EFFECT OF STENT DESIGN PARAMETERS ON HEMODYNAMICS AND BLOOD DAMAGE IN A PERCUTANEOUS CAVOPULMONARY ASSIST DEVICE

摘要

Hypoplastic Right Heart Syndrome is a type of congenital heart defect where the right ventricle is underdeveloped in an infant to pump blood from the body to the lungs. The three-staged surgical Fontan procedure provides a temporary treatment; however, in most of the cases, a heart transplantation is required due to postoperative complications. Cunently, there are no devices commercially available in the market to provide a therapeutic assistance to these patients until a donor heart is available. Thus, a novel dual propeller pump concept is developed to provide cavopulmonary assistance to these patients. The designed blood pump would be percutaneously inserted via the Femoral vein and deployed at the center of the Total Cavopulmonary Connection (TCPC). The two propellers, each placed in the Superior Vena Cava (SVC) and the Inferior Vena Cava (IVC) are connected by a single shaft and rotating at same speed. The device is supported with the help of a self-expanding stent whose outer walls are anchored to the inner walls of the IVC and the SVC. Each of the IVC and the SVC propeller without the stent provides a modest pressure augmentation of 5-6 mm Hg. To expand on this, the current study focusses on studying the effect of the introduction of stent around the propeller on the hemodynamic performance of the pump. Five different stent design parameters, viz. the strut thickness, width, number, the stent length and number of strut columns were selected for a range of values. Each of the design parameters was varied by keeping all others constant and equal to the base stent design. All the stent models were analysed to see their effect on pressure rise, flow pattern and blood damage using 3D CFD analysis. The blood damage potential for different studied designs was predicted using a non-linear mathematical power law model along with Lagrangian particle tracking to predict the blood flow path. The introduction of stent resulted in pressure reduction of around 0.4 and 0.2 mm Hg around the IVC and SVC propeller with an increase in blood damage index (BDI) by almost 2 times for the final dual propeller pump assembly. It was observed that the blood damage potential was directly related to the amount of pressure rise where the stent length, stent column number, strut width, and strut thickness had a converse effect showing a reduction in pressure rise and blood damage with their increment. While the number of struts gave a desirable effect of increasing pressure rise and reducing blood damage with its increment. The study also demonstrated that the introduction of stent around a circulatory pump increases the Wall Shear Stress (WSS) value at the stent-artery wall interface thereby preventing the occurrence of restenosis and thrombosis initiating due to very low WSS (< 0.5 Pa). Thus, this study acts as an initial step to design a protective stent support around a percutaneous assist device by analysing the sensitivity of stent design parameters on the hemodynamic performance of the pump.