The design modification of advanced ventricular assist device to enhance pulse augmentation and regurgitant flow shut-off

Cleveland Clinic Continuous-Flow Total Artificial Heart: Progress Report and Technology Update

Cleveland Clinic's continuous-flow total artificial heart (CFTAH) is being developed at our institution and has demonstrated system reliability and optimal performance. Based on the results from recent chronic in vivo experiments, CFTAH has been revised, especially to improve biocompatibility. The purpose of this article is to report our progress in developing CFTAH. To improve biocompatibility, the right impeller, the pump housing, and the motor were reviewed for design revision. Updated design features were based on computational fluid dynamics analysis and observations from in vitro and in vivo studies. A new version of CFTAH was created, manufactured, and tested. All hemodynamic and pump-related parameters were observed and found to be within the intended ranges, and the new CFTAH yielded acceptable biocompatibility. Cleveland Clinic's continuous-flow total artificial heart has demonstrated reliable performance, and has shown satisfactory progress in its development.

Preservation of pulsatility with universal ventricular assist device: In vitro assessment for biventricular support

BACKGROUND

The objective of this study was to assess the pulsatility preservation capability of the universal ventricular assist device (UVAD) when used as a biventricular assist device (BVAD). This evaluation was conducted through an in vitro experiment, utilizing a pulsatile biventricular circulatory mock loop.

METHODS

Two UVAD pumps were tested in a dual setup (BVAD) in the circulatory model with the simulated conditions of left heart failure (HF), right HF, and moderate/severe biventricular HF (BHF). The total flow, aortic pulse pressure, the pulse augmentation factor (PAF), the energy-equivalent pressure (EEP), and the surplus hemodynamic energy (SHE) were observed at various pump speeds to evaluate the pulsatility.

RESULTS

The aortic pulse pressure increased from the baseline (without pump) in all simulated hemodynamic conditions. The PAF ranged from 17%-35% in healthy, left HF, right HF, and mild BHF conditions, with the highest PAF of 90% being observed in the severe BHF condition. The EEP correlated with LVAD flow in all groups (R2  = 0.87-0.97) and increased from the baseline in all cases. The SHE peaked at approximately 5-6 L/min of LVAD support and was likely to decrease at higher LVAD pump flow. The largest decrease in SHE from the baseline, 53%, was observed in the mild BHF conditions with the highest LVAD and RVAD support.

CONCLUSIONS

The UVAD successfully demonstrated the ability to preserve pulsatility in vitro, and to optimize the cardiac output, as an isolated circulatory support device option (RVAD or LVAD) and when used for BVAD support.

Biventricular circulatory support using single-device and dual-device configurations: Initial pump characterization in simulated heart failure model

Objective

Severe biventricular heart failure (BHF) can be remedied using a biventricular assist device (BVAD). Two devices are currently in development: a universal ventricular assist device (UVAD), which will be able to assist either the left, right, or both ventricles, and a continuous-flow total artificial heart (CFTAH), which replaces the entire heart. In this study, the in vitro hemodynamic performances of two UVADs are compared to a CFTAH acting as a BVAD.

Methods

For this experiment, a biventricular mock circulatory loop utilizes two pneumatic pumps (Abiomed AB5000™, Danvers, MA, USA), in conjunction with a dual-output driver, to create heart failure (HF) conditions (left, LHF; right, RHF; biventricular, BHF). Systolic BHF for four different situations were replicated. In each situation, CFTAH and UVAD devices were installed and operated at two distinct speeds, and cannulations for ventricular and atrial connections were evaluated.

Results

Both CFTAH and UVAD setups achieved our recommended hemodynamic criteria. The dual-UVAD arrangement yielded a better atrial balance to alleviate LHF and RHF. For moderate and severe BHF scenarios, CFTAH and dual UVADs both created excellent atrial pressure balance. Conversely, when CFTAH was atrial cannulated for LHF and RHF, the needed atrial pressure balance was not met.

Conclusion

Comprehensive in vitro testing of two different BVAD setups exhibited self-regulation and exceptional pump performance for both (single- and dual-device) BHF support scenarios. For treating moderate and severe BHF, UVAD and CFTAH both functioned well with respect to atrial pressure regulation and cardiac output. Though, the dual-UVAD setup yielded a better atrial pressure balance in all BHF testing scenarios.

Mechanical circulatory support devices and treatment strategies for right heart failure

The importance of right heart failure (RHF) treatment is magnified over the years due to the increased risk of mortality. Additionally, the multifactorial origin and pathophysiological mechanisms of RHF render this clinical condition and the choices for appropriate therapeutic target strategies remain to be complex. The recent change in the United Network for Organ Sharing (UNOS) allocation criteria of heart transplant may have impacted for the number of left ventricular assist devices (LVADs), but LVADs still have been widely used to treat advanced heart failure, and 4.1 to 7.4% of LVAD patients require a right ventricular assist device (RVAD). In addition, patients admitted with primary left ventricular failure often need right ventricular support. Thus, there is unmet need for temporary or long-term support RVAD implantation exists. In RHF treatment with mechanical circulatory support (MCS) devices, the timing of the intervention and prediction of duration of the support play a major role in successful treatment and outcomes. In this review, we attempt to describe the prevalence and pathophysiological mechanisms of RHF origin, and provide an overview of existing treatment options, strategy and device choices for MCS treatment for RHF.

Characterization and Development of Universal Ventricular Assist Device: Computational Fluid Dynamics Analysis of Advanced Design

We are developing a universal, advanced ventricular assist device (AVAD) with automatic pressure regulation suitable for both left and right ventricular support. The primary goal of this computational fluid dynamics (CFD) study was to analyze the biventricular performance of the AVAD across its wide range of operating conditions. An AVAD CFD model was created and validated using in vitro hydraulic performance measurements taken over conditions spanning both left ventricular assist device (LVAD) and right ventricular assist device (RVAD) operation. Static pressure taps, placed throughout the pump, were used to validate the CFD results. The CFD model was then used to assess the change in hydraulic performance with varying rotor axial positions and identify potential design improvements. The hydraulic performance was simulated and measured at rotor speeds from 2,300 to 3,600 revolutions/min and flow rates from 2.0 to 8.0 L/min. The CFD-predicted hydraulic pressure rise agreed well with the in vitro measured data, within 6.5% at 2300 rpm and within 3.5% for the higher rotor speeds. The CFD successfully predicted wall static pressures, matching experimental values within 7%. High degree of similarity and circumferential uniformity in the pump's flow fields were observed over the pump operation as an LVAD and an RVAD. A secondary impeller axial clearance reduction resulted in a 10% decrease in peak flow residence time and lower static pressures on the secondary impeller. These lower static pressures suggest a reduction in the upwards rotor forces from the secondary impeller and a desired increase in the pressure sensitivity of the pump. The CFD analyses supported the feasibility of the proposed AVAD's use as an LVAD or an RVAD, over a wide range of operating conditions. The CFD results demonstrated the operability of the pump in providing the desired circumferential flow similarity over the intended range of flow/speed conditions and the intended functionality of the AVAD's automated pressure regulation.

Effects of blood pump orientation on performance: In vitro assessment of universal advanced ventricular assist device

An advanced ventricular assist device (VAD), which is under development in our institution, has specific features that allow changes in the axial rotor position and pump performance by intrapump pressure difference. However, performance could be influenced by the pump orientation because of the effect of gravity on the rotor position. The purpose of this study was to evaluate the effects of pump orientation on the pump performance, including pulse pressure and regurgitant flow through the pump when the pump was stopped. Bench testing of the VAD was performed on a static or pulsatile mock loop with a pneumatic device to simulate the native ventricle. The pump performance, including pressure-flow curve, pulsatility, and regurgitant flow, was evaluated at several angles, ranging from -90° (inlet pointed upward) to +90° (inlet pointed downward) at pump speeds of 2000, 2500, 3000, and 3500 rpm. The pump performance was slightly lower at +90° at all rotational speeds, compared with -90°. The pulse pressure on the pulsatile mock loop (80 bpm) was 50 mm Hg without pump support, remained at 50 mm Hg during pump support, and was not changed by orientation (-90°, 0°, and +90°). When the pump was stopped, the regurgitant flow was near 0 L/min at all angles. Pump orientation had a minor effect on pump performance, with no effect on pulse pressure or regurgitant flow when the pump was stopped. This indicates that the effect of gravity on the rotor assembly is insignificant.

Evaluation of cardiac beat synchronization control for a rotary blood pump on valvular regurgitation with a mathematical model

We have studied the cardiac beat synchronization (CBS) control for a rotary blood pump (RBP) and revealed that it can promote pulsatility and reduce cardiac load. Besides, patients with LVAD support sometimes suffer from aortic and mitral regurgitation (AR and MR). A control method for the RBP should be validated in wider range of conditions to clarify its benefits and pitfalls prior to clinical application. In this study, we evaluated pulsatility and cardiac load reduction obtained with the CBS control on valvular failure conditions with a mathematical model. Diastolic assist could reduce cardiac load on the left ventricle by decreasing external work of the ventricle even in MR cases while it was not so effective in AR cases. Systolic assist can still promote pulsatility in AR and MR cases; however, aortic valve function should be carefully confirmed since pulse pressure can be wider not due to systolic assist but to AR.

An advanced universal circulatory assist device for left and right ventricular support: First report of an acute in vivo implant

Background

The Advanced ventricular assist device (Advanced VAD) is designed as a universal pump intended to prevent backflow in the event of pump stoppage, to maintain physiological pulse pressure, and to be used as both a left and right VAD. The purpose of this study was to evaluate the performance of the Advanced VAD as both a left and right VAD in an acute in vivo study in calves.

Methods

The Advanced VAD was implanted through a median sternotomy in 5 healthy calves (weight, 71.4-91.2 kg) as a left VAD (n = 3) or a right VAD (n = 2). After implantation, hemodynamic parameters, including general performance and pump stoppage, were evaluated.

Results

The Advanced VAD was successfully implanted as a left and right VAD without cardiopulmonary bypass. The speed range of the Advanced VAD was 2500 to 3500 rpm as a left VAD and 2000 to 2500 rpm as a right VAD. Up to 4.3 L/min was achieved for both left and right VAD configurations. To demonstrate the automatic shut-off feature, the pump was stopped without clamping the outflow graft. The outflow graft was then clamped, which produced no significant changes in the arterial pressure waveform. The pulse pressures under the left VAD configuration were 38 mm Hg, 17 mm Hg, 14 mm Hg, and 16 mm Hg at baseline, 2500 rpm, 3000 rpm, and 3500 rpm, respectively.

Conclusions

This acute in vivo study demonstrated the pump performance, anatomical fitting as both left VAD and right VAD, and regurgitant flow shut-off feature of the Advanced VAD.

In vitro performance of trans-valve left ventricular assist device installed at aortic valve position

In this study, we developed a trans-valve left ventricular assist device (LVAD) that unites a rear-impeller axial-flow blood pump (AFBP) and a polymer membrane valve placed at the aortic valve position. The diameter and length of the rear impeller AFBP was 12 and 63 mm, respectively. The polymer membrane valve was similar to the jelly-fish valve consisting of a valve leaflet made of silicone rubber (thickness 0.5 mm), valve ring (diameter: 25 mm), and valve spokes. The trans-valve LVAD was examined in a mock circulation. An implantable pulsatile flow (PF) VAD was connected to an atrial reservoir to simulate the left ventricle (LV), and the Hall valve was worn in the inflow port, and the trans-valve LVAD was placed in the outflow port as an outflow valve. When the motor rotational speed increased to 26 400 rpm, the mean aortic flow increased from 4.2 to 5.3 L/min, mean aortic pressure increased from 83.4 to 100 mm Hg, and mean motor current of the implantable PF VAD decreased from 1.18 to 0.94 A (unloading effect on LV -21%). The energy equivalent pressure increased from 85.2 to 102 mm Hg, and surplus hemodynamic energy (SHE) decreased by -15.4% from the baseline. In conclusion, the trans-valve LVAD has an advantage of preserving pulsatility without any complicated mechanism and is a novel and promising LV support device.