Hydrodynamic function of tilting disc prostheses and bileaflet valves in double valve replacement

To determine the energy loss attributable to prosthetic valve size and design in double valve replacement, energy consumption of mitral valves (size #25 to #29), of two different designs (Bjork Shiley tilting disc and Carbomedics bileaflet valves), in combination with a small (#21) and large sized (#27) aortic prosthesis, were analyzed in a flow simulator.

A pulsatile flow simulator was used to reproduce physiological ventricular dynamics and to match the input and output impedances of the human left ventricle. Hydrodynamic performance was determined as stroke work, closing work and leak work for each combination of valves at low flow (5 liters per minute) and high flow (9 liters per minute) conditions.

At low flow no decrease of energy requirement was found with the use of a mitral valve larger than #25. At high flow the #27 and #29 mitral valves required less energy compared to a #25 mitral valve, in combination with a large aortic prosthesis. The #29 mitral prosthesis revealed similar results as the #27. With the use of a large aortic prosthesis a remarkable reduction of total flow work was shown. These results were found in both designs. In comparison of the two designs, tilting disc valves required more energy for stroke and closure of the valve, although less energy for leakage. In total, energy requirements were higher for tilting disc valves.

A hydrodynamic advantage for the use of a mitral valve larger than #25 was found only with the combination of a large aortic prosthesis and high flow. Hydrodynamic data favor the use of bileaflet prosthesis especially for a patient who is expected to exercise.