Physiologic factors influence the interaction between blood, materials, and flow characteristics in mechanical valves, creating shear stress that increases the potential for thrombogenicity. This non-physiologic blood flow is the primary reason mechanical valves require anticoagulation.

Impact of Shear Stress
Shear stress is the major cause of thromboembolic complications in mechanical valves

• Surfaces of all mechanical valve quickly become coated with blood proteins to which platelets adhere.

• Mechanical valve flow characteristics, primarily relating to shear stress, can cause platelet activation.
• A valve that better manages shear stress lowers platelet activation and has a lower propensity to clot.
• The ATS Open Pivot® Heart Valve provides a solution to better manage shear stress.²    

Managing blood flow quality in a mechanical valve, especially through the pivot, can lower velocity and turbulence for reduced shear stress and minimized thrombogenic activity.

Echocardigraphic Comparison of the Open Pivot to Cavity Pivot
Echocardiographic images show lower velocity, fan-shaped less turbulent regurgitant flow through an Open Pivot valve compared to the two long, higher velocity, more turbulent jets found with cavity pivot valve designs.

 
 The Shear Stress Difference of the ATS Open Pivot Mechanical Heart Valve Animation 
 

 
Shear Stress Brochure 

Thromboresistance by design.
The ATS Open Pivot Heart Valve is the only bileaflet valve that eliminates the major cause of thromboembolic complications in mechanical valves – increased shear stress created by recessed areas in the pivot area.³  

In the ATS Open Pivot Valve:

• Positive relief pivot points eliminate indentations that create potential areas of stasis and platelet aggregation in cavity pivot valves.
• Leaflets “float” on spherical pivots and are retained in place by leaflet stops.
• The Open Pivot design provides more open blood flow, resulting in gentler, passive pivot washing in both forward and regtrograde flow, thereby reducing shear stress.³ 
• In contrast, recessed areas in the cavity pivot design encourage platelet aggregation that requires vigorous mechanical scraping and high-velocity flushing. The high-velocity regurgitant jets increase shear stress, contributing to the risk of thrombogenesis.

Superior hemodynamic and thrombogenic performance.⁴
The ATS Open Pivot® design reduced average shear stress and platelet activation during the regurgitant flow phase while the cavity pivot generated higher platelet activation values during the reguritant flow phase at all ranges of shear stress accumulation. Overall, the ATS valve may offer a lower thrombogenic potential owing to its different hinge mechanism design.²

• Comparison of the hemodynamic and thrombogenic performance of two bileaflet mechanical heart valves using a CFD/FSI model. – Dumont K, et al. [Summary] Journal of Biomechanical Engineering 2007; 129:558-566. Link to PubMed-PMID 17655477

Cavity Pivot Resulted in a 30% Increase in Platelets Reaching Activation

• This computational fluid dynamic (CFD) model illustrates the difference in hemodynamic and thrombogenic performance of the Open Pivot valve versus a cavity pivot design. Note the broader, lower velocity flow through the Open Pivot valve compared to the narrower, longer, higher velocity jet in the cavity pivot design.²
• Computational fluid dynamic model closely matches echocardiography.

ATS Open Pivot® Heart Valve