Canary in the cardiac-valve coal mine. Flow velocity and inferred shear during prosthetic valve closure –predictors of blood damage and clotting

Abstract

Objective: To demonstrate a clear link between predicted blood shear forces during valve closure and thrombogenicity that explains the thrombogenic difference between tissue and mechanical valves and provides a practical metric to develop and refine prosthetic valve designs for reduced thrombogenicity. Methods: Pulsatile and quasi-steady flow systems were used for testing. The instantaneous valve flow area was measured using analog opto-electronics with output calibrated to the projected dynamic valve area. Flow velocity during the open and closing periods was determined from the instantaneous volumetric flow rate divided by valve flow area. For the closed valve interval, data obtained from quasi-steady back pressure/flow tests was used. Performance ranked by the derived valvular flow velocity and maximum negative closing flow velocity for all valves is experimental evidence for potential clinical thrombogenicity. Clinical, prototype and control valves were tested. Results: Establishment of a link between blood shear force and thrombogenicity led to optimization of a prototype mechanical bi-leaflet valve. The flow velocity metric was used to empirically design a 3-D printed model (BV3D) for softer valve closure dynamics which implicates reduced thrombogenic potential. Conclusions: The relationship between leaflet geometry, flow velocity and predicted shear at valve closure illuminated an important source of prosthetic valve thrombogenicity. With an appreciation for this relationship and based on our experiment generated comparative data, we achieved optimization of valve prototypes with potential for reduced thrombogenicity.