Localized transvalvular pressure gradients in mitral bileaflet mechanical heart valves and impact on gradient overestimation by Doppler

Ultrasound for In Vitro, Noninvasive Real-Time Monitoring and Evaluation of Tissue-Engineered Heart Valves

Tissue-engineered heart valves are developed in bioreactors where biochemical and mechanical stimuli are provided for extracellular matrix formation. During this phase, the monitoring possibilities are limited by the need to maintain the sterility and integrity of the valve. Therefore, noninvasive and nondestructive techniques are required. As such, optical imaging is commonly used to verify valve's functionality in vitro. It provides important information (i.e., leaflet symmetry, geometric orifice area, and closing and opening times), which is, however, usually limited to a singular view along the central axis from the outflow side. In this study, we propose ultrasound as a monitoring method that, in contrast to established optical imaging, can assess the valve from different planes, scanning the whole three-dimensional geometry. We show the potential benefits associated with the application of ultrasound to bioreactors, in advancing heart valve tissue engineering from design to fabrication and in vitro maturation. Specifically, we demonstrate that additional information, otherwise unavailable, can be gained to evaluate the valve's functionality (e.g., coaptation length, and effective cusp height and shape). Furthermore, we show that Doppler techniques provide qualitative visualization and quantitative evaluation of the flow through the valve, in real time and throughout the whole in vitro fabrication phase.

Echocardiographic evaluation of prosthetic heart valves

The specific flow pattern and imaging features of prosthetic heart valves poses major challenges for the Doppler echocardiographic assessment of prosthetic valve structure and function. A comprehensive approach that integrates several semi-quantitative and quantitative parameters obtained from multiple views is key to appropriately detect and quantitate prosthetic valve dysfunction and complications. In patients with prosthetic valves, and particularly in those with mitral prostheses, transesophageal echocardiography is often required to confirm and/or complement information obtained by transthoracic echocardiography. Three-dimensional echocardiography may provide incremental information for the identification of the underlying etiology of prosthetic valve stenosis or regurgitation. Transcatheter aortic valve implantation has rapidly expanded in the past 10 years and paravalvular regurgitation is frequent following this procedure. Given that paravalvular regurgitant jets are often multiple, irregular, and eccentric, the grading of this type of regurgitation is particularly challenging and requires an integrative multiwindow, multiplane, multiparametric approach.