In Vitro Characterization of Bicuspid Aortic Valve Hemodynamics Using Particle Image Velocimetry

Abstract

The congenital bicuspid aortic valve (BAV) is associated with increased leaflet calcification, ascending aortic dilatation, aortic stenosis (AS) and regurgitation (AR). Although underlying genetic factors have been primarily implicated for these complications, the altered mechanical environment of BAVs could potentially accelerate these pathologies. The objective of the current study is to characterize BAV hemodynamics in an in vitro system. Two BAV models of varying stenosis and jet eccentricity and a trileaflet AV (TAV) were constructed from excised porcine AVs. Particle Image Velocimetry (PIV) experiments were conducted at physiological flow and pressure conditions to characterize fluid velocity fields in the aorta and sinus regions, and ensemble averaged Reynolds shear stress and 2D turbulent kinetic energy were calculated for all models. The dynamics of the BAV and TAV models matched the characteristics of these valves which are observed clinically. The eccentric and stenotic BAV showed the strongest systolic jet (V = 4.2 m/s), which impinged on the aortic wall on the non-fused leaflet side, causing a strong vortex in the non-fused leaflet sinus. The magnitudes of TKE and Reynolds stresses in both BAV models were almost twice as large as comparable values for TAV, and these maximum values were primarily concentrated around the central jet through the valve orifice. The in vitro model described here enables detailed characterization of BAV flow characteristics, which is currently challenging in clinical practice. This model can prove to be useful in studying the effects of altered BAV geometry on fluid dynamics in the valve and ascending aorta. These altered flows can be potentially linked to increased calcific responses from the valve endothelium in stenotic and eccentric BAVs, independent of concomitant genetic factors.

Hemodynamic and Cellular Response Feedback in Calcific Aortic Valve Disease

“…71 They found that the smaller EOAs of bicuspid valves lead to a significant increase in fluid velocity, vorticity, TPG, and ventricular side shear stresses compared with normal tricuspid valves ( Figure 2D). However, some amount of each of these hemodynamic features seems to be critical in proper valve function.…”

“…For example, the normal tricuspid valve requires some amount of vorticity to facilitate rapid valve closure after systole. 71 Using a similar particle tracking and aortic valve explantation technique, Yap et al 75,76 were also able to demonstrate that the shear stresses on the ventricular side of the valve are higher than those on the aortic side. The ventricular side shear stress peaked at 64 to 71 dynes/cm 2 during systole and reversed in direction at the end of systole for only 15 to 25 milliseconds at 40 to 51 dynes/cm 2 .…”

“…68 As this equation suggests, TPG increases quadratically with increases in blood velocity, which is directly affected by the EOA of the aortic valve. 68,70,71 One complicating factor in correctly diagnosing and treating AS is simultaneous hypertension, which occurs in 35% to 45% of patients with AS. 68 Elevated blood pressure levels can decrease the TPG measured with conventional methods (eg, echocardiography), making it difficult to detect the onset of AS.…”

Effect of Bicuspid Aortic Valve Cusp Fusion on Aorta Wall Shear Stress: Preliminary Computational Assessment and Implication for Aortic Dilation

“…Phase-contrast magnetic resonance imaging (PC MRI) and echocardiographic measurements in BAV patients [7]- [10], as well as in vitro particle-image velocimetry measurements [11]- [13] and in silico simulations in idealized ascending aorta (AA) geometries [14]- [17] have revealed the existence of abnormal helical flow patterns and fluid wall shear stress (WSS) overloads in AA regions vulnerable to aortic medial degeneration. In addition, the particular leaflet fusion type affects the expression of dilation and thinning of the AA downstream of a BAV.…”

Emerging Trends in Heart Valve Engineering: Part IV. Computational Modeling and Experimental Studies

“…7). 17,26,[45][46][47]64,66,68,76,77,88,91,97,98,103,130,138 However, PIV methods were mainly two dimensional until Bru¨cker introduced Stereo-PIV based on the use of two digital cameras and PIV algorithms to study the flow past artificial heart valves. 21 The testing requirements for performing stereo-PIV for characterizing the flow through mechanical heart valves has been well described by Morbiducci et al 115 Another breakthrough in PIV was the development of defocusing digital particle image velocimetry (D-DPIV).…”