3D High-Frame-Rate Imaging of Natural Shear Waves in the Parasternal View of the Heart

Most clinical studies use a 2D parasternal long-axis view to measure natural shear waves after valve closure for myocardial stiffness assessment. However, its 3D wave propagation direction and its alignment with the 2D imaging plane are not well understood. Previous 3D research has mainly focused on wave propagation from an apical view, primarily tracking the longitudinal component of wave motion instead of the transverse component observed in the parasternal view. Therefore, this work aims to bridge this gap by using 3D high-frame-rate imaging in the parasternal view in 6 healthy volunteers (~750 volumes/s), and compared its results to 2D measurements (~1000 frames/s). We found a more complex wave propagation pattern after mitral valve closure encompassing two wave excitation sources, whereas the wave propagation after aortic valve closure clearly originated near the left ventricular outflow tract. The extent of the wave excitation region varied across volunteers. For the septal wall – tracked in 2D shear wave imaging, the overall wave propagation was from base to apex, which is theoretically in line with the 2D imaging plane orientation. However, wave speed estimations were lower for 3D measurements than for 2D (-0.7 m/s for mitral valve and -0.5 m/s for AVC, on average), potentially due to misalignment of the 2D imaging plane with the longitudinal direction of the heart.