Flow characterization of the ADVANTAGE and St. Jude Medical bileaflet mechanical heart valves.

BACKGROUND AND AIM OF THE STUDY: The study aim was to characterize time-dependent flow fields and flow structures within the ADVANTAGE (ADV) and St. Jude Medical (SJM) prosthetic bileaflet mechanical heart valves. METHODS: Three-dimensional unsteady computational fluid dynamic simulations were conducted in the aortic position for both valves. Flow boundary conditions were acquired from an in-vitro experiment. The governing equations were solved by a finite volume method that employed a moving cell technique to simulate the motion of the valve leaflet in the cardiac cycle. The computed velocities were subsequently validated using the velocities measured in the in-vitro experiment. RESULTS: Both valves had similar flow phenomena at the geometric symmetry plane of the valve housing, and both experienced a waterhammer effect upon closure. However, flow characteristics in the pivots differed distinctively between both valves. More dynamic flow activity was observed at the bi-level butterfly pivots of the ADV valve. Flow vena contracta and large flow boundary separation zones at the central flow orifice were captured adjacent to the pivots of the SJM valve. During valve opening, retrograde systolic flow at the bottom of the pivot was observed. No persistent flow stases were seen in the pivots of either valves. CONCLUSION: Although overall flow characterization for both valves was similar, flow features within each valve's pivots correlated to the pivot design. The bi-level butterfly pivot design of the ADV valve appeared to provide relatively easy passages for pivot flow washing.

An integrated macro/micro approach to evaluating pivot flow within the Medtronic ADVANTAGE bileaflet mechanical heart valve.

BACKGROUND AND AIM OF THE STUDY: An integrated macro/micro approach was used to evaluate flow within the pivots of the Medtronic ADVANTAGE bileaflet heart valve. Results were compared with those obtained with the St. Jude Medical bileaflet heart valve. METHODS: The integrated macro/micro approach consists of both a macroscopic hydrodynamic performance assessment and a three-part microscopic flow analysis. The hydrodynamic performance assesses the basic dynamic functions of the valves, while the microscopic flow analysis uses pivot flow visualization, computational fluid dynamics and laser Doppler velocimetry to determine pivot flow characteristics. Pivot flow visualization captures two-dimensional images of the pivot flow, defines the computational fluid dynamics boundary conditions, and validates the computational result. Three-dimensional unsteady computational fluid dynamics simulation reconstructs pivot flow structures. Laser Doppler velocimetry maps pivot velocity field and provides velocity validation for the computational simulation. RESULTS: The macroscopic hydrodynamic performance assessment showed the ADVANTAGE and St. Jude Medical valves to be comparable under identical flow conditions. The three techniques in the microscopic analysis mutually confirmed that the pivot design of the ADVANTAGE valve permits continuous-flow washing in the pivot recess, the pivots of both valves are completely wiped twice in a cardiac cycle, and no persistent pivot flow stases are observed. CONCLUSION: The integrated macro/micro approach represents a powerful systematic method for determining detailed microscopic flow structures inside the pivots of bileaflet mechanical valves. The use of this technique during the design process of a bileaflet valve can eliminate the persistent flow stases that lead to thrombus formation.