The hemodynamic effects of the LVAD outflow cannula location on the thrombi distribution in the aorta: A primary numerical study

The Impact of Left Ventricular Assist Device Outflow Graft Positioning on Aortic Hemodynamics: Improving Flow Dynamics to Mitigate Aortic Insufficiency

Heart failure is a global health concern with significant implications for healthcare systems. Left ventricular assist devices (LVADs) provide mechanical support for patients with severe heart failure. However, the placement of the LVAD outflow graft within the aorta has substantial implications for hemodynamics and can lead to aortic insufficiency during long-term support. This study employs computational fluid dynamics (CFD) simulations to investigate the impact of different LVAD outflow graft locations on aortic hemodynamics. The introduction of valve morphology within the aorta geometry allows for a more detailed analysis of hemodynamics at the aortic root. The results demonstrate that the formation of vortex rings and subsequent vortices during the high-velocity jet flow from the graft interacted with the aortic wall. Time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) indicate that modification of the outflow graft location changes mechanical states within the aortic wall and aortic valve. Among the studied geometric factors, both the height and inclination angle of the LVAD outflow graft are important in controlling retrograde flow to the aortic root, while the azimuthal angle primarily determines the rotational direction of blood flow in the aortic arch. Thus, precise positioning of the LVAD outflow graft emerges as a critical factor in optimizing patient outcomes by improving the hemodynamic environment.

Thrombotic Risk of Rotor Speed Modulation Regimes of Contemporary Centrifugal Continuous-flow Left Ventricular Assist Devices

Contemporary centrifugal continuous-flow left ventricular assist devices (LVADs) incorporate dynamic speed modulation algorithms. Hemocompatibility of these periodic unsteady pump operating conditions has been only partially explored. We evaluated whether speed modulation induces flow alterations associated with detrimental prothrombotic effects. For this aim, we evaluated the thrombogenic profile of the HeartWare ventricular assist device (HVAD) Lavare Cycle (LC) and HeartMate3 (HM3) artificial pulse (AP) via comprehensive numerical evaluation of (i) pump washout, (ii) stagnation zones, (iii) shear stress regimens, and (iv) modeling of platelet activation status via the platelet activity state (PAS) model. Data were compared between different simulated operating scenarios, including: (i) constant rotational speed and pump pressure head, used as reference; (ii) unsteady pump pressure head as induced by cardiac pulsatility; and (iii) unsteady rotor speed modulation of the LC (HVAD) and AP (HM3). Our results show that pump washout did not improve across the different simulated scenarios in neither the HVAD nor the HM3. The LC reduced but did not eliminate flow stagnation (-57%) and did not impact metrics of HVAD platelet activation (median PAS: +0.4%). The AP reduced HM3 flow stagnation by up to 91% but increased prothrombotic shear stress and simulated platelet activation (median PAS: +124%). Our study advances understanding of the pathogenesis of LVAD thrombosis, suggesting mechanistic implications of rotor speed modulation. Our data provide rationale criteria for the future design optimization of next generation LVADs to further reduce hemocompatibility-related adverse events.

Evaluating medical device and material thrombosis under flow: current and emerging technologies

This review highlights the importance of flow in medical device thrombosis and explores current and emerging technologies to evaluate dynamic biomaterial Thrombosis in vitro.

Innovative Modeling Techniques and 3D Printing in Patients with Left Ventricular Assist Devices: A Bridge from Bench to Clinical Practice

Left ventricular assist devices (LVAD) cause altered flow dynamics that may result in complications such as stroke, pump thrombosis, bleeding, or aortic regurgitation. Understanding altered flow dynamics is important in order to develop more efficient and durable pump configurations. In patients with LVAD, hemodynamic assessment is limited to imaging techniques such as echocardiography which precludes detailed assessment of fluid dynamics. In this review article, we present some innovative modeling techniques that are often used in device development or for research purposes, but have not been utilized clinically. Computational fluid dynamic (CFD) modeling is based on computer simulations and particle image velocimetry (PIV) employs ex vivo models that helps study fluid characteristics such as pressure, shear stress, and velocity. Both techniques may help elaborate our understanding of complications that occur with LVAD and could be potentially used in the future to troubleshoot LVAD-related alarms. These techniques coupled with 3D printing may also allow for patient-specific device implants, lowering the risk of complications increasing device durability.

The Effects of Left Ventricular Assist Device Support Level on the Biomechanical States of Aortic Valve

Background

Although aortic valve disease caused by left ventricular assist device (LVAD) support has attracted more and more attention, the precise biomechanical effects of LVAD support level on the aortic valve are still unclear.

Material/Methods

A structural finite element models study was conducted using an ideal aortic valve geometric model. Four different study conditions were designed, according to the reduction of the open duration of the aortic valve. The isotropic hyperelastic constitutive equation was chosen to reflect the mechanical property of the leaflets. The distribution of the stress, strain, and transient dynamics of the leaflet were calculated.

Results

Along with the increase of LVAD support level, the open duration of the aortic valve was also reduced by the increase of LVAD support (low support level case 0.23 seconds versus middle support level case 0.2 seconds versus high support level case 0.14 seconds). Moreover, along with the increase of support mode of LVAD, the von Mises stress in most leaflet areas was increased from the low stress level (0–0.4 MPa) to the middle region (0.4–0.8 MPa). Once the leaflets were continuously closed, the high stress level (larger than 0.8 MPa) was observed. In contrast, the support level of LVAD only had slight effects on the distribution of von Mises strain. According to the aforementioned results, maintaining the open duration of aortic valve longer than 0.2 seconds could achieve better performance of biomechanical states of leaflets.

Conclusions

This study could provide useful information on the determination of optimal LVAD support strategy.

Helical Flow Component of Left Ventricular Assist Devices (LVADs) Outflow Improves Aortic Hemodynamic States

Background

Although LVADs are confirmed to have strong effects on aortic hemodynamics, the precise mechanisms of the helical flow component of LVAD outflow are still unclear.

Material/Methods

To clarify these effects, 3 cases – normal case, flat flow case, and realistic flow case – were designed and studied by using the CFD approach. The normal case denoted the normal aorta without LVAD support, and the flat flow case represented the aorta with the outflow cannula. Similarly, the realistic flow case included the aortic model, the model of outflow cannula, and the model of LVAD. The velocity vector, blood streamline, distribution of wall shear stress (WSS), and the local normalized helicity (LNH) were calculated.

Results

The results showed that the helical component of LVAD outflow significantly improved the aortic hemodynamics. Compared with the flat flow case, the helical flow eliminated the vortex near the outer wall of the aorta and improved the blood flow transport (normal case 0.1 m/s vs. flat flow case 0.14 m/s vs. realistic flow case 0.30 m/s) at the descending aorta. Moreover, the helical flow was confirmed to even the distribution of WSS, reduce the peak value of WSS (normal case 0.92 Pa vs. flat flow case 7.39 Pa vs. realistic flow case 5.2Pa), and maintain a more orderly WSS direction.

Conclusions

The helical flow component of LVAD outflow has significant advantages for improving aortic hemodynamic stability. Our study provides novel insights into LVAD optimization.

Prevention and Treatment of Thrombotic and Hemorrhagic Complications in Patients Supported by Continuous-Flow Left Ventricular Assist Devices

PURPOSE OF REVIEW

The purpose of this review is to describe the current knowledge in prevention and treatment of thrombotic (pump thrombosis and ischemic stroke) and bleeding (gastrointestinal and hemorrhagic stroke) complications in patients supported by continuous-flow left ventricular assist devices (CF-LVAD).

RECENT FINDINGS

Left ventricular assist devices (LVADs) are now widely used for the management of end-stage heart failure. Unfortunately, in spite of the indisputable positive impact LVADs have on patients, the frequency and severity of complications are limitations of this therapy. Stroke, pump thrombosis, and gastrointestinal bleeding are among the most serious and frequent complications in these patients. The balance between hemorrhagic and thrombotic complications in patients supported with CF-LVAD is difficult as most patients do not necessarily fit a "bleeder" or a "clotter" profile but rather move from one side to the other of the thrombotic/bleeding spectrum. Further research is necessary to better understand the risk factors and mechanisms involved in the development of these complications.

The study on hemodynamic effect of series type LVAD on aortic blood flow pattern: a primary numerical study

Background

Left ventricular assist device (LVAD) has become an alternative treatment for end-stage heart failure patients. Series type of LVAD, as a novel LVAD, has attracted more and more attention. The hemodynamic effects of series type LVAD on aortic blood pattern are considered as its important characteristics; however, the precise mechanism of it is still unclear.

Methods

To clarify the hemodynamic effects of series type LVAD on aortic blood flow pattern, a comparative study on the aortic blood flow pattern and hemodynamic states were carried out numerically for two cases, including series type LVAD support and normal condition. The steady-state computational fluid dynamic (CFD) approach was employed. The blood flow streamline, blood velocity vector and distribution of wall shear stress (WSS) were calculated to evaluate the differences of hemodynamic effects between both conditions.

Results

The results demonstrated that the aortic flow pattern under series type LVAD showed significant different from that of normal condition. The strength of aortic swirling flow was significantly enhanced by the series type LVAD support. Meanwhile, the rotating direction of swirling flow under LVAD support was also dominated by the rotating direction of series type LVAD. Moreover, the blood velocity and WSS under LVAD support were also significantly enhanced, compared with that under normal condition.

Conclusion

The hemodynamic states, including the aortic swirling flow characteristic, was significantly dominated by LVAD support. Present investigation could provide not only a useful information on the vascular complications caused by LVAD support, but also provide a useful guide for optimal the structure of the series type LVAD.