Where is the common sense in aortic valve replacement? A review of hemodynamics and sizing of stented tissue valves

Abstract

Heated debates revolve around the hemodynamic performance of stented aortic tissue valves. Because the opening area strongly influences the generation of a pressure gradient over the prosthesis, and the outer diameter determines which valve actually fits into the aortic root, it would seem logical that the valve with the greatest opening area in relation to its outer diameter should allow the best hemodynamic performance. Interestingly, neither of these 2 parameters is reflected by the manufacturing companies' size labels or suggested sizing strategies. In addition, it is known that valves with the same size label from different companies may differ significantly in their actual dimension (outer diameter). Finally, the manufacturer-suggested sizing strategies differ so much that expected differences from valve design may get lost because of differences in sizing. These size and sizing differences and the lack of information on the geometric opening area complicate true hemodynamic comparisons significantly. Furthermore, some fluid dynamic considerations regarding the determination of opening area by echocardiography (the effective orifice area) introduce additional obscuring factors in the attempt to compare hemodynamic performance data of different stented tissue valves. We analyzed the true dimensions of different tissue prostheses and the manufacturer-suggested sizing strategies in relation to published effective orifice areas. We have demonstrated how sizing and implantation strategy have much greater impact on postoperative valve hemodynamics than valve brand or type. In addition, our findings may explain the different opinions regarding valve hemodynamics of different tissue valves.