In Vitro Comparison of Aortic Valve Prostheses in a 3D-Printed Aortic Arch Using State-of-the-Art 4D Imaging

Background: Aortic valve replacement is one of the most common procedures in cardiac surgery. Despite the large variety of aortic valve prostheses, it is not thoroughly known, how a valve replacement affects the hemodynamics in the aortic arch. Therefore, we developed a mock circulatory loop (MCL) to compare different types of established surgical aortic valve prostheses (SAV) and their corresponding flow patterns in a three-dimensional (3D)-printed, flexible aortic arch using magnetic resonance imaging and Doppler ultrasound.

Method: The MCL simulated physiologic, pulsatile flow conditions with a heart rate of 55/min and physiologic blood pressure (120/80 mm Hg). A cardiac output of 4.1 L/min was achieved. A 40% solution of glycerin in water was used as a blood-mimicking fluid. First, we compared three biological SAV and two mechanical SAV in a flexible, straight tube and then in a patient-derived, 3D-printed aortic arch. Pressure sensors were used for validation of the MCL. Time-resolved 3D magnetic resonance phase contrast imaging (4D-MRI) and vector flow Doppler ultrasound served as imaging methods. Hemodynamic parameters such as wall shear stress, flow velocities, volume flow rate, pressure gradients and valve-specific flow patterns were analyzed.

Results: We could successfully display and analyze blood-flow with both imaging techniques. Hemodynamic parameters were plausible and correlated between ultrasound and 4D-MRI. The analysis of flow in the straight tube revealed valve-specific flow-patterns, which also occurred in the 3D-printed aortic arches. The blood flow in the arches was more complex forming helixes and more vortices than in the straight tube. Proximal peak velocities were higher, whereas flow volumes were lower in biological SAV than in mechanical SAV. In most of the phantoms, we observed two regions with high flow velocity and high wall shear stress at the outer curvature of the aortic arch. The porcine SAV showed a complex flow pattern with regurgitation in diastole.

Conclusion: The MCL in combination with 4D-MRI and vector flow ultrasound analysis provides a unique option for the hemodynamic comparison of SAV. With the possibility of 3D-printing patient-specific aortic phantoms, the MCL could be a useful tool for personalized surgical planning and prevent patient-prosthesis mismatch.