Systolic counterclockwise rotation of the left ventricular apex with respect to the base has been defined as left ventricular (LV) twist or torsion. If rotation of the base during systole is small, we hypothesized that the dynamics of twist can be well characterized through the measurement of apical rotation alone. A device was designed to measure apical rotation in a simpler, more direct fashion, providing continuous high-fidelity dynamic measurements. The device consists of a light source, a position-sensitive diode, and a small rotating mirror that is coupled to the apex of the heart by a wire. As the wire rotates, apical rotation (measured in degrees) can be calculated from the position of the deflected light beam. The timing of apical rotation was compared with simultaneous recordings of electrocardiogram, LV pressure, and LV diameter measurements. An initial clockwise rotation (untwist) of 4 +/- 2 degrees (SD) occurred during isovolumic contraction followed by counterclockwise rotation (twisting) through ejection, reaching maximum apical rotation of -15 degrees just before the end of systole. Rapid untwisting during isovolumic relaxation was shown with near-complete dissipation of twist by the first one-third of the diastolic filling period. Caval occlusion caused a downward and leftward shift of the pressure-apical rotation loops, and more twist/untwist was seen to occur during the respective isovolumic contraction and relaxation periods. We conclude that this device provides precise timing and definition of rapid changes during isovolumic contraction and relaxation, confirms results obtained by more laborious methods, and provides an easy method to measure the dynamics of apical rotation continuously during interventions such as load changes.

The interventricular septum, which flattens and inverts in conditions such as pulmonary hypertension, is considered by many to be an unstressed membrane, in that its position is assumed to be determined solely by the transseptal pressure gradient. A two-dimensional finite element model was developed to investigate whether compression and bending moments (behavior incompatible with a membrane) exist in the septum during diastole under abnormal loading, i.e., pulmonary artery (PA) constriction. Hemodynamic and echocardiographic data were obtained in six open-chest anesthetized dogs. For both control and PA constriction, the measured left ventricular and right ventricular pressures were applied to a residually stressed mesh. Adjustments were made to the stiffness and end-bending moments until the deformed and loaded residually stressed mesh matched the observed configuration of the septum. During PA constriction, end-bending moments were required to obtain satisfactory matches but not during control. Furthermore, substantial circumferential compressive stresses developed during PA constriction. Such stresses might impede septal blood flow and provoke the unexplained ischemia observed in some conditions characterized by abnormal septal motion.

The effects of load, contractility, and heart rate manipulations on LV twist as measured throughout the cardiac cycle by the optical apex rotation method are manifested by changes in both the amplitude and dynamics of torsion. LV twist at ED and ES is primarily a function of volume; this relation appears to be unaltered by heart rate, afterload, and contractility. Whereas decreased load caused early untwisting, increases in preload, afterload, heart rate, and contractility caused a consistent pattern of delay in twist relaxation.

Despite lower spatiotemporal resolution of 3D echocardiography, LV twist and torsion can be computed accurately.