Jul 4, 2017 | By Benedict

Researchers at Georgia Institute of Technology and the Piedmont Heart Institute are using patient-specific 3D printed heart valve models to improve the success rate of transcatheter aortic valve replacement (TAVR) procedures. Their aim is to avoid the problem of paravalvular leakage.

Submerged 3D printed valve during flow testing

In a study published in JACC: Cardiovascular Imaging, researchers from the two institutes have shown that 3D printed models based on CT scans of a patient’s heart behave similarly to real valves.

This is big news with regard to the researchers’ efforts to combat paravalvular leakage, a relatively rare TAVR complication that involves blood leaking between cardiac tissue and the implanted valve due to insufficient sealing.

“Paravalvular leakage is an extremely important indicator in how well the patient will do long term with their new valve,” said Zhen Qian, chief of Cardiovascular Imaging Research at Piedmont Heart Institute, part of Piedmont Healthcare.

“The idea was, now that we can make a patient-specific model with this tissue-mimicking 3D printing technology, we can test how the prosthetic valves interact with the 3D printed models to learn whether we can predict leakage.”

TAVR, a minimally invasive procedure that involves wedging a replacement valve into the aortic valve's place, is generally identified as an appropriate procedure for patients who might suffer serious complications from open-heart surgery.

Leakage can occur when the replacement valve doesn’t fit perfectly, and this unwanted complication can ultimately lead to an earlier death for the patient.

Zhen Qian and Kan Wang both worked on the 3D printed models

“In preparing to conduct a valve replacement, interventional cardiologists already weigh a variety of clinical risk predictors, but our 3D printed model gives us a quantitative method to evaluate how well a prosthetic valve fits the patient,” Qian said.

A multi-material 3D printer is used to create the 3D printed heart valves. This allows the researchers to control the “diameter and curving wavelength” of the printing material so that the model more closely represents the physiological properties of the tissue.

The model can even represent specific conditions such as calcium deposition, a common underlying factor of aortic stenosis.

“Previous methods of using 3-D printers and a single material to create human organ models were limited to the physiological properties of the material used,” Zhang said.

“Our method of creating these models using metamaterial design and multi-material 3D printing takes into account the mechanical behavior of the heart valves, mimicking the natural strain-stiffening behavior of soft tissues that comes from the interaction between elastin and collagen, two proteins found in heart valves.”

Inside the 3D printed heart valve

(Images: Rob Felt)

In total, 18 patients underwent CT scans to provide images for the 3D printed models. All of these patients had previously received heart valve replacements.

The 3D printed models taken from these patients were then paired with prosthetic valves of a similar type and size to the ones used in the specific patient’s own replacement procedure. Then, inside a warm-water (body temperature) testing environment, the prosthetics were fitted to their corresponding 3D printed models.

Special “radiopaque beads” and software were used to measure how far the prosthetic and the 3D printed valve model moved apart, causing leakage. Any inconsistencies that resulted in bad sealing were assigned values that formed a “bulge index,” and the researchers found that patients who had experienced actual leakage received a higher bulge index.

So the models were accurate at showing which patients were likely to experience leakage, and were even able to show the location and severity of the complication. The 3D printed valve method was especially useful in cases where balloons are used to expand the prosthetic valve for a better fit, though there are also other methods for predicting leakage, such as measuring how much calcium has accumulated on the patient’s natural valve.

“The results of this study are quite encouraging,” Qian said. “Even though this valve replacement procedure is quite mature, there are still cases where picking a different size prosthetic or different manufacturer could improve the outcome, and 3D printing will be very helpful to determine which one.”

The researchers plan to continue working on the project, evaluating the use of the 3D printed valves as a pre-surgery planning tool, testing more models, and finding new ways to analyze the results of their testing.

“Eventually, once a patient has a CT scan, we could create a model, try different kinds of valves in there, and tell the physician which one might work best,” Qian said. “We could even predict that a patient would probably have moderate paravalvular leakage, but a balloon dilatation will solve it.”

We first reported on Georgia Tech’s 3D printed heart valve research last year.



Posted in 3D Printing Application



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