Procoagulant Properties of Flow Fields in Stenotic and Expansive Orifices

Abstract

In the United States, over 125,000 mechanical heart valves (MHVs) are implanted each year. Flow through the MHV hinge can cause thromboemboli formation. The purpose of this study was to examine various orifice geometries representing the MHV hinge region and how these geometries may contribute to platelet activation and thrombin generation. We also characterized these flow fields with digital particle image velocimetry (DPIV). Citrated human blood at room temperature was forced through the orifices (400 and 800 microm ID) with a centrifugal bypass pump, continuously infusing calcium chloride to partially reverse the citrate anticoagulant. Blood samples were tested for the presence of thrombin-antithrombin complex (TAT) and platelet factor 4 (PF4). Velocity and shear stress were measured with DPIV using a blood analog fluid seeded with fluorescent microbeads. The results indicate that small changes in geometry, although they do not affect the bulk flow, change the coagulation propensity as blood flows through the orifices. A more abrupt geometry allows more stagnation to occur resulting in more thrombin generation. PF4 measurements indicated similar levels of platelet activation for all orifices. DPIV showed differences in the jets with respect to entrainment of stagnant fluid. These results help to pinpoint the important parameters that lead to flow stasis and subsequent thrombus formation.

A Numerical Investigation of Blood Damage in the Hinge Area of Aortic Bileaflet Mechanical Heart Valves During the Leakage Phase

“…These numerically computed results were shown to match well with experimental TAT measurements of flow through the same channel designs. The experimental study 13 showed significant difference (p < 0.05) in TAT measurements between channels with equal gap widths but different transition geometries. For the present numerical study, the computed BDI difference of 0.851 dynes s/cm 2 between a CM and SJM valve with equal hinge gap widths is at the high end of the range of BDI differences in the previous numerical study.…”

“…Using real blood is essential to thoroughly understand blood damage and valverelated thromboembolic complications. Fallon et al 13 performed in vitro experiments of whole human blood flow through converging-diverging channel geometries that were designed to be similar to existing BMHV hinge designs. In order to quantify platelet damage, thrombin-antithrombin III (TAT) levels were measured for steady flow through each of the channel geometries.…”

Emerging Trends in Heart Valve Engineering: Part II. Novel and Standard Technologies for Aortic Valve Replacement

“…This is achieved in combination with experimental approaches by examining the effect of distinct flow phases on platelet activation. 88 Particle image velocimetry is another in vitro technique that can be used to study systolic and diastolic flow of regurgitant jets, 29,34 valve orifices, 30 and at the leaflet insertion hinges. 43 More information on computational and experimental valve studies are provided in Part IV of this review series.…”

Emerging Trends in Heart Valve Engineering: Part III. Novel Technologies for Mitral Valve Repair and Replacement

“…65 Others have recently used particle image velocimetry to measure steady diastolic leakage flow of regurgitation jets, 22,28 orifices, 23 and at the hinges 36 of mechanical valves. Valve optimization is difficult as areas of high velocity and viscous shearing may lead to platelet activation and hemolysis, while areas with low velocity can promote thrombus formation due to increased residence time.…”