The shortening fraction of myocardial fibers and its layered distribution,as derived from cine-mr imaged left ventriculograms

Abstract

Purpose: to evaluate the mean shortening fraction and its SD through the wall calculated from multiple cine-MR views, as an estimate of left ventricular globar function.

Material and Methods: the average myocardial fiber shortening fraction was calculated by means of a simple truncated ellipsoid nested shell model. Left ventricular parameters, acquired by cine-MR imaging, from 20 healthy volunteers served as input. Fiber angles, ventricular torsion and a gradient increase in wall thickening from epicard to endocard were part of the model.

Results: the average fiber shortening fraction was 0.203 (0.158–0.246)±0.021 diastolic lengths. It varied only moderately with variations in fiber angle values and not at all when the torsion angles were varied within physiological limits. the average shortening fraction correlates well with the systolic increase in chamber oblonguity (k=0.837), with the ejection fraction (k=0.877), and even better with the calculated wall thickening (k=0.973). the average epicardial shortening fraction 0.169 (0.142–0.202)±0.016 increased gradually through the wall to the endocardial value 0.250 (0.212–0.290)±0.024. the increase in chamber length-width ratio from diastole to systole reduced the SD of the shortening fraction through the wall layers to a minimum.

Conclusion: the fiber shortening fraction expresses the layered contraction of the myocardial wall, the wall thickening, and also the endocardial wall motion. the ejection fraction expresses only the latter. the shortening fraction and its SD through the wall may prove a valuable additional tool for estimating ventricular globar function.