SEPTAL FUNCTION DURING LEFT-VENTRICULAR UNLOADING

Background Left ventricular (LV) unloading with mechanical support dev ices alters biventricular geometry and impairs right ventricular (RV) contractility, but its effect on septal systolic function remains unkn own. Methods and Results To evaluate the effects of LV volume and pres sure unloading on septal geometry and function, LV preload was abruptl y reduced by clamping left atrial pressure between 0 and -2 mm Hg in s even open-chest, anesthetized dogs by use of a pressure-control servom echanism to withdraw blood from the left atrium. With left atrial pres sure clamping, maximal LV pressure decreased 30+/-12% (mean+/-SD) (P<. 0001) and LV end-diastolic cross-sectional area (determined by two-dim ensional echocardiography) decreased by 53+/-16% (P<.0001). This cause d the septum to shift toward the left (RV septal free-wall dimension i ncreased; P<.004) and flatten (radius of curvature increased; P<.0002) , while LV septal free-wall dimension fell (P<.0001). Septal end-diast olic thickness increased 23+/-15% (P<.0005), reflecting a decline in s eptal preload. Systolic septal thickening decreased (P<.002), while sy stolic septal output (Septal Output=Septal ThickeningXHeart Rate) fell from 30+/-17 to 15+/-22 cm/min (P<.002). This was associated with mov ement along the septal Frank-Starling equivalent (septal output versus end-diastolic septal thickness [preload] relation) to a less producti ve portion of the curve. Conclusions LV unloading not only altered int erventricular septal geometry but also reduced septal systolic thicken ing and output, all of which may contribute to impaired RV contractili ty during mechanical LV support.