Assessment and comparison of left ventricular shear in normal and situsinversus totalis hearts by means of magnetic resonance tagging

摘要

Situs inversus totalis (SIT) ischaracterized by complete mirroring of gross cardiac anatomy andposition combined with an incompletely mirrored myofiber arrange-ment, being normal at the apex but inverted at the base of the leftventricle (LV). This study relates myocardial structure to mechanicalfunction by analyzing and comparing myocardial deformation pat-terns of normal and SIT subjects, focusing especially on circumfer-ential-radial shear. In nine control and nine SIT normotensive humansubjects, myocardial deformation was assessed from magnetic reso-nance tagging (MRT) image sequences of five LV short-axis slices.During ejection, no significant difference in either circumferentialshortening (EcC) or its axial gradient (AEcC) is found between corre-sponding LV levels in control and SIT hearts. Circumferential-radialshear (ecr) has a clear linear trend from apex-to-base in controls, whilein SIT it hovers close to zero at all levels. Torsion as well as axialchange in Ecr (Aecl) is as in controls in apical sections of SIT hearts butdeviates significantly towards the base, changing sign close to the LVequator. Interindividual variability in torsion and Aecr values is higherin SIT than in controls. Apex-to-base trends of torsion and Aecr in SIT,changing sign near the LV equator, further substantiate a structuraltransition in myofiber arrangement close to the LV equator itself.Invariance of ecc and Aecc patterns between controls and SIT subjectsshows that normal LV pump function is achieved in SIT despitepartial mirroring of myocardial structure leading to torsional and shearpatterns that are far from normality.