Septal Function During Left Ventricular Unloading

Abstract

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 Thickening×Heart 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.