(H-297) The Role of Prosthetic Aortic Valve Sizing on Blood Residence Time

Introduction:: Cardiovascular diseases are the leading causes of illness and death all around the world. The third most common cardiovascular disease is aortic stenosis (AS). The most effective treatment for AS is the replacement of the stiffened valve with a prosthetic valve. A major metric for prosthetic valve performance is the transvalvular pressure drop which is a measure of how much pressure, and energy, is lost as the heart pumps blood through the valve. Larger valves exhibit a smaller pressure drop because they restrict the flow to a lesser degree. This phenomenon has led to a trend for surgeons to implant the largest prosthetic valve possible, and in some cases, to expanding the aorta to fit even larger valves. However, there has been relatively little work done on determining the effects of valve oversizing on the blood flow inside the Aorta.


Materials and Methods:: An in vitro experimental apparatus was used to test different prosthetic valve sizes in to identify how they affected residence time inside the sinus bulge. A pulsatile piston pump drove a blood analogue through different valves and into a glass sinus and aortic arch. The blood analogue was then pumped up a water column that served to provide a physiological back pressure and ensure proper prosthetic valve function. The experimental setup was housed inside a tank filled with the blood analogue and heated to body temperature which served to provide a degree of index matching. The glass sinus and aorta provided optical access for quantitative flow measurements. Dye residence experiments and Digital particle image velocimetry (DPIV) were used to measure fluid stasis in several different combinations of prosthetic valve sizes and sinus sizes.


Results, Conclusions, and Discussions:: We conducted experiments on prosthetic aortic valves that ranged from 21 mm to 25 mm in diameter. These were tested inside a range of sinus bulge diameters. Large valves with limited spacing between the sinus wall and the sides of the valves experienced increased dye residence time which indicated an increased risk of thrombus formation. DPIV was then used to quantify the decrease in average velocity and velocity standard deviation that was associated with the decrease in valve washout performance. Finally, we propose a novel metric which predicts whether any valve-sinus combination would underperform.

Our results indicate that valve to sinus sizing plays a large role in sinus hemodynamics and valve oversizing can lead to greatly increased residence time and thrombosis risk. This phenomenon is most likely due to oversized valves having very small gaps between themselves and the sinus walls. We have also identified a metric that can predict the threshold at which valves become oversized. This metric was based on the systolic formation number and other values which surgeons could readily measure prior to surgical valve replacements.




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