Parametric Modeling Helps Determine Prosthetic Valve Size

A new study describes how three-dimensional (3D) printing can evaluate how different valve sizes will interact with each patient's unique anatomy, before the procedure is actually performed.

Developed by researchers at the Max Planck Institute of Colloids and Interfaces (MPIKG; Potsdam, Germany), the Wyss Institute for Biologically Inspired Engineering (Boston, MA, USA), Massachusetts General Hospital (MGH; Boston, USA), and other institutions, the software program uses parametric modeling to generate virtual 3D models of the leaflets, using seven calcification coordinates visible on computerized tomography (CT) scans. The resulting model, which incorporates both leaflets and their associated calcified deposits, is then 3D printed.

The 3D-printed multi-material valve model incorporates flexible leaflets and rigid calcified deposits that mimic the artificial valve deployment, as well as providing haptic feedback. A custom sizer that fits inside the 3D-printed valve model is also printed and wrapped with a thin layer of pressure-sensing film to map the contacts between the sizer and the 3D-printed valves and their associated calcified deposits. The sizer is gradually expanded until the correct fit is achieved. Subsequently, the researchers conducted a retrospective study of 30 patients who underwent transcatheter aortic valve replacement (TAVR).

3D printed adjustable sizers were then positioned in the aortic root models and sequentially opened to larger valve sizes, progressively flattening the calcified leaflets against the aortic wall. Optimal valve size and fit were determined by visual inspection and quantitative pressure mapping of interactions between the sizer and models. The researchers found that pressure testing provided a physical map of areas with an inadequate seal that corresponded to areas of paravalvular leak, as demonstrated by post-procedural transthoracic echocardiogram (TTE). The study was published on October 2, 2018, in the Journal of Cardiovascular Computed Tomography.

“If you buy a pair of shoes online without trying them on first, there's a good chance they're not going to fit properly. Sizing replacement TAVR valves poses a similar problem, in that doctors don't get the opportunity to evaluate how a specific valve size will fit with a patient's anatomy before surgery,” said corresponding author James Weaver, PhD, of the Wyss Institute. “Our integrative 3D printing and valve sizing system provides a customized report of every patient's unique aortic valve shape, removing a lot of the guesswork and helping each patient receive a more accurately sized valve.”

“Being able to identify intermediate- and low-risk patients whose heart valve anatomy gives them a higher probability of complications from TAVR is critical, and we've never had a non-invasive way to accurately determine that before,” said study co-author Beth Ripley, MD, PhD, of the University of Washington (Seattle, USA). “Those patients might be better served by surgery, as the risks of an imperfect TAVR result might outweigh its benefits. Additionally, being able to physically simulate the procedure might inform future iterations of valve designs and deployment approaches.”

The leaflet modeling software and the 3D printing protocol are freely available online for researchers or clinicians who wish to use them.

Related Links:
Max Planck Institute of Colloids and Interfaces
Wyss Institute for Biologically Inspired Engineering
Massachusetts General Hospital