Delineation of normal human left ventricular twist throughout systole by tagged cine magnetic resonance imaging

Myofibril shortening and the oblique fiber orientation of the left ventricu lar myocardium results in a twisting motion of the left ventricle. Advances in cardiac magnetic resonance imaging (MRI) have made it possible to label the myocardium noninvasively and track this motion (twist) through the car diac cycle, but little data exist on its complete systolic time course. The purpose of this study tvas to delineate the normal human systolic time cou rse of ventricular twist using tagged cine-MRI. Tagged cine-MRI was perform ed in 10 healthy subjects. The mean systolic twist angle relative to the sh ort axis centroid for the 10 volunteers was calculated. Interstudy and intr a- and inter-observer variability were assessed. During isovolumic contract ion, all ventricular twist was counter-clockwise. Later in systole, rite ba sal segments changed direction and rotated in a clockwise direction, wherea s the apical segments continued counterclockwise rotation. The midpoint for rotation was 45 +/- 8% of ventricular length. The mean short mis net ventr icular twist (apex-base) at 80% systole was 12.6 +/- 1.5 degrees. The four wall segments showed heterogeneity in twist (lateral wall, 20.6 +/- 1.7 deg rees; anterior wall, 17.5 +/- 5.1 degrees; inferior wall, 8.8 +/- 4.9 degre es; septum, 3.5 +/- 2.4 degrees). The anterior and lateral walls demonstrat ed significantly higher ht isr than the other walls (p < 0.01). Torsion inc reased steadily throughout systole after isovolumic contraction, whereas tw ist displayed rate changes. The mean interstudy and intra- and interobserve r differences were less than 2.1 degrees. The close similarity in twist bet ween subjects and the low interstudy and inter/intraobserver variation indi cates that twist is a robust parameter of myocardial function. Torsion vari es smoothly during systole, which may play a role in minimizing oxygen cons umption. These data cart serve as a baseline from which to compare alterati ons in regional myocardial function in disease.