Septal function during left ventricular unloading

Background: Left ventricular (LV) unloading with mechanical support devices alters biventricular geometry and impairs right ventricular (RV) contractility, but its effect on septal systolic function remains unknown. Methods and Results: To evaluate the effects of LV volume and pressure unloading on septal geometry and function, LV preload was abruptly reduced by clamping left atrial pressure between 0 and -2 mm Hg in seven open- chest, anesthetized dogs by use of a pressure-control servomechanism to withdraw blood from the left atrium. With left atrial pressure clamping, maximal LV pressure decreased 30±12% (mean±SD) (P<.0001) and LV end- diastolic cross-sectional area (determined by two-dimensional echocardiography) decreased by 53±16% (P<.0001). This caused the septum to shift toward the left (RV septal free-wall dimension increased; P<.004) and flatten (radius of curvature increased; P<.0002), while LV septal free-wall dimension fell (P<.0001). Septal end-diastolic thickness increased 23±15% (P<.0005), reflecting a decline in septal preload. Systolic septal thickening decreased (P<.002), while systolic septal output (Septal Output=Septal ThickeningxHeart Rate) fell from 30±17 to 15±22 cm/min (P<.002). This was associated with movement along the septal Frank-Starling equivalent (septal output versus end-diastolic septal thickness [preload] relation) to a less productive portion of the curve. Conclusions: LV unloading not only altered interventricular septal geometry but also reduced septal systolic thickening and output, all of which may contribute to impaired RV contractility during mechanical LV support.