I3 - Risk Assessment of Shear Stress-Induced Clotting for a 3D-Printed Left Ventricular Assist Device (LVAD) Treatment in Pediatric Cardiology

Introduction: : Hypoplastic Left Heart Syndrome (HLHS) is a rare but severe congenital defect that affects approximately 1 in every 5,000 live births, characterized by the underdevelopment of the left ventricle, mitral and aortic valves, and the ascending aorta [1]. As a result, children require a series of complex surgeries—Norwood, Glenn, and Fontan procedures—within the first few years of life to reconstruct circulation pathways [2]. Even with these staged interventions, many children experience poor long-term outcomes and ultimately require a heart transplant. This is due to poor oxygenation coming from the heart of a HLHS patient. Currently, the Abbott HeartMate 3 is the only FDA-approved long-term Left Ventricular Assist Device (LVAD), but it is not optimized for pediatric use [3]. Beyond structural concerns, shear stress-induced thrombosis remains one of the most critical risks in LVADs, particularly as non-physiological shear levels can activate platelets and promote clot formation [4]. This project introduces a pediatric-specific 3D printed LVAD prototype designed and tested through both in vitro flow loop and computational modeling techniques, with a focus on optimizing flow performance while reducing thrombotic risk.

Materials and

Methods: : The 3D printed pediatric LVAD prototype was designed using Autodesk Fusion 360 and fabricated with Formlabs Tough 1500 resin via SLA 3D printing to simulate the impeller and flow housing geometry. To better understand anatomical constraints, comparative 3D models of a normal heart and one with HLHS were created using Materialise Mimics from pediatric computed tomography (CT) scan data. These models informed geometric scaling and guided design iterations to align with pediatric cardiovascular anatomy. A closed-loop in vitro circulatory model was constructed using water. Impeller rotational speed (RPM) was measured using a laser tachometer. Shear stress analysis was performed by incrementally increasing RPM and calculating both average scalar and wall shear stresses using MATLAB and Autodesk CFD. This preliminary biological testing served to evaluate material toxicity and mechanical integration at the interface of a planned suture ring, which may be incorporated in future iterations to anchor the pump more effectively within the heart or great vessels.

Results, Conclusions, and Discussions::

Results: As voltage increased from 5 V to 12 V, the flow rate rose from approximately 1800 mL/min to over 3500 mL/min (n = 5, Figure 3A), demonstrating ability to provide physiologically appropriate output for pediatric patients. Error bars represent standard deviation (n = 3). The RPM-voltage relationship, revealing a nearly linear increase in RPM with voltage, ranging from approximately 500 RPM at 1 V to over 6000 RPM at 11.5 V, with consistent behavior across repeated trials (Figure 3B). Analysis of the fluid shear stress was performed using computational fluid dynamics. Scalar and wall shear stress at increasing RPMs (3000–6000 RPM) using computational flow rate experiments on Autodesk CFD with an input pressure of 8 mmHg. Scalar shear stress values rose from ~0.75 Pa to ~1.53 Pa, while wall shear stress increased from ~0.18 Pa to ~0.42 Pa. These values remain well below the reported clinical threshold of 10 Pa associated with shear-induced platelet activation and thrombus formation [6], indicating a limited potential clotting risk. Together, these results indicate that the a balance between flow output and shear safety, supporting its potential for safe and effective pediatric LVAD application.

Conclusions: Initial testing of the pediatric LVAD prototype demonstrated that it can achieve physiologically relevant flow rates while maintaining shear stress levels well below thrombogenic thresholds. The device delivered flow outputs exceeding 3500 mL/min at 12 V, falling within the desired range for pediatric cardiac support. Importantly, both scalar and wall shear stress remained below 2 Pa throughout testing as seen in Figure 1, significantly lower than the 10 Pa threshold associated with platelet activation and thrombus formation in continuous-flow LVADs [8]. This suggests a safe hemodynamic profile, an important consideration since LVADs can be associated with shear-induced clotting and complications such as Extrinsic Outflow Graft Obstruction (EOGO) [3]. A major strength of this approach lies in the use of SLA 3D printing, which enables rapid prototyping and anatomical customization. This allows the LVAD housing and inflow/outflow cannulae to be tailored to individual pediatric anatomies using patient-specific imaging data.

Acknowledgements and/or References (Optional)::

References: [1] Centers for Disease Control and Prevention. (2021); [2] Children’s Hospital of Philadelphia. (2021); [3] U.S. Food and Drug Administration. (2024); [4] American College of Cardiology. (2024); [5] Gaies, M. G., et al. (2019); [6] Weingart, S. (2019); [7] MyLVAD. (2022); [8] Chen, et al. (2019)