Transmural strain distribution across the cardiac wall and its dependency on measurement site

The transmural behavior of myocardial deformation remains a matter of debate, with conflicting findings in literature. The aim of this study was to measure the transmural strain profiles at different sites inside myocardium of the left ventricle, using a high resolution dedicated imaging system with transducers attached directly to the epicardium. The myocardial wall was divided into 5 equally sized layers. Tissue velocities were estimated as a function of depth using phase shift Doppler. 4th order Butterworth filters were applied to reduce noise in the velocity estimates, in both depth and time directions, and radial strain rate and strain were calculated. Second order polynomials were fit to the end-systolic strain values, obtained after normalization of the myocardial thickness. The results were averaged over all acquisitions at each measurement site. The results show a concave transmural strain profile near the apex, and a convex strain profile near the base of the left ventricle. Near the apex, the maximal radial strain occurred at the endocardial border, while near the base, the highest strains were found more towards the mid-myocardium.