Recently, continuous-flow ventricular assist devices (CF-VADs) have supplanted older, pulsatile-flow pumps, for treating patients with advanced heart failure. Despite the excellent results of the newer generation devices, the effects of long-term loss of pulsatility remain unknown. The aim of this study is to compare the ability of both axial and centrifugal continuous-flow pumps to intrinsically modify pulsatility when placed under physiologically diverse conditions. Four VADs, two axial-and two centrifugal-flow, were evaluated on a mock circulatory flow system. Each VAD was operated at a constant impeller speed over three hypothetical cardiac conditions: normo-tensive, hypertensive, and hypotensive. Pulsatility index (PI) was compared for each device under each condition. Centrifugal-flow devices had a higher PI than that of axial-flow pumps. Under normo-tension, flow PI was 0.98 6 0.03 and 1.50 6 0.02 for the axial and centrifugal groups, respectively (p < 0.01). Under hypertension, flow PI was 1.90 6 0.16 and 4.21 6 0.29 for the axial and centrifugal pumps, respectively (p ¼ 0.01). Under hypotension, PI was 0.73 6 0.02 and 0.78 6 0.02 for the axial and centrifugal groups, respectively (p ¼ 0.13). All tested CF-VADs were capable of maintaining some pulsatile-flow when connected in parallel with our mock ventricle. We conclude that centrifugal-flow devices outperform the axial pumps from the basis of PI under tested conditions.
Left ventricular assist devices (LVADs) are blood pumps that augment the function of the failing heart to improve perfusion, resulting in improved survival. For LVADs to effectively unload the left ventricle, the inflow cannula (IC) should be unobstructed and ideally aligned with the heart's mitral valve (MV). We examined IC orientation deviation from a hypothesized conventional angle (45° right-posterior) and the approximate angle for direct IC-MV alignment in many patients. Three-dimensional anatomic models were created from computed tomography scans for 24 LVAD-implanted patients, and angles were measured between the IC and the apical z-axis in both the coronal and the sagittal planes. Common surgical IC angulation was found to be 22 ± 15° rightward and 21 ± 12° posterior from the apical z-axis; 38% (n = 9) of patients fell in this range. Direct IC-MV angulation was found to be 34 ± 8° rightward and 15 ± 7° posterior; only 8% (n = 2) of patients fell in this range. Rightward deviation toward ventricular septal wall and anterior deviation toward LV anterior freewall are associated with mortalities more so than leftward and posterior deviation. In conclusion, anatomic reconstruction may be a useful preoperative tool to obtain general population and patient-specific alignment for optimal LVAD implantation.
Fluid-pumping technology is a mature engineering subject area with a well-documented knowledge base. However, the pump design optimization techniques accepted in industry are geared toward steady-state constant-flow conditions. In contrast, the implantation of a continuous-flow pump to aid the output of the human left ventricle subjects the device to perpetual variation. This study measures pressure-flow performance characteristics for both axial- and centrifugal continuous-flow rotary blood pumps across a wide range of pressure differential values under uniform conditions by means of a novel open-loop flow system. The axial-flow devices show lower hydraulic efficiency. All pumps yield best efficiency point at a head to flow coefficient ratio of approximately 1.7. The open-loop flow system accounts for the dynamic changes associated with human heart physiology and allows for more precise characterization of existing heart pumps and those in development.
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