Differential Impact of Blood Pressure Control Targets on Epicardial Coronary Flow After Transcatheter Aortic Valve Replacement

Background: The cause for the association between increased cardiovascular mortality rates and lower blood pressure (BP) after aortic valve replacement (AVR) is unclear. This study aims to assess how the epicardial coronary flow (ECF) after AVR varies as BP levels are changed in the presence of a right coronary lesion. Methods: The hemodynamics of a 3D printed aortic root model with a SAPIEN 3 26 deployed were evaluated in an in vitro left heart simulator under a range of varying systolic blood pressure (SBP) and diastolic blood pressure (DBP). ECF and the flow ratio index were calculated. Flow index value 0.9 for SBP ≥130 mmHg. However, at an SBP of 120 mmHg, the flow ratio was 0.63 (p ≤ 0.0055). With decreasing DBP, no BP condition yielded a flow ratio index that was less than 0.91. Conclusions: Reducing BP to the current recommended levels assigned for the general population after AVR in the presence of coronary artery disease may require reconsideration of levels and treatment priority. Additional studies are needed to fully understand the changes in ECF dynamics after AVR in the presence and absence of coronary artery disease

Gradient and pressure recovery of a self-expandable transcatheter aortic valve depends on ascending aorta size: In vitro study

Objective: In this study we aimed to understand the role of interaction of the Medtronic Evolut R transcatheter aortic valve with the ascending aorta (AA) by evaluating the performance of the valve and the pressure recovery in different AA diameters with the same aortic annulus size. Methods: A 26-mm Medtronic Evolut R valve was tested using a left heart simulator in aortic root models of different AA diameter (D): small (D = 23 mm), medium (D = 28 mm), and large (D = 34 mm) under physiological conditions. Measurements of pressure from upstream to downstream of the valve were performed using a catheter at small intervals to comprehensively assess pressure gradient and pressure recovery. Results: In the small AA, the measured peak and mean pressure gradient at vena contracta were 11.5 ± 0.5 mm Hg and 7.8 ± 0.4 mm Hg, respectively, which was higher (P \u3c .01) compared with the medium (8.1 ± 0.4 mm Hg and 5.2 ± 0.4 mm Hg) and large AAs (7.4 ± 1.0 mm Hg and 5.4 ± 0.6 mm Hg). The net pressure gradient was lower for the case with the medium AA (4.1 ± 1.2 mm Hg) compared with the small AA (4.7 ± 0.8 mm Hg) and large AA (6.1 ± 1.4 mm Hg; P \u3c .01). Conclusions: We have shown that small and large AAs can increase net pressure gradient, because of the direct interaction of the Medtronic Evolut R stent with the AA (in small AA) and introducing higher level of turbulence (in large AA). AA size might need to be considered in the selection of an appropriate device for transcatheter aortic valve replacement

Statistical characteristics of turbulent chemical plumes

M.S.Donald R. Webste

Sinus Hemodynamics in Representative Stenotic Native Bicuspid and Tricuspid Aortic Valves: An In-Vitro Study

(1) The study’s objective is to assess sinus hemodynamics differences between stenotic native bicuspid aortic valve (BAV) and native tricuspid aortic valve (TrAV) sinuses in order to assess sinus flow shear and vorticity dynamics in these common pathological states of the aortic valve. (2) Representative patient-specific aortic roots with BAV and TrAV were selected, segmented, and 3D printed. The flow dynamics within the sinus were assessed in-vitro using particle image velocimetry in a left heart simulator at physiological pressure and flow conditions. Hemodynamic data calculations, vortex tracking, shear stress probability density functions and sinus washout calculations based on Lagrangian particle tracking were performed. (3) (a) At peak systole, velocity and vorticity in BAV reach 0.67 ± 0.02 m/s and 374 ± 5 s−1 versus 0.49 ± 0.03 m/s and 293 ± 3 s−1 in TrAV; (b) Aortic sinus vortex is slower to form but conserved in BAV sinus; (c) BAV shear stresses exceed those of TrAV (1.05 Pa versus 0.8 Pa); (d) Complete TrAV washout was achieved after 1.5 cycles while it was not for BAV. (4) In conclusion, sinus hemodynamics dependence on the different native aortic valve types and sinus morphologies was clearly highlighted in this study

Controlling the Flow Separation in Heart Valves Using Vortex Generators

A comprehensive computational study is performed to investigate the effectiveness of vortex generators (VGs) applied to mechanical bi-leaflet heart valves. Co-rotating and counter-rotating VG configurations are compared to a control valve without VGs. Detailed flow fields are obtained and used to elucidate the underlying flow physics. It was found that VGs reduce flow separation over the leaflets and hence reduce the Reynolds shear stress (RSS) in the vicinity regions of heart valve. The co-rotating VG configuration demonstrates a better performance compared with the counter-rotating configuration in terms of the RSS, turbulent kinetic energy production and velocity distributions, especially in the peripheral jet flows. The fraction of blood damage in the co-rotating configuration shows a 4.7% reduction in comparison to the control case, while a 3.7% increase is observed in the counter-rotating configuration. The passive flow control technique of applying co-rotating VG illustrates a great potential to help mitigate the hemodynamic factors leading to potential blood damage risk

Atrial and ventricular flows across a transcatheter mitral valve

OBJECTIVES: The objective of this study was to evaluate the haemodynamic performance of transcatheter mitral valve replacement (TMVR) Implant with a focus on turbulence and washout adjacent to the ventricular surface of the leaflets. TMVR holds the promise of treating a large spectrum of mitral valve diseases. However, the haemodynamic performance and flow dynamics of such replacements are not fully understood. METHODS: A tri-leaflet biopsrosthetic TMVR represented by Caisson implant of size 36A was implanted in the mitral position of a left heart simulator pulse duplicating system under physiological conditions. The 36A implant covers an anterior-posterior range of 26-32 mm and a commissure-to-commissure range of 30-36 mm. Transmitral pressure gradient, effective orifice area and regurgitant fraction were calculated. Particle image velocimetry was performed to evaluate turbulence in 2 perpendicular planes (Reynolds and viscous shear stresses, respectively). Additionally, dye experiments were performed to visualize washout. RESULTS: Transmitral pressure gradient was 1.29 ± 0.27 mmHg and effective orifice area was 2.96 ± 0.28 cm2. Regurgitant fraction was 14.13 ± 0.08%. Total washout was 4.27 cardiac cycles. Largest viscous shear stress reaches 3.7 Pa and 2.4 Pa in ventricle and atrium, respectively. Reynolds shear stress in the atrial side was side, the largest Reynolds shear stress reached ∼35 Pa. CONCLUSIONS: TMVR leads to favourable haemodynamics with low degree of turbulence combined with fast washout around the leaflets indicating promising potential for freedom from blood damage potential and thrombosis corroborated by initial clinical studies as part of the valves\u27s Early Feasibility Study

Theory to predict shear stress on cells in turbulent blood flow.

Shear stress on blood cells and platelets transported in a turbulent flow dictates the fate and biological activity of these cells. We present a theoretical link between energy dissipation in turbulent flows to the shear stress that cells experience and show that for the case of physiological turbulent blood flow: (a) the Newtonian assumption is valid, (b) turbulent eddies are universal for the most complex of blood flow problems, and (c) shear stress distribution on turbulent blood flows is possibly universal. Further we resolve a long standing inconsistency in hemolysis between laminar and turbulent flow using the theoretical framework. This work demonstrates that energy dissipation as opposed to bulk shear stress in laminar or turbulent blood flow dictates local mechanical environment of blood cells and platelets universally