Surface Coatings for Rotary Ventricular Assist Devices: A Systematic Review

Rotary ventricular assist devices (VADs) are frequently used to provide mechanical circulatory support to patients suffering from end-stage heart failure. Therefore, these devices and especially their pump impeller and housing components have stringent requirements on wear resistance and hemocompatibility. Various surface coatings have been investigated to improve the wear resistance or hemocompatibility of these devices. The aim of the present systematic review was to build a comprehensive understanding of these coatings and provide potential future research directions. A Boolean search for peer-reviewed studies was conducted in online databases (Web of Science, Scopus, PubMed, and ScienceDirect), and a preferred reporting items for systematic reviews and meta-analyses (PRISMA) process was followed for selecting relevant papers for analysis. A total of 45 of 527 publications were included for analysis. Eighteen coatings were reported to improve wear resistance or hemocompatibility of rotary VADs with the most common coatings being diamond-like carbon (DLC), 2-methacryloyloxyethyl phosphorylcholine (MPC), and heparin. Ninety-three percent of studies focused on hemocompatibility, whereas only 4% of studies focused on wear properties. Thirteen percent of studies investigated durability. This review provides readers with a systematic catalogue and critical review of surface coatings for rotary VADs. The review has identified that more comprehensive studies especially investigations on wear properties and durability are needed in future work.

Systematic Design of a Magnetically Levitated Brushless DC Motor for a Reversible Rotary Intra-Aortic Blood Pump

The IntraVAD is a miniature intra-aortic ventricular assist device (VAD) designed to work in series with the compromised left ventricle. A reverse-rotation control (RRc) mode has been developed to increase myocardial perfusion and reduce ventricular volume. The RRc mode includes forward rotation in systole and reverse rotation in diastole, which requires the IntraVAD to periodically reverse its rotational direction in synchrony with the cardiac cycle. This periodic reversal leads to changes in pressure force over the impeller, which makes the entire system less stable. To eliminate the mechanical wear of a contact bearing and provide active control over the axial position of the rotor, a miniature magnetically levitated bearing (i.e., the PM-Coil module) composed of two concentric permanent magnetic (PM) rings and a pair of coils-one on each side-was proposed to provide passive radial and active axial rotor stabilization. In the early design stage, the numerical finite element method (FEM) was used to optimize the geometry of the brushless DC (BLDC) motor and the maglev module, but constructing a new model each time certain design parameters were adjusted required substantial computation time. Because the design criteria for the module had to be modified to account for the magnetic force produced by the motor and for the hemodynamic changes associated with pump operation, a simplified analytic expression was derived for the expected magnetic forces. Suitable bearings could then be designed capable of overcoming these forces without repeating the complicated FEM simulation for the motor. Using this method at the initial design stage can inform the design of the miniature maglev BLDC motor for the proposed pulsatile axial-flow VAD.

A transapical-to-aorta double lumen cannula-based neonate left ventricular assist device efficiently unloads the left ventricle in neonate lambs

OBJECTIVE

We are developing a transapical-to-aorta double lumen cannula (TAA DLC) for a less-invasive/more dependable neonatal left ventricular assist device.

METHODS

The 18-Fr TAA DLC prototypes were bench tested and evaluated for 6 hours in neonate lambs (n = 6, 7.7-10 kg). The cardiac apex was exposed through a left anterolateral thoracotomy through the sixth intercostal space. The TAA DLC was inserted through a mattress stitch on apex, passing LV-aortic valve, into the ascending aorta with insertion/deployment guided by pressure waveform. The DLC was connected to blood pump. Cardiac output and aortic root blood flow were measured with perivascular flow sensors. Activated clotting time was maintained at 180-250 seconds.

RESULTS

The DLC pumped up to 1.8 L/min flow against 63 mm Hg drainage pressure and 145 mm Hg infusion pressure in bench testing. In all lambs, the DLC was inserted/deployed properly within 1 minute on the first attempt. Pumping flow was maintained at 1.2-1.3 L/min. Systolic arterial pressure decreased and diastolic arterial pressure/mean arterial pressure increased, indicating decreased afterload and increased perfusion pressure. Left ventricular end-diastolic pressure decreased from 13 ± 1 mm Hg to 6 ± 2 mm Hg, indicating decreased preload. Aortic root backward flow was 2.4% ± 0.6% without DLC and 3.5% ± 0.8% of cardiac output with DLC, indicating no significant DLC-induced aortic valve regurgitation. After 6 hours, free hemoglobin was <5 mg/dL with hemoglobin/platelets unchanged. No significant thrombus was found in pumps/DLCs. No trauma was found in LV, aortic valve, and aorta.

CONCLUSIONS

Our TAA DLC-based neonate left ventricular assist device efficiently unloaded the LV in lambs.