Augmentation of Left Ventricular Apical Endocardial Rotation With Inotropic Stimulation Contributes to Increased Left Ventricular Torsion and Radial Strain in Normal Subjects : Quantitative Assessment Utilizing a Novel Automated Tissue Tracking Technique

Background The difference in the left ventricular (LV) torsion of the endo- and epicardium (Endo, Epi) with inotropic stimulation and its relation to radial strain (RS) remain unclear. Methods and Results LV basal and apical short-axis images were recorded in 13 normal subjects at rest and during dobutamine infusion (5, 10μg・kg^<-1>・min^<-1>). A total of 8 points (anterior, lateral, posterior and septum in both Endo and Epi) were manually placed by 2-dimensional tissue tracking technique and the movement of these points during a cardiac cycle was tracked, after which the rotation angles and RS were calculated. LV torsion was defined as the net difference between the basal and apical rotations. In the LV apex, Endo-rotation increased (7.8±2.7 to 14.1±4.6 degrees, p<0.01), whereas Epi-rotation was unchanged, with dobutamine. The apical Endo-rotation was significantly greater than the Epi-rotation, although no difference was seen between the Endo and Epi in the LV base throughout the study. During dobutamine infusion, the LV Endo-torsion increased (9.5±2.8 to 19.3±4.8 degrees, p<0.01) and these values were greater than those for Epi. The apical RS increased with the dobutamine dose (39.0±9.3 to 61.9±15.5%, p<0.01), whereas basal RS initially increased at 5μg・kg^<-1>・min^<-1>, but thereafter showed no further increase at 10μg・kg^<-1>・min^<-1> of dobutamine. Conclusions Augmentation of LV rotation with inotropism was clearly observed in the apical Endo, thus causing increased LV endo-torsion and apical RS.