Transcatheter aortic valve implantations are now routine at a number of high-end hospitals around the world. Minimally invasive mitral valve replacements, on the other hand, are a lot more difficult and prone to post-op complications, and so are still a rarity. Yet, 60% of patients over 75 have mitral valve disease, and it’s an even bigger problem than aortic valves. We visited the Henry Ford Hospital in Detroit to learn about an innovative program where clinicians use 3D printing and computer simulations to help install replacement mitral valves without having to resort to open surgery.
The Center for Structural Heart Disease at Henry Ford Hospital is headed by Dr. William O’Neill, a guru in the field, who returned to Detroit following a sting at University of Miami Medical School. Dr. O’Neill and his team developed a process and compiled the tools and devices necessary to pre-plan transcatheter mitral valve replacements (TMVR). They worked with Materialise, a 3D printing company based in Plymouth, Michigan, to be able to consistently convert CT scans of hearts into computer simulations and 3D printed hearts that can be examined and manipulated to see which valves to implant and where to position them.
Though each of the pieces of this approach, such as CT scanning and 3D printing, are not uncommon, tying them together is still a challenge. We spoke with Bryan Crutchfield, a VP and GM of Materialise’s North American operations, who explained that converting CT scan data into 3D printer files is itself a complicated process. To produce useful models, the company developed software that cleans up a lot of the noise and anatomical fragments, and then clinicians with the help of Materialise’s specialists do some manual computer work to define the final model. These models are then printed right there at the hospital and can be examined and evaluated for different valves. Once that is done, the actual procedure becomes a lot easier and can be performed with greater confidence, leading to much improved clinical outcomes. And the numbers show this.
We spoke with Dr. Dee Dee Wang, a cardiologist who is Director of Structural Heart Imaging at Henry Ford Hospital and Medical Director of 3D Printing at Henry Ford Innovation Institute about the challenges of mitral valve implantation and how she overcomes these challenges using modern technology. The mitral anatomy is more complex than the aortic one, requiring considerably more planning to make sure an implant is placed correctly and fits the patient’s anatomy. One of the more common complications of minimally invasive mitral valve implantations is left outflow tract obstruction. This happens when the new valve protrudes into the ventricular outflow tract, creating another problem altogether. Sometimes the valve embolizes because it detaches from its implant site and floats away, creating an emergency that can only be dealt with open heart surgery. Since patients receiving transcatheter mitral valves are already high-risk for open heart surgery, this is obviously a critical problem.
Dr. Wang explained to us that about 20% of TMVR procedures using conventional imaging and sizing result in left ventricle outflow tract (LVOT) obstructions, which are also difficult to reverse and require open heart surgery. CT scans don’t provide the intuitive depth perception needed to size new valves correctly and calcified regions are poorly defined, making it even more of a guessing game. During open mitral valve procedures surgeons actually stick models of valves into the anatomy to see what would be a good fit, but this is impossible in a minimally invasive procedure. High quality 3D prints, on the other hand, reproduce this process and make it easy to understand the anatomy and unique challenges of positioning a valve in a difficult spot without it protruding too much into the left ventricle outflow tract.
The printed models are within one millimeter accuracy of the patient’s own hearts and have the necessary depth and handling for an interventional cardiologist to be able to play around with to see which valve to insert and where to deploy it. Dr. Wang seems proud that the manufacturing and prototype approach that they’ve taken at Henry Ford for repairing hearts mirrors Detroit and its auto industry. She has built up quite a collection of 3D printed patient hearts, which is starting to look like it may one day be a museum collection. These are still useful devices, as they can be referred back to when similar patient cases come in.
Our visit to Henry Ford was exciting and educational and we were quite impressed by the technology that’s employed in challenging transcatheter mitral valve procedures.
Finally, here’s a video story about a 16 year-old with a variety of heart problems that was helped by doctors by 3D printing his heart in preparation for the procedure:
Links: Materialise homepage and the company’s Products for Cardiologists and Cardiac Surgeons…
Related study in JACC: Cardiovascular Imaging: Predicting LVOT Obstruction After TMVR…