A study published in the May edition of The Journal of Heart Valve Disease, entitled, "Predicting ATS Open Pivot Heart Valve Performance with Computational Fluid Dynamics," confirms the excellent hemodynamic performance of the ATS Medical's Open Pivot Heart Valve. It might also explain the low rates of hemolysis and thromboembolic events previously published on the open pivot design.
Unlike all other mechanical heart valves, the pivot area of the ATS Open Pivot Heart Valve does not contain cavities or recesses, which could allow for areas of stagnant flow. Instead, the open pivot hinge protrudes gently into the blood flow, providing continuous passive washing, which is thought to be gentler on fragile blood cells. In contrast, cavity pivot mechanical valves rely on the small "ears" at the ends of the leaflets to mechanically push old blood out of the pivot cavities. This process, called mechanical sweeping, may not be as efficient as the free flow of blood in removing all old blood from the hinge areas. Also, the force of blood being squeezed through the more complicated structures of the cavity pivot may tend to injure red blood cells as they are thrown against these structures.
Using a new computational fluid dynamics model, scientists at the University of Ghent, Belgium, researched and reported on 3D flow through the ATS Open Pivot Heart Valve in two geometrical models. Use of this new technique is expected to significantly improve the understanding of the hemodynamic function of new and existing mechanical heart valves.
The results with the ATS valve in the expanding geometry showed opening to a maximum angle of 77.5°; this was confirmed in previous clinical and in-vitro studies. The mean and maximum transvalvular Doppler pressure gradients were 1.1 and 4.3 mmHg, respectively. The maximum shear stress calculated on the leaflet was 25 Pa. Maximum opening of the valve was achieved in the straight conduit; with mean and maximum pressure gradients of 2.1 and 4.6 mmHg, respectively. The maximum shear stress calculated on the leaflet was 35 Pa.
The authors confirmed previously published data illustrating the excellent flow through the ATS Open Pivot Heart Valve and concluded that valve hemodynamics and leaflet motion associated with the ATS Open Pivot Heart Valve are dependent on the shape of the patient's anatomy in which the valve is placed. In the expanding geometry model which simulates native human anatomy, the authors found that diverging blood flow interacts with the opening mechanism of the ATS Open Pivot Heart Valve to reduce transvalvular pressure gradients, shear stress on the leaflets and potential for damage to platelets and blood cells. This model could be used to predict pressure gradients, effective orifice area, performance index and shear stress loading of mechanical heart valves, and in future will serve as a major research tool to characterise the hemodynamics of existing and new mechanical heart valves.
The results of this study suggest that the low rates of hemolysis and thromboembolic events commonly reported for the ATS Open Pivot Heart Valve may be directly related to the flow patterns through the unique open pivot design.
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