Sizing strategy is a major determinant for postoperative pressure gradients in commonly implanted stented tissue valves

Aims: Heated debates revolve around hemodynamic performance of stented tissue valves. We and others reported differences in valve size nomenclature confusing direct comparisons. Relative valve opening has been suggested to be improved by designing pericardial valves with stents on the outside (Perimount), or the inside (Mitroflow) of the valve, but the sizing strategies and sizer dimensions are also different.

We reviewed hemodynamics of our patients having received aortic valve replacement (AVR) with the the Edwards Perimount or the Sorin Mitroflow, both valves, where size selection was based on intra-annular sizing. We speculated that differences in sizing strategy may be more important than differences in valve design.

Methods: We analyzed discharge echos (performed by the same examiner) from all patients having received a Perimount (n=521) or a Mitroflow (n=157) between 01/2007 and 11/2010. We obtained valve outer diameters from the manufacturers, and measured sizer dimensions with a calliper. We compared peak gradients (DP) and maximum velocity across the valve (Vmax) based on size label, outer diameter, or selected size based on suggested sizing strategy.

Results: The majority of implanted valves were size 23 (n=259). Their outer diameters were 31mm for Perimount, and 26mm for Mitroflow. Despite the smaller outer diameter, the lowest gradients were found in the Mitroflow: DP 22.22±7.74mmHg (Vmax 2.31±0.38m/s) vs. Perimount: DP 23.87±7.29mmHg (Vmax 2.41±0.34m/s) p<0.05, suggesting a design advantage. However, the 23 Mitroflow sizer was 25mm and the 21sizer was 23mm. In contrast, the 23 Perimount sizer was indeed 23mm. Thus, an intrannular sizing strategy for a patient with a 23mm annulus will result in the selection of a 21 Mitroflow but a 23 Perimount. Hemodynamic comparison of the 21 Mitroflow with the 23 Perimount eliminated the above described differences (21 Mitroflow: DP 26.19±10.09mmHg (Vmax 2.52±0.25m/s).

Conclusion: The potential hemodynamic advantage of the Mitroflow may be lost due to a “defensive” sizing strategy. The results underscore the importance of sizing strategy and surgical technique and supports the provision of replica sizers with the new generation valves.