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

Objective: We compared the haemodynamic performance of two pericardial aortic prostheses with the stent either on the outside (Perimount), or the inside (Mitroflow) of the valve cusps, with regard to sizing strategies and valve dimensions.

Methods: We analysed discharge echoes from all patients who received an isolated Perimount (n = 537) or Mitroflow (n = 164) between January 2007 and November 2010. We obtained outer valve diameters from the manufacturers, and measured sizer dimensions. We compared pressure gradients (ΔP) and maximum velocity across the valve (V(max)).

Results: The majority of implanted valves had a size label 23 (39.7% of the Perimount; 56.1% of the Mitroflow). The metric outer diameter for size label 23 was 31 mm for Perimount, and 26 mm for Mitroflow. Despite the smaller outer diameter of the Mitroflow compared with the Perimount, peak gradients were lowest in the Mitroflow (ΔP mmHg: 22.3 ± 7.8 for Mitroflow vs 23.9 ± 7.3 for Perimount, n.s.), suggesting a design advantage for the Mitroflow. However, the 23 Mitroflow sizer was 26 mm and the 21 sizer was 23 mm. In contrast, the 23 Perimount sizer was indeed 23 mm. Thus, an intrannular sizing strategy for a patient with a 23 mm annulus most likely results in the selection of 21 Mitroflow and 23 Perimount. Haemodynamic comparison of the 21 Mitroflow with the 23 Perimount reversed the above- described difference (ΔP mmHg: 26.0 ± 10.2 for Mitroflow vs 23.9 ± 7.3 for Perimount, P < 0.05). Multivariate analysis identified a 21 valve as a predictor of high pressure gradients, but found no differences between both valve types.

Conclusions: The potential haemodynamic advantage of the Mitroflow is lost due to the different sizing strategy. The results underscore the importance of an optimal sizing strategy, possibly by replica sizing.