Researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University have created a 3D printing workflow that allows cardiologists to predict the performance of artificial heart valves, and evaluate how different valve sizes will interact with each patient's unique anatomy, before the medical procedure is actually performed.
More than one in eight people aged 75 and older in the United States develop moderate-to-severe blockage of the aortic valve in their hearts. Many of these older patients have artificial valves implanted into their hearts using a procedure called transcatheter aortic valve replacement (TAVR), which deploys the valve via a catheter inserted into the aorta. However the challenge with this procedure is to create highly accurate, leak-free replacement heart valves that fit with a patient's anatomy.
After a 3D reconstruction of the heart anatomy is performed, the outer wall of the aorta and any associated calcified deposits are easily seen on a CT scan, but the delicate "leaflets" of tissue that open and close the valve are often too thin to show up well. "It often looks like the calcified deposits are simply floating around inside the valve, providing little or no insight as to how a deployed TAVR valve would interact with them," James Weaver, Ph.D., a Senior Research Scientist at the Wyss Institute explained.
To solve that problem, the researchers have created a software that uses parametric modeling to generate virtual 3D models of the leaflets using seven coordinates on each patient's valve that are visible on CT scans. The digital leaflet models were then merged with the CT data and adjusted so that they fit into the valve correctly. The resulting model, which incorporates the leaflets and their associated calcified deposits, was then 3D printed into a physical multi-material model.
The team also 3D printed a custom "sizer" device that fits inside the 3D-printed valve model and expands and contracts to determine what size artificial valve would best fit each patient.
Researcher discovered that the multi-material design of the 3D-printed valve models, which incorporate flexible leaflets and rigid calcified deposits into a fully integrated shape, could much more accurately mimic the behavior of real heart valves during artificial valve deployment, as well as provide haptic feedback as the sizer is expanded.
The team tested their system against data from 30 patients who had already undergone TAVR procedures, 15 of whom had developed leaks from valves that were too small. By applying the sizer and modeling software, the Wyss team proved capable of predicting the rate of leakage in these cases with 60-73% accuracy.
"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 co-author Beth Ripley, M.D., Ph.D, an Assistant Professor in the Department of Radiology at the University of Washington. "Those patients might be better served by surgery, as the risks of an imperfect TAVR result might outweigh its benefits."
Their work was performed in collaboration with researchers and physicians from Brigham and Women's Hospital, The University of Washington, Massachusetts General Hospital, and the Max Planck Institute of Colloids and Interfaces, and is published in the Journal of Cardiovascular Computed Tomography.