Summary of a key clinical experience article on the fundamentally different design of the ATS Open Pivot Mechanical Valve and its impact to reduce the shear stress associated with thrombogenicity in mechanical valves.

Comparison of the Hemodynamic and Thrombogenic Performance of Two Bileaflet Mechanical Heart Valves Using a CFD/FSI Model¹

Strong Scientific Explanation for Both the Significance of Platelet Activation by Regurgitant Mechanical Flow and the Lower Platelet Activation Potential with the ATS Open Pivot Mechanical Heart Valve

The authors compared the hemodynamic performance and thromboembolic potential of an ATS Open Pivot AP supra-annular mechanical heart valve and a St Jude Medical cavity pivot, Regent supra-annular mechanical heart valve. In a sophisticated computational fluid dynamic-fluid structure interaction model, a 22 mm ATS Open Pivot AP and a 21mm St. Jude Medical Regent were evaluated. These valves were chosen because they are closely matched with regard to the key inner diameter dimensions.

Similar to other studies, the pressure gradients and flow velocities were similar for each valve with the mean gradients of 3.9 mmHg for the ATS valve  The authors measured shear stress and platelet activation, in both forward and retrograde flow and the retrograde flow represented the greatest potential for platelets to reach the activation threshold.  The results illustrate lower average shear stress through the ATS Open Pivot valve and that 30% fewer platelets reached full activation during regurgitation through the Open Pivot valve compared to the cavity pivot valve.  The authors also speculate that even small differences in platelet activation may translate into significant differences in thrombogenic performance between valve designs.  And, how a difference in hinge design may translate into a difference in the thrombogenic potential of otherwise very similar bileaflet mechanical valves.

Key quotes include:
“. . . for the regurgitant flow phase the SJM exhibits a stronger regurgitant jet, particularly in the hinges region.  Owing to its different open pivot hinge design for the ATS valve, this jet is broken up into two much weaker jets.  Regurgitant jets were previously implicated in mechanical valve hemoloysis and platelet activation.”

“. . . the SJM valve generated higher platelet activation values during the regurgitant flow phase at all ranges of shear stress accumulation.  As this flow phase was previously implicated in high levels of platelet activation, it indicates that overall the ATS valve may offer a lower thrombogenic potential owing to its different hinge mechanism design.”

Journal of Biomechanical Engineering 2007; 129:558-566. Link to PubMed-PMID 17655477 

Reference

1. Dumont K, et al. Comparison of the hemodynamic and thrombogenic performance of two bileaflet mechanical heart valves using a CFD/FSI model. J Biomech Eng 2007; 129:558-566.