Proposed Methodology

After my initial literature review, I have learned tons about the anatomy and physiology of the aortic semilunar valve. But this has also made me realize how much there is to learn in this field. But with what I have learned and the guidance of my advisors I am confident in laying out the methodology  for my research project. Though I anticipate changes, the project will be broken up into these key stages:

1. Literature review of the aortic valve and transcatheter aortic valve repair and design of  a aortic root

I feel like my foundation is strong enough move forward in my project, but I will continue my lit. review for the duration of the project. Currently I am in stage two of my project. This involves a theoretic design of the aortic root which I will later make out of silicone.  I have decided to base my design of the aortic root off the design Mano Thrubrikar. This is an aortic valve design that is somewhat idealized and you would never see an aortic root this perfect in a living person, but it is a great baseline to work off of and adjust. For a visual, see figure 1. Once I have completed the theoretical design stage I can move into the computer aided design stage.


 2. Converting this design into a computer generated model.

For the computer aided design (CAD) stage, I will use the program SolidWorks to create an anatomical representation of a mock aortic root. It will be approximately 45mm long with an inner diameter of 21.9mm and a wall thickness of 2.4mm. See bellow to see how this program works.

3. Creating a mold for this model

After the model was made on SolidWorks I then have to convert it into a mold so that we can actually cast the model annulus. This should be fairly simple, but I will need to add in some sort of tapered holes so that the mold can be screwed together. From what I understand it will be a three piece mold. There will be an inner core and two outer faces. Each face will cover up the core and there will be a small space left in-between the core and faces. Once the silicone is injected it will occupy this space.

4. Casting silicone versions of aortic root with the mold

The next stage is self-explanitory in that we  will inject some sort of platinum cure silicone into the mold. In order to fully cure the silicone it will need to be placed in an oven for an extended period of time at around 75 degrees Celsius. 


5. Conditioning the silicone aortic root

After the annulus has been fully designed, injected and cured, I need to condition it. Because right now it is perfectly round and I realized. Due to the difficult nature of constructing them, leaflets were not added to this model. So the question is: how do I simulate calcification on leaflets without leaflets? And to answer that question: I don't know exactly. What is most likely to happen is, the volume occupied by the leaflets when they are open will have to be measured on a calcified valve, then on the CAD program this will be adapted to the aortic root design. So instead of creating of leaflets we will fill in the space that they would occupy with silicone.


6. Deployment of TAVI device into the silicone aortic root

At this point in the project we will actually deploy a TAVI device into the silicone aortic root. This will simulate a valve repair procedure in an individual with . The device that we will be testing is the Medtronic CoreValve. This device is a self-expanding (No balloon required to  deploy it) nitinol frame heart valve. It is one of the most commonly used devices in TAVI procedures. The problem that I see arising with this stage is deploying the device correctly. There is a small "landing zone" that this device must sit in to correctly seal,  as a consequence the accuracy of the data we collect is dependent on the deployment. Furthermore, we are deploying into a "mock root." Even though the silicone root was modeled after the real anatomical geometry of a person, it will have some inaccuracies.

7. Data collection with left heart simulator

Once the space between the device and the mock root has been sealed to the best of our ability, we test. The silicone root and device will be fastened into the Vivitro Pulse Duplicator system. This machine will simulate all the hydrodynamic conditions within the left side of the heart that the device will be exposed to while simultaneously collect the data on the volumetric flow of fluid through the device and the regurgitation infraction. This machine will show how much fluid is leaking through the device.

8. Leakage quantification through echocardiography

To further verify the data collected, additional testing needs to occur. In order to effectively see where the leakage is occurring, an echocardiographic machine needs to be used. This machine uses the Doppler  Effect to analyze fluid velocities throughout the entire device. With this machine will be looking around the seal of the device for anomalies in fluid velocity. Where there are anomalies, there is a high possibility that there is a leak.

9.Analysis of data

Once the data has been collected, it will need to be analyzed and categorized. I hope to compare the amount of leakage between each of our test trials and clinical cases of paravalvular leakage. If  I can show that the leakage occurred in same amount and in the same place as patient data, then I will have demonstrated that you CAN effectively replicate paravalular leaks in a lab setting. 

10. Development and beyond!

Assuming that I prove my hypothesis, the test method that was created in the SRP  can be used for further research. Researchers could potentially use this test method to quantify leakage in different brands and types of TAVI when compared to each other, or use the test method to develop treatments for leakage in a TAVI device. This SRP could be the step towards the next development in the field of transcathter valve repair or it could just demonstrate how not to build a mock aortic root. Well, I guess only time and hydrodynamic laws will tell.

Thank you for taking the time to read through one of my posts. Please comment if you have any questions or just want to be heard. I look forward to responding.