Project Goal

To improve pre-procedural planning for the LAAO procedure with the WATCHMAN device: an individualized approach to prevent procedural complications by identifying the ideal trans-septal puncture site and optimized WATCHMAN device size.

• 3D Computational Modeling
• 3D Printing
• R&D Design and Fabrication
• Predicting the Optimized WATCHMAN Device Size
• Procedural Simulation Testing

Resin Selection

3D Printed Model

The computational model is 3D printed using the Formlabs Form2 SLA 3D printer.

In order to perform procedural simulation testing, a custom tank must be designed and fabricated. A plastic tank will be customized in order to simulate the patient's entire anatomy that undergoes the procedure.

SolidWorks was used for designing the tank components and configuration. As seen in Figure 4, the cube is representative of the printing area for the model; thus, the maximum size the anatomical model could be. The 16 Fr Cook Sheath entering the tank simulates the sheath entering the patient's femoral vein.

There were two innovate designs used to create the testing environment to replicate the patient. As seen in Figure 5, a sheath support was designed with the goal in mind that the sheath, and thus delivery system, should be stationary as would be expected in the actual procedure. The notches on the base of the sheath support are used to attach suction cups. Thus, the support will be secured to the base of the tank and will not float, as the material used to 3D print the support is PLA (polyactic acid), when submerged in water. As seen in Figure 6, a shoe rack inspired design was used to create the support structure for the 3D printed model. Given that the model is patient-specific, the support system also needs to be adjustable for different model sizes, like an extendable shoe rack. The model is able to be elevated off of the base of the tank, such that the inferior vena cava (IVC) will be concentrically aligned with the the sheath and more accurately represent the procedural pathway. With the R&D design of the tank finalized, all of the components were fabricated.

In order to optimize the WATCHMAN device size, four methods were devised to determine the average LAA ostium measurement: measurements on the patient's CT images, measurements on the computational model in 3D view, measurements on the computational model in a plane-cut view, and circumferential measurements of the 3D printed model. As seen in Table 1, the average measurement is calculated from a maximum, minimum and additional measurement approaches. The average ostium measurement is used to predict the optimized device size when taking into consideration the recommended compression, of 8-20%, that the device needs to meet. Thus, the predicted device size is the 27mm for this patient case.

Procedural simulation testing is performed in order to identify complications that can potentially arise during the patient's actual procedure, especially since for this patient case there was more than one complication that occurred in their procedure.

The dilator is removed and the delivery system (DS) is inserted into the 16 Fr Cook Sheath. With the DS in position, the trans-septal puncture is manually performed. With septum punctured, the model is re-positioned in the support system and the DS is advanced across the septum to the LAA to deploy the WATCHMAN. For this patient case, the predicted 27mm device is being tested as the optimized device size. When trying the first deployment, the shoulder of the device popped out of the LAA ostium due to an inaccurate trajectory from the trans-septal puncture. In performing another trans-septal puncture to create a different trajectory for the DS, the septum tore. Thus, a manual deployment was performed and the 27mm device is secure within the LAA when an accurate trajectory is used.

The individualized 3D printed model is created from generating a 3D computational model from patient CT images, rendering the model and printing the model. The process to generate the specific physical model is shown to be accurate in comparing the testing data to the patient's surgical data results. The size of the heart remains unchanged throughout the procedural simulation. The 3D printed model is able to give a more accurate prediction of the device size, in comparison to the CT images and the virtual 3D model, as seen in Table 1.

From procedural simulation testing, the patient specific 3D printed model accurately replicates what actually occurred during the patient’s procedure. Physicians will be able to gain a better understanding of the patient’s anatomy and pathway that the catheter must travel to have successful device deployment. As seen in both the procedural simulation and the patient’s surgical data, successful deployment of the 27mm WATCHMAN device took three trials. Dr. Reeves explained that the simulation with the model yielded an adequate, but suboptimal result due to the challenging anatomy and incorrect trans-septal puncture location, which led to the second septal-puncture tearing the septum. The tear in the septum limited the accuracy in trajectory, but the overall procedural approach is able to be performed and allow for device deployment.

Even though the 3D printed model is proven to be anatomically accurate, there are still limitations with the resin. The Formlabs Elastic Resin has a durometer of 50A, which better approximates cardiac tissue than other resins. However, this resin still has a durometer greater than cardiac tissue, and does not mimic the viscoelasticity and surface properties. Considering this material limitation, more post-processing of or introduction of another material to the model should be considered to improve the material properties of the post-cured physical model to better approximate cardiac tissue.

Only one patient case is examined as in order for this methodology to be performed, a patient must have a set of CT images that have sufficient contrast that can be used to generate the computational model using the threshold method. This one patient case does not yield adequate data to confirm whether the methodology works for more than one patient. More cases will be needed to test the validity of this design.

Ethical

While patient's CT images, thus the DICOM files, are anonymized, patients may not agree with physicians sharing their CT images for medical research.

Global Impact

With a new methodology, physicians will be able to plan for procedural complications. Thus, there will be higher procedural success and the patient will undergo a safer procedure with minimized complications.

Health and Safety

The majority of the project is done computationally. The only health and safety concern is the use of isopropanol to post-process the 3D printed model. After post-processing is completed, the isopropanol is disposed of properly in accordance with hazardous waste and biohazard regulations.

Economical

Improved pre-procedural planning that relies on CT images could significantly reduce procedural costs, as the mandatory pre-procedurally Transesophageal Echocardiography (TEE) exam will not be required if changing imaging modalities. More importantly, the procedure time will be reduced and the number of WATCHMAN devices used will decrease, which will also decrease the cost for the procedure if less devices are used.