RELATION BETWEEN TORSION AND CROSS-SECTIONAL AREA CHANGE IN THE HUMANLEFT-VENTRICLE

During the ejection phase, motion of the left ventricular (LV) wall is such that all myocardial fibers shorten to the same extent. In a math ematical model of LV mechanics it was found that this condition could be satisfied only if torsion around the long axis followed a unique fu nction of the ratio of cavity volume to wall volume. When fiber shorte ning becomes non-uniform due to cardiac pathology, this pathology may be reflected in aberration of the torsional motion pattern. In the pre sent study we investigated whether the predicted regular motion patter n could be found in nine healthy volunteers, using Magnetic Resonance Tagging. In two parallel short-axis cross-sections, displacement, rota tion, and area ejection were derived from the motion of tags, attached non-invasively to the myocardium. Information from both sections was combined to determine area ejection, quantified as the change in the l ogarithm of the ratio of cavity area to wall area, and torsion, repres ented by the shear angle on the epicardium. Linear regression was appl ied to torsion as a function of area ejection. The slope thus found (- 0.173 +/- 0.024 rad, mean +/- S.D.) was similar to the slope as predic ted by the model of LV mechanics (-0.194 +/- 0.026 rad). In conclusion , the relation between area ejection and torsion could be assessed non invasively in humans. In healthy volunteers, the relation was close to what was predicted by a mathematical model of LV mechanics, and also close to what was found earlier in experiments on animals. (C) 1997 El sevier Science Ltd.