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Simulations of the ventricular flow patterns during left ventricular assist device (LVAD) support are mainly performed with idealized cylindrical inflow, neglecting the influence of the atrial vortex. In this study, the influence of the left atrium (LA) on the intra-ventricular flow was investigated via Computational Fluid Dynamics (CFD) simulations. Ventricular flow was simulated by a combined Eulerian (carrier flow)/Lagrangian (particles) approach taking into account either the LA or a cylindrical inflow section to mimic a fully support condition. The flow deviation at the mitral valve, the blood low-velocity volume as well as the residence time and shear stress history of the particles were calculated. Inclusion of the LA deflects the flow at the mitral valve by 25°, resulting in an asymmetric flow jet entering the left ventricle. This reduced the ventricular low-velocity volume by 40% (from 6.4 to 3.9 cm3), increased (40%) the shear stress experienced by particles and correspondingly increased (27%) their residence time. Under the studied conditions, the atrial geometry plays a major role in the development of intraventricular flow patterns. A reliable prediction of blood flow dynamics and consequently thrombosis risk analysis within the ventricle requires the consideration of the LA in computational simulations.

Malpositioning of left ventricular assist devices (LVAD) is a risk factor for thrombosis, but its identification from clinical imaging remains challenging. X-rays and CT scans were analyzed and parameters identified that correlated to pump thrombosis. Retrospective imaging data of patients ( n = 115) with HeartmateII (HMII) or HVAD were analyzed in two groups (pump-thrombosis PT, n = 15 vs matched control group NT, n = 15) using routine X-rays and CT scans. In CT, directional deviations of the inflow cannula in three-chamber and two-chamber view (α and β angles) were identified. In HVAD PT frontal radiographs showed reduced pump body area and smaller minor axis (PT 41.3 ± 4.8 mm vs NT 34.9 ± 6.0 mm, p = 0.026), and in the lateral radiographs the visibility of the inflow cannula served as a predictive parameter for PT. In HMII patients, no parameters were associated with PT. The angle α differed significantly (NT −1.2 ± 7.5°, PT −22.0 ± 4.7°, p = 0.006) in HVAD patients. Further, correlations of x-ray parameters with CT angles α and β showed that radiographs can be used to identify malpositioned pumps. Well-aligned inflow cannula positions are essential. HVAD patients with a posterior rotation of the inflow cannula have a higher risk of pump thrombosis. This risk can reliably be identified from routine radiographs.

Purpose Exercise capacity is usually evaluated by peak oxygen consumption (peak-VO2). However, assessment of peak-VO2 in patients with a left ventricular assist device (LVAD) might not be the best method to provide insight into their daily life activity. The aim of this study was to assess the postoperative activity of LVAD patients using actigraphy and to compare these patients to a healthy and a heart-transplanted (HTx) population. Methods Activity was continuously monitored using wrist-accelerometers in LVAD patients after implantation, during 4 weeks of rehabilitation following hospital discharge, and at 2 follow-up assessments. Peak-VO2 values measured during rehabilitation were correlated with activity. Additionally, actigraphy data from LVAD recipients were compared with data measured in healthy and HTx subjects. Results After hospital discharge a significant increase in physical activity of LVAD recipients was observed (55 ± 28 vs. 102 ± 23 Activity Scores, n = 11, p = 0.002). During rehabilitation as well as at the follow-ups (140 ± 43 and 253 ± 33 days post-implantation) no significant increase in activity was observed. Peak-VO2 values correlated to daily activity both in LVAD and HTx patients (r > 0.5). Average daily activity was significantly lower in LVAD and HTx patients than in the healthy population (130 ± 30 and 148 ± 60 vs. 245 ± 63 Activity Score; n = 18 in each group, p < 0.001). Conclusions Activity in LVAD recipients increased substantially after hospital discharge with no further significant improvement observed during a period of 8.5 months. Similarly to the peak-VO2, also the daily activity of LVAD recipients was 53% compared to healthy subjects. These results highlight the need for an optimized physical therapy in this patient cohort.

Aim Transparent hollow models are needed to visualize and quantify flow in various applications. To obtain the final transparent model, an intermediate molding of the fluid space with an easily removable material is required. Currently used materials to produce this intermediate molding have limitations: toxicity, cost, and a tendency to penetrate the final model, thereby degrading its transparency. In this work an alternative method is presented using chocolate as the fluid-space molding material. Methods Starting from a three-dimensional computer aided design (CAD) geometry, a fluid space model of a human aorta was produced out of chocolate. The replica was coated and cast in a block of highly transparent silicone (Sylgard184; Dow-Corning, Midland, MI, USA). After the silicone was cured, the chocolate was removed using hot water. The geometric accuracy of the fluid-space mold and the transparency of the final model were investigated. Results The mean divergence of the chocolate fluid-space mold from the original geometry was 5.7%. The silicone casting had no defects and perfect transparency for particle tracking. Fluid boundaries were invisible when tested with a fluid whose refractive index matched silicone. Conclusions The process we describe is a cheap and effective way to create transparent models that have excellent optical quality.