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 Thickening x 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.