Assessment of Cardiac Function During Axial-flow Left Ventricular Assist Device Support Using a Left Ventricular Pressure-derived Relationship: Comparison With Pre-load Recruitable Stroke Work

Background: In this study we evaluate load-independent ventricular function during left ventricular assist device (LVAD) support based solely on telemetered measurements of left ventricular (LV) pressure, which has not been reported previously. Methods: Adult sheep underwent placement of an axial-flow LVAD, a telemetered LV pressure manometer and instruments for pressure-volume analysis. In unsedated sheep, the simultaneous determination of both stroke work/end-diastolic volume (SW/EDP [PRSW]; slope: M_W) and LV triple-product (TP = LVSP · dP/dt · HR) vs LV end-diastolic pressure (TP/EDP; slope: M_TP) were performed before and then after β₁-blockade using the LVAD to acutely unload the ventricle. Results: LVAD support (4.5 ± 0.31 liters/min) was maintained for 1 week. During LV unloading "runs," the LVAD flow (Q_V) increased (up to 5.8 ± 0.71 liters/min), although there were decreases in SW (3,061 ± 747 to 1,556 ± 410 mm Hg ml^-1), LV TP (3,127 ± 397 to 1,019 ± 335 × 10⁵) and LV EDP (18.2 ± 1.2 to 9.7 ± 1.8 mm Hg). The TP/EDP and SW/EDV relationships established during the unloading runs were highly linear (R² up to 0.95) and their slopes were reduced by β-adrenergic blockade (p < 0.001). Conclusions: The TP/EDP relationship established during LVAD unloading of the LV was load-independent and sensitive to changes in cardiac inotropy, and correlated with PRSW.