Every year, tens of thousands of people are diagnosed with heart valve disease.
Some of them undergo a transcatheter aortic valve replacement (TAVR), where a heart valve is replaced with a prosthetic. There are a number of different prosthetics for heart surgeons to choose from, with different sizes from different manufacturers. If the valve doesn’t fit correctly, blood can flow around the prosthetic rather than through it.
Researchers at Georgia Institute of Technology and the Piedmont Heart Institute hope to cut down on this ‘paravalvular leakage’. They’re using medical imaging and 3D printing technologies to create individual models of patients’ hearts to help heart surgeons choose the right size prosthetics.
“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. “The idea was, now that we can make a patient-specific model with this tissue-mimicking 3-D printing technology, we can test how the prosthetic valves interact with the 3-D printed models to learn whether we can predict leakage.”
In a study published in the journal JACC: Cardiovascular Imaging, the researchers described how they created models from CT scans of the patients’ hearts, which could reliably predict the amount of leakage that would occur in the rule heart.
The models are 3D-printed using metamaterials that mimic the properties of human tissue. They can recreate unique properties of a patient’s heart, such as calcium deposition and the stiffness of the arterial walls.
“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,” said Chuck Zhang, an engineering professor at Georgia Tech.
“Our method of creating these models using metamaterial design and multi-material 3-D printing takes into account the mechanical behaviour of the heart valves, mimicking the natural strain-stiffening behaviour of soft tissues that comes from the interaction between elastin and collagen, two proteins found in heart valves.”
The researchers used the printed model hearts to test how closely different prosthetics fitted to the walls of the heart. The used warm water to mimic the temperature of the human body, and implanted the prosthetics inside the models in the exact same location that they’d been places in the hearts of real patients. They found that a poor fit in the model was associated with a higher level of leakage in the real patients.
“The results of this study are quite encouraging,” said Qian. “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.”