and anchoring methods were discussed, as well as catheter approach. Patient-specific complexities such as venous drainage were studied using the ability to provide a 360 degree point of view to the cardiac team. 2.3. 3D printing 3D printing of the model was achieved using a Objet500 Connex3Polyjet printer (Stratasys). This 3D printer uses UV-curable resin and a moving print head to build a solid model. While a tissue-mimicking material was not required for the final model since it would be used for visual purposes only, a soft material was nevertheless chosen for the print. Pure TangoPlus® prints has been shown to be slightly stiffer than aortic wall tissue (Garcia, Yang, et al. 2018;