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, usually caused by calcified deposits that build upon the valve's leaflets and prevent them from fully opening and closing.
Many of these older patients are not healthy enough to undergo open-heart surgeries; instead, they 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.
There are challenges with this procedure, however, including the need to choose the perfect-sized heart valve without ever actually looking at the patient's heart: too small, and the valve can dislodge or leak around the edges; too large, and the valve can rip through the heart, carrying a risk of death. Like Goldilocks, cardiologists are looking for a TAVR valve size that is "just right".
Researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University have created a novel 3D printing workflow that allows cardiologists to evaluate how different valve sizes will interact with each patient's unique anatomy before the medical procedure is actually performed.
This protocol uses CT scan data to produce physical models of individual patients' aortic valves, in addition to a "sizer" device to determine the perfect replacement valve size.
The 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.
"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 pose a similar problem, in that doctors do not get the opportunity to evaluate how a specific valve size will fit with a patient's anatomy before surgery," said James Weaver, Ph.D., a Senior Research Scientist at the Wyss Institute who is a corresponding author of the paper.
"Our integrative 3D printing and valve sizing system provide 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," said Weaver.
When a patient needs a replacement heart valve, they frequently get a CT scan, which takes a series of X-ray images of the heart to create a 3D reconstruction of its internal anatomy.
While the outer wall of the aorta and any associated calcified deposits are easily seen on a CT scan, the delicate "leaflets" of tissue that open and close the valve are often too thin to show up well.
"After a 3D reconstruction of the heart anatomy is performed, 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," Weaver explained.