Transmural myocardial strain distribution measured at high spatial and temporal resolution

Most studies of the distribution of radial strain across the left ventricular (LV) wall report increasing strain values from the epi- to the endocardial layer. The aim of this study was to estimate this strain using a novel ultrasound setup. In order to examine the transmural distribution of radial strain in 2 different LV regions, 2 miniature transducers with high temporal and high spatial resolution were directly attached to the heart's surface in the LV basal and apical region. The myocardium was divided into 5 equally sized layers. Tissue velocities (V) were estimated from the acquired RF signals using a time-delay estimator (TDE) after up-sampling the RF. The initial V estimates were regularized by fitting an active contour through the TDE's results versus depth. Finally, radial strain rate and strain were calculated resulting in a global motion-compensated assessment of radial strain across the LV wall. The results showed that radial strain increased from the epi- to endocardium in the apical segment while the highest strain values were observed more towards the mid-myocardium near the base. These findings are in agreement with finite element model (FEM) results suggesting that differences in transmural strain distribution could be due to differences in curvature at the base and apex which potentially could explain the conflicting data in the literature.