MECHANICS OF VENTRICULAR TORSION

Recent research suggests that left ventricular torsion is an important indicator of cardiac function. We used two theoretical models to stud y the mechanics of this phenomenon: a compressible cylinder and an inc ompressible ellipsoid of revolution. The analyses of both models accou nt for large- strain passive and active material behavior, with a musc le fiber angle that varies linearly from endocardium to epicardium. Re lative to the end- diastolic configuration, the predicted torsion exhi bits several experimentally observed features, including a peak near e nd systole, rapid untwisting during isovolumic relaxation, and increas ed twist near the apex. The magnitude of the twist is sensitive to the fiber architecture, the ventricular geometry, and the compressibility and contractility of the myocardium. In particular, the model predict s that the systolic twist increases with increasing compressibility, c ontractility, and wall thickness, while it decreases with increasing c avity volume. The peak twist approximately doubles (from about 0.02 to 0.04 rad cm(-1)) with a doubling of myocardial compressibility or wit h a change in the endocardial/epicardial muscle fiber angles from 90/- 90 degrees to 60/-60 degrees. The twist is less sensitive to changes i n contractility and ventricular geometry. These findings provide a bas is for interpreting measurements of ventricular torsion in the clinica l setting. (C) 1996 Elsevier Science Ltd.