Researchers may have found a way to boost the success of transcatheter aortic valve replacements, thanks to advances in 3-D printing technology.
In a new study published in JACC: Cardiovascular Imaging, researchers reveal the creation of 3-D printed models that could enable doctors to predict how well a prosthetic heart valve will fit a patient, reducing their likelihood of paravalvular leakage.
Transcatheter aortic valve replacement (TAVR) is a surgical procedure used to treat patients with aortic valve disease, whereby the function of the aortic valve - that is, the valve between the left ventricle and the aorta - is impaired.
TAVR - also referred to as transcatheter aortic valve implantation - is a minimally invasive procedure. It involves inserting a replacement prosthetic aortic valve into the damaged aortic valve through a catheter. Once inserted, the prosthetic valve expands and takes on the job of a healthy aortic valve.
While TAVR is a safer alternative for patients at high risk of complications with open heart surgery, it is not risk-free.
One complication of TAVR is paravalvular leakage, whereby blood leaks from the prosthetic aortic valve and flows around it, rather than through it. This may raise the risk of endocarditis - an infection of the inner lining of the heart - and heart failure.
Paravalvular leakage most commonly occurs when the prosthetic valve fails to achieve a precise fit within the patient's damaged aortic valve. As such, there is a need to find better ways to predict the fit of a prosthetic valve.
Study co-author Zhen Qian, chief of Cardiovascular Imaging Research at Piedmont Heart Institute in Atlanta, GA, and colleagues have developed 3-D heart valve models that they believe could meet this need.
Creating 3-D heart valve models
To create their models, researchers utilized cutting-edge 3-D printing technology, which allowed them to simulate the physiological properties of heart valve tissue using a variety of different synthetic materials.
"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," says study co-author Chuck Zhang, of the Stewart School of Industrial and Systems Engineering at Georgia Institute of Technology in Atlanta, GA.
"Our method of creating these models using metamaterial design and multi-material 3-D 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."
The team's heart valve models were based on computed tomography (CT) images of 18 patients who had received TAVR. Once built, the researchers lined the models with radiopaque beads, which helps to identify any dislocation of heart-valve mimicking tissue.
The 'bulge index' score
Next, the researchers identified the type and size of the prosthetic valve that each of the 18 patients had received during TAVR.
In a warm water environment - in order to imitate human body temperature - prosthetic valves of the same size and type were then implanted in the 3-D models. The location of these valves mimicked the location of the prosthetic valves in the patients.
Using medical imaging and computer software, the team monitored the location of the radiopaque beads in the 3-D models before and after prosthetic valve implantation. This allowed them to identify any disparities indicating that the prosthetic valve was a poor fit.
These disparities were used to create a "bulge index." The researchers found that they could use the bulge index to predict the severity of paravalvular leakage after undergoing TAVR; the greater the bulge index score, the higher their severity of paravalvular leakage.
The researchers found that the level of calcium buildup on a patient's damaged heart valve could also be used to predict the severity of paravalvular leakage, but they note that in some cases, the 3-D printed models were more accurate.
While the 3-D heart valve models require further refinement, Qian says that the current study findings are "encouraging."
"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 3-D printing will be very helpful to determine which one," Qian notes.
In a nutshell, the researchers believe that their 3-D heart valve models have the ability to transform care for patients who undergo TAVR.
"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. We could even predict that a patient would probably have moderate paravalvular leakage, but a balloon dilatation will solve it."