January 1, 2007Open Access

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

Structured PICO

Does inotropic stimulation with dobutamine augment left ventricular endocardial and epicardial torsion and radial strain in normal subjects?

Population

13 normal healthy volunteers, mean age 30±2.6 years. An additional 3 normal volunteers and 8 patients were recruited to validate the LV torsion values against tagged MRI.

Intervention

Dobutamine infusion intravenously at a rate of 5 μg/kg/min during the first 5 minutes and then at 10 μg/kg/min during the next 5 minutes

Comparator

Baseline conditions at rest

Outcome

Left ventricular (LV) torsion (defined as the net difference between basal and apical rotations) and radial strain (RS) measured by 2-dimensional tissue tracking techniquesurrogate

Inotropic stimulation with dobutamine selectively augments apical endocardial rotation, leading to increased left ventricular torsion and radial strain, highlighting the importance of endocardial dynamics in systolic function.

Abstract

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, 10 microg x kg (-1) x 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 5 microg x kg(-1) x min(-1), but thereafter showed no further increase at 10 microg x kg(-1) x 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.

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