Evaluation of the novel total artificial heart Realheart in a pilot human fitting study.

Heart failure affects >26 million patients worldwide. Current cardiac devices save lives, but patients suffer complications. Hence, improved devices are needed. Realheart TAH is a novel total artificial heart which has shown promising results in acute pig studies. However, the device design needed to be evaluated in humans. Virtual implantations demonstrated the device fits in two of three patients, but that there was some interference with the left lung. Herein, we used an innovative 3D-printed model with swivelling device components to test the device in human cadavers. Our new method demonstrated how to optimize design to improve the surgical fit.

Virtual Fitting and Hemodynamic Simulation of the EVAHEART 2 Left Ventricular Assist Device and Double-Cuff Tipless Inflow Cannula.

Inflow malposition during surgery, postoperative pump migration, inflow obstruction, and right ventricular compression are major contributors to low flow and adverse events in patients with ventricular assist devices (VADs). These position abnormalities can lead to adverse events including ischemic stroke. To address these problems, we conducted a virtual anatomical fitting study and hemodynamic simulation on iterative cannula designs, resulting in the EVAHEART 2 with the novel double-cuff tipless (DCT) inflow cannula and smaller pump design. Anatomical fitting was based on computed tomography scans of six patients with heart failure, and a fluid-structure-integration (FSI) model of the left ventricle with a lumped parameter model of the entire cardiovascular system during VAD support was created. Using this model, the hemodynamics of three inflow cannula insertion lengths for two patient-specific ventricles were calculated for both full and partial VAD support. The DCT cannula with the smaller pump housing proved resistant to obstruction even when the pump housing was adjusted. The complete system also had a smaller pump pocket size than the other designs and avoided position abnormalities that commonly lead to adverse events. Compared with conventional cadaver studies, virtual fitting and numerical simulations are more beneficial and economical for iteratively designing medical devices.

Computational Fluid Dynamics Assessment Associated with Transcatheter Heart Valve Prostheses: A Position Paper of the ISO Working Group.

The governing international standard for the development of prosthetic heart valves is International Organization for Standardization (ISO) 5840. This standard requires the assessment of the thrombus potential of transcatheter heart valve substitutes using an integrated thrombus evaluation. Besides experimental flow field assessment and ex vivo flow testing, computational fluid dynamics is a critical component of this integrated approach. This position paper is intended to provide and discuss best practices for the setup of a computational model, numerical solving, post-processing, data evaluation and reporting, as it relates to transcatheter heart valve substitutes. This paper is not intended to be a review of current computational technology; instead, it represents the position of the ISO working group consisting of experts from academia and industry with regards to considerations for computational fluid dynamic assessment of transcatheter heart valve substitutes.

Design of a right ventricular mock circulation loop as a test bench for right ventricular assist devices.

Right heart failure (RHF), e.g. due to pulmonary hypertension (PH), is a serious health issue with growing occurrence and high mortality rate. Limited efficacy of medication in advanced stages of the disease constitutes the need for mechanical circulatory support of the right ventricle (RV). An essential contribution to the process of developing right ventricular assist devices (RVADs) is the in vitro test bench, which simulates the hemodynamic behavior of the native circulatory system. To model healthy and diseased arterial-pulmonary hemodynamics in adults (mild and severe PH and RHF), a right heart mock circulation loop (MCL) was developed. Incorporating an anatomically shaped silicone RV and a silicone atrium, it not only enables investigations of hemodynamic values but also suction events or the handling of minimal invasive RVADs in an anatomical test environment. Ventricular pressure-volume loops of all simulated conditions as well as pressure and volume waveforms were recorded and compared to literature data. In an exemplary test, an RVAD was connected to the apex to further test the feasibility of studying such devices with the developed MCL. In conclusion, the hemodynamic behavior of the native system was well reproduced by the developed MCL, which is a useful basis for future RVAD tests.

Effects of Interaction Between Ventricular Assist Device Assistance and Autoregulated Mock Circulation Including Frank-Starling Mechanism and Baroreflex.

A mock heart circulation loop (MHCL) is a hydraulic model simulating the human circulatory system. It allows in vitro investigations of the interaction between cardiac assist devices and the human circulatory system. In this study, a preload sensitive MHCL, the MHCLAUTO , was developed to investigate the interaction between the left ventricle and left ventricular assist devices (LVADs). The Frank-Starling mechanism was modeled by regulating the stroke volume (SV) based on the measured mean diastolic left atrial pressure (MLAPdiast ). The baroreflex autoregulation mechanism was implemented to maintain a constant mean aortic pressure (MAP) by varying ventricular contractility (Emax ), heart rate (HR), afterload/systemic vascular resistance (SVR) and unstressed venous volume (UVV). The DP3 blood pump (Medos Medizintechnik GmbH) was used to simulate the LVAD. Characteristic parameters were measured in pathological conditions both with and without LVAD to assess the hemodynamic effect of LVAD on the MHCLAUTO . The results obtained from the MHCLAUTO show a high correlation to literature data. The study demonstrates the possibility of using the MHCLAUTO as a research tool to better understand the physiological interactions between cardiac implants and human circulation.

Real-Time Visualization of Platelet Interaction With Micro Structured Surfaces.

Improving the hemocompatibility of artificial implants by micro structuring their surfaces has shown promising results, but the mechanisms which lead to this improvement are not yet understood. Therefore, we built a test setup for real-time visualization of platelet interaction with a plain and two micro structured surfaces. The micro structures, defined by the distance of the plain surface area between the structures, were chosen to be 3 and 30 µm, representing a positive and a negative effect on the hemocompatibility. The main part of the test setup was a flow chamber containing films of low density polyethylene (LDPE) with the differently structured surfaces. For different wall shear stresses, no considerable differences were observed in the platelet-surface interaction for all surface types. Whereas, major differences in flow behavior were observed when comparing the surfaces to each other. The platelets "rolled" along the smooth surface, being in constant contact with the surface material. Although the platelets "rolled" over the surface with small structures as well, they were only in contact with the tips of the structure and therefore had less surface contact with the foreign material. The increased distance and height of the structures of the last surface led to a trapping of platelets between the structures. This resulted in a longer contact time with the foreign material as well as a larger contact area, which both increase the risk of platelet activation, adhesion, and finally clotting. Our results showed the mechanisms which lead to these effects and thus revealed why micro structuring of surfaces impacts the hemocompatibility. Furthermore, we established a test setup which can be used for future investigations on the platelet-structure interactions.