Four-dimensional assessment of left ventricular torsion in mitral valve prolapse using CMR

The heterogeneity in myofiber helicity across the cardiac wall causes twisting (torsion) in the left ventricle (LV) during contraction, which is a significant contributor to its pumping function. Although important progress has been made in identifying and studying a quantitative “global” metric for torsion, four-dimensional (4D) torsion characteristics in the LV remain underexplored. We propose an imaging-based framework that uses myocardial motion obtained from cine cardiac magnetic resonance (CMR) scans of the LV to calculate torsion. We performed our LV torsion analysis in a mitral valve prolapse (MVP) human patient (n=1) pre- and post-MV repair. Establishing a high-fidelity torsion measure in the LV offers a rigorous regional marker to investigate the potential reversal of cardiac remodeling post-surgical interventions, such as MV repair. After image acquisition, a non-rigid image registration algorithm was used to calculate 4D LV displacements. Twisting was evaluated through (i) an in-plane rotation-based approximation (referred to as T_2D) and (ii) a three-dimensional formulation involving in-plane and through-plane strains (referred to as T_3D). Comparing T_2D to T_3D, broad regions of positive (counter-clockwise) rotation, captured through T_3D, were unrepresented by T_2D despite a qualitative agreement between the two metrics in capturing the average regional torsion. Also, the presence of comprehensive transmural positive torsion at the apical section was opposed to negative epicardial torsion at the midsection. Such variations in torsional behavior, captured by T_3D, are expected due to transmural helicity in fiber orientation. Overall, the underlying effects of through-plane shear in characterizing LV torsion were evidenced, and the image registration framework offered a comprehensive tool to capture 4D myocardial torsion that can complement conventional LV global markers.