Preload Dependency of Left Ventricular Torsion: The Impact of Normal Saline Infusion

Abstract

Background: Left ventricular (LV) rotation results from contraction of obliquely oriented myocardial fibers. The net difference between systolic apical counterclockwise rotation and basal clockwise rotation is left ventricular torsion (LVT). Although LVT is altered in various cardiac diseases, determinants of LVT are incompletely understood. Methods and Results: LV end-diastolic volume (LVEDV), LV apical and basal rotation, peak systolic LVT, and peak early diastolic untwisting rate (UTR) were measured by speckle tracking echocardiography in healthy subjects (n=8) before and after infusion of a weight-based normal saline bolus (2.1±0.3 L). Saline infusion lead to a significant increase in end-diastolic LV internal diameter (45.9±3.7 versus 47.6±4.2 mm; p=0.002) and LVEDV (90.0±21.6 versus 98.3±19.6 mL; p=0.01). Stroke volume (51.3±10.9 versus 63.0±15.5 mL; p = 0.003) and cardiac output (3.4±0.8 versus 4.4±1.5 L/min; p = 0.007) increased while there was no change in heart rate and blood pressure. There was a significant increase in the magnitude of peak systolic apical rotation (7.5±2.4 versus 10.5±2.8 degrees; p < 0.001) but no change in basal rotation (-4.1±2.3 versus -4.8±3.1 degrees; p = 0.44). Accordingly, peak systolic LVT increased by 33% following saline infusion (11.2±1.3 versus 14.9±1.7 degrees; p < 0.001). This saline-induced increase in LVT was associated with a marked increase in peak early diastolic UTR (72.3±21.4 versus 136.8±30.0 degrees/s; p < 0.001). Conclusions: Peak systolic LVT and peak early diastolic UTR are preload dependent. Changes in LV preload should be considered when interpreting results of future LVT studies.