# Cardiac Radiofrequency Ablation Simulation Using a 3D-Printed Bi-Atrial Thermochromic Model
## 2 Materials and Methods
### Atrial Model and Simulator Build-Up  
Having verified the RFA-sensitivity and formulated the thermochromic and BaSO4-doped paints, we proceeded to develop the complete simulator. To ensure reproducibility and cost-effectiveness of the simulator, most parts were manufactured using FDM or stereolithography (SLA) 3D-printing. The simulator comprises four main components: the cardiac model, its base, a transparent tank and its lid (with patch holders).  
The computer model of the atria and associated great vessels was designed via medical image segmentation and processing. An adult male contrast-enhanced chest computer tomography (CT) scan was segmented using the semi-automatic segmentation feature of ITK-SNAP (University of Pennsylvania, Philadelphia, PA, USA). Following this initial step, the segmentation was refined using the smoothing tool (Level 2) in Seg3D (University of Utah, Salt Lake City, UT, USA). Subsequently, the dilation-erosion function was applied to create an inner mold of this segmentation. The final hollow model was the differential result between the segmentation and the inner mold, giving a wall thickness of 1 mm. This model was exported to Fusion360 (Autodesk, San Rafael, CA, USA) and extruded by 1.5 mm to give an overall wall thickness of 2.5 mm. The pulmonary veins were cut to a length of 20 mm. The venue cavae were cut and lofted to a standard-diameter tube fitting size (inner diameter: 16 mm, outer diameter: 23 mm). The model was divided into two sections for 3D printing to allow for the use and easy removal of support material. The exported meshes were sliced using Cura (Ultimaker, Utrecht, The Netherlands) and manufactured using a Chiron FDM 3D-printer (Anycubic, Shenzhen, China). A transeptal puncture was made in the atrial septum for right-to-left access. Paint was applied to the inner surface of model in four layers with a 3 h drying time between each layer. Following this, the two sections of the model were welded together using a digital soldering iron, ensuring not to transfer heat to the inner coats of paint. Finally, the outside of the model was coated with paint in a similar manner to the inside.  
The simulator system was contained within a 48 \(\times\) 39 \(\times\) 31 cm transparent box (Really Useful Plastic Box, Baddord, UK) with catheter entry points connecting to each of the venue cavae via silicone tubing. The entry point for the inferior vena cava was extended outside the box using silicone tubing to simulate realistic pathlength from femoral venous access sites. The box was filled to a depth of 25 cm with 38 \(\lx@math@degree\)C 0.9% w/w saline solution to simulate the human thorax and its conductive properties. The lid of the box was designed to allow compatibility with the CARTO3 EAMS. Six tubes were integrated into the lid to accommodate the six CARTO3 patches, with three patches above the heartmodel (simulating the patches on a patient's anterior chest wall) and three at the bottom (simulating the patches on the posterior chest wall). The tubes were constructed using standard polyvinylchloride (PVC) pipes and gasketed screw-on end-cap fittings with polytetrafluoroethene tape to ensure no leaks were present. The model base was designed using Fusion360 to hold the model in place during the simulation and 3D printed using a Photon SLA printer (Anycubic, China). The model rests on the base with a foam insert, custom clamps hold the venue cavae, and a hook-and-loop strap goes around the body of the model. This arrangement allows models with variable geometry to be firmly held in the simulator and to be inserted and removed easily.