Currently available ventricular-assist devices: capabilities, limitations and future perspectives

Effect of Rotary Blood Pump Pulsatility on Potential Parameters of Blood Compatibility and Thrombosis in Inflow Cannula Tips

Purpose

Rotary Blood Pump (RBP) pulsatile strategies relative to the native cardiac cycle have been widely studied because of their benefits to hemodynamics. However, the effects that inducing pulses has on the blood compatibility of ventricular assist device (VAD) support have not yet been understood. Inflow cannulae have been found to be associated with thrombosis under conventional constant speed support of RBPs. To prevent further risks to blood compatibility, it is necessary to understand the relationship between cannula tip design and the induced pulsatility. The purpose of this study was to evaluate the flow field of 5 different tip geometries under RBP pulsatile support using stereo-particle image velocimetry (PIV).

Methods

Inflow cannulae with conventional tip geometries (blunt, blunt with 4 side ports, beveled with 3 side ports, and cage) and a custom designed crown tip were studied. All cannulae were interposed between a mixed-flow RBP and a silicone left ventricle. The contractile function and hemodynamics were reproduced in a mock circulation loop (MCL). The RBP was configured to induce synchronous and counter-synchronous pulses relative to cardiac cycles while supporting the failing ventricle.

Results

Between both pulsing strategies, low shear volume ([Formula: see text], potential parameter of thrombus formation) showed no significant difference. However, counter-synchronous pulsatile mode induced less increase of both high shear volume ([Formula: see text], potential parameter of platelet activation) and recirculation volume (Vz>0, potential parameter of thrombus formation).

Conclusions

Although the clinical relationship cannot be inferred from this measurement, when considering the inflow tips only, a necessary trade-off should be made between adverse effects on blood compatibility and benefits for hemodynamics during RBP pulsatile mode.

Assisting the failing heart

Anesthesiologists increasingly encounter patients who have a spectrum of heart failure ranging from stable chronic heart failure to acute heart failure to cardiogenic shock. Improved medical therapy has increased the survival of patients who have chronic heart failure but not of patients who have acute heart failure. New surgical techniques and mechanical devices may offer alternatives to certain patients who have refractory heart failure This article provides an overview of established and newer pharmacologic and nonpharmacologic therapies and surgical interventions to manage patients who have heart failure, including the perioperative management of heart transplantation and ventricular assist devices.

Three-dimensional magnetic resonance flow analysis in a ventricular assist device

OBJECTIVE

The assessment of flow characteristics inside ventricular assist devices by magnetic resonance imaging techniques may provide insight into the mechanisms underlying the high rate of thromboembolic events after implantation of a ventricular assist device. Furthermore, these investigations may form the basis to optimize the device's design and its need for anticoagulation. The purpose of this study was to integrate a clinical routine ventricular assist device into a flow circuit with realistic geometric and pulsatile inflow conditions. Combination with flow-sensitive magnetic resonance imaging at 3 T permitted the detailed analysis of local and global 3-dimensional flow dynamics in a realistic environment.

METHODS

A commercially available ventricular assist device was integrated into a magnetic resonance-compatible flow circuit. Flow-sensitive 3-dimensional magnetic resonance imaging was performed to measure time-resolved 3-directional flow velocities in the entire device. Advanced computer-aided 3-dimensional flow visualization methods were used to derive a comprehensive picture of flow dynamics within the ventricular assist device system.

RESULTS

On the basis of the ventricular assist device model system, magnetic resonance imaging, and flow visualization, the first 4-dimensional functional magnetic resonance imaging analysis of flow characteristics inside an operating clinical routine ventricular assist device chamber system is reported. Detailed visualization of flow patterns and local changes in flow characteristics were successfully performed and revealed locally accelerated, vortical, and helical flow regions inside the geometry of the device.

CONCLUSIONS

Complex flow patterns such as vortex formation and locally accelerated flow demonstrate the potential of the presented method to further deepen the understanding of complex and regionally different flow characteristics inside ventricular assist devices.